Response of freshwater algae (Scenedesmum spp.) to phenylurea herbicides

The response of Scenedesmus spp. to three phenylureas, namely Maloran, dicuran, and Patoran was investigated. Chlorophyll (a) content, ratio of chlorophyll (a/b), growth rate and dry weight of algae tended to decrease as the concentration of herbicide in the bioassay media was increased. The inhibitory effect of the studied herbicides followed the order; Maloran > Dicuran > Patoran. At low concentration levels, patoran led to an increase in Chl. (a) content, Chl. (a/b) ratio and maximum growth rate. Uptake of the studied compounds by algal cells was at its maximum value in the presence of low herbicide concentrations and tended to decrease as the herbicide concentration was increased. Scenedesmus algal cells were able to recover and attained their normal growth rate and morphological characteristics when the cells were transferred to a herbicide-free medium. The pH value of the algal media gradually increased as algal growth proceeded. In media containing inhibitory levels of phenylureas, the pH value was unchanged. Statistical analysis indicated that changes in Chl. (a) induced by the herbicides were significant.