Environmental characterization of surface runoff from three highway sites in Southern Ontario, Canada: 2. Toxicology

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Highway runoff is a significant source of contaminants entering many freshwater systems. A battery of bioassays was used to assess the degree of runoff toxicity. The toxicity results are described in the spatial and temporal context and are linked to the runoff chemistry. Runoff samples from three sites, representing different classes of highways (high, intermediate and low traffic intensity), were used to assess the degree of runoff toxicity. Runoff from the major multilane divided highway, with the highest traffic intensity (92,000 vehicles/24 h), had the highest levels of contaminants and displayed the greatest toxicity. Variations in toxic responses were observed both seasonally and throughout runoff events. The runoff samples containing high concentrations of road salts from winter maintenance were acutely toxic to Daphnia magna. In general, a sharp decline in runoff toxicity over time showed that the ‘first flush’ was the most toxic. Road solids present in runoff showed moderate to severe toxicity using a nematode bioassay. Consistently, a significant mixed function oxidase (MFO) induction was observed in rainbow trout exposed to runoff with high concentrations of polycyclic aromatic hydrocarbons (PAHs). The data show that vehicular operation, road maintenance and metal highway structures were significant contributors to contaminant-associated toxicity in road runoff.

Keywords: acute toxicity, bioassays, chronic toxicity, ‘first flush’, highway runoff, toxicity tests

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