Environmental characterization of surface runoff from three highway sites in Southern Ontario, Canada: 1. Chemistry

Highway runoff is a significant source of contaminants entering many freshwater systems. To provide information on effects of highway runoff on aquatic biota, runoff samples were collected from three sites representing different classes of highways with low, intermediate and high traffic intensities. Samples were analysed for chloride, trace metals and polycyclic aromatic hydrocarbons (PAHs). Runoff from a major multilane divided highway, with the highest traffic intensity, contained the highest levels of chloride (45–19,135 mg/L) and metals. Runoff solids from this highway contained the highest levels of PAHs (19.7–2142 mg/kg). PAHs were also high (9.83–237 mg/kg and 26.4–778 mg/kg) at the intermediate and low traffic intensity sites, respectively. High concentrations of potent mutagens and carcinogens such as benzo(a)pyrene (0.414–124.62 μg/g) and indeno-pyrene (0.549– 50.597 μg/g) were measured in the particulate phase of all runoff samples. Chloride concentrations of winter and early spring runoff were significantly higher (P<0.001, t ¼ 2.66) than during the rest of the year. Levels of contaminants depended on traffic intensity, road condition (age, composition, maintenance), the condition of metal structures (drains, guardrails, etc.) and seasonal conditions. A companion paper discusses spatial and temporal aspects of contaminant-associated toxicity of highway runoff.