ISO 19258:2005

INTERNATIONAL ISO
STANDARD 19258
First edition
2005-12-15
Soil quality — Guidance on the
determination of background values
Qualité du sol — Guide pour la détermination des valeurs de bruit
de fond
Reference number
©
ISO 2005
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ii © ISO 2005 – All rights reserved

Contents Page
Foreword. iv
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 1
4 General. 3
5 Procedures. 3
5.1 General. 3
5.2 Objectives and technical approaches . 4
5.2.1 General. 4
5.2.2 Substances and parameters. 4
5.2.3 Study area. 6
5.2.4 Time period. 7
5.2.5 Scale of sampling (Support) . 7
5.3 Evaluation of existing data . 7
5.3.1 General. 7
5.3.2 Completeness of data sets/minimum requirements . 8
5.3.3 Comparability of data (Sampling, nomenclatures, analyses) . 8
5.3.4 Elimination of outliers . 9
5.4 Collection of new data. 9
5.4.1 Sampling. 9
5.4.2 Soil analysis. 12
5.5 Data processing and presentation. 13
5.5.1 Statistical evaluation of data . 13
5.5.2 Data presentation and reporting . 14
6 Data handling/quality control . 15
Annex A (informative) Scale of sampling. 17
Annex B (informative) Outlier tests . 19
Bibliography . 23

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 19258 was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 7, Soil and site
assessment.
iv © ISO 2005 – All rights reserved

INTERNATIONAL STANDARD ISO 19258:2005(E)

Soil quality — Guidance on the determination of background
values
1 Scope
This International Standard provides guidance on the principles and main methods for the determination of
pedo-geochemical background values and background values for inorganic and organic substances in soils.
This International Standard gives guidance on strategies for sampling and data processing and identifies
methods for sampling and analysis.
This International Standard does not give guidance on the determination of background values for
groundwater and sediments.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 10381-1, Soil quality — Sampling — Part 1: Guidance on the design of sampling programmes
ISO 10381-5, Soil quality — Sampling — Part 5: Guidance on the procedure for the investigation of urban and
industrial sites with regard to soil contamination
ISO 11074:2005, Soil quality — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11074 and the following apply.
3.1
background content
content of a substance in a soil resulting from both natural geological and pedological processes and including
diffuse source inputs
3.2
background value
statistical characteristic (3.8) of the background content
3.3
contaminant
substance or agent present in the soil as a result of human activity
NOTE There is no assumption in this definition that harm results from the presence of the contaminant.
3.4
diffuse source input
input of a substance emitted from moving sources, from sources with a large area or from many sources
NOTE 1 The sources can be cars, application of substances through agricultural practices, emissions from town or
region, deposition through flooding of a river.
NOTE 2 Diffuse source input usually leads to sites that are relatively uniformly contaminated. At some sites, the input
conditions may nevertheless cause a higher local input such as near the source or where atmospheric deposition/rain is
increased.
[ISO 11074:2005]
3.5
pedo-geochemical content
content of a substance in a soil resulting from natural geological and pedological processes, excluding any
addition of human origin
NOTE It may be hardly possible to determine the precise pedo-geochemical content of certain substances in a soil
due to anthropogenic diffuse contamination.
3.6
pedo-geochemical background value
statistical characteristic (3.8) of the pedo-geochemical content
NOTE Any estimate of pedo-geochemical background value will be prone to a certain amount of error given the
uncertainty associated with determining the pedo-geochemical content.
3.7
soil
upper layer of the Earth's crust composed of mineral parts, organic substance, water, air and living organisms
[ISO 11074:2005]
3.8
statistical characteristic
numerical value calculated from a variate of a chosen parameter of the population
EXAMPLE Examples of the statistical characteristics are the mean, the median, the standard deviation or the
percentiles of the ordered frequency distribution.
3.9
study area
three-dimensional definition of the area where samples are to be obtained from and thus for which the
background value(s) are to be estimated
3.10
support
size, shape and orientation of a soil sample
NOTE For the purpose of analysing spatial variation in soils geostatistically (by estimation of the variogram of a soil
property), the support should be the same at each sampling site.
3.11
variate
set of observed values of a variable
EXAMPLE A variate could for instance be the series of numbers of the concentration of a substance in soil or
numerous, individual soil samples.
2 © ISO 2005 – All rights reserved

4 General
Soils retain the evidence of their past history including impacts due to natural events or human activities.
Chemical impacts related to human activities can be detected in soils all over the world, even in regions far from
any source of contamination. For this reason, the background contents of inorganic and organic substances in
soils consist of a pedo-geochemical fraction and an anthropogenic fraction. The ratio of these fractions varies
widely depending on the type of substances, the type of soil and land use, and the kind and extent of external
impacts.
For many inorganic substances, the background content of unpolluted soils is dominated by the pedo-
geochemical content and consequently by the mineralogical composition of the soils parent material. Pedogenetic
processes may lead to a redistribution (enrichment/impoverishment) and consequently to a horizon-specific
differentiation of the substances within a soil profile. Persistent organic substances in soils originate more often
from non-natural sources and therefore the background content of soils is governed by the kind and extent of
diffuse contamination from non-soil sources.
In practice, it is often difficult to distinguish clearly between the pedo-geochemical and the anthropogenic fraction
of the background content of soils. Nonetheless, a detailed knowledge of the background content as well as of its
natural fraction for the substances of concern is essential both for any evaluation of the current status of soils for
environmental or land use related aspects or just for scientific purposes within the scope of pedology or
geochemistry. To this end, so-called background values in terms of the statistical characteristics of both, the pedo-
geochemical and the anthropogenic fraction have to be determined.
A variety of different objectives can be identified for the determination of background values of inorganic and/or
organic substances in soils. The objectives themselves provide insufficient information to define the technical
programme that will produce the desired background values. Thus a number of technical approaches have to be
defined which together form the basis of the technical programme.
This guidance provides essential aspects of sampling strategies and procedures, minimum requirements
regarding the necessary steps and ways of sample pre-treatment, analytical methods and statistical
evaluation procedures for determining sound and comparable background values.
Guidance is given for
a) evaluating existing data from different data sources and
b) setting up complete investigation programs aiming to compile background values for a clearly defined
three-dimensional picture of the soil.
These situations are representing the two extreme starting positions for the process of compiling background
values. In practice, a third intermediate situation may be dealt with when additional data need to be collected
because the quantity or quality of the existing data is insufficient.
5 Procedures
5.1 General
The procedures to determine background values encompass aspects of sampling (strategy, procedure), soil
analysis (pre-treatment, extraction and measurement), data processing and presentation. In general, two
starting positions can be distinguished, namely
a) the evaluation of existing data mostly from different data sources, and
b) the collection of new data based on an appropriate investigation strategy.
5.2 Objectives and technical approaches
5.2.1 General
Before commencing any survey on background values in soils it is of crucial importance to define the objective
of the survey and the related technical approach.
The objective is, in general terms, the definition of 'why' background values are to be determined. The
technical approaches describe aspects like the 'where', 'what', 'how' and 'when'. Together the technical
approaches determine the technical programme that will provide the required background values.
NOTE It should be noted that a technical approach that is fit for one objective, will often be unfit for other objectives.
The objectives for defining background values might be:
⎯ to identify the current contents of substances in soils, e.g. in the context of soil-related directives;
⎯ to assess the degree of contamination by human activities;
⎯ to derive reference values for soil protection;
⎯ to define soil values for reuse of soil material and waste;
⎯ to calculate critical levels and tolerable additional critical loads;
⎯ to identify areas/sites with atypically enhanced levels of element contents due to geogenic reasons or
human impact;
⎯ etc.
In order to meet the objective, the technical approaches might include the following.
⎯ Definition of the substances and parameters
⎯ For example, the background values to be estimated may be the total heavy metal content or the
bioavailable heavy metal content. (See 5.2.2)
⎯ Definition of the study area
⎯ The (three-dimensional) definition of the area where samples are to be obtained from. This has to be
a detailed description of what is to be considered as the study area, and what is not. (See 5.2.3.)
⎯ Definition of the time period of interest:
⎯ Are the historical or current contents relevant for the objective? (See 5.2.4.)
⎯ Definition of the size and geometry (support) of the area sampled at a sampling location. (See 5.2.5.)
5.2.2 Substances and parameters
Background values can be determined for all kinds of inorganic and organic substances in soils as well as soil
characteristics. In practice, the more persistent and immobile compounds are of primary interest because of
their potential to adsorb and accumulate in soil, whereas remobilization and intrinsic biodegradation are of
less significance.
As well as the substances of concern, basic soil parameters and site characteristics (see 5.4.1.3) need to be
provided to assist in interpretation of the contents of substances. A number of so-called basic soil parameters
influence soil processes that affect the contents of inorganic and organic substances. Table 1 lists these
parameters which should be analysed according to the given International Standards.
4 © ISO 2005 – All rights reserved

Within the group of inorganic substances, trace elements (e.g. heavy metals, micronutrients) are most often
analysed (Table 2). Concerning the analytical methods, a distinction has to be drawn between different
extraction/preparation methods (Table 2), whereof very few determine the total content which may be needed
for instance for calculating element stocks. Besides total contents, the (eco-) toxicologically more relevant
mobile fractions (Table 2) are of increasing interest, e.g. if pathway-related questions are to be examined.
Analysis of parameters in Table 2 should be carried out according to International Standards given in Table 2.
Table 1 — Basic soil parameters
Parameter Method ISO International Standard
Texture Sieving, sedimentation ISO 11277
Fraction of coarse material Sieving ISO 11277
Amount of non-soil material Sieving/visual control ISO 11259, ISO 11277
Bulk density Direct measurement of undisturbed ISO 11272
soil samples, estimation form soil
water retention curves
pH pH-electrode ISO 10390
Content of organic carbon Dry combustion ISO 14235
Cation exchange capacity, exchangeable cations BASECOMP ISO 11260
BaCl ISO 13536
Carbonate content CO-evolution ISO 10693
Table 2 — Examples for the analysis of inorganic substances
Parameter Speciation/form Extraction/preparation ISO International Standard
Method
Extraction/preparation Determination
Metalloids, e.g. ISO 14869-1 ISO 14869-1
Alkaline fusion + X-ray
Total
fluorescence HF + HCIO
arsenic and selenium ISO 14869-2 ISO 11047
Metals, Pseudo total aqua regia ISO 11466 ISO 11047
barium, cadmium, EDTA
Complexing
chromium, cobalt, DTPA ISO 14870 ISO 11047
copper, iron, lead, NaNO
manganese, mercury, NH NO
4 3
Exchangeable
molybdenum, nickel, CaCl
thallium, zinc KCl
Cyanides Water soluble H O, leaching tests See NOTE. See NOTE.
NOTE There are a variety of extraction and analytical methods for soil-water in the series of International Standards on water
quality which may also be applicable. However, it is important to confirm that they will work with the extracts obtained form particular soil
material.
Surveys on organic substances usually refer to persistent compounds. The persistent organic contaminants
listed in Table 3 are some of the more commonly encountered, but the list is not complete. Analysis should be
carried out according to International Standards listed in Table 3.
Various methods are used for the analysis of organic substances. The aim of these methods is usually to
extract the greatest possible quantity of organic substances from soils. It is important to recognize that organic
compounds may be extracted from naturally occurring organic materials (e.g. organic matter, decaying
vegetation, peat, charcoal), and that non-specific analyses in particular may, therefore, give misleading results.
Table 3 — Examples for the analysis of organic substances
Substance/groups of substances Method ISO International Standard
PAH Soxhlet/HPLC/UV ISO 13877
Thin-layer chromatography ISO 7981-1
RP C-18/HPLC ISO 7981-2
GC/MS ISO 18287
Dioxins/Furane
Chlorophenols Hexane/GC/ECD ISO 8165-1
Chlorpesticides RP C-18/HPLC/UV ISO 11369
PCBs GC-ECD ISO 10382
Chlornaphthalene
Chlorparafin
Bromodiphenylethers
NOTE There are a variety of extraction and analytical methods for water in the series of International Standards on water quality
which may also be applicable. However it is important to confirm that they will work with the extracts obtained from a particular soil
material.
When collecting new data for determining background values, it is recommended that the investigation
program be designed with regard to additional questions that could arise in future. In most cases, carrying out
new sampling campaigns is much more expensive than analysing additional substances in the first place. To
this end, a suitable storage of soil samples for subsequent analyses of organic or inorganic substances is of
crucial importance. Besides the substances of concern (Tables 2 and 3) and additional soil parameters
(Table 1), it is essential to provide a comprehensive site description (see 5.4.1.3) for interpretation purposes.
The documentation of all the actions taken is of utmost importance if the data measured is to be of use for
other assessments in future investigations.
5.2.3 Study area
The definition of the study area (3.9) can be based on two different principles, that is:
⎯ a purely spatial definition (X, Y, Z), defining the contours of the study area by the coordinates within which
the study area lies. Apart from the definition in a horizontal plane, the soil depth that is to be studied
should also be defined;
⎯ a typological definition of the study area, based on one or more characteristic(s), e.g. soil type (for
example, the A-horizon of a specific soil type), land use (also considering the potential effects on the
background values), elevation level, etc.
Of course, it is possible to mix the spatial and typological definition of the study area.
EXAMPLE Examples of a mix of the spatial and typological definition of the study area might be:
— the grassland in a county or province;
— the A-horizon in an area defined by X- and Y-coordinates.
The definition of the study area must be detailed at a level where there cannot be any misinterpretation on
what is and what is not part of the study area. For an unambiguous definition of the study area, all actual point
and diffuse sources within the study area need to be defined. As the general objective is to determine
background values, a safety zone around that (type of) source might be defined and thereby excluding parts
of the more generally defined study area. It might also result in specific zones for which the data is to be
considered separately from the rest of the study area.
6 © ISO 2005 – All rights reserved

