STM Article Repository

Fourth instar larvae of Chironomus striatapennis were collected from breeding aquarium under
laboratory conditions and exposed for 96 hours to different doses of Pb, Cd and Hg for static bioassay
to measure the LC50. Ten fourth instar larvae were placed in 100 ml beaker with 50 ml of each test
solution. Larvae were exposed to six different concentrations, consisting of five trials. A control was
also maintained wherein organisms were exposed to distilled water. Larvae were not fed during the
toxicity tests. All beakers were free from tube forming materials. Data of mortality were subjected to
probit analysis. Chi square was used to test for heterogeneity and the result was found to be
significant (p<0.05) in all three metals. Results showed that sensitivity of larvae to metals was Hg> Cd
>Pb. C. striatapennis showed noticeable response in LC50 study and was sensitive to low doses of
heavy metals. Several secondary consumers have preferred this larva as their food. So unplanned
industrialization may increase the level of heavy metals in the aquatic ecosystem which will
accumulate slowly but definitely in different trophic levels and at the same time unusual death of these
larvae may indirectly change the equilibrium of the aquatic ecosystem. Static bioassay of heavy
metals revealed that larvae of Chironomus striatapennis was more sensitive to Hg than Cd and Pb
respectively. It was also observed that LC50 values were less than standard permissible limit of these
heavy metals. Unplanned industrialization may increase the level of heavy metals in the aquatic
ecosystem which will accumulate slowly but steadily in different trophic levels and at the same time
unusual death of these larvae may indirectly change the equilibrium of the aquatic ecosystem. As this
larva is a preferred food for different secondary consumers, heavy metal toxicity may responsible for
bio-accumulation of several heavy metals in chironomid larvae and make these larvae unsuitable for
consumption.