ISO 21226:2019

Soil quality - Guideline for the screening of soil polluted with toxic elements using soil magnetometry

This document specifies methods for the measurements of magnetic susceptibility of soils (κ) as an indicator of potential soil pollution/contamination with trace elements associated with technogenic magnetic particles (TMPs) and describes related procedures, protocols and guidelines to be applied as a screening geophysical method of determination of soil pollution with trace elements. The results of measurements are used for preparing the maps of magnetic susceptibility of soils in the area of interest. From these maps, the areas of elevated and high magnetic susceptibility indicating high trace element total pollution load are discriminated for further identification of pollutants by geochemical methods. This document is applicable to screening all TMPs-related anthropogenic emission sources including long-range transport of airborne elements, of which TMPs are carriers and indicators. Such emission sources comprise the majority of high-temperature industrial processes, where iron is present in any mineralogical form in raw materials, additives or fuels, is transformed into ferrimagnetic iron oxides (e.g. fossil solid and liquid fuels combustion, metallurgy, cement and ceramics industry, coke production, industrial waste landfills, land transport). This document is not applicable to screening anthropogenic emissions not associated with TMPs, e.g. organic pollutants or emissions from agricultural sources. NOTE 1 Copper, zinc and other non-ferrous metal ores also contain iron (in many sulfides) as this element is abundant in almost all environments. During smelting, the iron occurring in sulfides is transformed into ferrimagnetic oxides (TMPs). However, in such cases, the proportion of TMPs and related PTEs is usually less than at coal combustion or iron metallurgy, for example, and not all PTEs are physically associated and transported by TMPs. Non-airborne elements are deposited in the close proximity of the emission source, while TMPs can be used in these cases as indicators of airborne elements and of the spatial distribution of the total element deposition from a smelter in the area. In rare cases, some soils are developed on bedrock exhibiting geogenically high magnetism, which can cause false-positive results. This influence can, however, be easily indicated by measurements of magnetic susceptibility along soil profiles. This method is not applicable when the bedrock exhibits extremely high magnetic signals. NOTE 2 Such cases are rare.

Qualité du sol — Lignes directrices pour le diagnostic de la pollution du sol par des éléments toxiques en utilisant la magnétométrie

General Information

• Status: Published
• Publication Date: 11-Dec-2019
• ICS: 13.080.10 - Chemical characteristics of soils
• Technical Committee: ISO/TC 190/SC 3 - Chemical and physical characterization
• Drafting Committee: ISO/TC 190/SC 3/WG 10 - Screening methods
• Current Stage: 9093 - International Standard confirmed
• Start Date: 27-Jun-2025
• Completion Date: 13-Dec-2025

Overview

ISO 21226:2019 - Soil quality: Guideline for the screening of soil polluted with toxic elements using soil magnetometry - defines a standardized screening geophysical method that uses measurements of magnetic susceptibility (κ) to indicate potential soil pollution with trace elements associated with technogenic magnetic particles (TMPs). The standard specifies field and laboratory procedures, sampling protocols, data mapping and reporting guidelines to produce magnetic susceptibility maps that direct follow‑up geochemical analysis.

Key topics and technical requirements

• Measurement principle: Use of magnetic susceptibility as a proxy for cumulative anthropogenic deposition of potentially toxic elements (PTEs) carried by TMPs.
• Scope limitations: Applicable to TMP‑related airborne emissions (e.g., combustion, metallurgy, cement, waste landfills, transport). Not applicable to pollutants not associated with TMPs (organic contaminants, agricultural emissions) or to soils developed on bedrock with extremely high natural magnetism (rare).
• Sampling and measurement procedures:
  • Design of a measurement network for area screening.
  • Topsoil surface κ measurements in situ and vertical profile measurements using soil cores (minimum core dimensions specified in the standard).
  • Laboratory measurements (mass susceptibility, frequency dependence χfd) to identify superparamagnetic contributions and validate field data.
• Data processing and mapping: Creation of 2D/3D magnetic susceptibility maps, data analysis and discrimination of areas with elevated κ for targeted geochemical sampling.
• Reporting and validation: Requirements for a screening report and annexed guidance relating κ to trace element contamination, performance examples and validation summaries.

