Fate of Endogenous Steroid Hormones in Steer Feedlots Under Simulated Rainfall-Induced Runoff

Abstract

Steroid hormones pose potential risks to fish and other aquatic organisms at extremely low concentrations. To assess the factors affecting the release of endogenous estrogenic and androgenic steroids from feedlots during rainfall, runoff, and soil samples were collected after simulated rainfall on a 14-steer feedlot under different rainfall rates and aging periods and analyzed for six steroid hormones. While only 17α-estradiol, testosterone, and progesterone were detected in fresh manure, 17β-estradiol, estrone, and androstenedione were present in the surficial soil after two weeks. In the feedlot surficial soil, concentrations of 17α-estradiol decreased by approximately 25% accompanied by an equivalent increase in estrone and 17β-estradiol. Aging of the feedlot soils for an additional 7 days had no effect on estrogen and testosterone concentrations, but androstenedione concentrations decreased substantially, and progesterone concentrations increased. Androstenedione and progesterone concentrations in the surficial soil were much higher than could be accounted for by excretion or conversion from testosterone, suggesting that other potential precursors, such as sterols, were converted after excretion. The concentration of androgens and progesterone in the soil were approximately 85% lower after simulated rainfall, but the estrogen concentrations remained approximately constant. The decreased masses could not be accounted for by runoff, suggesting the possibility of rapid microbial transformation upon wetting. All six steroids in the runoff, with the exception of 17β-estradiol, were detected in both the filtered and particle-associated phases at concentrations well above thresholds for biological responses. Runoff from the aged plots contained less 17α-estradiol and testosterone, but more estrone, androstenedione, and progesterone relative to the runoff from the unaged plots, and most of the steroids had a lower particle-associated fraction.