EFFECTS OF PH AND TEMPERATURE ON THE ACUTE TOXICITY AND UPTAKE OF CARBARYL IN THE MIDGE, CHIRONOMUS-RIPARIUS

The simultaneous effects of pH and temperature upon the aquatic toxicity of carbaryl were determined in acute toxicity tests, uptake studies, and residue studies. Toxicity tests were conducted with fourth instar midge larvae, Chironomus riparius, in water held at pH values 4, 6 and 8 and at temperatures of 10°C, 20°C and 30°C. The toxicity of carbaryl varied significantly with changing pH and temperature. An increase in temperature from 10°C to 30°C at pH 4 resulted in a 2-fold increase in toxicity and a corresponding decrease in EC50 values (133 μg/l to 61 μg/l). The same increase in temperature at pH 6 resulted in a similar increase in toxicity (133 μg/l to 71 μg/l). Increasing temperature at pH 8 caused first a decrease (96 μg/l to 128 μg/l), then an increase (128 μg/l to 107 μg/l) in toxicity. Toxicity was highest at pH 4, 30° C and lowest at pH values 4 and 6, 10°C. There was no significant difference in toxicity at pH 4 and 6 at any tested temperature. Uptake of 14C-carbaryl by midge larvae was generally correlated with toxicity although exceptions were noted. Significantly more total radioactivity was absorbed by the midge larvae at pH 8 than at pH 6 or 4 at both 20°C and 30°C. The stability of carbaryl in water was enhanced by low pH and low temperature with 94% remaining after 24 h at pH 4, 10°C. Only 23% remained after 24 h at pH 8, 30°C. As water chemistry parameters changed, so too did the biological manifestations of carbaryl bioavailability such as acute toxicity and uptake by aquatic organisms. These manifestations are different than results based upon the individual influences of water chemistry parameters. © 1990.