Observations of mouthpart deformities in the Chironomus larvae exposed to different concentrations of nine heavy metals

Abstract

A study was conducted to observe the effects of heavy metal contamination on the formation of chironomus larval mouth part deformities as a model for biomonitoring exposure. Chironomus plumosus larvae were reared in the lab and exposed to nine heavy metals individually for 96 h LC50 experiments which included modifications in temperature. The mouth parts and antennae of the exposed chironomids were observed for the presence of deformities. Only clear and distinct deformities, such as fused, missing, extra, strong asymmetry, misshapen teeth with smooth edges, or a combination of these traits were counted as deformed individuals. The results showed that the occurrence of deformities was noted in all test animals exposed to the heavy metals but variations observed between heavy metals were not statistically significant; however, in the case of deformity P2 (mandibles lacking teeth), a significant difference was observed between heavy metals. Variation in the occurrence of deformities was observed to be significantly metal concentration dependant. Morphological deformities were observed to be greater with mercury with a frequency of deformities ranging 70–100%. Exposure to silver was observed to produce the lowest incidence of morphological deformities, ranging 12–55%. The occurrence of deformities in controls was observed to be negligible with frequencies ranging from nondetectable to 2%. The data suggest that use of chironomus as a model for biomonitoring exposure to metals is a reliable method to detect environmental contamination.