Chronic Toxicity of Mercury (HgCl2) to the Benthic Midge Chironomus riparius

In most aquatic ecosystems mercury accumulates more in the sediment than in water column. However, due to limited eco-toxicological data, it is difficult to predict the toxicity of these sediments. The present study evaluated the effects of inorganic mercury in spiked sediment on the survival, growth, and emergence of the midge Chironomus riparius and compared the results to mercury concentrations reported in streams and rivers in Africa. At 3.84 mg Hg/kg dry sediment, mercury significantly reduced larval survival and midges emergence success in comparison to control sediment (P<0.05). The growth of the larva was significantly inhibited (P<0.05) at 2.42 mg Hg/ kg dry weight, while emergence of C .riparius midges was significantly delayed at 0.93 mg/kg dry wt. These results indicate that mercury inhibits C. riparius characteristics at lower concentrations than those which have been measured in sediments from watersheds impacted with mercury like those found around artisanal gold mining in Africa. It is therefore possible that Chironomus and probably other fauna living in these watersheds are at risk.