Effect of exposure regime on the internal distribution of cadmium in Chironomus staegeri larvae (Insecta, Diptera)

Although insects are routinely used to test the acute toxicity of pollutants in water alone, little information exists on the influence of exposure regime on the accumulation of contaminants in these animals. We exposed fourth instar Chironomus staegeri larvae to 10 nM Cd in microcosms under two exposure regimes: a water only short-term (5 days) exposure, or a water and sediment long-term (140 days) exposure. Microautoradiography of whole animals demonstrated that the digestive tract was the principal organ of Cd accumulation under both exposure regimes. The majority of accumulated Cd was confined to a small section of the insect's midgut, suggesting uptake in this region. Our results suggest that the Cd exposure regime of Chironomus larvae would not alter the body organ in which Cd would exert: its toxicity. (C) 1998 Elsevier Science B.V. All rights reserved.