Toxic Mechanism Of Herbicide Topramezone To Chlorella Vulgaris

Topramezone is a new,highly selective herbicide of pyrazole structure for the post-emergence control of broadleaf and grass weeds in corn.Reports have confirmed that topramezone could elevate tyrosine levels,and histopathological evaluations showed dose-dependent increases of adverse effects in the thyroid,pancreas,liver and eyes in rats.There are few studies on the toxicity of topramezone,and we are unaware of any studies that have been reported in the literature as a result of overwater use of topramezone exposure to aquatic organisms.Chlorella vulgaris(C.vulgaris)is widely used in research on the response of aquatic ecosystems to chemicals,mainly due to their characteristics of small size,rapid propagation,and sensitivity to toxicants.Thus,C.vulgaris was used as the subject to study the toxicity of topramezone to evaluate the environmental safety of the pesticide in this paper.In this study,the toxicity mechanism of herbicide topramezone to C.vulgaris was studied,mainly on in relation to the cell growth,oxidative stress,cell morphology and photosynthetic activity were studied.Results showed that topramezone treatment was detrimental to C.vulgaris growth during the 24~96 h of exposure.The data corroborated that 20 mg L-1 topramezone induced the production of ROS,and caused oxidative stress,stimulated antioxidant system,lead to an increase of MDA and the changes of CAT,POD,SOD,GST activity.The changes in cells pigments content and relative transcript of photosynthesis-related genes,which implied 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.These results showed that herbicide 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 study helps to understand how topramezone affects C.vulgaris and provides a reference for the safe application of topramezone in the environment.