ACUTE AND CHRONIC EFFECTS OF 4 COMMERCIAL HERBICIDE FORMULATIONS ON CERIODAPHNIA-DUBIA

Toxicity tests with Ceriodaphnia dubia were conducted to determine acu te (48 h) and chronic (7-day survival and reproduction) effects of fou r commonly used herbicide formulations. The 48-h LC50s in decreasing o rder of toxicity were 14.36 mg/L (Micro-Tech(R)), 15.93 mg/L (Bicep(R) ), 32.99 mg/L (Extrazine(R)), and 35.36 mg/L (Lexone(R)). Reduced repr oduction 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(R)), 8.84 mg/L (Bicep(R)), 17.68 mg/L (Ex trazine(R)), and 8.84 mg/L (Lexone(R)). The acute-to-chronic ratios (A CRs) for Micro-Tech(R) (0.81), Bicep(R) (1.80), Extrazine(R) (1.86), a nd Lexone(R) (4.00) indicate a relatively narrow range between acute a nd chronic sensitivity in daphnids. A comparison of these response dat a to environmental concentrations suggests these herbicides are not li kely to directly impact invertebrates. Potential impacts on plants and human health should be of primary ecological and regulatory concern.