Impact of Sediment on Agrichemical Fate and Bioavailability to Adult Female Fathead Minnows: A Field Study

Precipitation induced runoff is an important pathway for agrichemicals to enter surface water systems and expose aquatic organisms to endocrine-disrupting compounds such as pesticides and steroid hormones. The objectives of this study were to investigate the distribution of agrichemicals between dissolved and sediment-bound phases during spring pulses of agrichemicals and to evaluate the role of suspended sediment in agrichemical bioavailability to aquatic organisms. To accomplish these objectives, suspended sediment and water samples were collected every 3 days from a field site along the Elkhorn River, located at the downstream end of a heavily agricultural watershed, and were screened for 21 pesticides and 21 steroids. Adult female fathead minnows (<i>Pimephales promelas</i>) were exposed in field mesocosms to river water containing varying sediment loads. Changes in organism hepatic gene expression of two estrogen-responsive genes, vitellogenin (<i>VTG</i>) and estrogen receptor alpha (<i>ERα</i>), as well as the androgen receptor (<i>AR</i>) were analyzed during periods of both low and high river discharge. Trends in agrichemical concentrations of both the dissolved and sediment phases as a function of time show that, while sediment may act as both a source and a sink for agrichemicals following precipitation events, the overall driver for molecular defeminization in this system is direct exposure to the sediment-associated compounds. This study suggests that endocrine disrupting effects observed in organisms in turbid water could be attributed to direct exposure of contaminated sediment