Abstract: Contaminants in water and sediments have the potential to exert teratogenic effects on benthos. Larvae of Chironomid (Diptera: Chironomidae) are highly sensitive to environmental changes in water. Morphological deformities in the mouthparts of chironomid larvae have been proposed as potential biomarkers in the assessment of sediment quality and environmental stress. Here, we reviewed the discovery, morphology, and types of mouthpart deformity in chironomids, showed the potential teratogenic contaminants and mechanisms, and explained the challenges of such research. Current progress on chironomid mouthpart deformities could be summarized into three aspects: (1) ubiquitous: mouthpart deformities in chironomid larvae commonly exist in polluted water, and abnormal morphologies in different taxa and different parts of the mouthpart have been well described; (2) regional variability: there are large discrepancies in deformity frequency among reports on different polluted waters, which might stem from the inconsistency of standards for deformity analysis and calculation of deformity incidence; and (3) causal nonlinearity: both trace metals and organic contaminants are found to have significant teratogenic effects on chironomid larvae, and series of bioassays on teratogenic effects of specific pollutants have been conducted globally, but the dose-effect relationship between specific contaminants and morphological abnormality is still ambiguous and the teratogenic processes and mechanisms should be demonstrated. Future studies using chironomid deformity in water quality monitoring and toxicity assessment of contaminants should focus on the following four issues: (1) establish clear dose-effect relationship between specific pollutants and chironomid deformity; (2) develop unambiguous indices to represent deformity occurrence; (3) establish laboratory protocols of standardized chironomid deformation assay; and (4) carry out domestic studies on mouthpart deformity in chironomid larvae through field investigation and laboratory bioassays, because related studies are scarcely conducted in China, to develop effective bioindicators suitable for local water quality assessment and early warning signals for the ecological effects of pollutants.

Key words: heavy metal pollution, organic pollution, chironomids, mouthpart deformity, water quality monitoring.