Research Product

Six pesticides were evaluated in laboratory studies to determine acute (96-h) toxicity, octanol-water partition coefficients (log P), solubility, and persistence in seawater. In addition, three of the six pesticides (synthetic pyrethroids) were tested using the eastern oyster (Crassostrea virginica) in long-term (28-day) tests to determine their respective bioconcentration factors (BCF). Acute toxicity tests provided the following decreasing order of toxicity to estuarine crustaceans and fishes: AC 222,705, fenvalerate, permethrin, chlorpyrifos, methyl parathion, and benthiocarb. The estuarine mysid (Mysidopsis bahia) was consistently the most sensitive species, with LC50 values as low as 0.008 µg/L. The sheepshead minnow (Cyprinodon variegatus) was generally the least sensitive (range of LC50 values = 1.1-1370 µg/L). log P values were inversely related to solubility in seawater. The following are the increasing order of log P values (range, 1.8-6.5) and decreasing order of solubility (range >1000-24 µg/L): methyl parathion, benthiocarb, chlorpyrifos, AC 222,705, fenvalerate, and permethrin. Pesticide half-lives in sediment-water studies ranged from 1.2 to 34 days and were in the following order of increasing persistence: methyl parathion, permethrin, benthiocarb, AC 222,705, chlorpyrifos, and fenvalerate. The steady-state BCF's of the three synthetic pyrethroids were 1900 for permethrin, 2300 for AC 222,705 and 4700 for fenvalerate. After termination of the exposure, each insecticide was depurated by oysters to nondetectable concentrations within one week.