EN ISO 19258:2018

SLOVENSKI STANDARD
01-december-2018
1DGRPHãþD
SIST EN ISO 19258:2011
SIST ISO 19258:2006
.DNRYRVWWDO1DYRGLOR]DGRORþDQMHYUHGQRVWLQDUDYQHJDR]DGMD,62
Soil quality - Guidance on the determination of background values (ISO 19258:2018)
Bodenbeschaffenheit - Leitfaden zur Bestimmung von Hintergrundwerte (ISO
19258:2018)
Qualité du sol - Lignes directrices pour la détermination des valeurs de bruit de fond (ISO
19258:2018)
Ta slovenski standard je istoveten z: EN ISO 19258:2018
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.

EN ISO 19258
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2018
EUROPÄISCHE NORM
ICS 13.080.99
English Version
Soil quality - Guidance on the determination of
background values (ISO 19258:2018)
Qualité du sol - Lignes directrices pour la Bodenbeschaffenheit - Leitfaden zur Bestimmung von
détermination des valeurs de bruit de fond (ISO Hintergrundwerte(ISO 19258:2018)
19258:2018)
This European Standard was approved by CEN on 3 August 2018.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 19258:2018 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 19258:2018) has been prepared by Technical Committee ISO/TC 190 "Soil
quality" in collaboration with Technical Committee CEN/TC 345 “Characterization of soils” the
secretariat of which is held by NEN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2019, and conflicting national standards shall
be withdrawn at the latest by March 2019.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 19258:2011.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 19258:2018 has been approved by CEN as EN ISO 19258:2018 without any modification.
INTERNATIONAL ISO
STANDARD 19258
Second edition
2018-08
Soil quality — Guidance on the
determination of background values
Qualité du sol — Recommandations pour la détermination des
valeurs de fond
Reference number
ISO 19258:2018(E)
©
ISO 2018
ISO 19258:2018(E)
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
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Published in Switzerland
ii © ISO 2018 – All rights reserved

ISO 19258:2018(E)
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 . 6
5.2.5 Scale of sampling . 7
5.3 Evaluation of existing data . 7
5.3.1 General. 7
5.3.2 Completeness of data sets/minimum requirements . 7
5.3.3 Comparability of data (sampling, nomenclatures, analyses) . 8
5.3.4 Examination of outliers . 8
5.4 Collection of new data . 9
5.4.1 Sampling. 9
5.4.2 Soil analysis .13
5.5 Data processing and presentation.14
5.5.1 Statistical evaluation of data .14
5.5.2 Data presentation and reporting .15
6 Data handling/quality control .16
Annex A (informative) Outlier tests .18
Annex B (informative) Examples of the main substances and parameters .22
Bibliography .24
ISO 19258:2018(E)
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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 7,
Impact assessment.
This second edition cancels and replaces the first edition (ISO 19258:2005), which has been technically
revised. The main changes compared to the previous edition are as follows:
— Clauses 2 and 3, and subclauses 5.3, 5.4, 5.4 and Annex B (formerly Annex C) have been completely
technically revised;
— 5.2.2 has been revised and the structure of its subclauses has been changed to 5.2.2.1, Basic
parameters, 5.2.2.2, Persistent compounds (split up into 5.2.2.2.1, Inorganic substances, and 5.2.2.2.2,
Organic substances), and 5.2.2.3 Non persistent compounds (added);
— text has been added to 5.2.5;
— “typological” has been replaced by “judgemental” throughout the document;
— “scale of sampling” has been deleted from Annex A;
— the Bibliography has been updated.
iv © ISO 2018 – All rights reserved

INTERNATIONAL STANDARD ISO 19258:2018(E)
Soil quality — Guidance on the determination of
background values
1 Scope
This document gives guidelines for the principles and main methods for the determination of
background values for inorganic and organic substances in soils at a local/regional scale. The site scale
is excluded.
It gives guidelines for sampling and data processing strategies. It identifies methods for sampling and
analysis.
