Mouthpart deformities of Chironomid larvae as an indicator of heavy metal polluted water

Abstract: Freshwater ecosystems are under increasing pressure from a variety of contaminants, including heavy metals from mining operations, which can have complex effects that are difficult to evaluate. To detect early warnings from elevated concentrations of metals, organisms are sought to be used as monitoring tools. For example, mouthpart deformities in Chironomid larvae have been proposed as a bioindicator of stress in aquatic environments. However, the frequency and cause of these deformations, and their sensitivity to different stressors remain uncertain. In this study, I evaluated the usefulness of mouthpart deformities as a tool to monitor the effects of heavy metals from mining in northern Sweden. To do this, the mouthparts of 3789 Chironomid individuals analyzed from 17 sites closely located to mining operations and tested against concentrations of metals and DOC in the water chemistry of lakes and rivers. The frequency of deformities ranged from 0.00 – 4.79 % across all sites. Metal concentrations ranged from ‘very low’ to ‘low’ based on biological effect risk assessments. Of these, copper (R2 = 0.73) and cobalt (R2 = 0.66) were found to be significantly correlated with frequency of deformities. Additionally, the occurrence of deformities declined with DOC concentration, this was a nonlinear relationship. Frequencies of deformities observed in this study were lower than what have been reported to similar studies. The result from this study, together with other studies, suggest that deformities in Chironomid larvae are sensitive to even low levels of certain metals and could potentially be a good biomonitoring tool for early warnings of contamination in freshwater environments.