Practical applications and users

ISO 21226:2019 is designed for practical use where rapid, cost‑effective screening of large areas is needed to detect soil pollution from airborne, high‑temperature industrial sources. Typical users include:

• Environmental consultants and remediation practitioners performing site assessments and brownfield screening.
• Soil scientists and geochemists integrating geophysical screening with targeted chemical analysis.
• Regulators and environmental agencies planning monitoring networks and risk prioritization.
• Industrial environmental monitoring teams (metallurgy, power plants, cement works) and researchers studying long‑range transport of trace elements.

Practical benefits include reduced sampling and laboratory costs by using magnetic susceptibility mapping to focus geochemical analyses on the most affected zones and improved spatial understanding of deposition patterns from TMP‑related emissions.

Related standards (if applicable)

ISO 21226:2019 complements other soil quality and geochemical sampling standards and geophysical survey guidance used by environmental professionals. Users should integrate this screening method with validated geochemical analyses and local regulatory frameworks when assessing soil contamination.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21226
First edition
2019-12
Soil quality — Guideline for the
screening of soil polluted with toxic
elements using soil magnetometry
Qualité du sol — Lignes directrices pour le criblage du sol pollué par
des éléments toxiques en utilisant la magnétométrie du sol
Reference number
©
ISO 2019
© ISO 2019
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
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below or ISO’s member body in the country of the requester.
ISO copyright office
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Published in Switzerland
ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 3
5 Fundamentals . 3
5.1 Screening principle . 3
5.2 Screening work processes . 4
5.3 Field measurements and works . 4
5.4 Laboratory measurements . 4
5.5 Data mapping . 4
5.6 Soil sampling for geochemical analysis . 4
6 Apparatus . 4
6.1 Field equipment . 4
6.2 Laboratory equipment . 5
6.3 Data mapping . 5
7 Procedures . 5
7.1 Measurement network . 5
7.2 Measurements of magnetic susceptibility at the topsoil surface . 5
7.3 Measurements of vertical magnetic susceptibility distribution . 6
7.3.1 General. 6
7.3.2 Topsoil core sampling . 6
7.3.3 Field measurements. 6
7.3.4 Laboratory measurements . 6
7.3.5 Topsoil magnetic profile analysis . 6
7.4 Magnetic susceptibility mapping and data analysis . 7
7.4.1 Data processing . 7
7.4.2 Magnetic susceptibility surface mapping . 7
7.4.3 Data analysis . 7
7.5 Soil sampling for geochemical analysis . 7
8 Screening report . 8
Annex A (informative) Relation between magnetic susceptibility and trace element
contamination of topsoil . 9
Annex B (informative) Measurement performance according to 7.1 and 7.2 .16
Annex C (informative) Example of a screening report to record measurement results
according to 9 .18
Annex D (informative) Validation summary .22
Bibliography .26
Foreword
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This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3,
Chemical and physical characterization.
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iv © ISO 2019 – All rights reserved

