STUDY ON THE ACUTE TOXICITY OF CHLOROCID 20 EC TO Tubifex sp. Lamarck, 1816

Mondal P., Mollah A. R. and Rahman M. M. 2008. Study on the Acute Toxicity of Chlorocid 20 EC to Tubifex sp. Lamarck, 1816. J .Soil .Nature. 2(3): 20-25 Static bioassay tests were conducted to assess the acute toxicity of chlorocid 20 Emulsified Concentration (EC) to Tubifex sp. Lamarck, 1816 during March to August 2006 in the Zoological Garden at Carzon hall campas of the Dhaka University. Tubifex sp. was exposed to the toxicant for different duration (24-96 hours) with and without debris in the exposure media. In the Bioassay test 1 (without debris), Lethal Concentration50 (LC50) values of chlorocid 20 EC at 24, 48, 72 and 96 hours of exposure time were 7.144 mg/l, 4.116 mg/l, 2.212 mg/l and 1.607 mg/l respectively and 9.690 mg/l, 6.943 mg/l, 5.708 mg/l and 4.084 mg/l respectively in Bioassay test 2 (with debris). The acute toxicity of chlorocid 20 EC gradually decreased with time, which was indicated by toxicity curve becoming asymptotic with the time. These asymptotes mark the approximate values of the threshold concentration (=incipient LC50). The results show that higher levels of toxicant are needed to induce mortality under debris condition. The pre-exposure acclimation to 0.50 mg/l of chlorocid 20 EC afforded slight resistance to the toxicant as evident by delayed and reduction in mortality, when challenged with higher lethal doses, compared to un-acclimated Tubifex sp.. Acclimation to 1.0 mg/l chlorocid 20 EC for a period of four days did not afford any protection to Tubifex sp. when challenged with lethal doses. The result of the experiment reveals that debris as well as pre-exposure acclimation with chlorocid 20 EC influences the mortality rate of Tubifex sp.