John Schaumloffel

Morphological abnormalities in Chironomus tentans exposed to cadmium—and copper-spiked sediments

The induction of mouthpart deformities and the developmental response with exposure to sediments spiked with three concentrations (9, 39, and 61 microgg(-1) Cd dry wt.) of cadmium (Cd) and three concentrations (30, 125, and 215 microgg(-1) Cu dry wt.) of copper (Cu) were investigated. Mouthpart deformity proportions in Chironomus tentans larvae were compared between metal-spiked and control populations and between parent and offspring (F1) populations. Cd- and Cu-treated sediments induced deformities (low Cd=13%, medium Cd=7%, high Cd=4%, low Cu=6%, medium Cu=9%, high Cu=6%) at significantly higher proportions than control (3%) sediments. No negative developmental response was determined. Larval sizes in metal-treated aquaria and control aquaria were not significantly different. F1 larvae from parents reared in medium and high Cu had significantly lower deformity rates than their parents. Our research adds to the growing evidence implicating heavy metals in general, and Cd and Cu specifically, as teratogenic agents.

Induction of morphological deformities in Chironomus tentans exposed to zinc‐ and lead‐spiked sediments

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.

Effects of exposure to a combination of zinc‐ and lead‐spiked sediments on mouthpart development and growth in Chironomus tentans

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.