Abstract

The acute toxicity of endosulfan and diazinon to the freshwater rotifer Brachionus calvciflorus was determinated after 24 hours exposure to these toxicants. The mean 24 hr‐LC50 values were 5.15 and 29.22 mg/L for endosulfan and diazion respectively. Based on these results, four sublethal concentrations were chosen to determined the median lethal time (LT50) at each concentration of toxicant tested. We also used a control with the solvent (acetone).

The concentration tested were 1/5, 1/4, 1/2 and 2/3th LC50 (24hr) for both pesticides. We found a decrease in the median lethal time (LT50) with increasing pesticide concentrations. The LT50 values ranged from 6.49 to 3.48 days after endosulfan treatment, and from 6.96 to 2.49 days after diazinon exposure. No effects on survival were observed in control animals exposed to the solvent.