Introduction
At the time of publishing this document, the mapping of soil pollution status is generally based on
geochemical methods that, despite development of new, more sophisticated and precise equipment,
have apparent disadvantages, among them uncertainty, as usually there is no satisfactory information
on the extent and range of pollution in the area. This results in the need of a large number of samples to
be collected, followed by expensive and time-consuming chemical analysis.
Among anthropogenic soil pollutants, trace elements [potentially toxic elements (PTEs)] are the most
problematic, widespread and persistent group that has accumulated in soil since the beginning of
industrial revolution, mostly due to dry and wet deposition of particulates originating from emissions
to the atmosphere. Due to the historical and persistent character of pollution, determination of soil
quality, sources, extent and range of pollution requires large-area dense environmental monitoring
network. In addition, identification of sources, pathways and extent of long-range transboundary
transport of airborne trace elements creates serious technical problems and uncertainties. This
has resulted in the development and broad application of soil magnetometry as easy-to-use, quick,
inexpensive but sensitive and reliable screening geophysical technique based on the measurements of
magnetic susceptibility in topsoil.
The method has not yet been standardized. For this purpose, a standard procedure, protocols and
guidelines for the using soil magnetometry as a screening method are developed primarily to support
the implementation of the two-stage optimized geophysical/geochemical method of measuring the
soil spatial anthropogenic pollution with airborne trace elements from the dry and wet deposition,
for further delineation of polluted soil areas to be adequately managed. The method provides data on
the volume-specific magnetic susceptibility, κ, which reflects cumulative anthropogenic pollution of
soil with trace elements, expressed as a PLI. The method is intended to serve as a screening and early
warning system to be applied at any scale, from local to large regional one, also for the investigation of
a long-range airborne element transport.
The application of this screening method alone does not allow determining the kind and concentrations
of specific trace elements in soils. To carry out a more precise survey of the anthropogenic soil pollution
with airborne trace elements, soil magnetometry as the screening geophysical “in situ” measurement
technique (the 1st stage) is to be integrated with the classical geochemical methods (the 2nd stage)
of the optimized procedure. Specifically, on the basis of geophysical methods used for screening, a
relevant dense geochemical monitoring network can be applied in the areas of diagnosed elevated risk,
thus reducing the number of samples and chemical analyses required.
INTERNATIONAL STANDARD ISO 21226:2019(E)
Soil quality — Guideline for the screening of soil polluted
with toxic elements using soil magnetometry
1 Scope
This document specifies methods for the measurements of magnetic susceptibility of soils (κ) as an
indicator of potential soil pollution/contamination with trace elements associated with technogenic
magnetic particles (TMPs) and describes related procedures, protocols and guidelines to be applied as
a screening geophysical method of determination of soil pollution with trace elements. The results of
measurements are used for preparing the maps of magnetic susceptibility of soils in the area of interest.
From these maps, the areas of elevated and high magnetic susceptibility indicating high trace element
total pollution load are discriminated for further identification of pollutants by geochemical methods.
This document is applicable to screening all TMPs-related anthropogenic emission sources including
long-range transport of airborne elements, of which TMPs are carriers and indicators. Such emission
sources comprise the majority of high-temperature industrial processes, where iron is present in any
mineralogical form in raw materials, additives or fuels, is transformed into ferrimagnetic iron oxides
(e.g. fossil solid and liquid fuels combustion, metallurgy, cement and ceramics industry, coke production,
industrial waste landfills, land transport). This document is not applicable to screening anthropogenic
emissions not associated with TMPs, e.g. organic pollutants or emissions from agricultural sources.
NOTE 1 Copper, zinc and other non-ferrous metal ores also contain iron (in many sulfides) as this element
is abundant in almost all environments. During smelting, the iron occurring in sulfides is transformed into
ferrimagnetic oxides (TMPs). However, in such cases, the proportion of TMPs and related PTEs is usually less than
at coal combustion or iron metallurgy, for example, and not all PTEs are physically associated and transported
by TMPs. Non-airborne elements are deposited in the close proximity of the emission source, while TMPs can
be used in these cases as indicators of airborne elements and of the spatial distribution of the total element
deposition from a smelter in the area.
In rare cases, some soils are developed on bedrock exhibiting geogenically high magnetism, which
can cause false-positive results. This influence can, however, be easily indicated by measurements of
magnetic susceptibility along soil profiles. This method is not applicable when the bedrock exhibits
extremely high magnetic signals.
NOTE 2 Such cases are rare.
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 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
topsoil
upper part of a natural soil that is generally dark coloured and has a higher content of organic matter
and nutrients when compared to the (mineral) horizons below, excluding the humus layer
Note 1 to entry: For arable land, topsoil refers to the ploughed soil depth, while for grassland it is the soil layer
with high root content.
3.2
subsoil
natural soil material below the topsoil (3.1) and overlying the parent material
Note 1 to entry: All or much of the original rock structure has been obliterated by pedogenic processes.
3.3
technogenic magnetic particles
different mineral forms of iron oxides exhibiting magnetic properties that are components of
anthropogenic emissions from high-temperature technologic processes and are carriers of airborne
trace elements
3.4
soil magnetometry
geophysical survey technique used for mapping spatial variations in the magnetic properties [mostly
magnetic susceptibility (3.5)] of topsoil (3.1) and subsoil (3.2)
3.5
magnetic susceptibility
measure of the ability of a material to be magnetized expressed in SI magnetic units, which is
proportional to the concentration of technogenic magnetic particles (3.3) in topsoil (3.1), indicating
cumulative anthropogenic contamination of soil with trace elements
3.6
mass magnetic susceptibility
magnetic susceptibility (3.5) divided by density of sample material, measured in a laboratory when the
mass of measured sample is known
3.7
frequency dependence of magnetic susceptibility
χ
fd
parameter revealing presence of superparamagnetic particles, being the result of natural (pedogenic or
biogenic processes)
3.8
magnetic susceptibility mapping
development of 2D or 3D maps with the use of measured data of magnetic susceptibility (3.5) in the area
of interest correlated with pollution load index
3.9
pollution load index
dimensionless index showing cumulative anthropogenic pollution of soil with trace elements used to
validate results of magnetic susceptibility (3.5) screening
3.10
contamination factor
ratio of specific metal concentration in soil and its background value in soil
2 © ISO 2019 – All rights reserved

