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MP4 Toxic Effects of Pesticide Mixtures
() Toxicity of atrazine, fipronil and imidacloprid individually and in mixture to larval grass shrimp.
Key, P1, Chung, K1, Fulton, M1, Siewicki, T1, 1 NOAA/National Ocean Service, Charleston, SC
ABSTRACT- The grass shrimp (Palaemonetes pugio) is a common inhabitant of salt marshes along the Atlantic coast of the US. Along the South Carolina coast, agricultural fields, golf courses and housing developments are often located adjacent to grass shrimp habitats, so all life history stages of these organisms face a significant risk of exposure to a variety of pesticides. This study examined the toxicity of three pesticides, singly and in mixture, to grass shrimp larvae, the most sensitive life stage. The pesticides tested included atrazine, an herbicide commonly used on turf grass and field crops; fipronil, a persistent insecticide increasingly used against termites and fire ants; and imidacloprid, a systemic insecticide used in agricultural products and in products for home gardens and turf grass. Fipronil was the most toxic to shrimp larvae with a 96-h LC50 of 0.68 g/L (95% CI 0.57 – 0.79 g/L). Shrimp larvae were less sensitive to imidacloprid with a 96-h LC50 of 308.8 g/L (95% CI 273.6 – 348.6 g/L). Atrazine was non-toxic to shrimp larvae at the environmentally relevant concentrations tested (EPA Water Quality Guideline at the time of testing of 26.7 g/L). In mixtures, fipronil plus atrazine and imidacloprid plus atrazine had no change in toxicity compared to fipronil and imidacloprid tested singly. Similarly, a fipronil/imidacloprid mixture did not show greater than additive toxicity. However, when atrazine was added to the fipronil/imidacloprid mix, greater than additive toxicity occurred. These results illustrate the complexity of pesticide mixtures. While highly toxic compounds such as fipronil and imidacloprid may not be more toxic to grass shrimp larvae in mixture, the addition of the relatively non-toxic atrazine can increase the toxicity of the mixture.
Key words: fipronil, atrazine, imidacloprid, Palaemonetes pugio
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