[Sensitivity of Chlorella vulgaris to metribuzin, puma and alachlor]

The relative sensitivities of Chlorella vulgaris to three commonly used herbicides metribuzin, puma and alachlor were determined by toxicity tests of 96-h static exposures. The results showed that the toxicities of metribuzin and alachlor to C. vulgaris increased with exposure time, and the density of C. vulgaris decreased with increasing concentrations of these two herbicides in the test media. The maximum specific growth rate of C. vulgaris exposed to metribuzin (0.24 mgL x L(-1)) and alachlor (12.8 mg x L(-1)) was 12.38% and 31.58% of the control, respectively. At low concentration, puma stimulated C. vulgaris growth, but at high concentration, it inhibited the growth significantly. The maximum specific growth rate of C. vulgaris under 0.08 mg x L(-1) puma was 111.44% of the control, and the toxicity of puma declined with increasing exposure duration. The EC50 value of metribuzin, puma and alachlor was 0.021, 0.937, and 5.54 mg x L(-1), respectively. The relative sensitivities of C. vulgaris to the three herbicides decreased in the order of metribuzin, puma and alachlor. The chlorophyll a content of C. vulgaris decreased with the increasing concentrations of metribuzin, puma and alachlor.