ISO/FDIS 7303

Simplified method for prediction of the oral bioaccessibility of metals and metalloids in soils

Méthode simplifiée pour la prédiction de la bioaccessibilité orale des métaux et des métalloïdes dans les sols

General Information

• Status: Not Published
• ICS: 13.080.30 - Biological properties of soils
• Technical Committee: ISO/TC 190/SC 7 - Impact assessment
• Drafting Committee: ISO/TC 190/SC 7 - Impact assessment
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 28-Jul-2025
• Completion Date: 28-Jul-2025

Standards Content (Sample)

FINAL DRAFT
International
Standard
ISO/TC 190/SC 7
Simplified method for prediction of
Secretariat: DIN
the oral bioaccessibility of metals
Voting begins on:
and metalloids in soils
2025-07-28
Voting terminates on:
2025-09-22
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 190/SC 7
Simplified method for prediction of
Secretariat: DIN
the oral bioaccessibility of metals
Voting begins on:
and metalloids in soils
Voting terminates on:
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Test principle . 2
5 Apparatus . 2
6 Reagents . 3
7 Procedure . 3
7.1 Sample pre-treatment .3
7.2 Preparation of test samples .3
7.3 Extraction procedure .3
8 Data handling, quality control and presentation of results .4
8.1 General .4
8.2 Expression of results . .5
8.3 Method performance characteristics .6
Annex A (informative) Method performance characteristics on reference materials . 7
Annex B (informative) Linear regression models used to predict the bioaccessibility of As, Cd
and Pb in soils .11
Annex C (informative) Graphic representation of prediction intervals .15
Annex D (informative) Method performance characteristics assessed by interlaboratory trial . 17
Bibliography .29

iii
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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of 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 www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 7, Impact
assessment.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
Soils enriched with metals and metalloids such as arsenic (As), cadmium (Cd), and lead (Pb) pose a potential
threat to human health if they are directly ingested or transferred through food. Incidental ingestion of
soil particles is considered an important exposure pathway of metals and metalloids, more specifically for
children through outdoor hand-to-mouth activities. In the current context of managing polluted sites and
soils, assessing human health risks from the ingestion of contaminated soil particles remains a challenging
area, with significant uncertainties in the methods used to protect public health. In some countries, current
practices of risk assessment are based on total concentrations of metals and metalloids measured in soils.
However, it is known that only a fraction of these metals and metalloids, i.e. the bioavailable fraction, is
assimilated by the body and is likely to induce a toxic effect. Estimating exposure based on the total
concentration of metals and metalloids therefore leads to overestimating the risk and possibly misclassifying
sites as being at risk. This overestimation leads to excessive measures and costs in terms of management of
these sites.
Taking into account the bioavailability of metals and metalloids in soils makes it possible to better assess
exposures and risks and thus optimize the management of associated sites. Bioavailability is in practice
estimated by the measurement of bioaccessibility, i.e. the soluble fraction that can be released into the
gastrointestinal tract and that can reach the bloodstream. Methods have been developed and validated to
mimic the availability of metals and metalloids in the human gastrointestinal tract. These in vitro laboratory
tests simulate in vivo results. Among these methods, ISO 17924 is a reference method for assessing the oral
bioaccessibility of As, Cd and Pb. Because ISO 17924 involves high technical skills and requires numerous
chemical and biological reagents to mimic biochemical conditions in the gastrointestinal tract, it can often
only be used for a small number of samples. If bioaccessibility needs to be estimated on many samples, a
simplified method to predict bioaccessibility is of great interest, in particular for reasons of time and cost.
It has been clearly shown that the bioaccessibility of metals and metalloids in soils critically depends on
soil type, their chemical speciation, and the solid-phase distribution in soils. Consequently, a simplified
single-extraction method applicable to a range of soils regardless of their pedological, physical and chemical
characteristics is needed. A simplified method to study jointly both the gastric and the intestinal phases is
particularly advantageous.
This document provides a rapid, simple, and reproducible approach for predicting the bioaccessibility of
metals and metalloids in gastric and gastrointestinal phases. The simplified method is specifically designed
for As, Cd and Pb in soil samples, as assessed using ISO 17924, and relies on mathematical equations.
These equations were derived from studies on French soil samples with a wide range of physicochemical
parameters (in terms of texture, pH, content of organic matter and carbonates) and metals and metalloids
concentrations (described in Reference [2]).
Digestion with hydrochloric acid (HCl) solution fulfils the criteria to be satisfied by an extractant for routine
analyses. It is easy for analytical laboratories to use and reproduces conditions that are close to human
physiological conditions (i.e. solid/liquid ratio, reagent, temperature, pH and residence time in the stomach).
It can be applied to a wide spectrum of soils (in terms of physicochemical parameters) and elements (more
specifically As, Cd and Pb) in a wide concentration range. This document differs from ISO 17924 in terms of
application and methodology. More specifically, the simplified test can be used as a suitable proxy to predict
the bioaccessibility of metals and metalloids in a first-tier screening on several soil samples. It is intended
to help users to select a few samples (approximately 10 % of samples but can be as high as 20 % to 30 %
depending on the size of the starting sample, heterogeneity of total concentrations and context, e.g. high pH
values, high carbonate content) in a second-tier study and as a validation approach complementary to the
method defined in ISO 17924 for better assessment of human exposure.
Because the ISO 17924 test has only been validated against in vivo data for As, Cd and Pb, the HCl test as
described in this document is only validated for approximation of the oral bioaccessibility of these elements
in soils. The simplified method could potentially be used for other elements; however, because no validation
exists for the other metals or metalloids, the data obtained could only be considered as a useful line of
evidence in interpreting results.

