Stress and toxicity of biologically important transition metals (Co, Ni, Cu and Zn) on phytoplankton in a tropical freshwater system: An investigation with pigment analysis by HPLC.

Stress and toxicity of four biologically important transition metals (Co, Ni, Cu and Zn) on phytoplankton in Godavari River (a tropical freshwater system) were studied to understand the fate of phytoplankton of freshwater if it receives metal contaminated water imposed by these four metals. Shift in community structure of phytoplankton and their different tolerance levels for different metals were also investigated. It was found that the variation of metal concentrations at lower level (1x10(-9) to 1x10(-8)M) did not show a dramatic change in the total biomass or concentrations of the pigment markers. At concentration of 1x10(-7)M of metal, Cu acted as a nutrient and helped to increase the biomass followed by Co, Ni and Zn. The variation in biomass in the freshwater system under exposure to different metals at high concentration of 1x10(-6)M indicates that Cu had strongest interactions with biotic ligand and was taken up by phytoplankton and acted as the most toxic metal followed by Zn, Co and Ni. Phytoplankton communities in Godavari River have different tolerance levels for different metals. Cu and Zn were found to be lethal at high concentration for both green algae and cyanobacteria. Cyanobacteria were found to be very sensitive to slight variation in Ni concentration and Co was found to be less toxic than Cu and Zn even at high exposed concentration.