EXTRACTION AND DISTRIBUTION OF SOIL ORGANIC AND INORGANIC SELENIUM INCOAL-MINE ENVIRONMENTS OF WYOMING, USA

Selenium (Se), an animal toxicant and aquifer contaminant, occurs in c oal mine environments of Wyoming. There is a paucity of information on solution-phase Se speciation in mine soils. The objectives of this st udy were to compare Se extraction efficiencies of various reagents and to characterize SeO32- (selenite), SeO42- (selenate) and 4 organic Se components in these extracts. Forty coal mine soils were extracted us ing DI (deionized) water, hot water (0.1% CaCl2), AB-DTPA, NaOH, and K H2PO4. Each solution was analyzed for total dissolved Se, and inorgani c and organic Se fractions. Both inorganic and organic Se fractions we re detected in the soil extracts. The order of Se (total, inorganic, a nd organic) extraction efficiency for different reagents was DI water < hot water < AB-DTPA much less than NaOH much less than KH2PO4. The i norganic-organic Se ratios in DI water, hot water, AB-DTPA, NaOH, and KH2PO4 extracts were 60:40, 26:74, 61:39, 87:13, and 52:48, respective ly, indicating predominance of inorganic Se in all but the hot water e xtract. Selenite was the dominant inorganic species in AB-DTPA and KH2 PO4 extracts, while SeO42- was the major Se species in the DI water, h ot water, and NaOH extracts. Significant correlations (P < 0.01) were observed among extractable inorganic Se [NaOH and KH2PO4 (r=0.95); hot water and AB-DTPA (r=0.89)], total soluble Se [DI water with hot wate r (r=0.98) and AB-DTPA (r=0.95)], and Se species [SeO32- in AB-DTPA wi th SeO42- in NaOH (r=0.94) and SeO32- in KH2PO4 (r=0.88)]. These corre lations are indicative of Se extraction efficiency, thermodynamically predicted chemical transformations (such as oxidation of SeO32- to SeO 42-), and probable interconversions between the organic and inorganic Se fractions (r=0.70 in KH2PO4 extracts); as a whole the correlations can be used as statistical validations of possible geochemical process es.