10.22376/ijpbs.2019.10.1.p1-12 Volume 4 Issue 4 2013 (October - December) In this study, we performed ecotoxicity tests of sodium arsenite on soil invertebrate lessThan i greaterThan Eisenia fetida lessThan /i greaterThan . Initially, broad range of sodium arsenite (0.1, 1, 10, 100mg/ml) was tested for mortality of lessThan i greaterThan E. fetida lessThan /i greaterThan after 24 hours in filter paper test. The narrow range doses (0-1mg/ml) were further tested to determine the EC lessThan sub greaterThan 50 lessThan /sub greaterThan and LD lessThan sub greaterThan 50 lessThan /sub greaterThan . The EC lessThan sub greaterThan 50 lessThan /sub greaterThan dose of sodium arsenite was considered at which 50% of earthworms exhibited rejection to the spot on filter paper in the spot rejection test. The LD lessThan sub greaterThan 50 lessThan /sub greaterThan of sodium arsenite resulting in mortality in 50% of lessThan i greaterThan Eisenia fetida lessThan /i greaterThan was studied with contact filter paper bioassay (24hrs) and soil bioassay (14 days). In the range finding test, there was no mortality in control and 0.1mg/ml but 100% mortality was observed at doses of 1mg and above after 24 hours. Thus, for further study smaller doses intervals in the range between 0-1mg/ml was selected for spot rejection, contact filter paper and soil bioassay. The percent mortality in each test was computed and was subjected to regression analysis to get a linear dose response curve and estimation of EC lessThan sub greaterThan 50 lessThan /sub greaterThan and LD lessThan sub greaterThan 50. lessThan /sub greaterThan The EC lessThan sub greaterThan 50 lessThan /sub greaterThan was estimated as 0.3mg/ml of sodium arsenite concentration to lessThan i greaterThan Eisenia fetida lessThan /i greaterThan . The 24hrs- LD lessThan sub greaterThan 50 lessThan /sub greaterThan was estimated as 0.4mg/cm lessThan sup greaterThan 2 lessThan /sup greaterThan in filter paper and 14 days -LD lessThan sub greaterThan 50 lessThan /sub greaterThan as 5mg/kg in soil bioassay. Thus it can be concluded that lessThan i greaterThan Eisenia fetida lessThan /i greaterThan exhibit sign of toxicity in environmental soils which are containing 1mg/kg and higher doses of sodium arsenite. PALLAVI KAUSHIK, SONAM MEENA AND MEGHA MATHUR Ecotoxicity, Eisenia fetida, sodium arsenite, bioassay, EC50 and LD50. 483-491