A Ten-Minute Bioassay to Test Metal Toxicity with the Freshwater Flagellate Euglena agilis

SIMPLE SUMMARY: Bioassays can offset the limitations of traditional chemical analyses (time constraints, high cost, and limited detection of interactions) in monitoring water pollution. Euglena, a flagellate green alga, is an attractive experimental model organism that has been used for toxicity testing for decades because it is easy to culture, grows rapidly, and responds quickly to environmental stresses. In the present study, we examined the effects of seven heavy metals in the native Korean E. agilis using six end points (motility, velocity, cell compactness, upward swimming, r-value, and orientation). The advantage of the ecotoxicity assay presented here is its rapidity. Unlike the usual 3–4 d of exposure time and work, this assay takes only 10 min to obtain results; moreover, it can be performed at room temperature under dark conditions. Therefore, this new method can be useful for the rapid toxicity screening of hazardous pollutants, as it may have operational advantages over test time. ABSTRACT: A chemical analysis of water quality cannot detect some toxicants due to time constraints, high costs, and limited interactions for detection. Bioassays would offer a complementary means to assess pollution levels in water. Euglena is a flagellate green alga and an excellent system for toxicity testing thanks to its ease of culture, rapid growth, and quick response to environmental stresses. Herein, we examined the sensitivity of E. agilis to seven heavy metals by analyzing six end-point parameters: motility, velocity, cell compactness, upward swimming, r-value, and alignment. Notably, the velocity of E. agilis was most sensitive to cadmium (96.28 mg·L(−1)), copper (6.51 mg·L(−1)), manganese (103.28 mg·L(−1)), lead (78.04 mg·L(−1)), and zinc (101.90 mg·L(−1)), while r-values were most sensitive to arsenic (12.84 mg·L(−1)) and mercury (4.26 mg·L(−1)). In this study, velocity and r-values are presented as useful biomarkers for the assessment of metal toxicity in Euglena. The metals As, Cd, Cu, and Pb were suitable for this test. The advantages of the ecotoxicity test are its rapidity: It takes 10 min to obtain results, as opposed to the typical 3–4 d of exposure time with intensive labor. Moreover, this test can be performed at room temperature under dark conditions.