Degradation of Synthetic Androgens 17α- and 17β-Trenbolone and Trendione in Agricultural Soils

Abstract

17Beta-trenbolone acetate (TBA) is a synthetic androgenic steroid hormone administered as a subcutaneous implant for growth promotion in beef cattle. TBA is converted metabolically to primarily 17alpha-trenbolone and trendione, and excreted in manure from implanted cattle. To predict the persistence of synthetic androgens once land-applied, aerobic degradation rates in two contrasting agricultural soil types (clay loam and a sandy soil) of both trenbolone isomers (17alpha and 17beta) and their primary metabolite trendione were measured and isomer interconversion was assessed. The impact of manure application was also evaluated in the clay loam soil. A pseudo first-order exponential decay model was derived assuming irreversible transformation and no impact of sorption on availability for degradation. The model generally resulted in good fits to the data. Both isomers degraded to trendione in a similar manner with half-lives (t1/2) on the order of a few hours to 0.5 days at applied concentrations of < or = 1 mg/kg. Similar degradation rates were observed in the presence and absence of manure applied at rates typical for land-application of cattle manure. Trenbolone degradation was concentration-dependent with degradation rates decreasing with increasing applied concentrations. Trendione, whether applied directly or produced from trenbolone, persisted longer than trenbolone with t1/2 values of 1 to 4 days. A small amount (1.5%) of conversion of trendione back to 17beta-trenbolone was observed during aerobic incubation regardless of the applied concentration. A small amount of 17alpha-isomer also converted back to 17beta-trenbolone, presumably through trendione. In autoclaved soils, no degradation of 17alpha- or 17beta-trenbolone was observed during the first 3 days, and trendione degradation was relatively small compared to a microbially active soil.