Occurrence Characteristics Of BFRs And HMs In Rice-soil Of E-waste Dismantling Area And Toxic Effects Of DBDPE-Cd Composite Pollution

In recent years,the generation of global electronic waste(e-waste)increased sharply,and the environmental pollution caused by the dismantlement of electronic waste cannot be ignored.Brominated flame retardants(BFRs)and heavy metals(HMs)were widely detected in the soil,water,sediment,atmosphere,plants,and animals in the e-waste dismantling area.To investigate the occurrence characteristics of BFRs and HMs in the rice fields and to carry out the ecological and human health risk assessment,the study area in this thesis was chosen to be the paddy filed surrounding the circular economy park in Guiyu Town,Guangdong Province,one of the world’s largest e-waste dismantling areas;decabromodiphenyl ethane(DBDPE),a typical BFR,and cadmium(Cd),a typical heavy metal,were both chosen as the target pollutants in paddy fields.Single and composite exposure modes were used to examine the enrichment levels of the target pollutants in rice seedlings,and indoor pot experiments were used to examine the toxicity effects and mechanisms of the two pollutants in the rice-soil system.The main results were summarized as follows:(1)In paddy soil,there were 283-927 μg·kg-1 and 54.7-437μg·kg-1 of traditional BFRs(polybrominated diphenyl ethers,PBDEs),and novel brominated flame retardants(NBFRs),respectively.BDE-209 and DBDPE were the main PBDEs and NBFRs in the soil,which accounted for 87%and 91%of the PBDEs and NBFRs in the soil,respectively.According to the hazard quotient(HQ)and target hazard quotients(THQ)values,BDE-47(HQ=1.98)in soil posed an obvious ecological risk;PBDEs and NBFRs in rice had THQ values less than 1 and had a low health risk for human via rice consumption.Mn,Zn,and Cr had the highest levels in the HMs of paddy soils,with the values of 210-880 mg·kg-1,39.1-243 mg·kg-1 and 59.2-215 mg·kg-1,respectively.The potential ecological risk factor(Eri)and THQ values indicated that Sb(ErSb=279)and Cd(ErCd=134)in the soil were at high risk and moderate risk,respectively;As,Pb,and Cd were the HMs with the highest health risks of human via rice consumption,with 90%,50%,and 40%of the sites with THQ>1,respectively.(2)Planting rice seedlings shifts Cd in the soil from mild acido-soluble fraction to residual fraction and the DBDPE in the soil can prevent this process,increasing the bioavailability of Cd.In soils with a Cd concentration of 5 mg·kg-1,the percentage of Cd in the residual fraction dropped from 14%to 8%,while the percentage of Cd in the mild acido-soluble fraction rose from 68%to 79%with the increase of DBDPE’s concentration.The same trend was seen in soils with a Cd concentration of 1 mg·kg-1.Proteobacteria,Bacteroidetes,and Acidobacteria made up the majority of the soil’s bacterial communities at the phylum level in all treatment groups,accounting for 72%-76%of the relative abundance.Alpha diversity revealed that DBDPE and Cd both decreased the bacterial diversity in the soil,while DBDPE could increase the community of bacterial.Both diversity and community of bacterial decreased under the composite exposure.Beta diversity revealed that the bacterial communities in composite contaminated soils were more strongly impacted by Cd.(3)In single exposure,DBDPE or Cd concentrations in rice seedlings were positively correlated with their concentrations in the soil and caused oxidative stress;DBDPE promoted some of the metabolic pathways in the root,while Cd significantly inhibited glycerophospholipid metabolism and flavonoid biosynthesis.In composite exposures,DBDPE and Cd have an impact on rice seedlings’ capacity to absorb and enrichment.Compared to the single exposure,translocation capacity of rice seedlings to DBDPE was increased in the composite treatments with lower Cd concentrations and decreased in the composite treatments with higher Cd concentrations,Cd exhibits the similar pattern;the root metabolic pathways with significant changes(p<0.05)in the composite exposure were glycerophospholipid metabolism,phenylalanine metabolism,phenylpropane biosynthesis,flavonoid biosynthesis,and flavone and flavonol biosynthesis,which were similar with the metabolic pathways that were significantly enriched by the single Cd exposure.The metabolites that were previously down-regulated in abundance by Cd were retuned,demonstrating that DBDPE reduced the metabolic toxicity of Cd.