A comparison of two methods to observe the effects of dual metal exposure to the chironomus larvae

Abstract

A study was conducted to investigate the effects of metal mixtures on the Chironomus plumosus. Two methods of preparing the mixtures were used, the Toxic Unit (TU) method and the parts per million (PPM) + PPM method. A comparison was undertaken between the two methods to observe the ease with which (1) experiment could be conducted and (2) whether LC₅₀ values could be obtained. In this study, it was noted that the PPM + PPM method was an easier method to conduct metal mixture experiments as the LC₅₀ values could be easily calculated for individual metals and compared with the LC₅₀ values of metals obtained from single metal experiments. The findings showed that the LC₅₀ value for zinc (Zn) was more toxic for chromium (Cr) when it was reduced from 9.6 to 0.3 mg L⁻¹, with silver the LC₅₀ value became 3.6 mg L⁻¹, 4.5 mg L⁻¹ with nickel (Ni). In the PPM + PPM method, the LC₅₀ value for Zn was observed to be 10.2 mg L⁻¹ when in mixture with chromium, 23.8 mg L⁻¹ with silver, and 13.4 mg L⁻¹ with Ni. Changes in the 96 h LC₅₀ value were found to be significant for all metals.

Keywords:

• dual metal exposure
• heavy metals
• chironomids
• toxic units
• PPM + PPM mixtures