3.11
natural background concentration
concentration of a substance that is derived solely from natural sources (i.e. of geogenic origin)
commonly expressed in terms of average, a range of values or a natural background value
Note 1 to entry: For the practical purposes of this document, this is mean element concentration in subsoil
measured in soil cores collected from studied area.
3.12
soil core
core collected from an uppermost soil layer (min. 200 mm long and 35 mm in diameter)
3.13
boundary depth
depth in soil profile where magnetic susceptibility (3.5) stabilizes after decreasing from its maximum
value, indicating the transition from the polluted layer to unpolluted part of soil profile
4 Symbols and abbreviated terms
PTE potentially toxic trace element
TMP technogenic magnetic particle
C element concentration in a sample
e
C baseline value for an element e
Bl-e
CF contamination factor
e
PLI pollution load index
SITE
κ magnetic susceptibility
χ mass magnetic susceptibility
χ frequency dependence of magnetic susceptibility
fd
5 Fundamentals
5.1 Screening principle
Magnetic iron oxides are components of industrial and urban dusts emitted to the atmosphere and
deposited on the soil surface. Anthropogenic emission sources of pollution containing technogenic
magnetic particles (TMPs) comprise metallurgy, combustion of fossil fuels, coke industry, cement and
ceramic industry, land transport, waste landfill sites and others.
Volume-specific magnetic susceptibility κ is directly proportional to the concentration of magnetic
particles within the sensor penetration area and reflects cumulative anthropogenic contamination
of soil with PTEs. High interdependence between the total historic dust dry and wet deposition, and
magnetic susceptibility has been well confirmed. Magnetic susceptibility can be measured quickly and
accurately in trace amounts as validated in Annex D. Magnetic susceptibility mapping of an area of
interest based on the measurements of magnetic susceptibility in topsoil (soil surface and uppermost
horizons), correlates with cumulative anthropogenic pollution with airborne trace elements expressed
as pollution load index (PLI). Annex A describes the relation between magnetic susceptibility and trace
element contamination taking place in topsoil.
5.2 Screening work processes
This screening method consists of two or three steps. All measurements may be performed either in
the field only (two-step procedure), or as field and laboratory works (three-step procedure):
— field measurements and works;
— laboratory measurements;
— data mapping.
The next step is related to the use of screening measurement data maps with delineated potentially
polluted areas for the targeted soil sampling within the proper geochemical analysis of soil
pollution status:
— soil sampling for geochemical analysis.
5.3 Field measurements and works
Field measurements and works to be carried out are as follows:
— surface measurements of magnetic susceptibility of topsoil;
— in situ measurements of magnetic susceptibility along soil profiles (optional);
— topsoil core sampling for laboratory measurements of magnetic susceptibility along soil profiles.
5.4 Laboratory measurements
Magnetic susceptibility is measured along soil profiles in a laboratory.
5.5 Data mapping
Data mapping to be completed are as follows:
— magnetic susceptibility mapping of the area;
— delineation of contaminated sites for further geochemical analysis.
5.6 Soil sampling for geochemical analysis
Soil sampling is necessary, in case geochemical analysis is additionally arranged. See 7.5.
6 Apparatus
The following equipment and devices are used.
6.1 Field equipment
6.1.1 Field magnetic susceptibility loop sensor.
6.1.2 GPS.
6.1.3 Datalogger coupled with GPS or laptop.
6.1.4 Topsoil core sampler.
6.1.5 Plastic tubes for the topsoil core sampler.
4 © ISO 2019 – All rights reserved

