Ongoing Research to Characterize the Complexity of Chemical Mixtures in Water Resources—Urban Stormwater

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A multiagency reconnaissance study of chemicals in urban stormwater, sampled from pipes or ditches during 50 runoff events at 21 sites in 17 states across the United States, demonstrated that stormwater runoff contains complex mixtures of chemicals including polycyclic aromatic hydrocarbons, pesticides, and pharmaceuticals that are indicative of multiple sources in the watershed.

Inside a Debris Cage at a Stormwater Outfall

Inside a debris cage, which is used to prevent pipe blockages, at one of 21 stormwater outfalls that was sampled prior to discharge to streams or stormwater ponds.

(Credit: Jason R. Masoner, U.S. Geological Survey, Oklahoma Water Science Center. Public domain.)

Municipalities and water-management agencies are increasingly using stormwater control measures to reduce the amount of stormwater runoff and minimize contaminant transport to receiving waterbodies. Stormwater ponds provide aquatic habitat, serve as recreational locations in urban setting, and are sometimes used as a water source for irrigation in surrounding landscapes. However, little is known about the contributions of complex chemical mixtures from stormwater runoff to receiving surface and groundwaters.

To address this data gap, the U.S. Geological Survey and U.S. Environmental Protection Agency, in collaboration with municipalities, completed a national-scale study of 21 sites in 17 states during storm events across the United States to better understand contaminant contributions from stormwater to receiving surface waters (stormwater ponds, infiltration ponds, and directly to streams) and groundwaters. Samples were collected from August 2016 to December 2017, and analyzed for 438 organic (for example, biogenic hormones, halogenated chemicals, household/industrial chemicals, methylmercury, pesticides, pharmaceuticals, and semivolatile organic chemicals) and 62 inorganic (for example, anions, cations, rare-earth elements, trace metals, and total mercury) elements or chemicals.

Study results indicate that stormwater transports complex mixtures of organic and inorganic chemicals that are associated with different watershed sources. For example, the number of organic chemicals detected in a single stormwater sample ranged from 18 to 103 (median=73) and about one-half (215) of the chemicals analyzed were detected among all samples.  Eleven organic contaminants were pervasive across all samples (greater than 90 percent detection): N,N-diethyl-meta-toluamide (DEET; insect repellent), nicotine (alkaloid stimulant), caffeine (psychoactive stimulant), carbendazim (broad-spectrum fungicide and benomyl metabolite), methyl-1H-benzotriazole (corrosion inhibitor), p-cresol (wood preservative), cotinine (nicotine metabolite), desulfinyl fipronil (fipronil-insecticide metabolite), bisphenol A (plastic component, paper receipts, and epoxy resin production), and fluoranthene and pyrene (polycyclic aromatic hydrocarbons). Concentrations of the 215 detected organic chemicals spanned over 6 orders of magnitude from less than 1 to more than 100,000 nanograms per liter.

A Stormwater Discharge Pond

A stormwater pond that receives runoff from a residential landscape. U.S. Geological Survey scientists analyzed samples of stormwater runoff collected during 2016 and 2017 at 21 sites for 438 organic chemicals and 62 inorganic elements.

(Credit: Jason R. Masoner, U.S. Geological Survey, Oklahoma Water Science Center. Public domain.)

This national-scale reconnaissance study provides a comprehensive snapshot of urban stormwater mixed contaminant profiles during sampling that can be useful as a baseline to indicate the chemicals to which wildlife could be exposed in surface waters receiving stormwater runoff. The baseline data could also be useful to understand chemicals that may enter groundwater through infiltration from stormwater ponds.

This research was funded by the Toxic Substances Hydrology and Contaminant Biology Programs of the U.S. Geological Survey Environmental Health Mission Area and the Office of Research and Development of the U.S. Environmental Protection Agency through Interagency Agreement DW-14-92448001-0.

More Information

Green Infrastructure and Urban Stormwater Impacts, U.S. Environmental Protection Agency