Study On The Toxic Effect Of Cadmium And Decabromodiphenyl Ether On Plants And The Accumulation Of The Pollutants In Plants

The e-waste dismantling activities leads to the contamination of heavy metals and polybrominated diphenyl ethers(PBDEs)in the surroundings.Cadmium(Cd)is a toxic element that can accumulate in edible plant tissues and negatively impact organisms.Decabromodiphenyl ether(BDE-209)is the most abundant PBDE in the environment and is highly hydrophobic and non-biodegradable.The biomagnification of BDE-209 through the food chain can be threatful to the ecosystem.Little research has focused on the combined phototoxicity of BDE-209 and Cd.In this study,rice and wheat were selected as the test plants to investigate the toxic effect of BDE-209 and Cd on rice seed germination and seedling growth.Meanwhile,the migration,accumulation and degradation of the contaminants in the plants were explored.Moreover,the study proposed a preliminary safety threshold for BDE-209 in agricultural soils.The results provide a scientific basis for the ecological risk assessment of the combined contamination of heavy metals and PBDEs and provide data support for the development of BDE-209 screening values in agricultural soils.The main results are summarized as follows:(1)In the rice seed germination tests,the single contamination of Cd and BDE-209 promoted the germination at lower levels and brought inhibition at higher levels.The combined effect of the two pollutants was mainly synergistic at low Cd stress and antagonistic at high Cd stress.There was a significant dose-effect relationship between Cd concentrations and various germination indicators,of which root parameters were most sensitive.BDE-209 concentrations only showed a dose-effect relationship with root elongation and biomass.The IC50(half maximal inhibitory concentration)of root biomass was 5.05 mg/L under Cd stress and 6.09 mg/L under BDE-209 stress.(2)In the rice seedling test,the single effect of Cd showed the suppression on the seedling growth,while BDE-209 brought promotion at lower concentrations.Under the joint effect of the two pollutants,BDE-209 alleviated the toxicity of Cd on the physiological and biochemical parameters of rice seedlings such as biomass,elongation,photo synthetic pigments and antioxidant system.Both Cd and BDE-209 increased the activities of antioxidant enzymes in seedling leaves at lower concentrations.Peroxidase and superoxide dismutase served as good indicators of Cd contamination and BDE-209 contamination,respectively.(3)In pot experiments of rice and wheat plants,the single stress of Cd and BDE-209 improved the growth index of crops at maturity at lower levels and brought suppression at higher levels.The combined effect of BDE-209 and low-concentration Cd enhanced the nutrient uptake and promoted the crop upgrowth(up to 52.1%and 58.2%in rice and wheat,respectively),while the interaction of BDE-209 and high-concentration Cd increased the phytotoxicity and led to a reduction in the crop yield(43.9%and 38.9%in rice and wheat,respectively).(4)The contents of the pollutants in crops were positively correlated with the concentrations of contaminated soils,and the bioaccumulation of Cd was stronger than that of BDE-209.The concentration of pollutants in the crops decreased in the upper tissues.The degradation of BDE-209 is much higher in the above-ground parts.The combined effect of lowlevel BDE-209 promoted the accumulation and migration of Cd in the plants and inhibited the uptake of Cd in the plant at higher concentrations.The safety threshold of BDE-209 in crops in China was derived from the intake thresholds recommended by EPA and EFSA,and the value is 152 ng/g.In this study,the calculated safety threshold of BDE-209 concentration in agricultural soils is 10 mg/kg.