Phytotoxicity comparison of organic contaminants and heavy metals using Chlorella vulgaris

Abstract

The green alga Chlorella vulgaris (C. vulgaris) is proposed as a test species for the phytotoxicity assessment of organic contaminants and heavy metals. The relationship between concentration and inhibition was established from the phytotoxic effects on C. vulgaris over a long-term exposure of 72 h. The concentration for 50% of maximal effect (EC50,metal) for Cr, Cd, Hg, Cu, Ni, Zn, and Pb was 0.11, 0.13, 0.22, 0.24, 0.28, 1.13, and 5.69 mg/L, respectively. On the other hand, the EC50,TOC total organic carbon (TOC) for trichloroisocyanuric acid (TCCA), 1-naphthylamine, sodium dodecylbenzene sulfonate, Ciprofloxacin, Acetaminophen, phenol was 0.02, 1.50, 5.99, 17.23, 55.79, and 236 mg/L, respectively. For raw sewage and secondary effluent from a domestic wastewater treatment plant (WWTP), EC50,TOC of 53.88 and 70.94 mg/L was obtained by concentrating organic matter through reverse osmosis. This result suggests that WWTPs reduce not only the organic compounds concentration, but also the phytotoxicity of wastewaters. Through a combined analysis of the concentrations of organic compounds and heavy metals, and the phytotoxicity of two typical industrial wastewaters, it was ascertained that the phytotoxicities of coking wastewater and brewery wastewaters were mainly caused by the organic contaminants. Nonetheless, the phytotoxicity of coking wastewater (toxicity index of EC50,% = 0.37%) was significantly higher than that of brewery wastewater (EC50,% = 32%). This difference in phytotoxicity may be because the coking wastewater contains more toxic organic contaminants (EC50,TOC = 32.95 mg/L) than the brewery wastewater (EC50,TOC = 258.4 mg/L).