Physiological response of freshwater microalga (Chlorella vulgaris) to triazine and phenylurea herbicides.

The effects of two herbicides used wide-spread, isoproturon (phenylurea) and terbutryn (triazine), on growth, dry weight, elemental composition, photosynthetic pigments and protein content, and cell volume assayed by flow cytometry in the freshwater microalgae Chlorella vulgaris were studied. Different parameters for algal activity show widely different sensitivities to these aquatic pollutants. After 96 h of herbicide exposure, terbutryn was the strongest inhibitor of growth, giving an EC50 value for growth twice lower than that for isoproturon cultures (EC50 terbutryn=0.097 microM; EC50 isoproturon=0.199 microM). However, lower concentrations of the triazine herbicide provoked an increase in the cellular density and growth rate of this microalga, not observed in the phenylurea-treated cultures. Cellular volume and dry weight of C. vulgaris cells were increased strongly in the presence of isoproturon and terbutryn. Other cellular parameters, such as pigment and protein content, were stimulated with both herbicides at higher concentrations.