6.1.6 Hammer.
6.1.7 Field core magnetic susceptibility meter (optional).
6.1.8 Laptop coupled with a field core magnetic susceptibility meter (optional).
6.2 Laboratory equipment
6.2.1 Dual-frequency laboratory magnetic susceptibility sensor.
6.2.2 Laboratory core magnetic susceptibility meter.
6.3 Data mapping
6.3.1 Visualization, contouring and surface modelling software.
NOTE Software used for terrain modelling, bathymetric modelling, landscape visualization, surface
analysis, contour mapping, 3D/2D surface mapping, gridding and volumetrics.
7 Procedures
7.1 Measurement network
The main purpose of surface measurements of magnetic susceptibility is the determination of spatial
distribution of pollution with trace elements. Basic measurements of magnetic susceptibility (κ) in the
area of interest are performed in the field in a possibly regular network that is designed as discussed
in Annex B.2. The grid density is selected depending on the size of an area to be screened, and the
availability of preliminary information concerning possible sources and extent of anticipated pollution,
but no less than 1/7 to 1/10 of the surveyed area, at the distance ratio DR approximately 1:1 to 1:2
between basic measurement points.
In the areas of identified elevated magnetic susceptibility, additional measurements should be
performed close to about every third basic point, at the considerably smaller distance ratio DR
approximately 1:5 to 1:10.
Within delineated areas of magnetic susceptibility higher than the average for the area, dense
measurements should be carried out. The measurement points may be sited in irregular distances.
7.2 Measurements of magnetic susceptibility at the topsoil surface
Magnetic susceptibility (κ) at the topsoil surface is measured in the field with a portable hand magnetic
susceptibility loop sensor in network points. The geographic position of each measurement point is
recorded with GPS as is shown in the scheme in Annex B.1. Within about 2 m radius around the GPS
position, at least 11 measurements (odd number) of magnetic susceptibility shall be taken. The soil
surface shall be available for a sensor, thus a thick vegetation or litter in the measurement point should
be racked aside.
The time needed for a single measurement is approximately 1 s.
The measurement results can be downloaded from a datalogger coupled with GPS and are ready for
analysis. The downloaded table for a single measurement includes coordinates and measured values of
soil magnetic susceptibility.
NOTE Extraordinary high values of magnetic susceptibility (outliers) can be caused by the occasional
occurrence in topsoil layer of metallic artefacts. The possible impact of artefacts is eliminated by the rejection of
the highest and the lowest values from the measured set of results when calculating mean value for a single point.
7.3 Measurements of vertical magnetic susceptibility distribution
7.3.1 General
The main purpose of measurements of magnetic susceptibility (κ) along the topsoil profile is: (a)
determination of vertical distribution of anthropogenic pollution of the soil with trace elements that
could be caused by different accumulation in organic horizons or by vertical migration of TMPs; (b)
detection of possible influence of magnetic properties of a bedrock; (c) evaluation of the background
magnetic susceptibility values;
Measurements of magnetic susceptibility along the soil profiles can be performed in two ways:
— by taking topsoil cores in the field and sending to the laboratory for magnetic susceptibility analysis;
— by in situ measurement of magnetic topsoil profile (optional).
The choice of field or laboratory measurements depends on the convenience, the need of obtaining
instant information for further measurement performance and availability of equipment.
7.3.2 Topsoil core sampling
The topsoil core samples should be taken in the parts of the area showing the highest magnetic
susceptibility (κ). Additionally, for a reference at least one core sample from the area of the lowest, and
also of the moderate magnetic susceptibility shall be taken. The number of sampling points should be
specified individually with regard of representativeness.
Cores are taken in the field in plastic tubes with the use of soil core sampler hammered into the soil
layer. Plastic tubes, after checking the core status, shall be protected from core destabilization within
the tube by capping from both sides with neutral caps, marked and wrapped tightly into thin plastic foil
for the protection from moisture loss.
7.3.3 Field measurements
In situ measurements are more time-consuming, and slow down the measurement campaign; they
preferably need dry weather for convenient performance. These measurements should be carried out if
the results are required for a further proper design and conducting spatial field measurements.
The automatic “in situ” measurement of magnetic topsoil profile can be performed with the use of
a core magnetic susceptibility meter for field measurements along the soil profile to detect vertical
distribution of pollutants and horizons of pollutant accumulation. These data in the form of tables and
graphs presenting magnetic susceptibility values vs layer depth are available instantly at the laptop
coupled with the meter.
NOTE 1 A core magnetic susceptibility meter for automated in situ measurements is not indispensable
equipment. The same results can be obtained with the use of a laboratory analysis of core samples taken in the field.
NOTE 2 In case of in situ measurements, the diameter of core sampler is compatible with core magnetic
susceptibility meter.
7.3.4 Laboratory measurements
Soil cores taken in the field in plastic tubes with the use of soil core sampler are measured in a laboratory
using a laboratory magnetic susceptibility sensor.
7.3.5 Topsoil magnetic profile analysis
Topsoil magnetic susceptibility profiles are analysed to determine:
a) origin of elevated magnetic susceptibility (anthropogenic or natural);
6 © ISO 2019 – All rights reserved