This document does not apply to the determination of background values for groundwater and
sediments.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 11074, 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.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
background concentration
concentration of an element or a substance characteristic of a soil type in an area or region arising from
both natural sources and anthropogenic diffuse sources such as atmospheric deposition
[SOURCE: ISO 11074:2015, 3.5.1, modified — In the definition, “an element or” has been introduced
before “a substance” and “anthropogenic” has replaced “non-natural”. Note 1 to entry has been
removed.]
3.2
background value
statistical characteristics (3.8) of the total (natural pedo-geochemical and anthropogenic) content of a
substances in soil
Note 1 to entry: Commonly expressed in terms of average, typical, median, mode, a range of values or a
background value.
[SOURCE: ISO 11074:2015, 3.5.2, modified — Note 1 to entry has been added from ISO 11075:2014, 3.5.1.]
ISO 19258:2018(E)
3.3
diffuse source input
input of a substance emitted from moving sources, from sources with a large area or from many sources
Note 1 to entry: In practice, two situations are commonly recognized: rural areas with diffuse source inputs
typically from land spreading and aerial deposition; and urban areas where the diffuse source inputs come
typically from traffic and industrial activities.
Note 2 to entry: Diffuse source input usually leads to sites that are relatively uniformly contaminated. At
some sites, the input conditions can nevertheless cause a higher local input, such as near the source or where
atmospheric deposition/rain is increased. Two types of main diffuse source input can be considered: one in rural
areas (e.g. atmospheric deposits, spreading); and one in urban areas (e.g. traffic, industries).
[SOURCE: ISO 11074:2015, 3.3.9, modified — Note 1 to entry has been replaced with new text. The last
sentence in Note 2 to entry has been added.]
3.4
pedo-geochemical concentration
concentration of a substance in a soil resulting from natural geological and pedological processes,
excluding any addition of anthropogenic origin
Note 1 to entry: It is difficult to determine the precise pedo-geochemical concentration of certain substances in
soil due to the presence of anthropogenic diffuse contamination.
3.5
pedo-geochemical background value
statistical characteristic (3.8) of the pedo-geochemical concentration (3.4)
Note 1 to entry: Any estimate of pedo-geochemical background value is prone to certain errors given the
uncertainty associated with determining the pedo-geochemical concentration.
[SOURCE: ISO 11074:2015, 3.5.9, modified — In the definition, “concentration” has replaced “content”.]
3.6
anthropogenic concentration
concentration of a substance in a soil resulting from anthropogenic origin
3.7
anthropogenic background value
statistical characteristic (3.8) of the anthropogenic background concentration (3.1) of a substance in soils
3.8
statistical characteristic
numerical value calculated from a variate (3.10) of a selected parameter of the population
EXAMPLE Mean, median, standard deviation, standard error, percentiles of the ordered frequency
distribution.
[SOURCE: ISO 11074:2015, 3.5.11, modified — “selected” has replaced “chosen” and “standard error”
has been added in the example.]
3.9
study area
three-dimensional definition of the area where samples are to be obtained from and, thus, for which the
background values (3.2) are to be determined
[SOURCE: ISO 11074:2015, 5.2.29]
3.10
variate
set of observed values of a variable
EXAMPLE Series of numbers of the concentration of a substance in soil; numerous, individual soil samples.
2 © ISO 2018 – All rights reserved

ISO 19258:2018(E)
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 determination of background
values of inorganic and organic substances in soils consists 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 concentration is dominated by the pedo-geochemical
concentration and, consequently, by the mineralogical composition of the soils’ parent material.
Pedogenetic processes can 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. Therefore, the background concentration 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 concentration of soils. Nonetheless, a detailed knowledge of
the background concentration and its natural fraction for the substances of concern is essential for any
evaluation of the current status of soils for environmental or land use related aspects, as well as 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 should 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 should be defined, which together form the basis of the technical programme.
This guidance identifies:
— essential requirements of sampling strategies and procedures;
— minimum requirements regarding the necessary steps and ways of sample pretreatment;
— analytical methods;
— statistical evaluation procedures for determining sound and comparable background values.
Guidance is given on:
a) evaluating existing data from different data sources;
b) setting up investigation programmes to compile background values for a clearly defined three-
dimensional picture of the soil.
These situations represent the two extreme starting positions for the process of compiling background
values. In practice, there is also a third intermediate situation in which additional data are collected
because the quantity or quality of the existing data are insufficient.
