Urban Stormwater: An Overlooked Pathway of Extensive Mixed Contaminants to Surface and Groundwaters in the United States

Increasing global
reliance on stormwater control measures to reduce
discharge to surface water, increase groundwater recharge, and minimize
contaminant delivery to receiving waterbodies necessitates improved
understanding of stormwater–contaminant profiles. A multiagency
study of organic and inorganic chemicals in urban stormwater from
50 runoff events at 21 sites across the United States demonstrated
that stormwater transports substantial mixtures of polycyclic aromatic
hydrocarbons, bioactive contaminants (pesticides and pharmaceuticals),
and other organic chemicals known or suspected to pose environmental
health concern. Numerous organic-chemical detections per site (median
number of chemicals detected = 73), individual concentrations exceeding
10 000 ng/L, and cumulative concentrations up to 263 000
ng/L suggested concern for potential environmental effects during
runoff events. Organic concentrations, loads, and yields were positively
correlated with impervious surfaces and highly developed urban catchments.
Episodic storm-event organic concentrations and loads were comparable
to and often exceeded those of daily wastewater plant discharges.
Inorganic chemical concentrations were generally dilute in concentration
and did not exceed chronic aquatic life criteria. Methylmercury was
measured in 90% of samples with concentrations that ranged from 0.05
to 1.0 ng/L.