Zinc toxicity to freshwater algae

Studies with natural phytoplankton from Lake Ontario as well as with pure cultures of two green and one diatom freshwater algal species revealed that the International Joint Commission water quality objective of 30 μg Zn/L was toxic to primary productivity and cell multiplication. The toxicity of Zn varied with its anionic forms, with nitrate being the most toxic, followed by chloride, sulphate, and acetate. Experiments with radioactive 65Zn indicated that Zn was rapidly taken up by the algae, and incorporated mainly into polysaccharide and nucleic acid fractions. These results indicate that an objective for Zn of 30 μg/L is too high to protect algae in the Great Lakes. Based on our results and other published data, a new objective of 10 μg Zn/L has been recommended to the International Joint Commission.