Effects of long-term exposure to industrial wastewater on photosynthetic performance of Euglena gracilis measured through chlorophyll fluorescence

The pollution of aquatic environments by industrial wastewater is one of the major environmental problems in the world. Due to factors like simplicity in application, cost-effective, rapid and sensitive response to pollutants, algae can be used as early indicator of pollution in aquatic environments. Euglena gracilis has been widely used as a model organism in assessment of various water pollutants with its different parameters as endpoints. Wastewater has been frequently reported to adversely affect aquatic organisms, but its effect on photosynthesis of phytoplankton, particularly in long-term exposure, has been addressed rarely. In the present study, long-term effects of wastewater samples from ten industries on photosynthesis of E. gracilis were assessed using a pulse-amplitude-modulated (PAM) fluorometer. Euglena cultures were exposed to different concentrations of wastewaters, and the effect on quantum yield of photosystem II (F (v)/F (m)), and relative electron transport rate (rETR) was assayed after 7 days of exposure. Five samples out of the total ten were found to adversely affect photosynthesis in Euglena. One sample was found to have a stimulatory effect on photosynthesis in Euglena. Unfiltered solutions were observed to affect rETR more severely than filtered ones of the same sample at the same concentration. By comparing the results with previous reports of short-term effects of wastewater on photosynthesis, it is concluded that wastewater can be a risk to photosynthesis in aquatic organisms in long-term exposure.