EXPERIMENTAL INDUCTION OF MORPHOLOGICAL DEFORMITIES IN CHIRONOMUS-RIPARIUS LARVAE BY CHRONIC EXPOSURE TO COPPER AND LEAD

Five consecutive generations of Chironomus riparius Meigen larvae were chronically exposed from egg to fourth instar to four sublethal conce ntrations of copper (0, 1, 10, 100 mu g L-1) and lead (0, 5, 50, 500 m u g L-1) in artificially spiked water (static with renewal), with diat omaceous earth as substrate and tetraphyl(R) as food, in order to test the induction of morphological deformities by these metals. The use o f diatomaceous earth was suboptimal because it caused high mortalities (>60%), independent of metal stress. The higher copper concentrations had a positive effect on the survivals relative to the control. Split medial mentum teeth were recorded in more than 10% of the larvae, but could not be related to metal stress. Deformities of the mentum and t he mandibles were recorded in second, third, and fourth instars expose d to both metals. Concentration and generation effects were noted for unusual number of mentum teeth (0-5.3%, lead), unusual number of mandi ble inner teeth (0-10.4%, copper and lead), and small open mentum gap (0-6.5%, copper). These experiments demonstrated the potential of both an essential and a non-essential metal to induce weak deformities in a small proportion of a C. riparius population as well as the inductio n of deformities which are independent of metal stress or fluctuating over the generations. The study shows the potential of midge deformiti es as a biomonitoring tool, but at the same time warns for a careful i nterpretation of deformity scores because of the influence of populati on dynamics on the final outcome of deformity frequencies and of the e xistence of deformities not related to pollution.