Soil Fractionation Study, Speciation, and Ivba Analysis in Lead and Arsenic Contaminated Soils.

Bioavailability research of soil metals has advanced considerably in the past two decades from default assumptions of 100% availability, to extensive in-vivo studies determining an upper bound prediction value, and to validated in-vitro bioaccessibility (IVBA) assays for extensive site-specific risk assessment. Early research determined the soil size fraction involved with soil ingestion was <250µm, and this fraction has been widely utilized in testing efforts for both in-vivo and in-vitro experiments. However, more recent studies indicate the <150µm size fraction represents the particles that adheres to childrens’ hands for hand to mouth transfer ingestion. At issue is the relevance of previous research with the <250µm soil fraction if new research focuses on the <150µm fraction. The objectives of this study were to investigate <250µm versus <150µm particle size for evaluating relative bioavailability of Pb and As from soil with respect to other soil fractions on the relative bioavailability estimation. Variety of soils with different soil properties were homogenized, oven-dried, and sieved to <250µm to >150µm, <150µm to >75µm, <75µm to >38µm, and <38µm. Sieved versus pulverized subsamples of both <250µm and <150 µm bulk soils were also used for analyses. We hypothesized that the total and extractable Pb and As might increase with decreasing particle size, but their bioavailability may remain same. We observed increase in both total and extractable Pb and As with decrease in soil size fractions; however, changes in % IVBA of Pb and As remained almost same in all the tested soils. No significant changes in Pb and As speciation were observed across the soil fractions. The results from this study demonstrates no difference in the use of <250µm versus <150µm particle size fraction for evaluating the relative oral bioavailability of contaminants from soils, and no concern exists if the IVBA method (EPA SOP 9200.2-86) is modified to utilize the <150µm size fraction for future bioavailability studies.