The definition of the study area as described is independent of whether the soil samples are still to be taken,
or whether already existing soil samples (or results) are to be used. In the latter situation, the detailed
definition of the study area will define which samples/results are to be included or excluded.
5.2.4 Time period
Background values are influenced both by the natural processes (pedogenesis, biogeochemical cycles) as
well as by diffuse source input. Two different time scales can be distinguished:
⎯ the period in which the background value may significantly vary due to natural processes;
⎯ the period in which the background value will most probably only change due to human influences
(except for large scale natural phenomena).
The second period is generally smaller than the first one.
It might be that a specific historic period is of interest when measuring background values. When a soil layer is
formed during this same period, it is indeed possible to determine background values for a certain time period.
When background values are to be re-determined after a period of time in order to determine if changes occur,
the time period between measurements should be based on (see also ISO 16133):
⎯ the expected enrichment of substances in soils (accumulation for example due to diffuse source input);
⎯ the expected loss of substances in soils (for example, due to leaching, biodegradation or plant uptake);
⎯ changes in concentration level that can be determined both analytically and statistically.
5.2.5 Scale of sampling (Support)
Variability in concentrations is by definition a scale-related characteristic. Depending on the volume for which
an analytical result is to be considered representative, the variability in concentrations encountered might be
different. The scale — or in more technical terms the (geo-statistical) support (3.10) — is therefore an
important technical aspect on which a decision is to be made prior to data collection.
For (mainly) two-dimensional surveys, the support is the size (and geometry) of the area sampled at a
sampling location.
The study will always involve a certain soil layer of depth. However, as in the horizontal plane, the dimensions
are much larger than in the vertical plane, the support in soil surveys is most often defined in a two-
dimensional way.
More information on support is given in Annex A.
5.3 Evaluation of existing data
5.3.1 General
When using existing data, specific care must be taken concerning the quality and comparability of data
particularly if the data originate from different sources. Data with appropriate information have to be
harmonized in a step-wise procedure with regard to the specific evaluation objectives. In general, the
harmonization of data sets results in a more or less significant reduction of the respective variate. Nonetheless,
the procedure of harmonization of data sets is inevitable to produce a sound and reliable evaluation. The
respective harmonization strategy should encompass aspects like
a) the check of the completeness of the data sets related to minimum requirements,
b) the harmonization of different sampling strategies, references, nomenclatures and analytical procedures,
c) the identification and elimination of contaminated samples (excluded from the population of background
values by definition).
5.3.2 Completeness of data sets/minimum requirements
In order to ensure a minimum level of data quality, it is essential to provide sufficient and sound information of
the data, for instance
⎯ the date of sampling,
⎯ the procedure used to select sampling locations (plots),
⎯ the scale of sampling (e.g. support),
⎯ the site location (coordinates),
⎯ the sampling depth intervals,
⎯ the number and configuration of samples (e.g. regular grid or random sampling) taken at a sampling
location (plot),
⎯ the method used to extract and analyse the components (including quality assurance and detection limits),
⎯ the site-specific information (e.g. pedology/lithology, land use).
This information can be used to screen the data on their suitability for the objective of compiling background
values.
The definition of minimum requirements on information of the data set depends, amongst others, on the
substances of concern, the area and spatial reference to be considered and the approach pursued to achieve
an adequate spatial representation of the point-related data.
Apart from the information listed above, the type and degree of accuracy, e.g. of site-specific information
depends on soil and other parameters influencing the behaviour and hence the contents of the substances in
soils. For instance, inorganic substances need to be related at first priority to lithogenic soil properties due to
their predominant geogenic origin, whereas the content of organic substances of soils is more strongly
correlated to, e.g. land-use-related parameters.
5.3.3 Comparability of data (Sampling, nomenclatures, analyses)
Different sampling strategies may have a crucial impact on the comparability of data sets. Problems arise here
in particular through the comparison of horizon versus depth level-related samples and that of mixed versus
individual samples. Further on, the representative nature of the variate for a sample population with regard to
the same support for an area needs to be taken into account. Also, an uneven spatial distribution of the
sampling points within an area may cause biased estimates of the parameters of the frequency distribution
due to an overestimation of some parts of the study area. Block-kriging is recommended to deal with this
problem. It is strongly recommended to carefully balance the possible inaccuracies introduced by merging
data sets from different campaigns, versus the advantage of an increasing number of samples and
consequently an increasing representation of a population.
The extent to which different sample pre-treatments and analytical procedures (extraction, measurements)
can be compared and harmonized has to be evaluated in each individual case, e.g. against the intended
accuracy of the background value. For inorganic substances, the analytical results originating from different
analytical procedures may be transformed by applying regression functions or constants provided the
respective relations are known. Alternatively, the analytical procedures may be grouped roughly according to
the operationally defined extracted fractions (see Table 2). The broader the ranges of classified background
values as target variables are, the lower may be the demand of data comparability. Nonetheless, the assessor
should bear in mind, that merging data sets analysed by different analytical procedures invariably requires
compromises to be made.
8 © ISO 2005 – All rights reserved

5.3.4 Elimination of outliers
According to definition 3.1, the background content of substances in soils includes the moderate diffuse input
into the soil. Therefore, locally contaminated sites are excluded from the population of background contents.
Consequently, data obviously stemming from locally contaminated sites have to be identified and eliminated
from the respective data set. To this end several statistical tests for identifying outliers are applicable, e.g. test
on distribution of the data, exploratory data analysis (boxplots), principle component analysis, etc. (See also
5.5.1.2.1 and Annex B.)
NOTE The removal of outliers has a significant effect on the resulting definition of the background value. The
statistical identification of an outlier by itself is insufficient for removing a high (or low) measurement out of the database
describing the background value. The statistical test does however provide a good method of defining which data should
be investigated in more detail, in order to see if an explanation can be found for the high value to be an outlier. If such an
explanation is found, the value is indeed an outlier and should be eliminated.
5.4 Collection of new data
5.4.1 Sampling
5.4.1.1 Sampling strategy
5.4.1.1.1 General considerations
The natural pedo-geochemical content and the usual content of substances in soil vary according to soil
parent material. They also depend on soil horizons, as pedogenic processes modify and redistribute
components in soils, leading generally to the formation of several soil horizons that may exhibit different
compositions.
Land use and distance to contamination sources also influence the content of substances in soils. Human
activity modifies soil composition through agriculture, waste spreading, building, atmospheric deposition from
industry, households, traffic, etc. A sampling site is considered here as a small portion of land, from a few
square metres to about 1 ha, where one sample of each of the soil layers or horizons of interest is collected.
This section presents two strategies for selecting the sampling sites within the study area: the systematic
approach and the typological approach. The choice of one of them is generally influenced by the degree of
pre-existing knowledge about the soil and land use. When relatively little is known, the systematic approach is
often more appropriate. However, these two approaches can be considered as typical ones in the continuum
of all possible strategies. Therefore, it is possible to build an intermediate strategy, mixing some aspects of the
systematic approach with others from the typological one.
5.4.1.1.2 Systematic approach
The sampling sites are located using a grid. The interval between the grid points is dependent on the
resolution desired for the determination of the pedo-geochemical and/or background content. In principle, the
interval between the sampling sites should be such that the minimum number of samples can be collected to
represent each of the defined soil units. A square grid can be used, with cells varying in size (available
monitoring recommendations should be considered).
For instance, square cells with a 16 km, 5 km or 2,5 km site can be used at the scale of a country, whilst
square cells of a few hundred meters are more appropriate for the study at the level of a small area.
If sampling at a given grid point is rendered impossible due to buildings, roads, water surface or any other
reason, a new location may be chosen using a systematic procedure. For instance, a deviation may be
permitted from the initial point by steps of a definite distance north, then east, then south and finally west.
For each selected site, consider moving the sampling area if it is potentially highly contaminated by near-by
point sources, or in a pedo-geochemical way, if any source could compromise the purpose of the study (e.g.
overhead power-lines should be avoided if the zinc content of soils is of interest).
Samples are taken from soil layers of definite depths or from a defined pedological horizon or horizons. If the
surface layers are contaminated by diffuse sources, the contents determined indicate the background content
in these soils. For relatively immobile substances (e.g. heavy metals), the deep layers and particularly those at
a depth below 40 cm are generally uncontaminated (provided local contamination by point sources can be
excluded), and the respective substance content can be considered as the pedo-geochemical content.
A comprehensive site and soil description (Table 5) should be done at the same time as the samples are
taken.
5.4.1.1.3 Typological approach
In the typological approach, the soil is stratified according to soil parent material (for inorganic substances),
soil type and land use. Sites potentially highly contaminated by adjacent point sources are rejected.
The typological approach needs detailed information about the area to be investigated. Information (such as
on geology, pedology, land use and sources of possible contamination) has to be gathered and evaluated in
order to elaborate the sampling scheme.
For inorganic substances, the first step of the stratification of the area refers to the soil parent materials.
Within each type of parent material stratum, the soil is stratified again on the basis of pedogenesis, if this is
considered to have markedly modified the distribution of substances in soil. Further stratification, e.g. for
organic substances is related to land use; it is recommended to distinguish between cultivated and forest soils
and soil under meadow or spontaneous vegetation. On a local scale, the best stratification is based on
pedology, e.g. that of the soil series, as this taxonomic level generally explains most of the variation of the soil
properties. Finally, the horizon to be sampled has to be chosen.
Within one stratum, the sampling sites should generally be chosen in such a way that the area is covered
representatively. The choice of the sampling sites can be carried out within each stratum using a random or
systematic sampling scheme.
NOTE Apart from the degree of pre-existing knowledge, the type of question largely determines the choice between a
random or a systematic sampling scheme. To estimate parameters of a frequency distribution of the background contents,
a random sampling approach is most appropriate. For mapping background contents, in general, a (centred) regular grid is
more appropriate.
5.4.1.2 Number of sampling sites
Background values cannot be summarized in a central parameter such as the mean. It is necessary to
describe the variability of a given content in soil as precisely as possible. In the case of a normal probability
distribution, the number of samples necessary for the estimation of the standard deviation is independent from
the standard deviation of the population. It can be determined using Table 4, which shows that a minimum
number of 30 samples is necessary to estimate the standard deviation of a normal population.
Table 4 — Maximum relative error on the estimation of the standard deviation
of a normal population, with a = 0,05; n: number of samples
n e (%)
r
10 57
20 35
30 27
40 23
50 21
10 © ISO 2005 – All rights reserved

