Citation:

Sowers, T., C. Nelson, M. Blackmon, M. Jerden, A. Kirby, G. Diamond, AND K. Bradham. Interconnected soil iron and arsenic speciation effects on arsenic bioaccessibility and bioavailability: a scoping review. JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH - PART B: CRITICAL REVIEWS. Taylor & Francis, Inc., Philadelphia, PA, 25(1):1-22, (2022). https://doi.org/10.1080/10937404.2021.1996499

Impact/Purpose:

This is a review article focusing on how unique soil chemistry and bioaccessibility assay chemistry may influence bioaccessibility and bioavailability measurements. We use previously published datasets to draw conclusions regarding the impact of arsenic and iron speciation on bioaccessibility and bioavailability measurements. This work is important as it highlights our current understanding of chemical drivers of soil As bioaccessibility and bioavailability, while also presenting current weaknesses in the literature base that should be addressed. Results and discussion included here will be useful for all future contaminant bioaccessibility/bioavailability studies, particularly in ORD, academia, and other sectors of research. Additionally, this information may be critical to risk assessors and when measuring bioaccessibility/bioavailability at contaminated sites in support of EPA’s OLEM/OSRTI and Regional offices.

Description:

Extensive research has examined arsenic (As) bioavailability in contaminated soils and is routinely assessed using in vitro bioaccessibility (IVBA) assays. Analysis of differences in bioaccessibility measurements across IVBA assays and phases is expected to provide valuable insights into geochemical mechanisms controlling soil As bioaccessibility and bioavailability. Soil iron (Fe) content and As speciation are expected to significantly influence IVBA gastric and intestinal phases due to fluctuations in precipitation-dissolution chemistry and sorption reactivity as pH and assay chemical complexity changes. The aim of this review was to examine these relationships by 1) conducting a meta-analysis (n = 47 soils) determining the influence of total Fe on As bioaccessibility measurements and 5 IVBA assays and 2) investigating the effect of As speciation on gastric/intestinal phase IVBA and in vitro-in vivo correlations. Our findings indicate that soil Fe content and As speciation heterogeneity are important in elucidating variability of bioaccessibility measurements across IVBA assays and gastrointestinal phases. Greater focus on coupled As speciation and Fe precipitation chemistry may (1) improve our understanding of soil geochemical factors and assay constituents that influence As in vitro-in vivo correlations and (2) resolve variability in the precision of oral relative bioavailability (RBA) estimated using IVBA assays for soils possessing heterogenous As speciation and Fe composition.

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