Predicted aquatic exposure effects from a national urban stormwater study

A multi-agency study of 438 organic and 62 inorganic chemicals measured in urban stormwater during 50 total runoff events at 21 sites across the United States demonstrated that stormwater discharges can generate localized, aquatic exposures to extensive contaminant mixtures, including organics suspected to cause adverse aquatic-health effects. The aggregated risks to multiple aquatic trophic levels (fish, invertebrates, plants) of the stormwater mixture exposures, which were documented in the national study, were explored herein by calculating cumulative ratios of organic-contaminant in vitro exposure-activity cutoffs ( n-ary sumation (EAR)) and health-benchmark-weighted cumulative toxicity quotients ( n-ary sumation (TQ)). Both risk assessment approaches indicated substantial (moderate to high) risk for acute adverse effects to aquatic organisms across multiple trophic levels (fish, macroinvertebrates, non-vascular/vascular plants) at or near stormwater discharge points across the United States. The results are interpreted as potential orders of magnitude underestimates of actual aquatic risk in stormwater control wetlands or in the immediate vicinity of such discharges to surface-water receptors, because the 438 organic-compound analytical space assessed in this study is orders of magnitude less than the 350 000 parent compounds estimated to be in current commercial use globally and the incalculable chemical-space of potential metabolites and degradates.

Automated summary

A comprehensive study of stormwater runoff events at 21 sites across the United States measured 438 organic and 62 inorganic chemicals, revealing localized contamination with potential adverse effects on aquatic health. By assessing cumulative ratios of exposure-activity cutoffs and cumulative toxicity quotients, the study found moderate to high risks for acute adverse effects on aquatic organisms across multiple trophic levels near stormwater discharge points. However, these results are likely significant underestimations of actual risk due to the limited number of compounds analyzed compared to those in commercial use and potential metabolites.