However, probability distributions of substances in soils are rarely normal. They are often positively skewed
but not necessarily log-normal. The estimation of the required number of samples to assess variability of such
a distribution can then be equal to the number of samples necessary to draw a representative histogram or to
calculate representative percentile. To this end, a minimum number of 30 samples is recommended.
5.4.1.3 Soil description
The interpretation of background contents of soils requires general information about the study area. The most
relevant parameters for the soil description of the study area are listed in Table 5. It is important to bear in
mind that the reliability of data interpretation strongly depends on a profound knowledge of the study area,
hence collection of parameters, indicated in Table 5, should be as comprehensive as possible.
Table 5 — Parameters for site and soil description
Parameter ISO
International
Standard
Landform and topography Topography, landform, land element, position coordinates, slope ISO 11259
microtopography
Land use and vegetation Land use, human influence, vegetation ISO 11259
Geology and lithology Kind of parent material, effective soil depth ISO 11259
Surface characteristics Rock outcrops, surface coarse fragments, erosion phenomena, surface ISO 11259
sealing, surface cracks, other characteristics
Soil-water-relationship Surface water balance, rainfall, evapotranspiration, groundwater ISO 11259
recharge, presence and depth of water table, site drainage, moisture
conditions
Soil type/soil profile Soil unit in regards of the classification system used ISO 11259
description
Sequence and depth of diagnostic horizons, kind of boudaries
Soil colour (matrix, mottling)
Organic matter
Texture, coarse elements, presence of non-soil material pedofeatures
Carbonates, field-pH, electrical conductivity
Structure, voids, fracturing, inhomogeneties
Compactness and consistence
Total estimated porosity
Roots, worm channels, biological activity
5.4.1.4 Sampling depth
Background contents and values vary with soil depth due to pedogenesis, use and type and source of
contamination. Sampling can be carried out on a fixed depth basis (i.e. layer) or according to definite horizon
types. Sampling according to the depth is easier as it does not need the identification of the horizon type. But
it will give a less precise measurement of the background contents, as it does not enable control of the
variability due to horizon differentiation and use.
As anthropogenic contamination mainly enters soil at the surface, the concentration measured in the upper
layers or horizons is regarded as a background content for those substances which are introduced in soil as a
consequence of human activity. The determination of these substances in the deep layers or horizons gives
an estimation of their pedo-geochemical content. For the substances that are not introduced in soils by human
activity, the analysis of any of the layers or horizons of this soil gives an estimation of the pedo-geochemical
content of this layer or horizon.
Note that in some cases, a contamination may also enter the soil from underground (e.g. by contaminated
ground water).
5.4.1.5 Sampling period
Sampling should be spread over a period of time chosen to limit the temporal variation of the background
contents.
When soil parameters do not vary within one year, which is the common case for most soil substances,
sampling can be carried out at any period of the year.
Practical aspects, mainly concerning the access to the soil horizon or layer, have to be considered before
choosing the sampling period. For instance, it may be difficult to sample deep horizons during a wet season,
due to the presence of a water table close to the surface. On the contrary, sampling during the dry season
may be rendered difficult by drought, which makes soil hard to penetrate with the sampling tools. Access to
cultivated plots may be difficult because of growing crops. In this case, it is advisable to sample shortly after
harvest and/or immediately after sowing.
5.4.1.6 Sampling technique
Sampling should be performed in accordance with ISO 10381-1 and ISO 10381-5. The following
recommendations may generally be taken into account. The sampling techniques depend on the depth or
horizon that has to be sampled. If only the surface horizon or layer has to be sampled, a hand corer or
equivalent tool can be used.
If deep horizons or layers have to be represented, a powered corer would be preferable. All sampling tools
must be designed and/or used in order to avoid cross contamination among layers or horizons.
Sampling in a soil pit is generally recommended because it provides a clear distinction of the soil horizons and
other soil characteristics. It allows the soil description to be carried out at the same time of sampling for
analysis. Sampling should then be performed from the bottom to the top in order to avoid cross contamination
by soil material falling from the upper horizons on the lower ones.
Mixing several cores taken on the site area, according to a systematic or a random design can make
composite samples of each of the layers or horizons. When sampling in a soil pit, it is recommended to clear a
sufficient surface of the sampled horizon in order to take several cores to be mixed together.
All of the materials used for sampling, transport, labelling and storage of the samples must not release
significant amounts of the elements or substances that are to be determined.
5.4.2 Soil analysis
5.4.2.1 General considerations
Two sets of parameters can be measured on the samples. The first one is made of the concentrations of the
substances of interest. T
...

SLOVENSKI STANDARD
01-december-2006
.DNRYRVWWDO±1DYRGLOR]DGRORþDQMHYUHGQRVWLQDUDYQHJDR]DGMD
Soil quality -- Guidance on the determination of background values
Qualité du sol -- Guide pour la détermination des valeurs de bruit de fond
Ta slovenski standard je istoveten z: ISO 19258:2005
ICS:
13.080.99 Drugi standardi v zvezi s Other standards related to
kakovostjo tal soil quality
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL ISO
STANDARD 19258
First edition
2005-12-15
Soil quality — Guidance on the
determination of background values
Qualité du sol — Guide pour la détermination des valeurs de bruit
de fond
Reference number
©
ISO 2005
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ii © ISO 2005 – All rights reserved

Contents Page
Foreword. iv
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 1
4 General. 3
5 Procedures. 3
5.1 General. 3
5.2 Objectives and technical approaches . 4
5.2.1 General. 4
5.2.2 Substances and parameters. 4
5.2.3 Study area. 6
5.2.4 Time period. 7
5.2.5 Scale of sampling (Support) . 7
5.3 Evaluation of existing data . 7
5.3.1 General. 7
5.3.2 Completeness of data sets/minimum requirements . 8
5.3.3 Comparability of data (Sampling, nomenclatures, analyses) . 8
5.3.4 Elimination of outliers . 9
5.4 Collection of new data. 9
5.4.1 Sampling. 9
5.4.2 Soil analysis. 12
5.5 Data processing and presentation. 13
5.5.1 Statistical evaluation of data . 13
5.5.2 Data presentation and reporting . 14
6 Data handling/quality control . 15
Annex A (informative) Scale of sampling. 17
Annex B (informative) Outlier tests . 19
Bibliography . 23

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 19258 was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 7, Soil and site
assessment.
iv © ISO 2005 – All rights reserved

INTERNATIONAL STANDARD ISO 19258:2005(E)

Soil quality — Guidance on the determination of background
values
1 Scope
This International Standard provides guidance on the principles and main methods for the determination of
pedo-geochemical background values and background values for inorganic and organic substances in soils.
This International Standard gives guidance on strategies for sampling and data processing and identifies
methods for sampling and analysis.
This International Standard does not give guidance on the determination of background values for
groundwater and sediments.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 10381-1, Soil quality — Sampling — Part 1: Guidance on the design of sampling programmes
ISO 10381-5, Soil quality — Sampling — Part 5: Guidance on the procedure for the investigation of urban and
industrial sites with regard to soil contamination
ISO 11074:2005, Soil quality — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11074 and the following apply.
3.1
background content
content of a substance in a soil resulting from both natural geological and pedological processes and including
diffuse source inputs
3.2
background value
statistical characteristic (3.8) of the background content
3.3
contaminant
substance or agent present in the soil as a result of human activity
NOTE There is no assumption in this definition that harm results from the presence of the contaminant.
3.4
diffuse source input
input of a substance emitted from moving sources, from sources with a large area or from many sources
NOTE 1 The sources can be cars, application of substances through agricultural practices, emissions from town or
region, deposition through flooding of a river.
NOTE 2 Diffuse source input usually leads to sites that are relatively uniformly contaminated. At some sites, the input
conditions may nevertheless cause a higher local input such as near the source or where atmospheric deposition/rain is
increased.
[ISO 11074:2005]
3.5
pedo-geochemical content
content of a substance in a soil resulting from natural geological and pedological processes, excluding any
addition of human origin
NOTE It may be hardly possible to determine the precise pedo-geochemical content of certain substances in a soil
due to anthropogenic diffuse contamination.
3.6
pedo-geochemical background value
statistical characteristic (3.8) of the pedo-geochemical content
NOTE Any estimate of pedo-geochemical background value will be prone to a certain amount of error given the
uncertainty associated with determining the pedo-geochemical content.
3.7
soil
upper layer of the Earth's crust composed of mineral parts, organic substance, water, air and living organisms
[ISO 11074:2005]
3.8
statistical characteristic
numerical value calculated from a variate of a chosen parameter of the population
EXAMPLE Examples of the statistical characteristics are the mean, the median, the standard deviation or the
percentiles of the ordered frequency distribution.
3.9
study area
three-dimensional definition of the area where samples are to be obtained from and thus for which the
background value(s) are to be estimated
3.10
support
size, shape and orientation of a soil sample
NOTE For the purpose of analysing spatial variation in soils geostatistically (by estimation of the variogram of a soil
property), the support should be the same at each sampling site.
3.11
variate
set of observed values of a variable
EXAMPLE A variate could for instance be the series of numbers of the concentration of a substance in soil or
numerous, individual soil samples.
2 © ISO 2005 – All rights reserved

