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BS ISO 21266: 2019

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

Mike Smith

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BS ISO 21266: 2019

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.

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.