Bioavailability research of soil metals has advanced considerably from default values to validated in-vitro bioaccessibility (IVBA) assays for site-specific risk assessment. Previously, EPA determined the soil size fraction representative of dermal adherence and consequent soil ingestion was <250 µm. This size fraction was widely utilized in testing efforts for both in-vivo and in-vitro experiments. However, recent studies indicate the <150 µm size fraction better represents the particle size that adheres to skin for potential ingestion.At issue is the relevance of validated in-vivo and in-vitro methods developed with <250 µm upon moving to the <150 µm fraction. The objectives of this study were to investigate <250 µm versus <150 µm particle size and particle size groups for evaluating lead and arsenic IVBA and speciation. Soils with different properties were homogenized, oven-dried, and sieved: <250 µm to >150 µm, <150 µm to >75 µm, <75 µm to >38 µm, and <38 µm. Sieved versus ground subsamples of <250 µm and <150 µm bulk soils were also used for IVBA and synchrotron-based lead and arsenic speciation. Although we observed increased in total and IVBA extractable lead and arsenic with decreased soil particle size, changes in %IVBA of Pb and As (dependent on the ratio of extractable to total) remained consistent in all the tested soils. No significant changes in Pb and As speciation were observed across the soil fractions. The results suggest utilizing the more relevant <150 µm fraction will not undermine currently validated IVBA protocols in future bioavailability studies.
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