4 General
Soils retain the evidence of their past history including impacts due to natural events or human activities.
Chemical impacts related to human activities can be detected in soils all over the world, even in regions far from
any source of contamination. For this reason, the background contents of inorganic and organic substances in
soils consist of a pedo-geochemical fraction and an anthropogenic fraction. The ratio of these fractions varies
widely depending on the type of substances, the type of soil and land use, and the kind and extent of external
impacts.
For many inorganic substances, the background content of unpolluted soils is dominated by the pedo-
geochemical content and consequently by the mineralogical composition of the soils parent material. Pedogenetic
processes may lead to a redistribution (enrichment/impoverishment) and consequently to a horizon-specific
differentiation of the substances within a soil profile. Persistent organic substances in soils originate more often
from non-natural sources and therefore the background content of soils is governed by the kind and extent of
diffuse contamination from non-soil sources.
In practice, it is often difficult to distinguish clearly between the pedo-geochemical and the anthropogenic fraction
of the background content of soils. Nonetheless, a detailed knowledge of the background content as well as of its
natural fraction for the substances of concern is essential both for any evaluation of the current status of soils for
environmental or land use related aspects or just for scientific purposes within the scope of pedology or
geochemistry. To this end, so-called background values in terms of the statistical characteristics of both, the pedo-
geochemical and the anthropogenic fraction have to be determined.
A variety of different objectives can be identified for the determination of background values of inorganic and/or
organic substances in soils. The objectives themselves provide insufficient information to define the technical
programme that will produce the desired background values. Thus a number of technical approaches have to be
defined which together form the basis of the technical programme.
This guidance provides essential aspects of sampling strategies and procedures, minimum requirements
regarding the necessary steps and ways of sample pre-treatment, analytical methods and statistical
evaluation procedures for determining sound and comparable background values.
Guidance is given for
a) evaluating existing data from different data sources and
b) setting up complete investigation programs aiming to compile background values for a clearly defined
three-dimensional picture of the soil.
These situations are representing the two extreme starting positions for the process of compiling background
values. In practice, a third intermediate situation may be dealt with when additional data need to be collected
because the quantity or quality of the existing data is insufficient.
5 Procedures
5.1 General
The procedures to determine background values encompass aspects of sampling (strategy, procedure), soil
analysis (pre-treatment, extraction and measurement), data processing and presentation. In general, two
starting positions can be distinguished, namely
a) the evaluation of existing data mostly from different data sources, and
b) the collection of new data based on an appropriate investigation strategy.
5.2 Objectives and technical approaches
5.2.1 General
Before commencing any survey on background values in soils it is of crucial importance to define the objective
of the survey and the related technical approach.
The objective is, in general terms, the definition of 'why' background values are to be determined. The
technical approaches describe aspects like the 'where', 'what', 'how' and 'when'. Together the technical
approaches determine the technical programme that will provide the required background values.
NOTE It should be noted that a technical approach that is fit for one objective, will often be unfit for other objectives.
The objectives for defining background values might be:
⎯ to identify the current contents of substances in soils, e.g. in the context of soil-related directives;
⎯ to assess the degree of contamination by human activities;
⎯ to derive reference values for soil protection;
⎯ to define soil values for reuse of soil material and waste;
⎯ to calculate critical levels and tolerable additional critical loads;
⎯ to identify areas/sites with atypically enhanced levels of element contents due to geogenic reasons or
human impact;
⎯ etc.
In order to meet the objective, the technical approaches might include the following.
⎯ Definition of the substances and parameters
⎯ For example, the background values to be estimated may be the total heavy metal content or the
bioavailable heavy metal content. (See 5.2.2)
⎯ Definition of the study area
⎯ The (three-dimensional) definition of the area where samples are to be obtained from. This has to be
a detailed description of what is to be considered as the study area, and what is not. (See 5.2.3.)
⎯ Definition of the time period of interest:
⎯ Are the historical or current contents relevant for the objective? (See 5.2.4.)
⎯ Definition of the size and geometry (support) of the area sampled at a sampling location. (See 5.2.5.)
5.2.2 Substances and parameters
Background values can be determined for all kinds of inorganic and organic substances in soils as well as soil
characteristics. In practice, the more persistent and immobile compounds are of primary interest because of
their potential to adsorb and accumulate in soil, whereas remobilization and intrinsic biodegradation are of
less significance.
As well as the substances of concern, basic soil parameters and site characteristics (see 5.4.1.3) need to be
provided to assist in interpretation of the contents of substances. A number of so-called basic soil parameters
influence soil processes that affect the contents of inorganic and organic substances. Table 1 lists these
parameters which should be analysed according to the given International Standards.
4 © ISO 2005 – All rights reserved

Within the group of inorganic substances, trace elements (e.g. heavy metals, micronutrients) are most often
analysed (Table 2). Concerning the analytical methods, a distinction has to be drawn between different
extraction/preparation methods (Table 2), whereof very few determine the total content which may be needed
for instance for calculating element stocks. Besides total contents, the (eco-) toxicologically more relevant
mobile fractions (Table 2) are of increasing interest, e.g. if pathway-related questions are to be examined.
Analysis of parameters in Table 2 should be carried out according to International Standards given in Table 2.
Table 1 — Basic soil parameters
Parameter Method ISO International Standard
Texture Sieving, sedimentation ISO 11277
Fraction of coarse material Sieving ISO 11277
Amount of non-soil material Sieving/visual control ISO 11259, ISO 11277
Bulk density Direct measurement of undisturbed ISO 11272
soil samples, estimation form soil
water retention curves
pH pH-electrode ISO 10390
Content of organic carbon Dry combustion ISO 14235
Cation exchange capacity, exchangeable cations BASECOMP ISO 11260
BaCl ISO 13536
Carbonate content CO-evolution ISO 10693
Table 2 — Examples for the analysis of inorganic substances
Parameter Speciation/form Extraction/preparation ISO International Standard
Method
Extraction/preparation Determination
Metalloids, e.g. ISO 14869-1 ISO 14869-1
Alkaline fusion + X-ray
Total
fluorescence HF + HCIO
arsenic and selenium ISO 14869-2 ISO 11047
Metals, Pseudo total aqua regia ISO 11466 ISO 11047
barium, cadmium, EDTA
Complexing
chromium, cobalt, DTPA ISO 14870 ISO 11047
copper, iron, lead, NaNO
manganese, mercury, NH NO
4 3
Exchangeable
molybdenum, nickel, CaCl
thallium, zinc KCl
Cyanides Water soluble H O, leaching tests See NOTE. See NOTE.
NOTE There are a variety of extraction and analytical methods for soil-water in the series of International Standards on water
quality which may also be applicable. However, it is important to confirm that they will work with the extracts obtained form particular soil
material.
Surveys on organic substances usually refer to persistent compounds. The persistent organic contaminants
listed in Table 3 are some of the more commonly encountered, but the list is not complete. Analysis should be
carried out according to International Standards listed in Table 3.
Various methods are used for the analysis of organic substances. The aim of these methods is usually to
extract the greatest possible quantity of organic substances from soils. It is important to recognize that organic
compounds may be extracted from naturally occurring organic materials (e.g. organic matter, decaying
vegetation, peat, charcoal), and that non-specific analyses in particular may, therefore, give misleading results.
Table 3 — Examples for the analysis of organic substances
Substance/groups of substances Method ISO International Standard
PAH Soxhlet/HPLC/UV ISO 13877
Thin-layer chromatography ISO 7981-1
RP C-18/HPLC ISO 7981-2
GC/MS ISO 18287
Dioxins/Furane
Chlorophenols Hexane/GC/ECD ISO 8165-1
Chlorpesticides RP C-18/HPLC/UV ISO 11369
PCBs GC-ECD ISO 10382
Chlornaphthalene
Chlorparafin
Bromodiphenylethers
NOTE There are a variety of extraction and analytical methods for water in the series of International Standards on water quality
which may also be applicable. However it is important to confirm that they will work with the extracts obtained from a particular soil
material.
When collecting new data for determining background values, it is recommended that the investigation
program be designed with regard to additional questions that could arise in future. In most cases, carrying out
new sampling campaigns is much more expensive than analysing additional substances in the first place. To
this end, a suitable storage of soil samples for subsequent analyses of organic or inorganic substances is of
crucial importance. Besides the substances of concern (Tables 2 and 3) and additional soil parameters
(Table 1), it is essential to provide a comprehensive site description (see 5.4.1.3) for interpretation purposes.
The documentation of all the actions taken is of utmost importance if the data measured is to be of use for
other assessments in future investigations.
5.2.3 Study area
The definition of the study area (3.9) can be based on two different principles, that is:
⎯ a purely spatial definition (X, Y, Z), defining the contours of the study area by the coordinates within which
the study area lies. Apart from the definition in a horizontal plane, the soil depth that is to be studied
should also be defined;
⎯ a typological definition of the study area, based on one or more characteristic(s), e.g. soil type (for
example, the A-horizon of a specific soil type), land use (also considering the potential effects on the
background values), elevation level, etc.
Of course, it is possible to mix the spatial and typological definition of the study area.
EXAMPLE Examples of a mix of the spatial and typological definition of the study area might be:
— the grassland in a county or province;
— the A-horizon in an area defined by X- and Y-coordinates.
The definition of the study area must be detailed at a level where there cannot be any misinterpretation on
what is and what is not part of the study area. For an unambiguous definition of the study area, all actual point
and diffuse sources within the study area need to be defined. As the general objective is to determine
background values, a safety zone around that (type of) source might be defined and thereby excluding parts
of the more generally defined study area. It might also result in specific zones for which the data is to be
considered separately from the rest of the study area.
6 © ISO 2005 – All rights reserved

The definition of the study area as described is independent of whether the soil samples are still to be taken,
or whether already existing soil samples (or results) are to be used. In the latter situation, the detailed
definition of the study area will define which samples/results are to be included or excluded.
5.2.4 Time period
Background values are influenced both by the natural processes (pedogenesis, biogeochemical cycles) as
well as by diffuse source input. Two different time scales can be distinguished:
⎯ the period in which the background value may significantly vary due to natural processes;
⎯ the period in which the background value will most probably only change due to human influences
(except for large scale natural phenomena).
The second period is generally smaller than the first one.
It might be that a specific historic period is of interest when measuring background values. When a soil layer is
formed during this same period, it is indeed possible to determine background values for a certain time period.
When background values are to be re-determined after a period of time in order to determine if changes occur,
the time period between measurements should be based on (see also ISO 16133):
⎯ the expected enrichment of substances in soils (accumulation for example due to diffuse source input);
⎯ the expected loss of substances in soils (for example, due to leaching, biodegradation or plant uptake);
⎯ changes in concentration level that can be determined both analytically and statistically.
5.2.5 Scale of sampling (Support)
Variability in concentrations is by definition a scale-related characteristic. Depending on the volume for which
an analytical result is to be considered representative, the variability in concentrations encountered might be
different. The scale — or in more technical terms the (geo-statistical) support (3.10) — is therefore an
important technical aspect on which a decision is to be made prior to data collection.
For (mainly) two-dimensional surveys, the support is the size (and geometry) of the area sampled at a
sampling location.
The study will always involve a certain soil layer of depth. However, as in the horizontal plane, the dimensions
are much larger than in the vertical plane, the support in soil surveys is most often defined in a two-
dimensional way.
More information on support is given in Annex A.
5.3 Evaluation of existing data
5.3.1 General
When using existing data, specific care must be taken concerning the quality and comparability of data
particularly if the data originate from different sources. Data with appropriate information have to be
harmonized in a step-wise procedure with regard to the specific evaluation objectives. In general, the
harmonization of data sets results in a more or less significant reduction of the respective variate. Nonetheless,
the procedure of harmonization of data sets is inevitable to produce a sound and reliable evaluation. The
respective harmonization strategy should encompass aspects like
a) the check of the completeness of the data sets related to minimum requirements,
b) the harmonization of different sampling strategies, references, nomenclatures and analytical procedures,
c) the identification and elimination of contaminated samples (excluded from the population of background
values by definition).
5.3.2 Completeness of data sets/minimum requirements
In order to ensure a minimum level of data quality, it is essential to provide sufficient and sound information of
the data, for instance
⎯ the date of sampling,
⎯ the procedure used to select sampling locations (plots),
⎯ the scale of sampling (e.g. support),
⎯ the site location (coordinates),
⎯ the sampling depth intervals,
⎯ the number and configuration of samples (e.g. regular grid or random sampling) taken at a sampling
location (plot),
⎯ the method used to extract and analyse the components (including quality assurance and detection limits),
⎯ the site-specific information (e.g. pedology/lithology, land use).
This information can be used to screen the data on their suitability for the objective of compiling background
values.
The definition of minimum requirements on information of the data set depends, amongst others, on the
substances of concern, the area and spatial reference to be considered and the approach pursued to achieve
an adequate spatial representation of the point-related data.
Apart from the information listed above, the type and degree of accuracy, e.g. of site-specific information
depends on soil and other parameters influencing the behaviour and hence the contents of the substances in
soils. For instance, inorganic substances need to be related at first priority to lithogenic soil properties due to
their predominant geogenic origin, whereas the content of organic substances of soils is more strongly
correlated to, e.g. land-use-related parameters.
5.3.3 Comparability of data (Sampling, nomenclatures, analyses)
Different sampling strategies may have a crucial impact on the comparability of data sets. Problems arise here
in particular through the comparison of horizon versus depth level-related samples and that of mixed versus
individual samples. Further on, the representative nature of the variate for a sample population with regard to
the same support for an area needs to be taken into account. Also, an uneven spatial distribution of the
sampling points within an area may cause biased estimates of the parameters of the frequency distribution
due to an overestimation of some parts of the study area. Block-kriging is recommended to deal with this
problem. It is strongly recommended to carefully balance the possible inaccuracies introduced by merging
data sets from different campaigns, versus the advantage of an increasing number of samples and
consequently an increasing representation of a population.
The extent to which different sample pre-treatments and analytical procedures (extraction, measurements)
can be compared and harmonized has to be evaluated in each individual case, e.g. against the intended
accuracy of the background value. For inorganic substances, the analytical results originating from different
analytical procedures may be transformed by applying regression functions or constants provided the
respective relations are known. Alternatively, the analytical procedures may be grouped roughly according to
the operationally defined extracted fractions (see Table 2). The broader the ranges of classified background
values as target variables are, the lower may be the demand of data comparability. Nonetheless, the assessor
should bear in mind, that merging data sets analysed by different analytical procedures invariably requires
compromises to be made.
8 © ISO 2005 – All rights reserved

