| Persistent organic pollutants(POPs)have been the focus of environmental research in recent years,but the research on polyhalogenated carbazoles(PHCZs)at home and abroad is still in the preliminary stage,and the assessment of the pollution characteristics and toxicity equivalent of PHCZs in the aquatic environment is very limited.This study took the PHCZs in the surface sediments and sediment columns of the middle and lower reaches of the Yangtze River basin from Anhui Province to Chongming Island as the research object,measured the concentration of PHCZs in different environmental media,analyzed the distribution characteristics and sediment records of PHCZs in the Yangtze River basin,explored its pollution sources,and evaluated the toxic equivalent of PHCZs.In addition,the adsorption performance of polyvinyl chloride(PVC)on monomer halocarbazole(1,3,6,8-tetrabromcarbazole)was studied through adsorption experiments.The main research results are as follows:(1)Ten PHCZs homologues were detected in 15 surface sediments,with a concentration range of 1.58-5.45 ng/g and a median concentration of 3.11 ng/g.Compared with the concentration of PHCZs around the world,the concentration of PHCZs in the surface sediments of the study area is relatively low.Pearson correlation analysis showed that 3-chlorocarbazole(3-CCZ),3,6-dibromocarzole(36-BCZ),1,3,6,8-tetrabromocarzole(1368-BCZ)and 1,3,6,8-tetrachlorocarbazole(1368-CCZ)were the main pollutants in the study area.3-CCZ and 2,3,6,7-tetrabromocarzole(2367-CCZ)and 1368-BCZ may have similar migration characteristics.Although the toxic equivalent(TEQ)value of PHCZs in surface sediments is relatively low,the synergistic or superimposed effect caused by the coexistence of PHCZs and other persistent organic pollutants(such as dioxins,polybrominated diphenyl ethers and polycyclic aromatic hydrocarbons)cannot be ruled out.(2)The concentration of Σ PHCZs in the three sediment cores C1,C2 and C3 in the middle and lower reaches of the Yangtze River basin are 0.01-3.07 ng/g(mean1.06 ng/g),0.01-2.91 ng/g(mean 0.83 ng/g),0.01-1.31 ng/g(mean 0.84 ng/g),respectively.On the whole,the concentration level of PHCZs in the sediment column in the study area is lower than that in the upper reaches of Lake Michigan and the Great Lakes,but higher than that in the northern South China Sea.The deposition records of PHCZs show that PHCZs began to enter the environment in the 1960 s,and its time coincides with the historical time of China’s industrial and agricultural development.1368-BCZ first appeared in the deep layer of the column core,indicating that it is more likely to come from natural sources.There is a significant positive correlation between the concentration of PHCZs and the content of TOC in the sediment column,the number of particles with particle size less than 1 mm.The adsorption equilibrium time of PVC microplastics for 1368-BCZ is about 8h.Before 8h,the adsorption amount is in direct proportion to time.After 8h,the adsorption amount reaches the maximum value(about 4200ng/g),which will not change with time.The linear correlation coefficients of quasi-first-order and second-order kinetics are between 0.90-0.98,indicating that the adsorption process is the coexistence of physical and chemical reactions,in which chemical adsorption may be the main adsorption force,and 1368-BCZ may be adsorbed on the surface of PVC microplastics through electrostatic or complexation.The maximum adsorption concentration of PVC microplastics on 1368-BCZ is 600ng/g.Langmuir and Freundlich model equations can better fit the adsorption data of PVC microplastics on1368-BCZ,indicating that the adsorption is monolayer adsorption,and the adsorption point and functional group distribution on the surface of the microplastics are uneven.In addition,the value of n is less than 1,which indicates that the adsorption process is nonlinear. |
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