Bio-assessment and remediation of arsenic (arsenite As-III) in water by Euglena gracilis

Arsenic (As) is a serious pollutant of water bodies. Its presence in water can cause severe health problems in humans and may also induce serious toxicological effects in aquatic organisms. Euglena gracilis, a unicellular freshwater flagellate, is considered very sensitive to environmental pollutants. The aim of the present study was to evaluate the responses of different parameters in E. gracilis toward arsenite (As-III) toxicity and to assess As-III removal potential of E. gracilis from water by calculating bio-concentration factor (BCF). Under the optimized experimental conditions (0.1 to 10 mg L−1 of As-III, (pH 6.8) 7-day exposure), various parameters of E. gracilis like cell growth, motility, cell velocity (speed), cell shape, gravitactic orientation, biochemical parameters, and oxidative-stress markers were measured as endpoints. The experimental results showed that cell growth and photosynthetic pigments (chlorophyll a, b, and total carotenoids) were significantly affected at higher concentrations of As-III, while slight stimulation was observed in motility, orientation, and cell compactness of E. gracilis. Similarly, an increase was observed in total soluble protein and sugar content which can be regarded as a protective strategy in response of As-III stress. The adverse effects of As-III in E. gracilis can be attributed to oxidative stress as revealed by the results for oxidative markers. E. gracilis removed 13.3% of As-III from the medium with a calculated 0.27 mg As-III g−1 DW of E. gracilis. The calculated BCF, an index of the potential of accumulating metal/metalloids, in this study was 27 showing E. gracilis as accumulator but not hyper-accumulator of As-III. It is concluded that cell growth and photosynthetic pigments in E. gracilis were adversely affected by As-III and can be used as indicators of the adverse effects of As-III to aquatic autotrophs. E. gracilis can be recommended as accumulator (but not hyper-accumulator) for removal of As-III from water.