5.3.4 Elimination of outliers
According to definition 3.1, the background content of substances in soils includes the moderate diffuse input
into the soil. Therefore, locally contaminated sites are excluded from the population of background contents.
Consequently, data obviously stemming from locally contaminated sites have to be identified and eliminated
from the respective data set. To this end several statistical tests for identifying outliers are applicable, e.g. test
on distribution of the data, exploratory data analysis (boxplots), principle component analysis, etc. (See also
5.5.1.2.1 and Annex B.)
NOTE The removal of outliers has a significant effect on the resulting definition of the background value. The
statistical identification of an outlier by itself is insufficient for removing a high (or low) measurement out of the database
describing the background value. The statistical test does however provide a good method of defining which data should
be investigated in more detail, in order to see if an explanation can be found for the high value to be an outlier. If such an
explanation is found, the value is indeed an outlier and should be eliminated.
5.4 Collection of new data
5.4.1 Sampling
5.4.1.1 Sampling strategy
5.4.1.1.1 General considerations
The natural pedo-geochemical content and the usual content of substances in soil vary according to soil
parent material. They also depend on soil horizons, as pedogenic processes modify and redistribute
components in soils, leading generally to the formation of several soil horizons that may exhibit different
compositions.
Land use and distance to contamination sources also influence the content of substances in soils. Human
activity modifies soil composition through agriculture, waste spreading, building, atmospheric deposition from
industry, households, traffic, etc. A sampling site is considered here as a small portion of land, from a few
square metres to about 1 ha, where one sample of each of the soil layers or horizons of interest is collected.
This section presents two strategies for selecting the sampling sites within the study area: the systematic
approach and the typological approach. The choice of one of them is generally influenced by the degree of
pre-existing knowledge about the soil and land use. When relatively little is known, the systematic approach is
often more appropriate. However, these two approaches can be considered as typical ones in the continuum
of all possible strategies. Therefore, it is possible to build an intermediate strategy, mixing some aspects of the
systematic approach with others from the typological one.
5.4.1.1.2 Systematic approach
The sampling sites are located using a grid. The interval between the grid points is dependent on the
resolution desired for the determination of the pedo-geochemical and/or background content. In principle, the
interval between the sampling sites should be such that the minimum number of samples can be collected to
represent each of the defined soil units. A square grid can be used, with cells varying in size (available
monitoring recommendations should be considered).
For instance, square cells with a 16 km, 5 km or 2,5 km site can be used at the scale of a country, whilst
square cells of a few hundred meters are more appropriate for the study at the level of a small area.
If sampling at a given grid point is rendered impossible due to buildings, roads, water surface or any other
reason, a new location may be chosen using a systematic procedure. For instance, a deviation may be
permitted from the initial point by steps of a definite distance north, then east, then south and finally west.
For each selected site, consider moving the sampling area if it is potentially highly contaminated by near-by
point sources, or in a pedo-geochemical way, if any source could compromise the purpose of the study (e.g.
overhead power-lines should be avoided if the zinc content of soils is of interest).
Samples are taken from soil layers of definite depths or from a defined pedological horizon or horizons. If the
surface layers are contaminated by diffuse sources, the contents determined indicate the background content
in these soils. For relatively immobile substances (e.g. heavy metals), the deep layers and particularly those at
a depth below 40 cm are generally uncontaminated (provided local contamination by point sources can be
excluded), and the respective substance content can be considered as the pedo-geochemical content.
A comprehensive site and soil description (Table 5) should be done at the same time as the samples are
taken.
5.4.1.1.3 Typological approach
In the typological approach, the soil is stratified according to soil parent material (for inorganic substances),
soil type and land use. Sites potentially highly contaminated by adjacent point sources are rejected.
The typological approach needs detailed information about the area to be investigated. Information (such as
on geology, pedology, land use and sources of possible contamination) has to be gathered and evaluated in
order to elaborate the sampling scheme.
For inorganic substances, the first step of the stratification of the area refers to the soil parent materials.
Within each type of parent material stratum, the soil is stratified again on the basis of pedogenesis, if this is
considered to have markedly modified the distribution of substances in soil. Further stratification, e.g. for
organic substances is related to land use; it is recommended to distinguish between cultivated and forest soils
and soil under meadow or spontaneous vegetation. On a local scale, the best stratification is based on
pedology, e.g. that of the soil series, as this taxonomic level generally explains most of the variation of the soil
properties. Finally, the horizon to be sampled has to be chosen.
Within one stratum, the sampling sites should generally be chosen in such a way that the area is covered
representatively. The choice of the sampling sites can be carried out within each stratum using a random or
systematic sampling scheme.
NOTE Apart from the degree of pre-existing knowledge, the type of question largely determines the choice between a
random or a systematic sampling scheme. To estimate parameters of a frequency distribution of the background contents,
a random sampling approach is most appropriate. For mapping background contents, in general, a (centred) regular grid is
more appropriate.
5.4.1.2 Number of sampling sites
Background values cannot be summarized in a central parameter such as the mean. It is necessary to
describe the variability of a given content in soil as precisely as possible. In the case of a normal probability
distribution, the number of samples necessary for the estimation of the standard deviation is independent from
the standard deviation of the population. It can be determined using Table 4, which shows that a minimum
number of 30 samples is necessary to estimate the standard deviation of a normal population.
Table 4 — Maximum relative error on the estimation of the standard deviation
of a normal population, with a = 0,05; n: number of samples
n e (%)
r
10 57
20 35
30 27
40 23
50 21
10 © ISO 2005 – All rights reserved

However, probability distributions of substances in soils are rarely normal. They are often positively skewed
but not necessarily log-normal. The estimation of the required number of samples to assess variability of such
a distribution can then be equal to the number of samples necessary to draw a representative histogram or to
calculate representative percentile. To this end, a minimum number of 30 samples is recommended.
5.4.1.3 Soil description
The interpretation of background contents of soils requires general information about the study area. The most
relevant parameters for the soil description of the study area are listed in Table 5. It is important to bear in
mind that the reliability of data interpretation strongly depends on a profound knowledge of the study area,
hence collection of parameters, indicated in Table 5, should be as comprehensive as possible.
Table 5 — Parameters for site and soil description
Parameter ISO
International
Standard
Landform and topography Topography, landform, land element, position coordinates, slope ISO 11259
microtopography
Land use and vegetation Land use, human influence, vegetation ISO 11259
Geology and lithology Kind of parent material, effective soil depth ISO 11259
Surface characteristics Rock outcrops, surface coarse fragments, erosion phenomena, surface ISO 11259
sealing, surface cracks, other characteristics
Soil-water-relationship Surface water balance, rainfall, evapotranspiration, groundwater ISO 11259
recharge, presence and depth of water table, site drainage, moisture
conditions
Soil type/soil profile Soil unit in regards of the classification system used ISO 11259
description
Sequence and depth of diagnostic horizons, kind of boudaries
Soil colour (matrix, mottling)
Organic matter
Texture, coarse elements, presence of non-soil material pedofeatures
Carbonates, field-pH, electrical conductivity
Structure, voids, fracturing, inhomogeneties
Compactness and consistence
Total estimated porosity
Roots, worm channels, biological activity
5.4.1.4 Sampling depth
Background contents and values vary with soil depth due to pedogenesis, use and type and source of
contamination. Sampling can be carried out on a fixed depth basis (i.e. layer) or according to definite horizon
types. Sampling according to the depth is easier as it does not need the identification of the horizon type. But
it will give a less precise measurement of the background contents, as it does not enable control of the
variability due to horizon differentiation and use.
As anthropogenic contamination mainly enters soil at the surface, the concentration measured in the upper
layers or horizons is regarded as a background content for those substances which are introduced in soil as a
consequence of human activity. The determination of these substances in the deep layers or horizons gives
an estimation of their pedo-geochemical content. For the substances that are not introduced in soils by human
activity, the analysis of any of the layers or horizons of this soil gives an estimation of the pedo-geochemical
content of this layer or horizon.
Note that in some cases, a contamination may also enter the soil from underground (e.g. by contaminated
ground water).
5.4.1.5 Sampling period
Sampling should be spread over a period of time chosen to limit the temporal variation of the background
contents.
When soil parameters do not vary within one year, which is the common case for most soil substances,
sampling can be carried out at any period of the year.
Practical aspects, mainly concerning the access to the soil horizon or layer, have to be considered before
choosing the sampling period. For instance, it may be difficult to sample deep horizons during a wet season,
due to the presence of a water table close to the surface. On the contrary, sampling during the dry season
may be rendered difficult by drought, which makes soil hard to penetrate with the sampling tools. Access to
cultivated plots may be difficult because of growing crops. In this case, it is advisable to sample shortly after
harvest and/or immediately after sowing.
5.4.1.6 Sampling technique
Sampling should be performed in accordance with ISO 10381-1 and ISO 10381-5. The following
recommendations may generally be taken into account. The sampling techniques depend on the depth or
horizon that has to be sampled. If only the surface horizon or layer has to be sampled, a hand corer or
equivalent tool can be used.
If deep horizons or layers have to be represented, a powered corer would be preferable. All sampling tools
must be designed and/or used in order to avoid cross contamination among layers or horizons.
Sampling in a soil pit is generally recommen
...