v
FINAL DRAFT International Standard ISO/FDIS 7303:2025(en)
Simplified method for prediction of the oral bioaccessibility
of metals and metalloids in soils
1 Scope
This document deals with the assessment of human exposure to metals and metalloids from ingestion of
soil. It specifies a simplified method for the prediction of the oral bioaccessibility of metals and metall
...

ISO/TC 190/SC 07/WG 4 7
Secretariat: DIN
Date: 2025-05-1307-14
Simplified method for prediction of the oral bioaccessibility of metals
and metalloids in soils
FDIS stage
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.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Fax: [phone]
EmailE-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test principle . 2
5 Apparatus . 3
6 Reagents . 3
7 Procedure . 3
7.1 Sample pre-treatment . 3
7.2 Preparation of test samples . 4
7.3 Extraction procedure . 4
8 Data handling, quality control and presentation of results . 4
8.1 General . 4
8.2 Expression of results . 5
8.3 Method performance characteristics . 7
Annex A (informative) Method performance characteristics on reference materials . 8
Annex B (informative) Linear regression models used to predict the bioaccessibility of As, Cd
and Pb in soils . 12
Annex C (informative) Graphic representation of prediction intervals . 19
Annex D (informative) Method performance characteristics assessed by interlaboratory trial . 23
Bibliography . 38

