Toxicity of Particulates in Urban Stormwater on Indicator and Commercial Aquatic Species

Particulate matter transported by the urban rainfall-runoff represents a wide gradation of particles from colloidal sizes to gravel and debris sizes. These particles are a potential concern not only because of the environmental and ecological issues related to particles, but also since many contaminants are bound to the surface of particles and transported through the aquatic environment. This study examined rainfall-runoff events captured from an instrumented MS4 watershed. Untreated runoff has higher accumulative mortalities than runoff treated through only physical filtration; indicating the role of particulates on toxicity. The LT₅₀ and NOET values indicate that higher particulate loads associated with mass-limited events were most toxic; and for mass-limited events that toxicity decreased across the event. Oxygen consumption results indicate as total particulate concentrations increase, the suspended particles are more toxic than settleable and sediment particles. Information in this paper is helpful in selecting unit operations targeted for controlling the particulate quality of runoff through a unit operation and process design approach for BMPs in order to improve for toxicity reduction through the separation of particulate matter.