Toxicity Evaluation of Highway Stormwater Runoff

Document Type: Article


1 Department of Civil and Environmental Engineering, University of California at Davis Davis, CA

2 Formerly, John Muir Institute of the Environment, University of California at Davis, Davis, CA 95616; Currently, MLJ Environmental, LLC, Davis, CA



This paper is prepared to present the results of two major toxicity investigations of highway runoff in the state of California and verify or reject the hypothesis of whether highway runoff is toxic.  Two major toxicity studies were: (1) statewide highway runoff toxicity evaluation and (2) hydrographic (first flush) toxicity evaluation of runoff from highly urbanized highways.  Extensive grab and composite runoff samples were collected from numerous highway sites throughout the state of California for multiple storm events and multiple years. Wide ranges of toxicity testing, including the three U.S.EPA standard species, marine species, green algae growth and Microtox™ were performed on grab and composite samples.  The results obtained revealed that the highway runoff is generally toxic, and the toxicity is mostly associated with heavy metals and organic compounds such as herbicides, pesticides, and surfactants. While outside of the scope of this study, an independent performance evaluation of stormwater treatment showed that toxicity removal after best management treatments (BMPs) is possible even though some influent samples entering the BMP were toxic.