Human health risk assessment of lead exposure from soil ingestion in a French pilot study: insights from the application of a new bioaccessibility approach.

Abstract

Despite the consensus on the importance of considering the bioavailability of metal(loid)s by measuring their bioaccessibility when assessing exposure, integrating these parameters into risk calculations often involves proprietary approaches that lack adequate justification. This is the case with the in vitro unified bioaccessibility method (UBM), which is widely used in Europe to assess the bioaccessibility of metal(loid)s in the event of soil ingestion. This study proposes a comprehensive operational approach that incorporates bioaccessibility to refine human exposure and risk assessments. A pilot study of 45 Pb-contaminated soil samples collected in and around Paris highlighted the importance of carefully following soil preparation protocols. Specifically, sieving the soil to 250 µm without mechanical milling is recommended for determining both bioaccessible and total concentrations. A simplified test using dilute hydrochloric acid can predict the bioaccessibility of metal(loid)s in first-tier screening. This affordable, single-extraction method is easy to use in analytical laboratories and is both fast and reproducible. For second-tier validation studies, the UBM protocol should be applied to a limited number of samples. With the new approach, the relative bioavailability can be directly calculated using an in vivo/in vitro equation in the stomach compartment, thus, enabling UBM validation. The results of the pilot study demonstrated that to refine exposure assessments, adjusting chronic daily intake using relative bioavailability data was more effective than were classical approaches based on total concentrations. This method offers a promising perspective for stakeholders in managing polluted sites and soils.