ISO 22190:2020

INTERNATIONAL ISO
STANDARD 22190
First edition
2020-03
Soil quality — Use of extracts for the
assessment of bioavailability of trace
elements in soils
Qualité du sol — Utilisation d'extraits pour l'évaluation de la
biodisponibilité des éléments traces dans les sols
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Background . 2
4.1 General . 2
4.1.1 Presence of trace elements in the soil matrix . 2
4.1.2 Neutral extracts for measurement of actual availability (ISO 21268-1) . 4
4.1.3 Acid extracts for measurement of potential availability (ISO 17586) . 4
4.2 Tiered approach based on bioavailability . 5
5 General procedure using an extract . 5
6 Reporting . 6
7 Calibration . 6
7.1 Introduction . 6
7.2 Applicability of soil extracts . 7
7.3 Limits of soil extracts to estimate trace element bioavailability . 7
Annex A (informative) Calibration towards biological targets . 8
Annex B (informative) Examples of transfer functions .11
Bibliography .12
Foreword
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This document was prepared by Technical Committee ISO/TC 190, Soil Quality, Subcommittee SC 7, Soil
and site assessment.
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iv © ISO 2020 – All rights reserved

Introduction
As already mentioned in ISO 17402, laboratory and field studies have demonstrated that biological
effects are not related to the total concentration of a contaminant in the soil. Instead, an organism
responds only to the fraction that is biologically available (bioavailable) for that organism. In the
conservative approach of exposure assessment as typically described in a regulatory context, it is
assumed that the total concentration of a contaminant present in a soil or soil-like material is available
for uptake by organisms, including man, which will overestimate the risks. Therefore, a risk assessment
can be optimised by using an approach that is based on estimated exposure representing the available,
effective concentration of the contaminant(s) and on (existing) intrinsic toxicity data.
In standardization of methods for assessing the bioavailability of trace elements a framework of
standards is used with the following layering of standards (see Figure 1). Starting point is ISO 17402 in
which chemical and biological methods are distinguished and where guidance for selection of relevant
methods is given. If a chemical method is to be used to establish environmental availability, there are
the following possibilities:
a) Extractions based on equilibrium. For this approach standards are available or under development.
b) Method based on non-equilibrium. For this approach standards are not yet under development.
If these standards become available they will also be included in this document (dashed line in
Figure 1).
The methods referred to in this standard are all based on extraction. Extraction can be considered as a
model to simulate the pore water concentration. The extraction methods give results that can be used
in assessment and this standard gives guidance for that use.
The method for human bioaccessibility (ISO 17924) is not presented in Figure 1. It is an extraction
method that simulates the human intestinal system and is specific for assessment of human risks.
Key
Red this document
Grey existing standards
Green not yet available — for future development
Figure 1 — Layering of standards for bioavailability of trace elements
(situation April 2018)
In the scientific research to bioavailability a large number of definitions and concepts are in use, which
reflect the discussion in the scientific world. However, for regulatory purposes a more clear and simple
approach is necessary. In a regulatory context, contaminants are either bioavailable or non-bioavailable.
To support decisions, both should be measurable.
As presented in Figure 2, the bioavailable fraction can be measured using the method described in this
document.
vi © ISO 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 22190:2020(E)
Soil quality — Use of extracts for the assessment of
bioavailability of trace elements in soils
1 Scope
This document provides guidance on the use of chemical methods establishing the bioavailability of
trace elements in soil and soil-like materials and to stimulate the use of bioavailability in assessments.
The methods themselves are not subject of this document.
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
ISO 17402, Soil quality — Requirements and guidance for the selection and application of methods for the
assessment of bioavailability of contaminants in soil and soil materials
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11074, ISO 17402 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
bioavailability
degree to which chemicals present in the soil can be absorbed or metabolised by a human or ecological
receptor or are available for interaction with biological systems
Note 1 to entry: The concept of bioavailability is further explained in ISO 17402.
Note 2 to entry: This document follows the approach of Reference [20] as illustrated in Figure 2, in which all
defined fractions are measurable as further explained in Clause 4.
Note 3 to entry: In ISO 17924 a definition specific for human uptake through ingestion is defined as the fraction
of a substance present in ingested soil that reaches the systemic circulation (blood stream).
[SOURCE: ISO 11074:2015, 5.2.2, modified — Note 2 to entry was added and the following note to entry
renumbered.]
3.2
environmental availability
fraction of contaminant physico-chemically driven by desorption processes potentially available to
organisms
[SOURCE: ISO 17402:2008, 3.3]
3.3
environmental bioavailability
fraction of the environmentally available compound which an organism takes up through physiologically
driven processes
[SOURCE: ISO 17402:2008, 3.5]
3.4
toxicological bioavailability
internal concentration of pollutant accumulated and/or related to a toxic effect
3.5
actual availability
concentration present in the soil pore water to which organisms are directly exposed.
Note 1 to entry: This definition refers to internal concentrations in humans, mammals and other organisms.
[SOURCE: ISO 17402:2008, 3.18]
3.6
potential availability
amount present in the soil sample (mg/kg) that can be released from the solid phase to the pore water
within a specific time frame
3.7
bioaccessibility
fraction of a substance in soil or soil-like material that is liberated in (human) gastrointestinal juices
and thus available for absorption or the amount available to cross an organism’s cellular membrane
from the environment if the organism has access to the chemical
Note 1 to entry: See ISO 10390 for more information on the chemical.
[SOURCE: ISO 17924:2018, 3.2, modified — The definition was modified by adding "or the amount
available to cross an organism’s cellular membrane from the environment if the organism has access to
the chemical" and a Note 1 to entry was added.]
4 Background
4.1 General
4.1.1 Presence of trace elements in the soil matrix
Because the total exposure of organisms depends on time, the available fraction is not a fixed fraction,
but should be divided into multiple fractions or be described as a continuum. The release of the
contaminants depends on local environmental conditions (e.g. pH). The simplest approach determines:
a) an actually available fraction or the actual dissolved amount at ambient conditions;
b) a potentially available fraction, which is the maximum amount that can be released to the soil
pore water under (predefined) worst-case conditions. This can also be expressed as the reactive
fraction;
c) a non-available fraction.
All together represent the total concentration. For environmental purposes it is generally accepted that
the amount measured using aqua regia (see ISO 11466) represents the total concentration. In Figure
...