Complete bleaching of the algal mass was observed from 3rd day of exposure period onwards in the exposed set when compared to control algal cells. Gradually tiny blue-green particles started making their appearance in the white turbid mass as observed in the naked eye after 15th-20th days of recovery period. The maximum allowable concentration (MAC) recorded for this alga for 15th days exposure was 0.33 mg l-1. The LC value was 0.51 mg l-1, the 10 LC value was 0.76 mg l-1, LC value was 1.14 mg l-1 and LC value was 1.26 mg l-1, for this particular alga, Anabaena 50 90 100 cylindrica. The control set showed 100% survival through out the experimental periods. Out of the select concentrations, safe MAC value of 0.33 mg l-1 was selected as 'A'; LC or PS of 0.76 mg l-1 was selected as 'B' and LC 50 50 90 or PS value of 1.14 mg l-1 was selected as 'C' for conducting future experiments. The optical density value increased 10 from 0.024-0.118 on 15th day of exposure in the control set. The optical density value in case of set 'A' increased from 0.024-0.116 on 15th day of exposure when compared to inoculation day value but when compared to the control set value on 15th day of exposure, optical density showed an insignificant decrease. In optical density study the "A" concentration value was more than the control value on all days of exposure except on 15th day of exposure where a lower value was recorded. In case of "B" concentration the value increased to 0.072 on 15th day of exposure. All the values were less than the control set. Where as, in case of 'C', the optical density value initially increased from 0.024- 0.031 on 9th day and than the value decreased with the increase on exposure period. A maximum decrease by 1.7%, 39% and 73.7% was recorded on 15th day of exposure when compared to the control value in case of concentration A, B and C, respectively. The dry weight increased from 1.14�0.4 mg-14.14�0.7 mg on 15th day of exposure in the control set. At conc.-A, the dry weight increased from 1.14�0.4 mg-3.2�1.1 mg on 3rd day of exposure and the dry weight further increased to 13.2�0.9 mg on 15th day of exposure. At conc.-B, the dry weight increased on 15th day of exposure when compared to control. At conc.-C, the dry weight decreased significantly on 15th day of exposure when compared to the control value.