Acute and chronic effects of four commercial herbicide formulations on Ceriodaphnia dubia

Toxicity tests with Ceriodaphnia dubia were conducted to determine acute (48 h) and chronic (7-day survival and reproduction) effects of four commonly used herbicide formulations. The 48-h LC50s in decreasing order of toxicity were 14.36 mg/L (Micro-Tech^®), 15.93 mg/L (Bicep^®), 32.99 mg/L (Extrazine^®), and 35.36 mg/L (Lexone^®). Reduced reproduction was detected at concentrations below 48-h LC50s for three of the formulations. The 7-day chronic values (ChV) based on reproduction were 17.68 mg/L (Micro-Tech^®), 8.84 mg/L (Bicep^®), 17.68 mg/L (Extrazine^®), and 8.84 mg/L (Lexone^®). The acute-to-chronic ratios (ACRs) for Micro-Tech^® (0.81), Bicep^® (1.80), Extrazine^® (1.86), and Lexone^® (4.00) indicate a relatively narrow range between acute and chronic sensitivity in daphnids. A comparison of these response data to environmental concentrations suggests these herbicides are not likely to directly impact invertebrates. Potential impacts on plants and human health should be of primary ecological and regulatory concern.