5 Procedures
5.1 General
The procedures to determine background values encompass aspects of sampling (e.g. strategy,
procedure), soil analysis (e.g. pretreatment, extraction, 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;
ISO 19258:2018(E)
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 that are determined.
The technical approaches describe aspects such as the “where”, “what”, “how” and “when”. Together,
the technical approaches determine the technical programme that will provide the required
background values.
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 could be:
— to identify the current concentrations of substances in soils, e.g. in the context of soil-related
regulations;
— 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 chemical substance contents due to
geogenic reasons or human impact, etc.
In order to meet the objective, the technical approaches could include:
— definition of the substances and parameters, e.g. the background values to be estimated may be the
total metal concentration or the bioavailable metal concentration (see 5.2.2);
— definition of the study area, e.g. the (three-dimensional) definition of the area where samples are
obtained from, including 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, e.g. whether the historical or current concentration is
relevant for the objective (see 5.2.4);
— definition of the size and geometry of the area to be sampled at a sampling location (see 5.2.5);
— definition of the pretreatment of the sample (see 5.4.2.2) and the fraction of soil to be analysed.
5.2.2 Substances and parameters
5.2.2.1 Basic 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 substances are of primary interest
because of their potential to adsorb and accumulate in the soil. Substances in which the concentration
can be influenced by 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) should
be provided to assist in the interpretation of the concentrations of substances. A number of so-called
basic soil parameters influence soil processes that affect the concentrations of inorganic and organic
4 © ISO 2018 – All rights reserved

ISO 19258:2018(E)
substances. Table B.1 lists these parameters, which should be analysed in accordance with the given
International Standards.
5.2.2.2 Persistent compounds
5.2.2.2.1 Inorganic substances
Within the group of inorganic substances, trace elements (e.g. metals, micronutrients) are most often
analysed (see Table B.2). While constituting an urban geochemical background, it is recommended to
analyse the whole package listed in Table B.2; most of these elements are found with high values due to
human activities, but some minerals can appear with high value naturally.
Concerning the analytical methods, a distinction should be drawn between different extraction/
preparation methods (see Table B.2), as very few methods determine the total concentration that could
be needed, e.g. when calculating element stocks. Besides total concentrations, the (eco-) toxicologically
more relevant mobile fractions (see Table B.2) are of increasing interest, e.g. if pathway-related
questions are to be examined. An analysis of the parameters in Table B.2 should be carried out in
accordance with International Standards given in Table B.2.
5.2.2.2.2 Organic substances
Surveys on organic substances usually refer to persistent compounds. The persistent organic
contaminants listed in Table B.3 are some of the more commonly encountered, but the list is not complete.
Analysis should be carried out in accordance with the International Standards listed in Table B.3. The
list should be adapted according to the objectives of the determination of background values.
It is not recommended to sample and analyse non-persistent substances as they will not be detected
by the laboratory because of their behaviour (e.g. volatilization, high degradation). These kinds of
substances are normally analysed for detecting sources of contamination.
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 can be extracted from naturally occurring organic materials (e.g. organic matter,
decaying vegetation, peat, charcoal), and that non-specific analyses, in particular, can, therefore, give
misleading results.
When collecting new data for determining background values, it is recommended that the investigation
programme 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, suitable storage of soil samples for subsequent analyses of organic or
inorganic substances is of crucial importance. Besides the substances of concern (see Tables B.2 and
B.3) and additional soil parameters (see Table B.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 are to be of use for other assessments in future investigations.
NOTE Guidance on the storage of soil samples is provided in ISO 18512.
5.2.2.3 Non-persistent compounds
In some cases, generating background values on non-persistent substances could be of interest. Special
care should be taken when volatile, degradable organic substances or transformable, inorganic species
are the subject of the study. A detailed description and documentation of sampling and analysis is of
particular importance in such cases. Storage or archiving of samples is not recommended because of
the behaviour of such organic and inorganic species.
ISO 19258:2018(E)
5.2.3 Study area
The definition of the study area (see 5.2.3) can be based on two different principles:
— 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 horizon of interest
that is to be studied should also be defined;
— a typological definition of the study area, based on one or more characteristics, e.g. soil type (such
as the A-horizon of a specific soil type), land use (also considering the potential effects on the
background values), elevation level.
