The present study documented considerable risk of insecticide toxicity

The present study documented considerable risk of insecticide toxicity to invertebrates within the urban creeks. Bifenthrin was likely responsible for toxicity to H. azteca, fipronil and its sulfone degradate likely responsible for toxicity to C. dilutus, and both compounds could pose a risk to multiple other macroinvertebrate species. The same compounds investigated in the present study are widely used in many other countries, and this TH287 work illustrates the co-occurrence and toxicity of multiple insecticides in urban runoff. Each compound has the potential for toxicity to a unique subset of species within receiving waters, thus toxicity testing with multiple species provides the best means to assess these risks. The co-occurrence of bifenthrin, fipronil, chlorpyrifos, and imidacloprid in the creeks, as well as many other urban runoff contaminants not measured in the present study, could also pose a risk due to additive or synergistic effects that are largely unknown given the current state of knowledge.