Exposure of Chironomus riparius larvae (diptera) to lead, mercury and beta-sitosterol: effects on mouthpart deformation and moulting

Mouthpart deformation in chironomid larvae is induced by exposure to chemic al contaminants and is becoming an established bio-indicator in sediment as sessment programmes. However, concentration-response relationships with cau sal agents have only been established occasionally and with varying success . In this laboratory study, instar II and III larvae were exposed to sub-le thal concentrations of lead, mercury and beta-sitosterol. A significant def ormation response was induced in the pecten with lead and mercury. Deformat ion frequencies of the mentum after metal exposures were not significantly different from the control. Moulting was retarded by both metals and was we ll correlated with mouthpart deformation. The beta-sitosterol is an endocri ne disrupter, which was used to test the hypothetical cause-effect relation between disruption of ecdyson functioning and chironomid deformation. In t he present study, exposure to sublethal concentrations of beta-sitosterol d id not result in any effect on deformation or moulting. As such, the propos ed hypothesis of endocrine disrupters as primary causal agents of chironomi d deformation could not be substantiated. Acetone, which was used as a solv ent to apply beta-sitosterol caused a significant increase of mentum deform ation. The ground filtration paper used as substrate seemed to induce defor mities as well. Substrate contamination, acetone and (especially) inbreedin g were most probably responsible for the high deformation frequencies in th e control conditions. (C) 2000 Elsevier Science Ltd. All rights reserved.