Evaluation of the toxicity of herbicide topramezone to Chlorella vulgaris: Oxidative stress, cell morphology and photosynthetic activity.

Topramezone is a new, highly selective herbicide of pyrazole structure for the post-emergence control of broadleaf and grass weeds in corn. In this study, the effects of topramezone on C. vulgaris, especially in relation to the cell growth, oxidative stress, cell morphology and photosynthetic activity were assessed. Results showed that topramezone treatment was detrimental to C. vulgaris growth during the 24-96h of exposure. The changes in cells pigments content and relative transcript of photosynthesis-related genes, which implies that topramezone disrupted the photosynthetic system. Moreover, topramezone induced membrane permeability in a significant proportion of cells with a maximum damage rate of 40.40%, and morphology of cells was more complicated than the control group. TEM images also revealed that topramezone compromised the integrity of the cells. The data corroborated topramezone induced ROS triggered oxidative stress, leading to an increase of MDA. These results suggested that topramezone could have significant effects on growth and physiological functions in algae species, and we supposed that this herbicide affected all of these parameters and the observed effects can be explained by the generation of oxidative stress. This research helps to understand how topramezone affects C. vulgaris and provides a scientific basis for applications of topramezone in aquatic environment.