Relations between heavy metals in aquatic sediments and in Chironomus larvae of Belgian lowland rivers and their morphological deformities

Levels of Cd, Pb, Cu, and Zn were measured in fourth-instar Chironomus gr. thummi and in three sediment fractions of Belgian lowland rivers, extracted with 1 M NH4-acetate, 1 M HCl, and 70% HNO3-30% H2O2. The percentages of deformed larvae and the mean population severities (MPS) of deformity for the head structures were compared by means of Pearson and linear and polynomial regressions against the metal concentrations in the different compartments. All correlations found were positive. Mentum deformities correlated with all lead fractions (MPS) and the larval copper fraction (percent deformed), while the pecten epipharyngis deformities correlated with the sediment lead fractions and the HCl fraction of copper. Premandible deformities correlated with the copper sediment HNO3-H2O2 fraction and with extreme values of cadmium and zinc. The study demonstrated a variety of deformity response curves to trace metals. At one site, higher lead concentrations were found in larvae with a deformed mentum, compared with normal larvae. Mentum deformities appeared to be potential predictors of lead levels in the sediments and the larvae, while pecten epipharyngis deformities may be an indicator of lead and copper in the sediments.