The toxicity and impact of solid waste extract of the solid waste of a chlor-alkali industry was studied on a crop field inhabiting blue-green alga. The exposed alga accumulated significant amount of mercury during the period of experiment. Significant decrease in dry weight, chlorophyll content, phaeophytin and carotene content which are important pigments responsible for photosynthesis was observed and the toxicant containing mercury affected these pigments drastically. Where as, at lower concentration (sub-lethal) no inhibitory effect was observed, Rather the toxicant containing mercury showed stimulatory effect, where, dry weight, chlorophyll and phaeophytin content increased significantly when compared to control algal pigments. Significant amount of residual mercury in BGA was responsible for the damage caused to the exposed BGA at higher concentrations of the SE. Hence, care should be taken to dispose the dumped solid waste so that the leached chemicals will not enter into crop fields.