Protective effects of certain environmental factors on the toxicity of zinc, mercury, and methylmercury to Chlorella vulgaris

Abstract

The specific growth rate and final yield of Chlorella vulgaris treated with zinc, mercury, and methylmercury declined with increase in metal concentration. Methylmercury was most toxic and at 1 × 10^-3 mg/liter concentration it reduced survival by about 50%. Approximately 50% mortality occurred at 25 and 0.4 mg/liter concentration of zinc and mercury, respectively. The total chlorophyll content decreased and the carotenoids/chlorophyll ratio increased with increase in heavy metal concentration. Of the various factors investigated, pH, phosphate, and calcium produced a highly significant (p < 0.001) effect on metal toxicities, and magnesium produced a less significant effect (p < 0.1). The present study suggests that alkaline and hard eutrophic waters might help protect freshwater organisms against heavy metal toxicity.