It is possible, of course, to combine the spatial and typological definition of the study area.
EXAMPLE A combination of spatial and typological definitions of the study area could 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 should be detailed at a level where there cannot be any misinterpretation
of 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 should be defined.
As the general objective is to determine background values, a safety zone around that (type of) source
can be defined, which thereby excludes parts of the more generally defined study area. There could also
be specific zones in which the data are considered separately from the rest of the study area.
Samples to be used for the determination of background values should not be taken from near potential
localized sources of contamination (e.g. roads, industrial sites).
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 (e.g. pedogenesis, biogeochemical
cycles) as well as by anthropogenic diffuse source input. Two different time scales can be distinguished:
— the period in which the background value can vary significantly 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 could 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 the following (see also ISO 16133):
— the expected enrichment of substances in soils (accumulation, e.g. due to diffuse source input);
— the expected loss of substances in soils (e.g. due to leaching, biodegradation, plant uptake);
— changes in concentration level that can be determined both analytically and statistically.
6 © ISO 2018 – All rights reserved

ISO 19258:2018(E)
5.2.5 Scale of sampling
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 could be different. The scale is, therefore, an important technical aspect on which a
decision is to be made prior to data collection.
The study will always involve a certain soil layer for depth. However, as in the horizontal plane, the
dimensions are much larger than in the vertical plane, the scale in soil surveys is most often defined in
a two-dimensional way.
The variability of the natural pedo-geochemical concentration and of the background concentration
often increases with the size of the study area (population), but decreases with the size of the
sample support (scale of sampling). Increasing the sampling support is a method that can reduce the
variability of the background concentration. However, increasing the sampling support often makes the
sampling more laborious and is only recommended under conditions where the sampling and sampling
preparation errors can be minimized. It is recommended to use the same scale of sampling if the natural
pedo-geochemical value is used to evaluate soil contamination. If the background values are used to
support delineation of contaminated land, it is recommended to use the same scale of sampling. For
large scale sampling support, composite sampling (see 5.4.1.6) is often preferred in order to avoid the
handling of excessively large amounts of soil.
5.3 Evaluation of existing data
5.3.1 General
When using existing data, specific care should be taken concerning the quality and comparability of
data, particularly if the data originate from different sources, by consideration of the measurement
uncertainty. Data with appropriate information should be harmonized in a step-wise procedure with
regard to the specific evaluation objectives. In general, the harmonization of data sets results in a
[36]
more or less significant reduction of the bias between the data sets . Harmonization of sample sets
is essential if sound and reliable evaluation of the combined data is to be achieved. The harmonization
strategy should include:
a) a check on the completeness of the data sets (including estimates of the uncertainty of each
measurement);
b) a harmonization of different sampling strategies, references, nomenclatures and analytical
procedures;
c) an identification and elimination of contaminated samples (excluded from the population of
background values by definition).
NOTE Natural anomalies of the pedo-geochemical background can generate high values that can appear
as contaminated samples. It is important to anticipate these cases with an accurate desk study in order to not
eliminate these samples.
5.3.2 Completeness of data sets/minimum requirements
In order to ensure a minimum level of data quality, sufficient and sound information about the data
should be provided, for example:
— the date of sampling;
— the procedure used to select sampling locations (plots);
— the scale of sampling (area or local);
— the site location (coordinates);
— the sampling depth intervals;
ISO 19258:2018(E)
— the number and configuration of samples (e.g. regular grid, random sampling) taken at a sampling
location (plot);
— the method of sample preparation (e.g. dying, crushing, sieving);
— the method used to extract and analyse the components (including quality assurance data, estimate
of analytical uncertainty and detection limits in accordance with ISO 18400-106);
— the site-specific information (e.g. pedology/lithology, land use);
— the urban areas specificities (e.g. excavated materials).
This information can be used to screen the data on their suitability for the objective of compiling
background values.
The minimum information required about a data set depends, among other things, on the substances of
concern, the area, spatial reference to be considered and the approach pursued to achieve an adequate
spatial representation of the sampling location.
