Estrogens are considered the primary source of estrogenic activity in wastewater effluents. When

effluents are discharged, the estrogens impart estrogenic toxicity to the receiving water, which

in turn may disrupt the reproductive system of fish. This research investigates the existence,

severity, and attenuation of estrogenic toxicity in shallow streams. A simple analytical mass

transport model was developed to simulate the fate and transport of estrogens in shallow mixing

zones. The model requires minimal input data and can be integrated with other hydraulic models

to predict the effects of changes in water flow and estrogen load. It was implemented in a study

of estrogen transport in a small creek in Central Virginia that receives effluent from a wastewater

treatment plant (WWTP). Significant levels of 17b-estradiol and low concentrations of estrone,

estriol, and bisphenol-A were detected in over a hundred water samples collected from the creek.

The WWTP effluent was identified as the primary source of these compounds. The measured

estrogenic toxicity in the mixing zone was largely attributed to the 17b-estradiol. Results from

model simulations indicated slow degradation of 17b-estradiol (kd = 3.0/day). Further, dilution

by mixing was found to be the primary attenuation mechanism for the estrogenic toxicity. These

findings provide insights on the factors that determine estrogen attenuation in shallow waters

and can help identify engineering controls for reducing the resulting estrogenic toxicity due to

effluent discharges.