Prediction and Experimental Evaluation of Soil Sorption by Natural Hormones and Hormone Mimics

Surface runoff from manure-fertilized fields is a significant source of endocrine-disrupting compounds (EDCs) in the environment. Sorption by soils may play a major role in the environmental fate of manure-borne EDCs, including 17 alpha- and 17 beta-estradiol (17 alpha-E2 and 17 beta-E2), estrone (El), melengestrol acetate (MGA), 17 alpha- and 17 beta-trenbolone (17 alpha-TB and 17 beta-TB), trendione (TND), and zeranol (alpha-ZAL). As a measure of sorption behavior, the organic carbon-normalized partition coefficients (K-OC) of 17 beta-E2, E1, MGA, and alpha-ZAL were experimentally determined for three agricultural soils with initial EDC concentrations spanning from similar to 0.01 to >1 mu M. Sorption isotherms were linear for most solute-soil combinations. Measured K-OC values were compared to those predicted using a suite of single-parameter and polyparameter linear free energy relationships (sp- and pp-LFERs). Sp-LFER models were based on experimentally determined octanol-water partition coefficients (K-OW), whereas pp-LFER solute descriptors were calculated indirectly from experimentally determined solvent-water partition coefficients or the program ABSOLV. Log K-OC predictions by sp-LFERs were closest to the experimentally determined values, whereas pp-LFER predictions varied considerably due to uncertainties in both solute and sorbent descriptors determined by ABSOLV or estimates using the partition coefficient approach.