Eco-toxicological impact of industrial effluent waste on the photosynthetic efficiency ona rice field inhabiting blue-green alga under laboratory controlled conditions

Present study aims at understanding the impact of mercury contained industrial effluent along with solid waste on the pigment content and photosynthetic efficiency of a blue-green alga inhabiting crop fields under laboratory controlled conditions. With the increase in exposure period, on 15th day, the chlorophyll content decreased when compared to control value. The depletion in chlorophyll content on 15th day of exposure and non recovery on 15th day of recovery indicated stress. The increment on initial days of exposure can be inferred to be an impact of initial excitement because of the mercury contained toxicant. At this stage, it is premature to say that mercury at lower concentration caused stimulation or regulation in growth of the alga. The phaeophytin content increased with the increase in exposure period up to 12th day of exposure, when compared to respective control value. But on 15th day of exposure, the pigment content decreased when compared to control value. During recovery period even after 15 days of recovery, the exposed alga could not recover to its control value. These observations indicated that mercury contained toxicant might have shown an initial induction on the alga but at higher exposure period and higher concentration showed inhibitory effect. The increase in phaeophytin on 12th day of exposure was neither indicative of stimulation nor a case of induction, as both can be a possibility at the early stages of inoculation but not at the middle of the experiment or exposure. The observed results clearly indicated that the observed stimulation in photosynthetic rate was probably a case of excitation at the initial stages of the exposure but not an indication of stimulation or regulation. This experiment has shown the dichotomous behaviour of the toxicant, where stimulation at lower concentration and inhibition at higher concentration was observed. At all concentrations, inhibition in respiration rate was noted. Higher concentration of the toxicant induced inhibition due to accumulation of mercury in the algal body.