NORME ISO
INTERNATIONALE 19258
Première édition
2005-12-15
Qualité du sol — Guide pour la
détermination des valeurs de bruit de
fond
Soil quality — Guidance on the determination of background values

Numéro de référence
©
ISO 2005
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ii © ISO 2005 – Tous droits réservés

Sommaire Page
Avant-propos. iv
1 Domaine d'application. 1
2 Références normatives. 1
3 Termes et définitions. 1
4 Généralités. 3
5 Modes opératoires. 3
5.1 Généralités. 3
5.2 Objectifs et approches techniques. 4
5.2.1 Généralités. 4
5.2.2 Substances et paramètres . 4
5.2.3 Zone d'étude. 6
5.2.4 Période. 7
5.2.5 Échelle d'échantillonnage (support). 7
5.3 Évaluation de données existantes . 8
5.3.1 Généralités. 8
5.3.2 Exhaustivité des ensembles de données/exigences minimales . 8
5.3.3 Comparabilité des données (échantillonnage, nomenclatures, analyses). 9
5.3.4 Élimination des valeurs aberrantes . 9
5.4 Collecte de nouvelles données . 9
5.4.1 Échantillonnage . 9
5.4.2 Analyse du sol. 13
5.5 Traitement et présentation des données . 14
5.5.1 Évaluation statistique des données. 14
5.5.2 Présentation des données et rapport . 15
6 Exploitation des données/contrôle qualité . 16
Annexe A (informative) Échelle d'échantillonnage . 17
Annexe B (informative) Test de détection des valeurs aberrantes . 19
Bibliographie . 23

Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux de
normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général confiée
aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude a le droit de faire partie du
comité technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec
la Commission électrotechnique internationale (CEI) en ce qui concerne la normalisation électrotechnique.
Les Normes internationales sont rédigées conformément aux règles données dans les Directives ISO/CEI,
Partie 2.
La tâche principale des comités techniques est d'élaborer les Normes internationales. Les projets de Normes
internationales adoptés par les comités techniques sont soumis aux comités membres pour vote. Leur
publication comme Normes internationales requiert l'approbation de 75 % au moins des comités membres
votants.
L'attention est appelée sur le fait que certains des éléments du présent document peuvent faire l'objet de
droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour responsable de ne
pas avoir identifié de tels droits de propriété et averti de leur existence.
L'ISO 19258 a été élaborée par le comité technique ISO/TC 190, Qualité du sol, sous-comité SC 7, Évaluation
des sols et des sites.
iv © ISO 2005 – Tous droits réservés

NORME INTERNATIONALE ISO 19258:2005(F)

Qualité du sol — Guide pour la détermination des valeurs de
bruit de fond
1 Domaine d'application
La présente Norme internationale fournit des lignes directrices concernant la détermination des valeurs de
bruit de fond pédogéochimiques et des valeurs de bruit de fond des substances inorganiques et organiques
dans les sols.
La présente Norme internationale fournit également des lignes directrices en matière de stratégies
d'échantillonnage et de traitement des données et identifie des méthodes d'échantillonnage et d'analyse.
En revanche, la présente Norme internationale ne donne pas de lignes directrices concernant la détermination
des valeurs de bruit de fond pour les eaux souterraines et les sédiments.
2 Références normatives
Les documents de référence suivants sont indispensables pour l'application du présent document. Pour les
références datées, seule l'édition citée s'applique. Pour les références non datées, la dernière édition du
document de référence s'applique (y compris les éventuels amendements).
ISO 10381-1, Qualité du sol — Échantillonnage — Partie 1: Lignes directrices pour l'établissement des
programmes d'échantillonnage
ISO 10381-5, Qualité du sol — Échantillonnage — Partie 5: Lignes directrices pour la procédure
d'investigation des sols pollués en sites urbains et industriels
ISO 11074:2005, Qualité du sol — Vocabulaire
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions donnés dans l'ISO 11074:2005 et les suivants
s'appliquent.
3.1
teneur de fond
teneur d'une substance présente dans un sol du fait de processus géologiques et pédologiques naturels, y
compris des apports dus à une source diffuse
3.2
valeurs de bruit de fond
caractéristiques statistiques (3.8) de la teneur de fond
3.3
contaminant
substance ou agent présent dans le sol du fait de l'activité humaine
NOTE Cette définition n'implique aucunement que la présence du contaminant se traduit par un dommage.
3.4
apports dus à une source diffuse
apport d'une substance émise par des sources mobiles, des sources de grande étendue ou plusieurs sources
NOTE 1 Les sources peuvent être des automobiles, l'utilisation de substances dans le cadre de pratiques agricoles, les
émissions d'une ville ou d'une rivière, les dépôts dus aux crues d'une rivière.
NOTE 2 Les apports dus à une source diffuse conduisent habituellement à des sites à contamination relativement
uniforme. Pour certains sites, les conditions peuvent néanmoins être des facteurs d'augmentation de l'apport local,
comme à proximité de la source ou à l'endroit où les dépôts atmosphériques/pluviaux s'intensifient.
[ISO 11074:2005]
3.5
teneur pédogéochimique
teneur d'une substance présente dans un sol du fait de processus géologiques et pédologiques naturels, à
l'exception des substances introduites dans les sols du fait de l'activité humaine
NOTE Il peut être difficilement possible de déterminer la teneur pédogéochimique précise en certaines substances
d'un sol, du fait d'une contamination anthropogène diffuse.
3.6
valeur de bruit de fond pédogéochimique
caractéristiques statistiques (3.8) de la teneur pédogéochimique
NOTE Les estimations d'une valeur de bruit de fond pédogéochimique seront enclines à certaines erreurs, étant
donné l'incertitude associée à la détermination de la teneur pédogéochimique.
3.7
sol
couche supérieure de la couche terrestre, composée de parties minérales, de substance organique, d'eau,
d'air et d'organismes vivants
[ISO 11074:2005]
3.8
caractéristique statistique
valeur numérique calculée à partir de la variable aléatoire d'un paramètre choisi de la population
NOTE Exemples de caractéristiques statistiques: la moyenne, la valeur médiane, l'écart-type ou les percentiles de la
distribution de fréquence.
3.9
zone d'étude
définition tridimensionnelle de la zone où les échantillons doivent être prélevés et, par conséquent, pour
laquelle la ou les valeurs de bruit de fond doivent être estimées
3.10
support
taille, forme et orientation d'un échantillon de sol
NOTE Pour l'analyse géostatistique de la variation spatiale des sols (par estimation du variogramme d'une propriété
du sol), il convient que le support soit identique pour tous les sites d'échantillonnage.
3.11
variable aléatoire
ensemble des valeurs observées d'une variable
NOTE Une variable aléatoire peut, par exemple, correspondre à la série de valeurs de concentration d'une
substance dans le sol, pour de nombreux échantillons de sol distincts.
2 © ISO 2005 – Tous droits réservés

4 Généralités
Les sols conservent les traces de leur passé, y compris les impacts liés à des événements naturels ou aux
activités humaines. Il est possible de détecter les impacts chimiques relatifs aux activités humaines dans les
sols du monde entier, même dans les endroits éloignés de toute source de contamination. C'est pourquoi les
teneurs de bruit de fond des substances inorganiques et organiques dans les sols se composent d'une
fraction pédogéochimique et d'une fraction anthropogène. Le rapport de ces fractions varie largement en
fonction du type de substances, du type de sol et de son utilisation, ainsi que du type et de l'ampleur des
impacts externes.
Pour de nombreuses substances inorganiques, la teneur de bruit de fond des sols non pollués est dominée
par la teneur pédogéochimique et, par conséquent, par la composition minéralogique de la roche mère des
sols. Les processus pédogénétiques peuvent conduire à une redistribution (enrichissement/appauvrissement)
et, par conséquent, à une différenciation spécifique aux horizons des substances au sein d'un profil de sol.
Les substances organiques persistantes dans les sols proviennent le plus souvent de sources non naturelles
et la teneur de fond des sols est donc régie par le type et l'ampleur de la contamination diffuse par des
sources non pédologiques.
Dans la pratique, il est souvent difficile de distinguer clairement les fractions pédogéochimique et
anthropogène de la teneur de fond des sols. Néanmoins, une connaissance approfondie de la teneur de fond
ainsi que de la fraction naturelle des substances à inventorier est essentielle, que ce soit pour l'évaluation de
l'état actuel des sols du point de vue des aspects environnementaux ou de l'usage du sol, ou pour des études
scientifiques touchant à la pédologie ou à la géochimie. Pour ce faire, les valeurs de bruit de fond, en termes
de caractéristiques statistiques de la fraction pédogéochimique et de la fraction anthropogène, doivent toutes
deux être déterminées.
Il est possible d'identifier différents objectifs pour la détermination des valeurs de bruit de fond de substances
inorganiques et/ou organiques dans les sols. Les objectifs proprement dits ne fournissent pas suffisamment
d'informations pour définir le programme technique qui produira les valeurs de bruit de fond souhaitées. Par
conséquent, il faut définir plusieurs approches techniques qui, ensemble, formeront la base de ce programme
technique.
Ces lignes directrices indiquent les aspects essentiels des stratégies d'échantillonnage et des modes
opératoires, les exigences minimales concernant les étapes requises et les modes de prétraitement des
échantillons, les méthodes analytiques et les procédures d'évaluation statistique destinées à déterminer des
valeurs de bruit de fond fiables et comparables.
Ces lignes directrices sont données pour permettre
a) l'évaluation des informations existantes à partir de différentes sources de données, et
b) la mise en place de programmes d'investigation complets destinés à acquérir les valeurs de bruit de fond
afin d'obtenir une image tridimensionnelle et clairement définie du sol.
Ces deux situations représentent les deux situations initiales extrêmes du processus d'acquisition des valeurs
de bruit de fond. Dans la pratique, une troisième situation intermédiaire peut se présenter lorsqu'il est
nécessaire de collecter des données supplémentaires en raison de la quantité ou de la qualité insuffisantes
des informations existantes.
5 Modes opératoires
5.1 Généralités
Les modes opératoires pour déterminer les valeurs de bruit de fond englobent des aspects liés à
l'échantillonnage (stratégie, mode opératoire), à l'analyse des sols (prétraitement, prélèvement et mesurage)
ainsi qu'au traitement et à la présentation des données. En général, il est possible d'identifier deux situations
initiales, à savoir
a) l'évaluation des données existantes provenant principalement de sources d'informations différentes, et
b) la collecte de nouvelles données en fonction d'une stratégie d'investigation appropriée.
5.2 Objectifs et approches techniques
5.2.1 Généralités
Avant d'entamer une étude sur les valeurs de bruit de fond des sols, il est crucial de définir l'objectif de l'étude
et l'approche technique associée.
De manière générale, l'objectif consiste à expliquer «pourquoi» il faut déterminer les valeurs de bruit de fond.
Les approches techniques décrivent des aspects comme «où», «quoi», «comment» et «quand». Ensemble,
les approches techniques déterminent le programme technique qui fournira les valeurs de bruit de fond
requises.
Il convient de remarquer qu'une approche technique qui correspond à un objectif bien spécifique se révélera
souvent inappropriée à d'autres objectifs.
Les objectifs pour définir les valeurs de bruit de fond pourraient être les suivants:
⎯ identifier la teneur actuelle de substances dans les sols, par exemple dans le cadre des directives
relatives aux sols;
⎯ évaluer le degré de contamination par des activités humaines;
⎯ en déduire des valeurs de référence pour la protection des sols;
⎯ définir des valeurs pour la réutilisation du matériau du sol et des déchets;
⎯ calculer les niveaux critiques et les charges supplémentaires critiques tolérables;
⎯ identifier les zones/sites présentant des niveaux anormalement élevés de teneurs en éléments pour des
raisons géogéniques ou en raison de l'impact humain;
⎯ etc.
Afin d'atteindre cet objectif, les approches techniques pourraient inclure les éléments suivants.
⎯ Définition des substances et des paramètres:
par exemple, les valeurs de bruit de fond à estimer peuvent être la teneur totale ou biodisponible en
métaux lourds (voir 5.2.2).
⎯ Définition de la zone d'étude:
la définition (tridimensionnelle) de la zone où les échantillons doivent être prélevés; celle-ci doit décrire en
détail ce qui est considéré comme la zone d'étude et ce qui ne l'est pas (voir 5.2.3).
⎯ Définition de la période concernée: la teneur historique ou actuelle est-elle pertinente pour l'objectif visé?
(Voir 5.2.4.)
⎯ Définition de la dimension et de la géométrie (support) de la zone de prélèvement à l'emplacement
d'échantillonnage (voir 5.2.5).
5.2.2 Substances et paramètres
Il est possible de déterminer les valeurs de bruit de fond pour tous les types de substances inorganiques et
organiques présentes dans les sols, ainsi que les caractéristiques de ces derniers. Dans la pratique, les
composés les plus persistants et les plus immobiles sont les plus intéressants en raison de leur potentiel
d'adsorption et d'accumulation dans le sol, alors que la remise en mouvement et la biodégradation intrasèque
sont d'une plus faible importance.
4 © ISO 2005 – Tous droits réservés

