Selection and application of a rainbow trout toxicity testing procedure for screening Sacramento River Watershed, California samples.

A number of procedures have been developed to assess toxic effects on the early life stages of salmonid fish. In this study 13 rainbow trout embryo development relatively short-term (7 to 90 day) procedures were reviewed. Three 7-day methods from the published literature and three modifications developed at AQUA-Science (A-S) were evaluated in the laboratory. Based on that evaluation, A-S methods were selected for screening surface water samples (A-S 1) collected in the Sacramento River watershed (California) and for conducting toxicity identification evaluations (TIE) to identify cause(s) of toxicity. Test control performance, test sensitivity, and reference toxicant response variability in the A-S 1 were superior to those in commonly used freshwater toxicity testing methods. The incidence of Sacramento River watershed samples resulting in a notable decrease in embryo development was very low. Of 260 samples screened only 16 (6%) resulted in statistically significant inhibition of embryo development. Of the 16 toxic samples, nine caused minimal (less than 20% abnormal development) and four marginal (less than 30%) toxicity. Samples collected from the agriculture-dominated Colusa Basin Drain and rangeland/forest-dominated Battle Creek on June 16, 2005 caused significant toxicity. TIE procedures indicated that cationic chemicals were the primary cause of toxicity. Metals analysis did not reveal concentrations sufficient to inhibit embryo development, so the most probable cause of toxicity in the two samples was cationic chemicals (perhaps surfactants?) or metals that were not included in the analytical screening.

In situ water and sediment toxicity in an agricultural watershed.

The Salinas River receives inputs from extensive farmlands before flowing into the Salinas River National Wildlife Refuge and the Monterey Bay National Marine Sanctuary (CA, USA). Previous monitoring using laboratory toxicity tests and chemical analyses identified toxic agricultural drain-water inputs in this system. Using caged daphnids (Ceriodaphnia dubia) and amphipods (Hyalella azteca), we investigated in situ toxicity at stations downstream from an agricultural drain relative to a reference station. A flow sensor indicated highly variable inputs from irrigation, and daily synoptic chemical analyses using enzyme-linked immunosorbent assay techniques demonstrated fluctuating concentrations of organophosphate pesticides. Test organism mortality in the field coincided with contaminant concentrations that exceeded chemical effect thresholds for the test species. Laboratory toxicity tests using C. dubia were comparable to results from field exposures, but tests with H. azteca were not. Laboratory exposures can be reasonable surrogates for field evaluations in this system, but they were less effective for assessing short-term temporal variability. Results from the field toxicity studies corroborated results of bioassessment surveys conducted as part of a concurrent study. Toxicity identification evaluations indicated that organophosphate pesticides caused toxicity to daphnids and that effects of suspended solids were negligible.

Ecotoxicologic impacts of agricultural drain water in the Salinas River, California, USA.

The Salinas River is the largest of the three rivers that drain into the Monterey Bay National Marine Sanctuary in central California (USA). Large areas of this watershed are cultivated year-round in row crops, and previous laboratory studies have demonstrated that acute toxicity of agricultural drain water to Ceriodaphnia dubia is caused by the organophosphate (OP) pesticides chlorpyrifos and diazinon. We investigated chemical contamination and toxicity in waters and sediments in the river downstream of an agricultural drain water input. Ecological impacts of drain water were investigated by using bioassessments of macroinvertebrate community structure. Toxicity identification evaluations were used to characterize chemicals responsible for toxicity. Salinas River water downstream of the agricultural drain was acutely toxic to the cladoceran Ceriodaphnia dubia, and toxicity to C. dubia was highly correlated with combined toxic units (TUs) of chlorpyrifos and diazinon. Laboratory tests were used to demonstrate that sediments in this system were acutely toxic to the amphipod Hyalella azteca, a resident invertebrate. Toxicity identification evaluations (TIEs) conducted on sediment pore water suggested that toxicity to amphipods was due in part to OP pesticides; concentrations of chlorpyrifos in pore water sometimes exceeded the 10-d mean lethal concentration (LC50) for H. azteca. Potentiation of toxicity with addition of the metabolic inhibitor piperonyl butoxide suggested that sediment toxicity also was due to other non-metabolically activated compounds. Macroinvertebrate community structure was highly impacted downstream of the agricultural drain input, and a number of macroinvertebrate community metrics were negatively correlated with combined TUs of chlorpyrifos and diazinon, as well as turbidity associated with the drain water. Some macroinvertebrate metrics were also correlated with bank vegetation cover. This study suggests that pesticide pollution is the likely cause of ecological damage in the Salinas River, and this factor may interact with other stressors associated with agricultural drain water to impact the macroinvertebrate community in the system.

Monitoring of diazinon concentrations and loadings, and identification of geographic origins consequent to stormwater runoff from orchards in the Sacramento River watershed, U.S.A.

Diazinon contamination of California's rivers has resulted in placing several rivers on the federal Clean Water Act 303d list of impaired waterways. Impaired water body listing requires the development of Total Maximum Daily Loads (TMDL). Previous studies identified stormwater related diazinon pulses in California rivers. This study was conducted to monitor diazinon concentrations in the Sacramento River watershed after rainfall events, to ascertain whether pulses could be identified and, if concentrations of concern were observed, to estimate loadings and determine geographic origins of the insecticide. TMDL development requires knowledge of contaminant sources, loadings, and geographic origins. Flow and diazinon concentrations peaked in the Sacramento River at Sacramento after the three largest storms during January and February 1994. Diazinon concentrations peaked consequent to each of three storms. Diazinon concentrations measured in the Sacramento River at Sacramento exceeded the California Department of Fish and Game acute and chronic criteria for protection of aquatic life during January and February for nine and nineteen days, respectively. Multiple exceedances were observed throughout the watershed. Diazinon loading and geographic origin differed with each of the three storms. The design of this study provides a useful template for others attempting to identify loadings and sources of contaminants in surface waters and to rectify aquatic ecosystem contamination from various land use practices.

Ambient toxicity due to chlorpyrifos and diazinon in a central California coastal watershed.

The Salinas River watershed along the central coast of California, U.S.A., supports rapidly growing urban areas and intensive agricultural operations. The river drains to an estuarine National Wildlife Refuge and a National Marine Sanctuary. The occurrence, spatial patterns, sources and causes of aquatic toxicity in the watershed were investigated by sampling four sites in the main river and four sites in representative tributaries during 15 surveys between September 1998 and January 2000. In 96 hr toxicity tests, significant Ceriodaphnia dubia mortality was observed in 11% of the main river samples, 87% of the samples from a channel draining an urban/agricultural watershed, 13% of the samples from channels conveying agricultural tile drain runoff, and in 100% of the samples from a channel conveying agricultural surface furrow runoff. In six of nine toxicity identification evaluations (TIEs), the organophosphate pesticides diazinon and/or chlorpyrifos were implicated as causes of observed toxicity, and these compounds were the most probable causes of toxicity in two of the other three TIEs. Every sample collected in the watershed that exhibited greater than 50% C. dubia mortality (n = 31) had sufficient diazinon and/or chlorpyrifos concentrations to account for the observed effects. Results are interpreted with respect to potential effects on other ecologically important species.