EARLY SIGNS OF LETHAL EFFECTS IN DAPHNIA MAGNA (BRANCHIOPODA, CLADOCERA) EXPOSED TO THE INSECTICIDE CYPERMETHRIN AND THE FUNGICIDE AZOXYSTROBIN

This study presents the effects of sublethal concentrations of pesticides cypermethrin and azoxystrobin on the activity of several physiological parameters of egg-carrying Daphnia magna studied using a video-image technique. Single tethered daphnids were continuously recorded for 24h of pesticide exposure, and the activity of the heart, the filtering limbs, the mandibles, and the focal spine were subsequently analyzed. Acute toxicity tests based on the criteria of immobilization were performed on egg-carrying D. magna, and sublethal concentrations of 0.1, 1.0, and 10 mu g/L cypermethrin and 0.5, 1.0, and 2.0 mg/L azoxystrobin were established. At a concentration as low as 0.1 mu g/L cypermethrin, the 5% effective concentration after 24h of exposure (EC5,24h), the activity of the focal spine increased and the filtering limb activity decreased. The activity of the mandibles was reduced by exposure to 1.0 (EC18,24 h) and 10 mu g/L (EC41,24 h) cypermethrin, whereas heart activity increased at a concentration of 10 mu g/L (EC41,24 h). With regard to azoxystrobin, the activity of all response parameters except the focal spine decreased by exposure to 0.5 mg/L (EC4,24h) azoxystrobin. The focal spine was not affected by azoxystrobin. The results show that physiological mechanisms important for ingestion of food in D. magna may be impaired by low concentrations of commonly used pesticides. Environ. Toxicol. Chem. 2010;29:2371-2378. (C) 2010 SETAC