Modeling the fate and transport of 17β-estradiol in the South River watershed in Virginia.

Hormones excreted by livestock metabolisms often enter surface water through feces and urine and can potentially cause adverse impacts to aquatic biota. This study involved a modeling analysis of 17β-estradiol (E2), a prevalent estrogen, in the South River watershed located in Augusta County, Virginia from 2013 to 2015. Cattle manure, poultry litter, biosolids, septic systems, and wastewater treatment plants (WWTPs) were considered as sources of E2 in this study. The EPA's BASINS modeling framework was configured to track the fate and transport of E2. The first-order kinetics and the wash-off model were adopted to characterize the attenuation and the transport of E2. The modeling results indicated that the flow rate was a major input affecting the simulated E2 levels in the water. During storm events, E2 on the land surface was transported into the rivers by the surface runoff and the E2 released into streams was diluted by the high water flow. Variations of the simulated E2 concentrations in the South River depended on the relative magnitudes of the loads from point and nonpoint sources. Modeling results showed that E2 levels in the South River were below the lowest observable effect level (LOEL) for fish. However, the practices of storing manure before land application and fencing off rivers to keep cattle out of the water are encouraged to prevent the potential for high E2 levels in streams receiving feedlot runoff.