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Bioavailability and Bioaccessibility of Pollutants in Contaminated Soils: State of Present Knowledge and Research Avenues

Summary

As part of the management of polluted sites and soils, particularly in quantitative health risk assessments (QHRA), one of the exposures studied is soil ingestion. At present, QHSRs safely assume that all of a toxic substance present in the quantity of soil ingested by an individual will reach the target organs and generate a toxic effect. However, only a fraction of the quantity ingested 'actually' reaches the bloodstream (the concept of bioavailability) and the target organs. In the context of the ingestion of polluted soil by humans, a review of international knowledge is presented here:  - Clarification of the definitions of bioavailability and bioaccessibility; - Current use of these concepts, analysis (in vitro bioaccessibility tests, comparative tests, etc.), bioaccessibility results, modelling of bioavailability, methodology for incorporating these concepts into studies. Finally, an assessment is presented with a view to proposing a method for incorporating these parameters into HQRAs.

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Within the framework of the management of contaminated soils, and notably in quantitative health risk assessments (QHRA), ingestion is one of the exposure pathways studied. At present, as a margin of safety, 100% of the substance in the ingested soil is considered to reach the target organ and to have toxic effects. However, only a fraction of the total quantity ingested actually enters the bloodstream (bioavailability) and reaches the target organs. The correction term to be used when calculating the exposure dose must therefore be studied in order to take into account variations in the dose-effect relationship associated with the matrix. Research is currently being done to estimate bioavailability using in vitro bioaccessibility tests -- less expensive and easier to carry out than in vivo bioavailability tests. Bioaccessibility is the fraction of an ingested compound that is soluble in the gastrointestinal tract and can then be absorbed. This study clarifies the definitions of bioavailability and bioaccessibility. The present state of international knowledge concerning the human ingestion of soil is reviewed. This includes the current use of these notions in contaminated site and soil management, the investigations to be carried out, analysis and comparison of the various in vitro bioaccessibility tests, bioaccessibility results, bioavailability models, and methodology for incorporating these notions in health studies. These findings are summarised and a method is proposed for integrating bioavailability/bioaccessibility in QHRA in France.

Keywords: bioaccessibilité, ingestion, sol, test in vitro, facteur d'absorption relatif, évaluation des risques sanitaires, bioaccessibility, soil ingestion, in vitro method, relative absorption factor, human health risk assessment

Publication date: January 2012

Achievement: ICF Environnement, IPL SEDE

Reference: 10-0671/1A


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