The Toxic Effects And Toxic Mechanisms Of Two Kinds Of Polybrominated Diphenyl Ethers On Chinese Cabbage

Polybrominated diphenyl ethers?PBDEs?are excellent brominated flame retardants,widely used in various industrial products and consumer products.PBDEs are persistent organic pollutants in various environmental media,posing a serious threat to the safety of human health and ecosystem.At present,studies on the toxicity of PBDEs have been commonly conducted on animals,while the toxicological studies on plants are limited to only a few plant materials besides vegetables.Chinese cabbage?Brassica rapa L.ssp.Pekinensis?is one of the highest yielding and the most widely cultivated vegetables in China.Hence,Chinese cabbage seedings were used as a model plant to study the toxic effects of BDE-47 and BDE-209 on vegetables.In this paper,we systematically analyzed the toxic effects of BDE-47 on Chinese cabbage seedings in terms of growth,physiological metabolism,photosynthetic function and antioxidant capacity.In addition,the mechanism of their toxicity was also initially explored.This study can provide a theoretical basis for a further understanding of the phytotoxicity of PBDEs and the phytoremediation of contaminated soils.Understanding the toxicity of PBDEs on vegetables is of great significance for food safety and environmental protection.The main results of this study are as follows:1.Effects of BDE-47 and BDE-209 on plant growth of Chinese cabbageBDE-47 treatments significantly inhibited the growth of the seedlings of Chinese cabbage.After a 30-day hydroponic exposure to BDE-47 at different concentrations(25,50,75,and 100?g·L^-1),the plant height and fresh weight of Chinese cabbage seedlings were significantly decreased,whereas their root:shoot ratios were increased,indicating that BDE-47 inhibited the growth of the plant,especially the over-ground parts.Meanwhile,BDE-47 also affected the root activity of Chinese cabbage seedlings.BDE-209 treatments can also lead to growth inhibition of Chinese cabbage seedlings.After exposure to 5,10,15,20 mg·kg^-1 BDE-209 for 60 days,the plant height and shoot fresh weight of Chinese cabbage seedlings decreased with the increase of BDE-209 concentration.However,the toxicity of BDE-209 to Chinese cabbage seedlings was significantly less than that of BDE-47.2.Effects of BDE-47 and BDE-209 on physiological aspects of Chinese cabbageBoth BDE-47 and BDE-209 treatments can affect the cell structure and metabolic activities of Chinese cabbage.The chlorophyll content of Chinese cabbage leaves was sensitive to the toxicity of PBDEs stress,which decreased significantly at low concentration of BDE-47(10?g·L^-1)and BDE-209(5 mg·kg^-1).With the increase of treatment concentration,the leaf water content and soluble protein content of Chinese cabbage seedlings also decreased obviously compared with the control,meanwhile,the Proline content increased significantly.3.Effects of BDE-47 and BDE-209 on photosynthetic activity of Chinese cabbageBoth BDE-47 and BDE-209 treatments significantly inhibited the photoreaction process of Chinese cabbage leaves and affected the carbon assimilation ability of Chinese cabbage leaves,but BDE-47 had more obvious toxicity to the photosystem of Chinese cabbage than BDE-209.The chlorophyll fluorescence parameters showed that the BDE-47 and BDE-209 treatments induced a continuous decrease in the maximum quantum yield of PSII photochemistry at t=0?F_v/F_m?,the performance index(PI_abs)and the driving force for photosynthesis?DF?and a continuous increase in F_o,DI_o/CS,indicating that PBDEs caused severe damage to PSII in Chinese cabbage leaves.The results of net photosynthetic rate?P_n?showed that PBDEs stress not only inhibited the CO₂ assimilation ability of Chinese cabbage leaves,but also decreased the stomatal conductance?G_s?of the leaves,which indicated that the photosynthesis of Chinese cabbage leaves was significantly inhibited.4.Effects of BDE-47 and BDE-209 on the antioxidant defense system of Chinese cabbageThe antioxidases activities of Chinese cabbage leaves had different responses to BDE-47and BDE-209 stress.The SOD activities of Chinese cabbage leaves were elevated continuously with the increase of the BDE-47 concentration in the nutrient medium.The POD activities increased continuously under 10–75?g·L^-1 BDE-47 too,but dropped rapidly under 100?g·L^-1BDE-47.The CAT activities of the BDE-47 treated leaves were all slightly higher than that of the control group,which also increased first and then decreased.Under the stress of BDE-209,the SOD and POD activities of Chinese cabbage leaves were elevated with the increase of BDE-209 concentration,but the CAT activities began to decrease under the treatment of 10mg·kg^-1,There were no significant differences in the 10,15 and 20 mg·kg^-1 treatment groups.Compared with SOD and POD,CAT was less sensitive to the PBDEs toxicity.The three antioxidases were all involved in scavenging the reactive oxygen species?ROS?under the stress of PBDEs in Chinese cabbage.the mechanism of their toxicity was also initially explored.5.The preliminary study on the toxicity mechanisms of BDE-47 and BDE-209 on Chinese cabbageChronic toxicity and acute toxicity experiments showed that the plasma membrane permeability of Chinese cabbage leaves increased markedly after treated with BDE-47 and BDE-209,indicating that PBDEs stress can directly damage the integrity and stability of the cytoplasmic membrane of Chinese cabbage leaves.In addition,BDE-47 and BDE-209treatments significantly increased the content of superoxide radical(O₂^·-)and hydrogen peroxide?H₂O₂?in the leaves of Chinese cabbage,and then elevated the content of MDA and protein carbonylation.It indicated that the ROS induced by PBDEs led to membrane lipid peroxidation and protein carbonylation in the leaves of Chinese cabbage,which caused notable peroxidative damage to the biomacromolecules in the cells.Our results showed that Chinese cabbage?Qingmaye?was a sensitive vegetable to the toxicity of BDE-47 and BDE-209.BDE-47(10–100?g·L^-1)and BDE-209(5–20 mg·kg^-1)caused prominent toxic effects on Chinese cabbage seedlings,induced the overproduction of ROS(O₂^·-and H₂O₂),resulting in membrane lipid peroxidation and protein carbonylation,which in turn affected the growth and physiological metabolic activity of Chinese cabbage seedlings,especially the photosynthetic system damage of Chinese cabbage leaves.Therefore,the key mechanism of the phytotoxicity induced by PBDEs is the oxidative damage caused by the excessive ROS.Although the antioxidant enzyme system was activated under the stress of BDE-47 and BDE-209 in Chinese cabbage seedings,for resisting the peroxidative damage caused by the excessive ROS.However,with the increase of PBDEs concentration,the toxic effects caused by PBDEs could not be effectively alleviated.The above studies demonstrated the phytotoxicities of BDE-47 and BDE-209 on Chinese cabbage,which can provide valuable information for understanding the toxicity of PBDEs on vegetables.