Chronic toxicity of copper to a partial life cycle of the midge,Chironomus decorus

The development and hatchability ofChironomus decorus eggs were not affected by 0.1 to 5 mg/L of copper in water. The embryos developed normally and hatched at about the same time (after 55 hr of incubation). All larvae survived the duration of the test (72 hr) except those subjected to 5 mg/L of copper in water, which died after only partial emergence from the egg shell. Apparently, eggs were protected by their shell from copper. Growth ofC. decorus larvae was reduced significantly when they were reared in copper-spiked food-substrate (bound copper) from the age 1 to 15 days old (900–4,500 mg/kg of copper). The substrate copper concentration at which larval growth was reduced to 50% (EC50) was 1,602 mg/kg. Substrate copper caused deformities in the epipharyngeal plate of larval mouthparts and copper concentration higher than 1,800 mg/kg delayed adult emergence. The copper concentration in pupal exuviae and adults were positively correlated to copper concentration in the substrate in which they had been reared as larvae. Larval stage appeared to be the most sensitive to copper toxicity, while eggs were the least sensitive. Larval growth was the best indicator in detecting copper pollution, since it could detect copper at relatively low concentrations. The time to adult emergence was not considered a very good indicator, while larval deformities offered a quick tool to evaluate copper pollution.     

Acute toxicity of aqueous and substrate-bound copper to the midge,Chironomus decorus

Fourth instar larvae of the midge,Chironomus decorus, were exposed to copper in water and copper in food and substrate (bound forms). Copper present in aqueous forms was more toxic than when it was present in bound forms. The relationship between copper in water and copper in midges could be described by an exponential equation while the relationship between copper in substrate and midges was best described by a simple linear regression equation. Midge larvae accumulated copper from water and possessed some mechanisms to regulate copper uptake and excretion when exposed to copper concentrations of 0.05–1.0 mg/L (aqueous forms) and lost that ability when the concentration exceeded 1.0 mg/L. On the contrary, the midge larvae were unable to accumulate copper from food, since the estimated bioconcentration factor was between 0.10 and 0.16. When the midge larvae were exposed to copper in water, the uptake rate increased rapidly from 0–10 hr and then the rate increased very slowly or in some cases it reached a steady state after 10 hr. The steady state was attained within 1 to 3 hr when the midges were exposed to copper in food and substrate.