Estimation of Cd, Pb, and Zn bioavailability in smelter-contaminated soilsby a sequential extraction procedure

Chemical fractionation methods may be capable of providing an inexpensive e stimate of contaminant bioavailability and risk in smelter-contaminated soi l. In this study, the relationship between metal fractionation and methods used to estimate bioavailability of these metal contaminants in soil was ev aluated. The Potentially BioAvailable Sequential Extraction (PBASE) was use d for Cd, Pb, and Zn fractionation in 12 soils contaminated from Pb and Zn mining and smelting activities. The PBASE procedure is a four-step sequenti al extraction: extraction 1 (E1) is 0.5 M Ca(NO3)(2), E2 is 1.0 M NaOAc, E3 is 0.1 M Na(2)EDTA, and E4 is 4 M HNO3. Metal bioavailability for two huma n exposure pathways, plant uptake (phytoavailability) and incidental ingest ion (gastrointestinal, GI, availability), was estimated using a lettuce (La ctuca sativa L.) bioassay and the in vitro-GI Physiologically Based Extract ion Test (PBET). Metal in the PBASE E1 fraction was correlated with lettuce Cd (P < 0.001) and Zn (P < 0.05) and was the best predictor of Cd and Zn p hytoavailability. Only total metal content or the sum of all PBASE fraction s, Sigma E1-4, were correlated (P < 0.001) with PBET gastric phase for Pb. The sum of the first two PBASE fractions, Sigma E1-2, was strongly correlat ed (P < 0.001) with Pb extracted by the PBET intestinal phase. The PBASE ex traction method can provide information on Cd and Zn phytoavailability and GI availability of Pb in smelter-contaminated soils.