Rangeland grazing as a source of steroid hormones to surface waters.

Cattle and other livestock excrete endogenous steroid hormones, including estrogens, androgens, and progestins; therefore, allowing grazing livestock direct access to surface waters can result in the release of steroids in agricultural watersheds. Elevated concentrations of steroids are problematic because low concentrations of certain steroids can affect fish reproduction. To assess the occurrence and transport of steroids arising from grazing cattle, gas chromatography-tandem mass spectrometry (GC/MS/MS) was used to quantify a suite of estrogens, androgens, and progestins in small creeks impacted by rangeland grazing. Steroids were detected in 86% of samples from rangeland creeks where cattle had direct access to the water, with concentrations as high as 44 ng/L observed shortly after rain events at the beginning of the winter wet season. Estrogens were present at concentrations above the predicted no-effect concentrations for fish in 10-20% of the samples, and androstenedione was detected at concentrations higher than response thresholds for pheromonal communication in fish. The results suggest that, in certain cases, measures such as stream fencing in rangeland areas to limit direct discharge of animal wastes to surface waters or better manure management practices might be merited to protect ecosystem health.