Laboratory experiments were used to assess morphological responses of Chironomus tentans larvae exposed to three levels of zinc and lead. Chironomus tentans egg masses were placed into triplicate control and metal-spiked aquaria containing the measured concentrations 1,442, 3,383, and 5,562 microg/g Pb dry weight and 1,723, 3,743, and 5,252 microg/g Zn dry weight. Larvae were collected at 10-d intervals after egg masses were placed in aquaria until final emergence. Larvae were screened for mouthpart deformities and metal body burdens. Deformities increased with time of exposure in both Zn and Pb tanks. Deformity rates between the three Zn concentrations differed statistically, with low and medium Zn levels containing the highest overall deformity rates of 12%. Deformity rates for larvae held in the Pb aquaria were found to differ significantly. Larvae in the low-Pb tanks had a deformity rate of 9%. Larvae and water from both the Zn and Pb aquaria had increasing metal concentrations with increasing sediment metal concentration. Results demonstrate that Zn and Pb each induce chironomid mouthpart deformities at various concentrations. However, a clear dose-related response was not demonstrated. Our research provides more support for the potential use of chironomid deformities as a tool for the assessment of heavy metal pollution in aquatic systems.

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Exposures to either zinc or lead in contaminated sediments have been shown to induce characteristic deformities in larval chironomids. This study examined the effects of exposure to lead and zinc in combination on Chironomus tentans larvae. Proportions of mouthpart deformities in populations of larvae reared in sediments containing nominal combinations of lead and zinc were tested for additive, synergistic, and antagonistic interactions using logistic regression. Metal body burdens, body size measurements, and survival were used to evaluate toxicity and developmental impacts. Results demonstrate zinc and lead mixtures produce fewer deformities than the individual metal, so their interaction may be characterized as antagonistic. However, exposure to the metal mixtures also caused delayed development and failure to hatch. The apparent decline in deformities may be an artifact of higher mortalities or developmental effects. This research provides better understanding of some of the problems and considerations for use of chironomid population deformity proportions in bioassessments for sediment metal contamination.

Laboratory bioassays consisting of sediments spiked with three concentrations (30, 130, and 260 microg g-1 As dry wt) of arsenic (As+3) were used to assess morphologic responses and growth in Chironomus tentans larvae. Chironomid larvae were raised in contaminated sediments from egg stage to emergence, and mouthpart abnormalities, larval length, and larval head width were used as end points to determine differences between metal-spiked and control specimens. C. tentans exhibited significantly higher mouthpart deformity proportions, smaller body sizes, smaller head widths, and slower development than control larvae. Our results demonstrate a dose-response relationship between As and mentum deformities in C. tentans. However, the proportion of deformed larvae did not increase with time in the treatment tanks. Results demonstrate that As induces mouthpart abnormalities at various concentrations. This research provides more support for the use of chironomid abnormalities as a tool for the assessment of heavy-metal pollution in aquatic systems.

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