The toxicity and chemical composition of urban stormwater runoff

The effects of land use on the chemical composition of urban stormwater runoff and its subsequent acute toxicity to the aquatic invertebrate Daphnia pulex have been investigated in the Brunette drainage basin of Burnaby, British Columbia. Both land use and interval between rainfall events influenced the chemical composition and toxicity of the stormwater. The industrial and commercial land use sites were the major source of those trace metals most often considered toxic to aquatic invertebrates, with runoff from the commercial sites proving most frequently toxic to the test organism. Toxicity followed the sequence commercial > industrial > residential > open space. A detailed study of a single storm event indicated that while the “first-flush” of the storm contributed to toxicity—through the physical scouring of insoluble pollutants—some soluble pollutants, which were washed out of the watershed later in the storm event, also proved to be toxic. This finding has implications for the collection and treatment of stormwater runoff. Laboratory bioassays with synthetic stormwater composed of the trace metals Cu, Fe, Pb, and Zn at concentrations observed in field samples demonstrated that pH and suspended solids helped to regulate the toxicity of trace metals, and implicated the importance of these factors in natural stormwater toxicity. Key words: stormwater, street surface sediments, land use, buildup time, trace metals, toxicity, Daphnia bioassays, pH, suspended solids effects.