Effects of temperature on the toxicity of M-parathion, chlorpyrifos, and pentachlorobenzene to Chironomus tentans

This study examined the influence of temperature (10, 20, and 30 degrees C) on the acute toxicity and accumulation of two organophosphate (OP) insecti cides and a narcotic chemical to the midge (Chironomus tentans). OP insecti cides used in this study included chlorpyrifos and m-parathion, and pentach lorobenzene was the chosen narcotic. Chlorpyrifos was the most toxic chemic al tested, followed by m-parathion and then pentachlorobenzene. A positive correlation was found between temperature and toxicity for each of the chem icals tested. A reverse trend was noted for total OP insecticide body resid ues with decreased concentrations found at the higher temperatures. Pentach lorobenzene body residues remained constant at all temperatures. All three chemicals showed increased uptake rates at 20 and 30 degrees C in compariso n to 10 degrees C. The noted decrease in midge body residues at the higher temperatures fur the OP insecticides was contributed to increased biotransf ormation and elimination races at the higher temperatures. Overall, tempera ture had a greater influence on OP toxicity than for pentachlorobenzene, an d this may be due to accelerated biotransformation of the OPs to more toxic o-analog metabolites at the higher temperatures.