Citation:

Beyer, W., N. Basta, R. Chaney, P. Henry, D. Mosby, B. Rattner, K. Scheckel, D. Sprague, AND J. Weber. BIOACCESSIBILITY TESTS ACCURATELY ESTIMATE BIOAVAILABILITY OF LEAD TO QUAIL. G.A. Burton, Jr., and C. H. Ward (ed.), ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 35(9):2311-2319, (2016).

Impact/Purpose:

In both birds and mammals, Pb bioavailability and bioaccessibility are governed by the sorbed fraction of Pb, which may become solubilized in acidic gastric fluids. As digesta pass into the small intestine, where Pb is absorbed, the pH rises to 5-7, precipitating and sorbing some of the solubilized Pb. A bioaccessibility test should simulate the overall or most controlling process which affects bioavailability, often found to be gastric solubilization. The bioavailability of Pb to birds has previously been evaluated in Pb-contaminated floodplain soil along the Coeur d’Alene River Basin in Idaho. From a study in which soil was incorporated into the diet of mallard ducklings, the RBA of Pb was be estimated to be 44%. Working on another sample of soil from the same basin, Furman et al. correlated log blood Pb concentrations in mallards to soluble Pb concentrations measured in a physiologically based extraction method and showed how the use of P to remediate contaminated soil reduced both the bioaccessibility and the bioavailability of Pb. Our aims are to estimate the RBA of Pb in several Superfund soils to birds, to evaluate the accuracy of six previously developed bioaccessibility methods in predicting the measured bioavailability and, where possible, to relate observed differences in the bioavailability of Pb to particular soil variables or to soil mineral assemblages present.

Description:

Hazards of soil-borne Pb to wild birds may be more accurately quantified if the bioavailability of that Pb is known. To better understand the bioavailability of Pb to birds, we measured blood Pb concentrations in Japanese quail (Coturnix japonica) fed diets containing Pb-contaminated soils. Relative bioavailabilities were expressed by comparison with blood Pb concentrations in quail fed a Pb acetate reference diet. Diets containing soil from five Pb-contaminated Superfund sites had relative bioavailabilities from 33%-63%, with a mean of about 50%. Treatment of two of the soils with P significantly reduced the bioavailability of Pb. The bioaccessibility of the Pb in the test soils was then measured in six in vitro tests and regressed on bioavailability. They were: the “Relative Bioavailability Leaching Procedure” (RBALP) at pH 1.5, the same test conducted at pH 2.5, the “Ohio State University In vitro Gastrointestinal” method (OSU IVG), the “Urban Soil Bioaccessible Lead Test”, the modified “Physiologically Based Extraction Test” and the “Waterfowl Physiologically Based Extraction Test.” All regressions had positive slopes. Based on criteria of slope and coefficient of determination, the RBALP pH 2.5 and OSU IVG tests performed very well. Speciation by X-ray absorption spectroscopy demonstrated that, on average, most of the Pb in the sampled soils was sorbed to minerals (30%), bound to organic matter 24%, or present as Pb sulfate 18%. Additional Pb was associated with P (chloropyromorphite, hydroxypyromorphite and tertiary Pb phosphate), and with Pb carbonates, leadhillite, and Pb sulfide. The formation of chloropyromorphite reduced the bioavailability of Pb and the amendment of Pb-contaminated soils with P may be a thermodynamically favored means to sequester Pb.

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