Behavioural and histological effects of atrazine on freshwater molluscs (Physa acuta Drap. and Ancylus fluviatilis Müll. Gastropoda).

This study examines the direct and indirect effects of atrazine on two grazer species--Physa acuta and Ancylus fluviatilis--as assessed by changes in mortality rates, biomass, searching behaviour and histological properties. No direct effects were observed in the acute toxicity test (48 h) with 0.02, 0.2, 2, 10 and 20 mg l(-1) of atrazine. A chronic toxicity test (18 days) performed in six experimental channels with 15 microg l(-1) of atrazine showed significant changes in grazer behaviour, increased searching velocity and different movement patterns in animals exposed to herbicide. No significant effects were observed in rates of mortality and biomass. Kidney cells of Physa acuta displayed an important cell lysis when animals were exposed to 0.1 mg l(-1) of atrazine for 10 days, and this effect was not reversed after a decontamination process. These results provide evidence of behavioural and structural changes in freshwater molluscs due to a subacute atrazine concentration.