Fate of Endogenous Steroid Hormones in Runoff from Cattle Feedlots.

摘要

Steroid hormones, including estrogens, androgens, and progestogens, pose potential risks to sensitive aquatic organisms at extremely low concentrations. These compounds have been detected at concentrations high enough to affect aquatic life in water bodies impacted by animal agriculture. However, the mechanism through which steroids from animals reach surface waters and the factors affecting the transformation of the compounds after excretion are not well understood. To provide new insight into these issues, the occurrence, transformation, and partitioning of steroid hormones in cattle feedlot soil and runoff were studied at the laboratory, test plot, and field scales.;The current state of the science regarding steroid hormones from animal agriculture and the factors that could affect their fate and transport were reviewed (Chapter 1) To assess steroid fate and transport under controlled conditions, rainfall, runoff and soil samples were collected after simulated rainfall on a research steer feedlot under different rainfall rates and aging periods (Chapter 2). While only 17&agr;-estradiol, testosterone, and progesterone were detected in fresh manure, 17beta-estradiol, estrone, and androstenedione were consistently detected in the surficial soil (0-3 cm) after two weeks. Evidence of steroid transformation after excretion was observed in the feedlot soil, where concentrations of 17&agr;-estradiol decreased by approximately 25% accompanied by an equivalent increase in estrone and 17beta-estradiol.;To provide a better understanding of the interplay between microbial transformation reactions and partitioning, microcosms consisting of steer manure, soil, and water were studied (Chapter 3). Results indicated that the presence of manure caused rapid microbial transformation of steroid hormones, with nearly complete transformation of testosterone and progesterone and partial transformation of 17beta-estradiol within 24 hours. After 24 hours, the transformation of 17beta-estradiol ceased whenever more than 400 mg/L of manure was present. Stabilization of 17beta-estradiol may have been due to partitioning of the compound into organic matter in the manure or changes in the microbial community. The rate of transformation of all three classes of steroids was faster in steroid-amended microcosms, suggesting that, under field conditions, steroids may be more stable than predicted by studies employing steroid amendments. Under conditions encountered in feedlots and manure-applied fields, androgens and progesterone are likely to be transformed in the soil or in runoff while estrogens likely persist long enough to be released to surface waters.;To determine the efficacy of a vegetated treatment system typical of those used to control nutrients for steroid hormone removal, samples were collected from a solids settling basin, vegetated infiltration basin, and a vegetated treatment area before and after ten storms over six months at a cattle feedlot (Chapter 4). The solids settling basin removed approximately 70% of the measured steroid hormones in the feedlot runoff except for estrone and progesterone, which were unaffected. Discharges from the solids settling basin contained steroid hormone concentrations that were several orders of magnitude above thresholds for biological responses. Steroid hormone concentrations were much higher in the sediments of the solids settling basin relative to those detected in the feedlot soil suggesting that the removal was caused primarily by settling.;To determine the relative steroid hormone contributions of tile drains from manure-applied fields and feedlot runoff, feedlot runoff from a commercial feedlot was analyzed for steroid hormones after winter storms for 3 years, and tile drain discharges from an area containing dairies and manure-applied fields was analyzed for steroid hormones over a 2-month period (Chapter 4). Steroid hormone concentrations in the feedlot runoff were similar to those observed from our plot-scale studies described in Chapter 2, and contained steroid hormone concentrations that were several orders of magnitude above thresholds for biological response. Only one of the tile drains sampled ever contained steroid hormones, and estrone was the only steroid detected above quantification limits. Tile drains are unlikely to contribute a significant mass of steroids to surface waters relative to feedlot runoff unless they exhibit significant macropore flow. (Abstract shortened by UMI.).