Pyrethroid insecticides were detected in 76% of the total, and 67% of the bioaccessible sites (n=49). Total average sum of pyrethroids was 259 ng/g organic carbon and 43.9 ng/g of bioaccessible pyrethroids. Bifenthrin was the most commonly detected pyrethroid. Only 28% and 15% of sediments caused a decrease in H. azteca biomass and survival. Using a temperature-based focused toxicity identification evaluation, confirmed that pyrethroids were a causual factor in the toxicity of 10 of the 12 sediments tested. Prevalence of bioaccessible and total pyrethroids detected in urban streambed sediments indicating that more cost-effective Tenax extraction methods can be used to survey pyrethroids. While a significant relationship existed between Tenax concentrations and toxicity, this relationship was complicated by several factors, including the paucity of toxicological parameters, uncertainties in standard bioassays, and more contaminants present in sediment, which all point to the need for more bioavailability-based studies. Pyrethroid-resistant H. azteca were not found, but, other amphipods present in the pyrethroud-contaminated urban stream were more tolerant to permethrin exposure than non-resistant H. azteca. Bioaccessible and bioaccumulated polychlorinated biphenyl (PCB) concentrations did not change significantly during the holding time, however, the bioaccessible pyrethroid concentrations were more varied, suggesting that holding time of the sediments prior to bioassay can potentially bias the bioassay tests.