Response of Chironomids to Cu2+, Cd2+ and Pb2+ Metal Ions Using the 96-hour Toxicity Test and Evaluating Different Factors that Affect Metal Accumulation

The protection of aquatic habitat from damage requires proper assessment of the degree of ecosystem degradation and understanding of both the sensitivity of aquatic organisms to contaminants and their ecological requirements. Assessing the sensitivity of these organisms to contaminants was conducted through a series of toxicity tests. The 96-hour toxicity of Cu, Cd and Pb in chironomids was investigated. The LC50 obtained were 1.37 μg/mL for copper, 73.09 μg/mL for cadmium, and 38.47 μg/mL for lead. This gave an order of toxicity of Cu>Pb>Cd for chironomids for 96 hours of exposure. The three metals exhibited an increase in accumulation with increasing concentration of test solution. Among the three metals, lead was observed to be the most accumulating since it yielded the highest concentration in organisms. However, from the LC50 obtained, it is showed that cadmium is the least toxic. The fraction of metals that accumulated could be comprised of metals absorbed to external body parts or insoluble, intracellular metal. Such substances that bind contribute to the total body burden but do not generally contribute to the toxic effect level within the body of organisms. For Cd2+ and Pb2+ ions, accumulation in organisms decreased with presence of Na+ and Ca2+ in the test solution. Furthermore, for a mixture comprising of three metal ions, it was also found that there was a reduction in the amount of metals absorbed by the organisms and caused a lower concentration on organisms as compared when exposed to a single metal system which may be attributed to competition.