Toxicity of agricultural chemicals in Daphnia magna

Daphnia magna is a useful aquatic organism for testing ecological toxicities of environmental pollutants. However, there were only a few studies on agricultural chemicals using these organisms.

We investigated acute and subchronic toxicities of 30 agricultural chemicals commonly used in Japan in D. magna. Acute toxicity of the agricultural chemicals was determined using the concentrations yielding 50% immobility of D. magna after 24 hr and 48 hr exposure as end points. D. magna was cultivated with the chemical and algae until the first brood production. Lethal toxicity and the number of survival broods were determined within 13 days.

All insecticides among the agricultural chemicals exhibited the strongest acute toxicity (LC50 from 0.00053 to 0.037 mg/L). More than 50% of the herbicides and fungicides did not exhibit acute toxicity at 10 mg/L. Chlornitrofen, pencycuron, and fenitrothion showed significantly lower LC50 values at 8 days than at 24 hr and 48 hr. Isoprothiolane, flutolanil, and thiophanatemethyl significantly delayed the first brood at concentrations less than half of those for LC50 (8 days). Thiobencarb, iprodione, flutolanil, mepronil, and thiophanatemethyl significantly reduced the size of the first brood at concentrations less than half of those for LC50 (8 days).

In this study, chlornitrofen, pencycuron, and fenitrothion were suggested to have slow-acting toxicity. Also, thiobencarb, iprodione, flutolanil, mepronil, and thiophanatemethyl were suggested to have parthenogenetic toxicity.