Standards Development

Scope

This document deals with the assessment of human exposure from ingestion of soil. It specifies a simplified method for the estimation of the oral bioaccessibility of metal(loid)s from contaminated soils.

The method is a chemical extraction using hydrochloric acid (HCl) and can be used at least as a first-tier screening to predict 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 validated UBM (unified bioaccessibility method) test (ISO 17924)[1].

Soils, in sieved form (fraction < 250 µm without prior mechanical grinding) as recommended in ISO 17924, are extracted in an environment that simulate very simply the acidic conditions of the gastric compartment.

This document describes the protocol and the approach to calculate the oral bioaccessibility of As, Cd and Pb in soils, usually measured with ISO 17924. From the extractable concentrations of metal(loid)s by HCl, the predicted bioaccessibility in both the gastric and gastrointestinal phases is calculated by taking the equations from simple linear regressions.

In a second-tier study and a complementary validation approach, the ISO 17924 protocol is applicable to selected soil samples (approximately 10 % of samples) for better assessment of human exposure.

Note 1: Because the ISO 17924 test has only been validated against in vivo data for As, Cd and Pb, the HCl test is applicable to approximate oral bioaccessibility of these elements in soils. The simplified protocol could be used for other elements; however, because no validation exists for the other metals, the data obtained can only be considered as a useful line of evidence in interpreting results.

Note 2: The mathematical equations allowing to predict the bioaccessibility of As, Cd and Pb from the extractable concentrations by HCl were established from French soil samples with a wide range of physicochemical parameters (in terms of texture, pH, content of organic matter and carbonates) and metal(loid)s concentrations (described in.[2] The single-extraction method is applicable to predict the metal(loid)s 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.