Comparative Toxicity of Nine Metals to Two Malaysian Aquatic Dipterian Larvae with Reference to Temperature Variation

Abstract

A study was conducted to determine the suitability of using selected aquatic dipterian larvae for biomonitoring bioassays. The organisms included a member of the biting midge family that was identified as Culicoides furens and a member of the non-biting midge family, identified as Chironomus plumosus. Median lethal toxicity tests were conducted to observe the variation between metal sensitivities between the two larval forms and how variations in temperature could affect the experimental setup. Nine heavy metals were used in the study. It was observed that the 96 h LC₅₀ (in mg/L) for the different metals was found to be Zn-16.21 (18.55 ± 13.87); Cr-0.96 (1.08 ± 0.84); Ag-4.22 (6.87 ± 1.57); Ni-0.42 (0.59 ± 0.25); Hg-0.42 (0.59 ± 0.25); Pb-16.21 (18.31 ± 14.11); Cu-42.24 (45.18 ± 39.30); Mn-4.22 (7.19 ± 1.25); Cd-0.42 (0.59 ± 0.25) for the Chironomus plumosus and Zn-4.22 (6.56 ± 1.88); Cr-0.42 (0.54 ± 0.30); Ag-0.42 (0.54 ± 0.30); Ni-0.42 (0.54 ± 0.30); Hg-0.04 (0.07 ± 0.01); Pb-0.42 (0.54 ± 0.30); Cu-42.24 (45.18 ± 39.30); Mn-4.22 (6.56 ± 1.88); Cd-0.42 (0.54 ± 0.30) in the case of the Culicoides furens. With temperature as a variable the LC₅₀ values were observed to increase from 2.51 mg/L at 10°C to 4.22 ppm at 30°C and to reduce slightly to 3.72 mg/L at 35°C as seen in the case of Zn. It was also observed that at 40°C thermal toxicity and chemical toxicity overlapped as 100% mortality was observed in the controls. This trend was observed in all metals for both C. plumosus and C. furens. Thus indicating temperature played an important role in determining LC₅₀ values of toxicants.