Study On Toxicity Of Methyl Tert-Butyl Ether To Three Unicellular Freshwater Algae

Methyl tert-butyl ether(MTBE) is widely used as an additive to gasoline, for increasing oxygen content and reducing tailpipe emission of pollutants. As soon as leakage of gasoline storage tanks, it will bring some problems to aquatic environment and human health due to its high stability and mobility in ground water. However, little is known about the toxicity of MTBE to algae. Therefore, study on toxicity of MTBE to algae is important.Regarding Chlorella ellipsoidea, Anabaena spiroides and Aphanizomenon flos-aquae as testing organisms, the thesis compared dry weight and chlorophyll a concentration with absorbance at 680 nm of three algae. The results offered the absorbance is a good index which reflects the algal biomass.Then, the absorbance was used as index to measure acute and chronic toxicity of MTBE to three algae. The 96h-EC₅₀ value was regarded as the index of acute toxicity. The results showed that the toxic effect of MTBE is more intensive to A. spiroides than to C. ellipsoidea and A. flos-aquae.A 10～15 days' test was devised to evaluate the chronic toxicity. The results showed that lower concentration (≤1000 mg/L) MTBE would stimulate algal growth, however, higher concentration (≤1000 mg/L) MTBE would inhibit algal growth. The inhibit ratios increased as the concentration increase. However, the stimulating and inhibiting effect only occurred during the initial days. After that, it was decreased gradually till whole disappeared at the end.The joint toxicity of MTBE and estradiol were measured at different proportions on the basis of singal toxicity. Toxic unit, additional index and mixture toxic index were adopted to evaluate the joint toxic effects. The results of evaluation were synergistic effect.A growth model, with consideration of the effect of MTBE on the growth of algae was developed. It was demonstrated that the Logistic growth model show good fitting for the experimental data and the related coefficients are above 0.93. The maximum growth rate of alga minished as the concentration of MTBE increased.The results can provide reference for the risk of zoology.