Morphological Deformities in Chironomus Riparius Meigen Larvae after Exposure to Cadmium over Several Generations

In order to test the potential of chironomiddeformities for biomonitoring, induction of morphologicaldeformities in Chironomus riparius larvae was assessed afterchronic exposure (static with renewal) of eggs and subsequentinstars to sublethal nominal cadmium concentrations of 0, 3 (NOEC),9 (intermediate) and 27 (chronic LC50) μg Cd l-1 during 7to 10 generations. Deformities which could be associated with anindirect or direct cadmium effect were split medial mentum teeth(more frequent in 9 and 27 μg Cd l-1) and premandibledeformities (especially in 3 μg Cd l-1). The controlcontained more larvae with additional teeth in mentum and mandiblethan the metal-exposed conditions. In the 9 μg Cd l-1 condition the frequencies of larvae with split medial mentumteeth increased in the last four generations, to reach 40%. Theunpredictability of fluctuations of deformity frequencies over thegenerations was associated with parental effects and experimentalmanipulation. The deformity percentages correlated positively withthe mortalities and could be related to the induction of toleranceto cadmium, as was concluded on the basis of life cycle analysis ina previous paper. This experiment demonstrated a concentration-response relationship between deformities and sublethal levels ofcadmium. However, the observed generation fluctuations caution for(1) the use of single-generation experiments for definingecotoxicological threshold values, and (2) experimentally inducedgenetical drift in multi-generation experiments.