Acute, chronic and sublethal effects of the herbicide propanil on Daphnia magna.

Acute and chronic toxicity tests with propanil were conducted on Daphnia magna. The 24 and 48 h LC50 were 43.74 and 5.01 mg/l respectively. Chronic toxicity tests were carried out using sublethal propanil concentrations (0.07, 0.10, 0.21 and 0.55 mg/l) during 21 days. The effect of propanil on survival, reproduction and growth of D. magna organisms was monitored. The parameters used to evaluate herbicide effect on reproduction were: mean total young ones per female, mean brood size, time to first reproduction, mean number broods per female and intrinsic rate of natural increase (r). Survival and growth (body length) were also determined after 21 days of exposure to the herbicide. Reproduction was significantly reduced when propanil concentration increased in the medium. The intrinsic rate of natural increase (r) decreased with increasing concentrations of propanil especially in those animals exposed to 0.55 mg/l. However, growth as well as survival of the exposed organisms only decreased in daphnids exposed to the highest propanil concentration tested. The maximum acceptable toxicant concentration (MATC) was calculated for D. magna exposed to the herbicide using as parameter of evaluation the intrinsic rate of natural increase (r). The interpolation of these results gave MATC values of 0.08 mg/l herbicide. We have derived the EC50 values for some selected parameters on D. magna exposed to propanil. EC50 values indicated that reproductive parameters were very sensitive of the effect of propanil on daphnids. Finally, the daphnids were exposed to the same sublethal herbicide concentrations as in the chronic study and the effect of the toxicant on filtration and ingestion rates was determined. Feeding rates of D. magna declined with increasing propanil concentrations. The effective propanil concentrations at which feeding rates were reduced to 50% of that in controls (EC50) were also calculated.