An exploratory study of urban runoff toxicity

An exploratory study of urban runoff toxicity was undertaken at 14 urban sites, including two sites receiving runoff from major multi-lane divided highways (> 100,000 vehicles·day−1). To assess various types of toxicity, a battery of tests was used including Daphnia magna, Microtox™, sub-rmtochondnal particles, and the SOS Chromotest (for genotoxicity). The whole data set composed almost 70 samples and 350 test results, which were reduced to toxicity point values using a toxicity scale. About two fifths of all data did not show any toxic responses, one fifth indicated severe toxicity, one fifth confirmed toxicity, and one fifth potential toxicity. When comparing urban stormwater toxicity to that of multi-lane divided highway (MLDH) runoff, the main difference was noted for the severe toxicity level; almost 20% of MLDH samples were severely toxic compared to 1% of urban stormwater samples. The MLDH data were obtained at the edge of the pavement, and although attenuation of runoff toxicity during transport can be expected, particularly m grassed swales, additional research is required.