De même que les substances concernées, il est nécessaire de fournir les paramètres de base des sols et les
caractéristiques des sites (voir 5.4.1.3) pour faciliter l'interprétation des teneurs en substances. Un certain
nombre de «paramètres de base du sol» influencent les processus du sol, qui affectent à leur tour les teneurs
en substances inorganiques et organiques. Le Tableau 1 dresse la liste des paramètres qu'il convient
d'analyser selon les Normes internationales données.
Au sein du groupe des substances inorganiques, les éléments traces (par exemple les métaux lourds, les
micronutriments) sont ceux qui sont le plus souvent analysés (Tableau 2). Concernant les méthodes
analytiques, il est nécessaire de faire la distinction entre les différentes méthodes de digestion/d'extraction
(Tableau 2), dont très peu déterminent la teneur totale qui peut, par exemple, être nécessaire pour calculer
les éléments. Outre la teneur totale, les fractions mobiles plus pertinentes sur le plan (éco-)toxicologique
(Tableau 2) revêtent un intérêt croissant, par exemple si les questions relatives aux voies d'exposition doivent
être examinées. Il est recommandé de réaliser l'analyse des paramètres du Tableau 2 selon les Normes
internationales indiquées au Tableau 2.
Tableau 1 — Paramètres de base du sol
Paramètre Méthode Norme internationale ISO
Texture Tamisage, sédimentation ISO 11277
Fraction de matériau grossier Tamisage ISO 11277
Quantité de matériaux non pédologiques Tamisage/contrôle visuel ISO 11259, ISO 11277
Mesurage direct d'échantillons
de sol non perturbés, estimation
Masse volumique en vrac ISO 11272
à partir des courbes de rétention
d'eau du sol
pH Électrode pH ISO 10390
Teneur en carbone organique Combustion sèche ISO 14235
BASECOMP ISO 11260
Capacité d'échange cationique,
cations échangeables
BaCl ISO 13536
Teneur en carbonate Évolution du CO ISO 10693
Tableau 2 — Exemples pour l'analyse de substances inorganiques
Norme internationale ISO
Méthode d'extraction/
Paramètre Spéciation/Forme
de préparation
Extraction/préparation Détermination
Métalloïdes, par exemple Fusion alcaline + ISO 14869-1 ISO 14869-1
Total
fluorescence de rayons X
arsenic et sélénium ISO 14869-2 ISO 11047
HF + HCIO
Métaux: Pseudo-totale Eau régale ISO 11466 ISO 11047
baryum, EDTA
Complexable
cadmium, chrome, DTPA ISO 14870 ISO 11047
cobalt, cuivre, fer, NaNO
manganèse, mercure, NH NO
4 3
Échangeable ISO 11047
molybdène, nickel, CaCl
plomb, thallium, zinc KCl
Cyanures Soluble dans l'eau H O, essais de lixiviation Voir NOTE Voir NOTE
NOTE Il existe diverses méthodes d'extraction et méthodes analytiques pour l'eau du sol dans la série de Normes internationales
sur la qualité de l'eau qui pourront également être applicables. Toutefois, il est important de confirmer qu'elles conviendront aux extraits
obtenus à partir d'un matériau de sol particulier.

Les études portant sur les substances organiques se rapportent généralement aux composés persistants. Les
contaminants organiques persistants indiqués dans le Tableau 3 sont quelques-uns des plus couramment
rencontrés, mais la liste est incomplète. L'analyse doit être réalisée conformément aux Normes
internationales indiquées au Tableau 3.
Différentes méthodes sont utilisées pour l'analyse des substances organiques. Leur but est généralement
d'extraire la plus grande quantité possible de substances organiques présentes dans les sols. Il est important
de ne pas oublier que des composés organiques peuvent être extraits de matériaux organiques d'origine
naturelle (par exemple matière organique, végétation en décomposition, tourbe, charbon de bois) et que des
analyses non spécifiques, en particulier, peuvent donc produire des résultats erronés.
Tableau 3 — Exemples d'analyse des substances organiques
Substances/groupes de substances Méthode Norme internationale ISO
HAP Soxhlet/HPLC/UV ISO 13877
Chromatographie en couche mince ISO 7981-1
RP C-18/HPLC ISO 7981-2
GC/MS ISO 18287
Dioxines/Furanes
Chlorophénols Hexane/GC/ECD ISO 8165-1
Pesticides chlorés RP C-18/HPLC/UV ISO 11369
PCB GC-ECD ISO 10382
Chloronaphtalène
Paraffine chlorée
Bromodiphényléthers
NOTE Il existe diverses méthodes d'extraction et méthodes analytiques pour l'eau dans la série de Normes internationales sur la
qualité de l'eau qui pourront également être applicables. Toutefois, il est important de confirmer qu'elles conviendront aux extraits
obtenus à partir d'un matériau de sol particulier.
Pour recueillir de nouvelles données pour déterminer les valeurs de bruit de fond, il est recommandé de
concevoir le programme d'investigation en tenant compte des autres questions susceptibles de surgir à
l'avenir. Dans la plupart des cas, réaliser de nouvelles campagnes d'échantillonnage revient bien plus cher
que d'analyser des substances supplémentaires dès le départ. Ainsi, il est crucial de bien stocker les
échantillons de sol pour de futures analyses des substances organiques ou inorganiques. Outre les
substances concernées (Tableaux 2 et 3) et les paramètres supplémentaires des sols (Tableau 1), il est
essentiel de fournir une description détaillée du site (voir 5.4.1.3) à des fins d'interprétation. La documentation
de toutes les actions entreprises est de la plus haute importance si les données mesurées doivent servir à
d'autres évaluations lors de futures investigations.
5.2.3 Zone d'étude
La définition de la zone d'étude (3.9) peut reposer sur deux principes différents, à savoir:
⎯ une définition purement spatiale (X, Y, Z), délimitant le pourtour de la zone d'étude à l'aide des
coordonnées au sein desquelles elle se trouve. En plus de la définition dans le plan horizontal, il convient
également de définir la profondeur du sol à étudier;
⎯ une définition typologique de la zone d'étude, basée sur une ou plusieurs caractéristiques telles que le
type de sol (par exemple, l'horizon A d'un type de sol spécifique), l'usage du sol (en tenant compte
également des effets potentiels sur les valeurs de bruit de fond), l'altitude, etc.
6 © ISO 2005 – Tous droits réservés

Il est évidemment possible de combiner les définitions spatiale et typologique de la zone d'étude.
NOTE Exemples de combinaison des définitions spatiale et typologique de la zone d'étude:
⎯ les pâturages d'un département ou d'une région;
⎯ l'horizon A sur une zone définie par des coordonnées X et Y.
La définition de la zone d'étude doit être aussi détaillée que nécessaire pour ne laisser aucune place aux
erreurs d'interprétation entre ce qui fait partie ou non de cette zone. Pour décrire de manière univoque la zone
d'étude, il est nécessaire de définir toutes les sources ponctuelles et diffuses qu'elle contient réellement.
L'objectif général consistant à déterminer les valeurs de bruit de fond, une zone de sécurité autour de ce type
de source peut être définie, en excluant ainsi des parties de la zone d'étude plus généralement définie. Les
données provenant de ces zones de sécurité peuvent être exclues de la zone d'étude, ou bien être
considérées séparément de celles du reste de la zone d'étude.
La définition de la zone d'étude telle que décrite ici reste inchangée, que les échantillons de sol soient à
prélever ou qu'ils soient déjà disponibles (ou les résultats correspondants). Dans ce dernier cas, la définition
détaillée de la zone d'étude établira quels échantillons/résultats doivent être inclus ou exclus.
5.2.4 Période
Les valeurs de bruit de fond sont influencées à la fois par les processus naturels (pédogenèse, cycles
biogéochimiques) et par les apports dus à une source diffuse. Deux échelles de temps peuvent être
distinguées:
⎯ la période pendant laquelle la valeur de bruit de fond peut varier considérablement en raison de
processus naturels;
⎯ la période pendant laquelle la valeur de bruit de fond changera le plus probablement uniquement en
raison d'influences humaines (à l'exception des phénomènes naturels à grande échelle).
La seconde période est généralement plus courte que la première.
Il se peut qu'une période historique spécifique se révèle intéressante lors du mesurage des valeurs de bruit
de fond. Si une couche du sol s'est formée lors de la période considérée, il est possible d'y déterminer des
valeurs de bruit de fond pour cette période.
Si les valeurs de bruit de fond doivent être redéterminées après un certain temps afin de déceler d'éventuels
changements, il convient que l'intervalle entre les mesurages soit fondé sur les éléments suivants (voir
également l'ISO 16133):
⎯ l'enrichissement prévu des substances dans les sols (accumulation, par exemple, du fait d'apports dus à
une source diffuse);
⎯ la perte prévue des substances dans les sols (par exemple due à la lixiviation, à la biodégradation ou à
l'absorption par les plantes);
⎯ les modifications du niveau de concentration, qui peuvent être déterminées à la fois de manière
analytique et statistique.
5.2.5 Échelle d'échantillonnage (support)
La variabilité des concentrations est, par définition, une caractéristique liée à l'échelle. Suivant le volume pour
lequel un résultat analytique doit être considéré comme représentatif, la variabilité des concentrations
rencontrées peut être différente. L'échelle — ou en termes plus techniques, le support (géostatistique)
(3.10) — est donc un aspect technique important pour lequel une décision doit être prise avant la collecte des
données.
Pour les études (principalement) bidimensionnelles, le support est la dimension (et la géométrie) de la zone
échantillonnée à un emplacement d'échantillonnage.
L'étude impliquera toujours une couche de sol d'une certaine profondeur. Toutefois, comme, dans le plan
horizontal, les dimensions sont beaucoup plus grandes que dans le plan vertical, le support est le plus
souvent défini d'une façon bidimensionnelle dans les études du sol.
L'Annexe A fournit plus d'informations sur le support.
5.3 Évaluation de données existantes
5.3.1 Généralités
Lors de l'utilisation de données existantes, leur qualité et leur comparabilité doivent faire l'objet d'un soin
particulier, notamment si elles proviennent de différentes sources. Les données et les informations
appropriées doivent être harmonisées selon une procédure par étapes, en fonction des objectifs d'évaluation
spécifiques. En général, l'harmonisation des ensembles de données se traduit par une réduction plus ou
moins importante de leur variable aléatoire respective. Néanmoins, cette procédure est inévitable pour obtenir
une évaluation correcte et fiable. Il convient que la stratégie d'harmonisation tienne compte d'aspects comme
a) la vérification de l'exhaustivité des ensembles de données par rapport à des exigences minimales;
b) l'harmonisation des différentes stratégies d'échantillonnage, des références, des nomenclatures et des
modes opératoires d'analyse;
c) l'identification et l'élimination des échantillons contaminés (exclus de la population des valeurs de bruit de
fond par définition).
5.3.2 Exhaustivité des ensembles de données/exigences minimales
Afin de garantir un niveau minimal de qualité des données, il est essentiel de fournir des informations
suffisantes et fiables à leur sujet, par exemple
⎯ la date d'échantillonnage;
⎯ le mode opératoire utilisé pour sélectionner les emplacements d'échantillonnage (parcelles);
⎯ l'échelle de l'échantillonnage (par exemple support);
⎯ la localisation du site (coordonnées);
⎯ les intervalles de profondeur d'échantillonnage;
⎯ le nombre et la configuration des échantillons (par exemple quadrillage ou prélèvements aléatoires)
prélevés à un emplacement d'échantillonnage (parcelle);
⎯ la méthode utilisée pour extraire et analyser les composants (y compris l'assurance qualité et les limites
de détection);
⎯ les informations spécifiques au site (par exemple pédologie/lithologie, usage du sol).
Ces informations peuvent être utilisées pour trier les données en fonction de leur compatibilité avec l'objectif
d'acquisition des valeurs de bruit de fond.
La définition des exigences minimales concernant les informations des ensembles de données dépend, entre
autres, des substances concernées, de la zone et de la référence spatiale à considérer, ainsi que de
l'approche adoptée pour obtenir une représentation spatiale adéquate des données ponctuelles. Mis à part les
informations indiquées ci-dessus, le type et le degré de précision, par exemple des informations spécifiques
au site, dépendent du sol et d'autres paramètres influençant le comportement et donc la teneur en certaines
substances dans les sols. Par exemple, les substances inorganiques doivent être liées en premier lieu aux
propriétés lithologiques du sol en raison de l'origine géogénique prédominante de ces substances, alors que
la teneur des sols en substances organiques est plus fortement corrélée à des paramètres liés à l'usage du
sol.
8 © ISO 2005 – Tous droits réservés

