An ecological risk assessment for mosquito insecticides

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Montana State University - Bozeman, College of Agriculture


West Nile Virus (WNV) has been a concern for people across the North America since the disease was observed in the summer of 1999. WNV has caused the largest arboviral encephalitis epidemic in U.S. history. In response, vector management programs have been implemented. Concerns have been raised about these programs My ecological risk assessments focused on six common mosquito adulticides used in vector management, including 3 pyrethroids, pyrethrins, 2 organophosphates, a synergist, and 4 larvicides. Both aquatic and terrestrial non-target organisms were considered for acute and chronic exposures to the adulticides and larvicides. Tier I exposure estimates for adulticides were derived using modeling software. A probabilistic assessment was conducted for the adulticides to account for variability within the exposure models. The larvicide risk assessment included an even settling model into a standard farm pond. Risk quotients (RQ) were obtained by comparing exposure to toxic endpoints. Organophosphates breached a risk quotient (RQ) level of concern (LOC) for amphipods.
All of the but one RQ calculated in the deterministic model were greater than the 95th percentile of possible outcomes. Daphnia magna's RQ when exposed to monomolecular films breached a USEPA RQ LOC. Two studies were conducted during the summers of 2004 through 2006 near Great Falls, Montana. In 2004 and 2005, a study was conducted to assess acute impacts of mosquito insecticides on non-target organisms after one application. The second experiment was conducted in 2005 and 2006 to assess chronic impacts of a mosquito adulticide on non-target terrestrial arthropods after multiple applications. For aquatic samples in the first study no overall treatment effects were observed. During the same study 1 of 54 responses had a significant overall treatment effect for terrestrial samples. Many of the responses for terrestrial samples suggested significant time effects and time by treatment effects. For the multiple spray study conducted in 2005 and 2006, six of the response variables collected via terrestrial samples exhibited significant overall treatment effects; none had fewer individuals in the treatment plots. Time and time by treatment effects were prevalent in 2005 but no discernable pattern was evident.




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