Photosynthesis and photosynthetic pigments in the flagellate Euglena gracilis – As sensitive endpoints for toxicity evaluation of liquid detergents

The present study was designed to validate the applicability of photosynthetic performance using a PAM fluorometer and photosynthetic pigments in Euglena gracilis as endpoint parameters in toxicity assessment of liquid detergents using a dish washing liquid detergent during short- (0–72 h) and long-term (7 days) exposure. In short-term experiments, the detergent affected the photosynthetic efficiency with EC50 values (calculated for Fv/Fm) of 22.07%, 7.27%, 1.4% and 2.34%, after 0, 1, 24 and 72 h, respectively. The relative electron transport rate (rETR) and quantum yield measured with increasing irradiances were also inhibited by the detergent. The most severe effect of the detergent on the light-harvesting pigments (μg mL−1) was observed after 72 h where chlorophyll a and total carotenoids were decreased at concentrations above 0.1% and chlorophyll b was decreased at concentrations above 0.5%. In long-term experiments, the detergent reduced the photosynthetic efficiency of cultures giving an EC50 value of 0.867% for Fv/Fm. rETR and quantum yield with increasing irradiance were shown to be adversely affected at concentrations of 0.1% or above. A decrease in chlorophyll a and total carotenoids (μg mL−1) was observed at concentrations of 0.05% detergent or above. Chlorophyll b was shown to be comparatively less affected by detergent stress, and a significant decrease was observed at concentrations of 0.5% or above. However, there was no prominent decrease in per cell (Euglena) concentration of any pigment. It can be concluded that photosynthesis and light-harvesting pigments in E. gracilis were sensitive to detergent stress and can be used as sensitive parameters in toxicity assessment of detergents in aquatic environments.