Apart from the information listed above, the type and degree of accuracy (e.g. of site-specific information)
depends on the soil and other parameters influencing the behaviour and, hence, the concentrations of
substances in the soil. For example, inorganic substances should be related at first priority to lithogenic
soil properties due to their predominant geogenic origin, whereas the concentration of organic
substances of soils is more strongly correlated to, for example, land-use-related parameters.
5.3.3 Comparability of data (sampling, nomenclatures, analyses)
Different sampling strategies can have a crucial impact on the comparability of data sets. Problems
arise, in particular, through the comparison of horizon versus depth level-related samples and that of
composite versus individual samples. In addition, the representative nature of the variate for a sample
population with regard to the same scale for an area should be taken into account. Also, an uneven
spatial distribution of the sampling points within an area can cause biased estimates of the parameters
of the frequency distribution due to an overestimation of some parts of the study area. Following an
initial review of the raw data on a map, an appropriate spatial interpolation method should be used.
Geographical information system (GIS) software is particularly useful for this task, especially for data
sets (see ISO 18400-104:—, 6.1 and Annex H). It is strongly recommended to carefully balance the
possible inaccuracies introduced by merging data sets from different campaigns with the advantage of
an increasing number of samples and, consequently, an increasing representation of a population.
The extent to which different sample pretreatments and analytical procedures (e.g. extraction,
measurements) can be compared and harmonized should be evaluated in each individual case (e.g.
against the intended accuracy of the background value). For all the 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 B.2).
If the ranges of classified background values as target variables are broader, the demands of data
comparability are lower. Nonetheless, the assessor should bear in mind that merging data sets analysed
by different analytical procedures invariably requires compromises to be made. By definition, the
background values are relatively low, except in natural high pedo-geochemical background zones. It
can be important to take into account detection and quantification limits of each device of analysis
when judging the comparability of data.
5.3.4 Examination of outliers
The background concentration of substances in soils includes the moderate diffuse input into the
soil. Therefore, locally contaminated sites and natural anomalies are excluded from the population of
background concentrations. Consequently, data obviously stemming from locally contaminated sites
should be identified and eliminated from the respective data set. The detection of data outliers and
unusual data behaviour is one of the main tasks in the statistical analysis of geochemical data. To
this end, several statistical tests for identifying outliers are applicable, e.g. tests on the distribution
8 © ISO 2018 – All rights reserved

ISO 19258:2018(E)
of the data, exploratory data analysis (boxplots) and principle component analysis (see also 5.5.1.2.1
and Annex A). In practice, the use of the boxplot for preliminary class selection to display spatial data
structure in a map has proven to be a powerful tool for identifying the key geochemical processes
behind a data distribution. Different outlier tests are available (e.g. Dixon test, Grubbs test) and should
[37]
be chosen according to the relevant assumptions for the study . In the case of multidimensional data
(samples from different soil horizons), principal component analysis can be important if dimensional
reduction is possible on transformed data.
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. On the contrary, if the explanation shows that it is a natural anomaly,
the outlier is not eliminated, but the scale of the study should be reconsidered. For example, if there
was a few high values that are likely to be due to natural processes, the options are either to increase
the spatial scale of the study to confirm this hypothesis or to consider the use of zoning/depth interval
classifications (e.g. due to lithology/geology) to better differentiate between different background
populations.
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 concentration and the usual concentration 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 could
exhibit different compositions. These parameters can also influence the variation of concentrations
and should be considered: soil organic matter, soil sorption coefficient, carbonate content, particle size,
moisture content, cation exchange capacity, pH.
Land use and distance to contamination sources also influence the concentration 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 one hectare, where one sample of each of the soil layers or
horizons of interest is collected.
Two strategies for selecting the sampling sites within the study area are presented: the systematic
approach (5.4.1.1.2) and the judgemental approach (5.4.1.1.3). 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 judgemental one. This hybrid approach is recommended when investigating in urban areas: the
systematic approach allows optimization of the coverage of the area, while the judgemental approach
allows flexibility in the location of sampling points within each cell so as to be able to focus on available
soil surface and excluding (potentially) contaminated soil.
5.4.1.1.2 Systematic approach
The sampling locations 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 backgro
...