| Abstract
| - Cattle and other livestock excrete endogenous steroidhormones, including estrogens, androgens, and progestins;therefore, allowing grazing livestock direct access tosurface waters can result in the release of steroids inagricultural watersheds. Elevated concentrations of steroidsare problematic because low concentrations of certainsteroids can affect fish reproduction. To assess theoccurrence and transport of steroids arising from grazingcattle, gas chromatography−tandem mass spectrometry(GC/MS/MS) was used to quantify a suite of estrogens,androgens, and progestins in small creeks impacted byrangeland grazing. Steroids were detected in 86% of samplesfrom rangeland creeks where cattle had direct accessto the water, with concentrations as high as 44 ng/L observedshortly after rain events at the beginning of the winterwet season. Estrogens were present at concentrationsabove the predicted no-effect concentrations for fish in 10−20% of the samples, and androstenedione was detectedat concentrations higher than response thresholds forpheromonal communication in fish. The results suggestthat, in certain cases, measures such as stream fencingin rangeland areas to limit direct discharge of animal wastesto surface waters or better manure management practicesmight be merited to protect ecosystem health.
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