iii
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 documentdocuments 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO'sISO’s adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 7, Impact
assessment.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Soils enriched with metals and metalloids such as arsenic (As), cadmium (Cd), and lead (Pb) pose a potential
threat to human health if they are directly ingested or transferred through food. Incidental ingestion of soil
particles is considered an important exposure pathway of metals and metalloids, more specifically for children
through outdoor hand-to-mouth activities. In the current context of managing polluted sites and soils,
assessing human health risks from the ingestion of contaminated soil particles remains a challenging area,
with significant uncertainties in the methods used to protect public health. In some countries, current
practices of risk assessment are based on total concentrations of metals and metalloids measured in soils.
However, it is known that only a fraction of these metals and metalloids, i.e. the bioavailable fraction, is
assimilated by the body and is likely to induce a toxic effect. Estimating exposure based on the total
concentration of metals and metalloids therefore leads to overestimating the risk and possibly misclassifying
sites as being at risk. This overestimation leads to excessive measures and costs in terms of management of
these sites.
Taking into account the bioavailability of metals and metalloids in soils makes it possible to better assess
exposures and risks and thus optimize the management of associated sites. Bioavailability is in practice
estimated by the measurement of bioaccessibility, i.e. the soluble fraction that can be released into the
gastrointestinal tract and that can reach the bloodstream. Methods have been developed and validated to
mimic the availability of metals and metalloids in the human gastrointestinal tract. These in vitro laboratory
[1]
tests simulate in vivo results. Among these methods, ISO 17924 is a reference method for assessing the oral
bioaccessibility of As, Cd and Pb. Because ISO 17924 involves high technical skills and requires numerous
chemical and biological reagents to mimic biochemical conditions in the gastrointestinal tract, it can often only
be used for a small number of samples. If bioaccessibility needs to be estimated on many samples, a simplified
method to predict bioaccessibility is of great interest, in particular for reasons of time and cost.
It has been clearly shown that the bioaccessibility of metals and metalloids in soils critically depends on soil
type, their chemical speciation, and the solid-phase distribution in soils. Consequently, a simplified single-
extraction method applicable to a range of soils regardless of their pedological, physical and chemical
characteristics is needed. A simplified method to study jointly both the gastric and the intestinal phases is
particularly advantageous.
This document provides a rapid, simple, and reproducible approach for predicting the bioaccessibility of
metals and metalloids in gastric and gastrointestinal phases. The simplified method is specifically designed
for As, Cd and Pb in soil samples, as assessed using ISO 17924, and relies on mathematical equations. These
equations were derived from studies on French soil samples with a wide range of physicochemical parameters
(in terms of texture, pH, content of organic matter and carbonates) and metals and metalloids concentrations
[2]
(described in Reference [2 ).]).
Digestion with hydrochloric acid (HCl) solution fulfils the criteria to be satisfied by an extractant for routine
analyses. It is easy for analytical laboratories to use and reproduces conditions that are close to human
physiological conditions (i.e. solid/liquid ratio, reagent, temperature, pH and residence time in the stomach).
It can be applied to a wide spectrum of soils (in terms of physicochemical parameters) and elements (more
specifically As, Cd and Pb) in a wide concentration range. This document differs from ISO 17924 in terms of
application and methodology. More specifically, the simplified test can be used as a suitable proxy to predict
the bioaccessibility of metals and metalloids in a first-tier screening on several soil samples. It is intended to
help users to select a few samples (approximately 10 % of samples but can be as high as 20- % to 30 %
depending on the size of the starting sample, heterogeneity of total concentrations and context, e.g.,. high pH
values, high carbonate content) in a second-tier study and as a validation approach complementary to the
method defined in ISO 17924 for better assessment of human exposure.
Because the ISO 17924 test has only been validated against in vivo data for As, Cd and Pb, the HCl test as
described in this document is only validated for approximation of the oral bioaccessibility of these elements
in soils. The simplified method could potentially be used for other elements; however, because no validation
v
exists for the other metals or metalloids, the data obtained could only be considered as a useful line of evidence
in interpreting results.
vi
FINAL DRAFT International Standard ISO/FDIS 7303:2025(en)

Simplified method for prediction of the oral bioaccessibility of metals
and metalloids in soils
1 Scope
This document deals with the assessment of human exposure to metals and metalloids from ingestion of soil.
It specifies a simplified method for the prediction of the oral bioaccessibility of metals and metalloids from
contaminated soils.
The method is a chemical extraction using hydrochloric acid (HCl) and can be used at least for first-tier
screening for prediction of the oral bioaccessibility of arsenic (As), cadmium (Cd) and lead (Pb) in soil samples.
It produces extracts that are representative of the bioaccessible concentrations measured by using the
[1]
validated UBM (unified bioaccessibility method) method (UBM) (ISO 17924) .). More specifically, from the
extractable concentrations of metal(loid)smetals and metalloids by HCl, the “predicted bioaccessibility” in
both the gastric and gastrointestinal phases is calculated using the equations and the prediction intervals
provided in thethis document, and which have been derived from simple linear regressions of data obtained
[2[2] ]
during validation studies . .
NOTE The simplified method is applicable to prediction of the metals and metalloids bioaccessibility in soil with
total concentrations range from 2 mg/kg to 2 600 mg/kg for As, from 0,2 mg/kg to 480 mg/kg for Cd, and from 4 mg/kg
to 50 000 mg/kg for Pb.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1
bioaccessibility
fraction of a contaminant present in ingested soil that is solubilised in the digestive fluids and thus available
for absorption
3.2 3.2
bioavailability
fraction of a contaminant present in ingested soil that reaches the systemic circulation
3.3 3.3
exposure
dose of a chemical that reaches the human body
3.4 3.4
simplified method
one-step procedure to assess the availability of metals and metalloids in soil by using a chemical extractant
4 Test principle
The principle of the method (Figure 1(Figure 1)) is to mimic the ability of the human body to dissolve metals
...