Integrated toxicological and hydrological assessments of diazinon and esfenvalerate (Pimephales promales, Ceriodaphnia dubia)

A 7-day-old fathead minnow (Pimephales promales) larval fish model was used to examine chemical interactions between two pesticides, esfenvalerate and diazinon, evaluate a sublethal endpoint, and conduct pulsed studies with esfenvalerate. Combinations of diazinon and esfenvalerate caused acute toxicity to fathead minnow larvae and appeared to have slightly more than additive effects (i.e., synergistic). Examination of the sublethal endpoint (i.e., swimming performance) revealed that fathead minnow larvae were impaired at or below the same effect level when compared to the survival endpoint. Swimming performance may be a more sensitive measure than survival for exposure to low concentrations (<0.13 μg/L) of esfenvalerate. Experimental results indicated additional laboratory evaluation strategies may enhance State water quality testing programs and evaluation of potential chemical interactions in water bodies is recommended.; Spatial and temporal diazinon concentrations were examined within an urban stream, Arcade Creek, in the Sacramento River basin, and a storm drain into the Creek. Diazinon concentrations and streamflow measurements within Arcade Creek were characterized for August 2000 to July 2001.{09}The highest concentrations of diazinon occurred in the first fall and winter flush events. The 90th percentile diazinon concentrations at three Creek sample sites were 830, 836, and 773 ng/L and the storm drain was 2 415 ng/L. Ceriodaphnia dubia (C. dubia) toxicity response to storm drain and Arcade Creek waters was evaluated. This study found C. dubia toxicity tests using “environmental renewal water” (daily renewal of creek water with consecutive daily creek grab samples) were a good indicator of real-world toxicity response to storm events. Recommended field strategies include conducting water flow measurements concurrently with chemical concentration measurements, quantifying chemical flux from point of discharge (including storm drains) to receiving waters, and capturing first storm flushes (important for determining loads to the receiving system).