5.3.3 Comparabilité des données (échantillonnage, nomenclatures, analyses)
L'adoption de stratégies d'échantillonnage différentes peut avoir un impact crucial sur la comparabilité des
ensembles de données. Il est notamment problématique de comparer des échantillons liés à l'horizon à des
échantillons liés à la profondeur, ou des échantillons composites à des échantillons individuels. Ensuite, il faut
prendre en compte la représentativité de la variable aléatoire pour une population d'échantillons par rapport
au même support pour une zone donnée. De plus, une distribution spatiale inégale des points
d'échantillonnage au sein d'une zone peut entraîner des estimations biaisées des paramètres de distribution
de fréquence en raison d'une surestimation de certaines parties de la zone d'étude. Le krigeage par bloc est
recommandé pour remédier à ce problème. Il est fortement conseillé d'évaluer avec soin les imprécisions que
présente la fusion d'ensembles de données provenant de différentes campagnes au regard de la meilleure
représentation de la population permise par un plus grand nombre d'échantillons.
La mesure dans laquelle différents prétraitements et procédures analytiques d'échantillons (extraction,
mesurage) peuvent être comparés et harmonisés doit être évaluée au cas par cas, par exemple par rapport à
la précision recherchée de la valeur de bruit de fond. Pour les substances inorganiques, les résultats obtenus
à partir de différents modes opératoires d'analyse peuvent être transposés en appliquant des fonctions de
régression ou des constantes, à condition de connaître les relations correspondantes. Il est également
possible de regrouper grossièrement les modes opératoires d'analyse en fonction des fractions extraites
d'après le mode opératoire (voir le Tableau 2). Plus les gammes de valeurs de bruit de fond prises comme
variables cible sont étendues, plus l'exigence de comparabilité des données peut être faible. Néanmoins, le
responsable de l'évaluation ne doit pas oublier que la fusion des ensembles de données analysés par
différentes procédures analytiques exige invariablement que certains compromis soient faits.
5.3.4 Élimination des valeurs aberrantes
Conformément à la définition 3.1, la teneur de fond des substances dans les sols inclut l'apport diffus modéré.
Par conséquent, les sites contaminés localement sont exclus de la population de la teneur de fond. C'est
pourquoi les données provenant manifestement de sites contaminés localement doivent être identifiées et
éliminées de l'ensemble de données correspondant. À cette fin, il est possible d'appliquer plusieurs tests
statistiques pour identifier les valeurs aberrantes, par exemple des tests sur la distribution des données,
l'analyse exploratoire des données (boîtes à moustaches), l'analyse en composantes principales, etc. (voir
également en 5.5.1.2.1 et l'Annexe B).
NOTE La suppression des valeurs aberrantes a un effet considérable sur la définition de la valeur de bruit de fond.
L'identification statistique d'une valeur aberrante ne suffit pas en soi à éliminer un mesurage élevé (ou bas) de la base de
données décrivant la valeur de bruit de fond. Mais le test statistique offre une bonne méthode pour définir quelles données
il convient d'étudier plus en détail afin de définir s'il existe une explication pouvant justifier que la valeur élevée soit une
valeur aberrante. Si une telle explication est trouvée, la valeur est effectivement une valeur aberrante et il convient de
l'éliminer.
5.4 Collecte de nouvelles données
5.4.1 Échantillonnage
5.4.1.1 Stratégie d'échantillonnage
5.4.1.1.1 Considérations générales
Les teneurs pédogéochimique naturelle et usuelle des substances dans le sol varient selon la roche mère du
sol. Elles dépendent également des horizons, puisque les processus pédogénétiques modifient et
redistribuent les composants dans les sols, ce qui conduit généralement à la formation de plusieurs horizons
pouvant présenter différentes compositions.
L'usage du sol et la distance jusqu'aux sources de contamination influencent également la teneur en certaines
substances dans les sols. L'activité humaine modifie la composition de ces derniers par l'agriculture, la
dissémination de déchets, les constructions, les dépôts atmosphériques provenant de l'industrie, des
ménages, de la circulation, etc. Un site d'échantillonnage est considéré ici comme étant une petite portion de
terre, de quelques mètres carrés à environ 1 ha, où un échantillon de chacune des couches ou de chacun des
horizons des sols présentant un intérêt est collecté.
Cette section présente deux stratégies de sélection des sites d'échantillonnage dans la zone d'étude:
l'approche systématique et l'approche typologique. Le choix de l'une ou l'autre méthode est généralement
dicté par le degré de connaissances disponibles sur le sol et son utilisation. L'approche systématique convient
souvent mieux lorsque peu d'informations sont disponibles. Toutefois, ces deux approches peuvent être
considérées comme des exemples types parmi les nombreuses stratégies possibles. Il est donc possible
d'élaborer une stratégie intermédiaire, combinant certains aspects de l'approche systématique et d'autres de
l'approche typologique.
5.4.1.1.2 Approche systématique
Les sites d'échantillonnage sont localisés à l'aide d'une grille. La distance entre les points du quadrillage
dépend de la résolution désirée pour la détermination de la teneur pédogéochimique et/ou de la teneur de
fond. En principe, il convient que la distance entre les sites d'échantillonnage soit telle qu'un nombre minimal
d'échantillons puisse être collecté afin de représenter chacune des unités de sol définies. Il est possible
d'utiliser un quadrillage dont les cellules sont de dimension variable (il convient de prendre en considération
les recommandations de contrôle disponibles).
Par exemple, des carrés de 16 km, 5 km ou 2,5 km de côté peuvent être utilisés à l'échelle d'un pays, alors
que des carrés de quelques centaines de mètres conviennent mieux à l'étude d'une petite zone.
Si des bâtiments, des routes, des étendues d'eau ou autres rendent impossible l'échantillonnage à un point de
données du quadrillage, il est possible de choisir un nouvel emplacement en recourant à une procédure
systématique. Par exemple, il est possible de décaler l'emplacement par rapport à la situation initiale d'une
distance définie vers le nord, vers l'est, vers le sud et, enfin, vers l'ouest.
Pour chaque site sélectionné, décaler la zone d'échantillonnage s'il est considéré qu'elle est potentiellement
hautement contaminée par des sources à proximité ou que, sur le plan pédogéochimique, une source peut
concerner l'objet de l'étude (exemple: il convient d'éviter les lignes électriques non enterrées si la teneur des
sols en zinc présente un intérêt).
Des échantillons sont prélevés dans des couches de sol situées à des profondeurs bien précises ou dans un
ou plusieurs horizon(s) pédologique(s) défini(s). Si les couches superficielles sont contaminées par des
sources diffuses, la teneur déterminée indique la teneur de fond dans ces sols. Pour des substances
relativement immobiles (par exemple des métaux lourds), les couches profondes et, en particulier, celles
situées à une profondeur de plus de 40 cm ne sont généralement pas contaminées (à condition que la
contamination locale par des sources ponctuelles puisse être exclue) et la teneur respective en substance
peut être considérée comme la teneur pédogéochimique naturelle.
Il convient de dresser une description exhaustive du site et des sols (Tableau 5) au moment du prélèvement
des échantillons.
5.4.1.1.3 Approche typologique
Dans l'approche typologique, le sol est stratifié selon sa roche mère (pour les substances inorganiques), son
type et son utilisation. Rejeter les sites potentiellement hautement contaminés par des sources ponctuelles
adjacentes.
L'approche typologique requiert des informations détaillées concernant la zone à étudier. Il est nécessaire de
collecter et d'évaluer des informations portant sur la géologie, la pédologie, l'usage du sol et les sources
possibles de contamination, afin d'élaborer le système d'échantillonnage.
Pour les substances inorganiques, la première étape de la stratification de la zone se rapporte aux roches
mères du sol. Au sein de chaque type de couches de roche mère, stratifier à nouveau le sol en fonction de la
pédogenèse s'il est considéré que cette dernière a modifié de façon prononcée la distribution des substances
dans le sol. Une autre stratification, par exemple pour les substances organiques, est liée à l'usage du sol: il
est conseillé de faire la distinction entre les sols cultivés et forestiers, et les sols situés sous la végétation
spontanée ou les prairies. À l'échelle locale, la meilleure stratification se fonde sur la pédologie, par exemple
celle de la série sol, puisque ce niveau taxonomique explique généralement la plupart des variations des
propriétés des sols. Enfin, il faut choisir l'horizon à échantillonner.
10 © ISO 2005 – Tous droits réservés

Au sein d'une strate, il convient généralement de choisir les sites d'échantillonnage de façon que la zone soit
couverte de manière représentative. Le choix des sites d'échantillonnage peut être effectué au sein de
chaque strate à l'aide d'un système d'échantillonnage aléatoire ou systématique.
NOTE Outre le degré de connaissances disponibles, l'objectif joue également un rôle déterminant dans le choix entre
un système d'échantillonnage aléatoire ou systématique. Une approche de prélèvement aléatoire convient généralement
mieux pour estimer les paramètres d'une distribution de fréquence de la teneur de fond. Tandis que pour cartographier la
teneur de fond, un quadrillage (centré) est généralement plus adapté.
5.4.1.2 Nombre de sites d'échantillonnage
Les valeurs de bruit de fond ne peuvent se résumer à un paramètre central tel que la moyenne. Il est
nécessaire de décrire la variabilité d'une teneur donnée dans un sol de façon aussi précise que possible.
Dans le cas d'une loi de probabilité normale, le nombre d'échantillons nécessaires pour estimer l'écart-type ne
dépend pas de l'écart-type de la population. Il peut être déterminé à l'aide du Tableau 4, qui montre qu'un
minimum de 30 échantillons est nécessaire pour estimer l'écart-type d'une population normale.
Tableau 4 — Erreur relative maximale pour l'estimation de l'écart-type
d'une population normale, où α = 0,05; n: est le nombre d'échantillons
e (%)
n
r
10 57
20 35
30 27
40 23
50 21
Toutefois, les lois de probabilité des substances dans les sols sont rarement normales. Elles sont souvent
positivement asymétriques, mais pas nécessairement log-normales. L'estimation du nombre requis
d'échantillons pour évaluer la variabilité d'une telle distribution peut alors être égale au nombre d'échantillons
nécessaires pour dresser un histogramme représentatif ou pour calculer un percentile représentatif. À cette fin,
un minimum de 30 échantillons est recommandé.
5.4.1.3 Description du sol
L'interprétation de la teneur de fond des sols requiert des informations générales sur la zone d'étude. Le
Tableau 5 dresse la liste des paramètres les plus pertinents pour la description du sol de la zone d'étude. Il
est important de ne pas oublier que la fiabilité de l'interprétation des données dépend énormément de la
connaissance approfondie de la zon
...