NOTE In the case of an anthropogenic origin of elevated magnetic susceptibility.
b) vertical distribution of pollutants resulted from;
1) Anthropogenic accumulation in organic horizon;
2) Vertical redistribution of iron minerals and pollutants in pore solution;
3) Geogenic magnetic susceptibility of bedrock that is usually visualized by the increase
with the depth. In this case, false-positive errors of soil magnetometry may indicate higher
anthropogenic soil pollution of the area with trace elements. Make a decision with respect to
the applicability of the method in the screened area.
c) background magnetic susceptibility values.
7.4 Magnetic susceptibility mapping and data analysis
7.4.1 Data processing
Of the measured magnetic susceptibility data set for each measurement point, the highest and the
lowest values shall be rejected, and the mean value calculated (with standard deviation).
7.4.2 Magnetic susceptibility surface mapping
The mean values of magnetic susceptibility shall be used as input data into a visualization, contouring
and surface modelling computer program in order to obtain 3D or 2D contour maps of magnetic
susceptibility distribution in the analysed area.
7.4.3 Data analysis
In the map, the areas within the contours of the highest magnetic susceptibility values indicate elevated
or high trace element concentrations. These areas should be selected for further geochemical analysis
in order to detect specific pollutants and evaluate the level of soil pollution.
In general, magnetic susceptibility values:
−5
— in the range within 0 to 30 × 10 SI magnetic units, considered to indicate low pollution with trace
elements;
−5 −5
— in the range within 30 × 10 to 70 × 10 SI magnetic units, indicating moderate pollution with
trace elements;
−5 −5
— in the range within 70 × 10 to 100 × 10 SI magnetic units, indicating elevated pollution with
trace elements;
−5
— above 100 × 10 SI magnetic units, indicating high pollution with trace elements.
7.5 Soil sampling for geochemical analysis
Topsoil core samples within a delineated high pollution area taken at the screening stage are ready for
geochemical analysis.
If more detailed geochemical analysis is required, a network with a denser grid within delineated high-
pollution area should be developed and additional core samples taken in accordance with a procedure
described in 7.3.2.
8 Screening report
The following information shall be documented in such a way that it is immediately available on request.
In the following list, at least, the items marked with an asterisk (*) shall be included in the screening
report. An example of the report form is provided in Annex C:
a) a reference to this document, i.e. ISO 21226:2019;
b) name and characterization of a screened site*;
c) date of measurements*;
d) weather conditions during measurements*;
e) graphic scheme of a screened site with a measurement network*;
f) a complete identification of the topsoil surface measurement positions (coordinates) in the grid*;
g) measured topsoil surface magnetic susceptibility values (κ) for the given measurement position;
h) values rejected
...