Toxicity And Bioaccumulation Of Isoproturon To Chlamydomonas Reinhardtii

Pesticides play an important role in modern agriculture. However, the wide use of pesticides has brought the residue and pollution in environment. The pesticide residue may affect the non-targets in the environment. Isoproturon (IPU) is a widely used phenylurea derived systemic herbicide that has been detected in aquatic environment in recent years. To evaluate the eco-toxicity of isoproturon to aquatic plants and its fate in the aquatic environment, this paper studied the eco-toxicity of isoproturon to the model organisms Chlamydomonas reinhardtii and the ability of bioaccumulation and biodegration of Chlamydomonas reinhardtii to IPU. This can help us understand the harm of IPU to aquatic environment, the overall effect of IPU on the structure and function of aquatic environment and its migration pattern. This could also provide some basis to the monitoring of pesticide contamination in aquatic ecosystems.The algae were cultivated with IPU at0,5,15,25,35and50μg L-1for3days. The cell density and chlorophyll content of Chlamydomonas reinhardti were determinated. The results showed that isoproturon inhibited the growth of Chlamydomonas reinhardtii, and reduced cell density and chlorophyll content of Chlamydomonas reinhardtii. The inhibition gradually increased with the treatment concentration of IPU. The cell density and chlorophyll content were found to be ideal indicators to evaluate the toxicity of isoproturon to Chlamydomonas reinhardtii. Algae were incubated with IPU0.25μg L-1in time-denpendent experiments. A declined toxicity with the exposure time was also observed in this study. When the algae exposed to IPU, the photosynthesis was inhibited. The decline of chlorophyll fluorescence parameters namely Fv/Fm and Yield were concerned with the concentration.The reaction of C. reinhardtii to oxidative stress induced by IPU was investigated. Production of reactive oxygen species (ROS) was observed when the miroalgae were exposed to IPU with the concentration ranged from5to50μg L-1. The result showed an increase in thiobarbituric acid reactive substances (TBARS) with the treatment concentration of IPU. To deal with oxidative damage and remove excessive ROS, activities of antioxidant enzymes in Creinhardtii substantially changed. The activities of SOD, CAT, APX and GST in C. reinhardtii were increased treated with IPU. A RT-PCR-based assay was performed to analyze the transcript abundance of SOD, APX, CAT and HO-1. The result was showed that the expression of SOD, APX and CAT was up-regulated by IPU exposure, with a pattern similar to the antioxidant enzyme activities. The up-regulation of HO-1expression in the cells exposed to IPU revealed in a concentration-dependent manner.Furthermore, the amount of IPU in algae and culture medium and the bioaccumulation and biodegration capability of C. reinhardtii to IPU were determined. The results were showed that C.reinhardtii could accumulate and concentrate IPU. After72h exposure with IPU, accumulation of IPU in Creinhardtii was added with increases in initial IPU levels. The significantly larger BCFs were observed at low levels of IPU. The BCF reached the peak level of284.24after exposure to IPU at5μg L-1. BCFs were increased with exposure time and reached the maximum value of135.70on day6. The amount of IPU accumulated in the microalgae during1,2,3,4,5and6days were respectively0.54,0.51,1.30,1.47,1.88and2.23μg g-1. The biodegradation of isoproturon in C. reinhardtii is very limited during the short time exposure. The capacity of biodegradation was enhanced at higher IPU lever. The biodegradation percentage of IPU at25μg L-1increased with the exposure time. On day6,12.1%of IPU was decreased by biodegradation.