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Title: Bioaccessibility tests accurately estimate bioavailability of lead to quail

Author
item BEYER, W - Us Geological Survey (USGS)
item BASTA, NICHOLAS - The Ohio State University
item Chaney, Rufus
item PAULA, F - Us Geological Survey (USGS)
item MOSBY, DAVID - Us Fish And Wildlife Service
item RATTMER, BARNETT - Us Geological Survey (USGS)
item SCHECKEL, KIRK - Us Environmental Protection Agency (EPA)
item SPRAGUE, DANIEL - Us Geological Survey (USGS)
item WEBER, JOHN - Us Fish And Wildlife Service

Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2016
Publication Date: 2/25/2016
Citation: Beyer, W.N., Basta, N.T., Chaney, R.L., Paula, F.P., Mosby, D., Rattmer, B.A., Scheckel, K.G., Sprague, D., Weber, J. 2016. Bioaccessibility tests accurately estimate bioavailability of lead to quail. Environmental Toxicology and Chemistry. 35:2311-2319. doi: 10.1002/etc.3399.

Interpretive Summary: When soil is ingested by humans or wildlife, contaminant metals in the soil may be dissolved in the stomach and absorbed and comprise risk to the animal. The extent of the risk is dependent on the bioavailability of the metals in the soil which is normally defined by feeding tests compared to soluble reference compounds such as Pb-acetate. When animal tests have been conducted with contaminated soils, chemical extraction tests which are well correlated with the measured bioavailability can be used rather than more feeding studies. The results of such testing is called “bioaccessibility” of the contaminant. In addition, research has identified several soil treatments particularly with phosphate rich materials, which can react with soil Pb to make it considerably less bioavailable. Some of the tests defined by swine and rat feeding indicated that phosphate amendments could considerably reduce bioavailability, but some of the chemical extraction tests did not correlate well with the measured bioavailability. Little testing has been done with birds to define risks from soil Pb, and no chemical extraction test has been correlated with the results of bird feeding tests with contaminated soils without and with phosphate treatment. Soils from several contaminated sites, some with phosphate treatment, were fed to Japanese quail for 15 days and blood Pb measured for comparison with promising chemical extraction tests including one established by U.S.-EPA. The blood lead results showed that phosphate treatment did substantially reduce bioavailability of soil from two locations. Several of the chemical extraction tests were well correlated with the blood lead concentrations, well enough to use for risk assessment. One important result was that the pH 1.5 test of the U.S.-EPA over-estimates bioavailability as had been shown by earlier studies. The study also revealed that when uncontaminated soil is mixed with the diet amended with Pb-acetate, absorption of Pb is significantly reduced showing that normal soil adsorption properties reduce risk of Pb in ingested soil.

Technical Abstract: 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, we incorporated Pb-contaminated soils or Pb acetate into diets for Japanese quail (Coturnix japonica), fed the quail for 15 days, and measured the resulting concentrations of Pb in their blood. Relative bioavailabilities were expressed by comparison with blood Pb concentrations in quail fed the 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 compared to untreated controls. The bioaccessibility of the Pb in the soils was then measured in six in vitro tests: 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." Linear regressions of relative bioavailability on bioaccessibility were positive for all six methods. Based on criteria of slope and coefficient of determination, the RBALP pH 2.5 and OSU IVG tests performed well and are recommended for use in ecological risk assessment. Several of the in vitro tests predicted bioavailability of Pb to quail and future studies are recommended to further evaluate these methods. Speciation by X-ray absorption spectroscopy demonstrated that, on average, most of the Pb in the sampled soils was adsorbed 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.