Stereoselective sorption by agricultural soils and liquid-liquid partitioning of trenbolone (17alpha and 17beta) and trendione.

Trenbolone acetate (TBA) is a synthetic anabolic hormone used for growth promotion in beef cattle, which excrete primarily 17alpha-trenbolone along with small amounts of 17beta-trenbolone and trendione. To aid in predicting transport of manure-borne TBA metabolites, multiconcentration sorption isotherms for 17alpha- and 17beta-trenbolone and trendione were generated with five autoclaved-sterilized soils that represented a range in soil properties. Hormone concentrations were measured independently in solution and soil phases, and quantified using liquid chromatography with electrospray mass spectrometry. In addition, partition coefficients between apolar hexane and water (K(hw)) and bipolar octanol and water (K(ow)) were measured for the three androgens to better ascertain the mechanisms that may be responsible for the sorption differences observed between isomers. In all five soils, trendione sorbed the most, and 17alpha- and 17beta-trenbolone isomers exhibited different sorption magnitudes. 17beta- trenbolone consistently sorbed a factor of 2 more than 17alpha-trenbolone. For all three androgens, sorption is proportional to the soil organic carbon (OC) content with average log OC-normalized distribution coefficients (log K(oc), L/kg OC) of 2.77 +/- 0.12 for 17alpha-trenbolone, 3.08 +/- 0.1 for 17beta-trenbolone and 3.38 +/- 0.19 for trendione, which suggests the dominance of hydrophobic partitioning. However, differences in K(hw) values between 17alpha- and 17beta-trenbolone were small indicating differences are not simply due to differences in aqueous activity. In contrast, similarly different K(ow) and K(oc) values for the two isomers indicate the likely contribution of H-bonding to stereoselective sorption.