Pollution Characteristics And Environmental Risk Assessment Of Polyhalogenated Carbazoles In Jiaozhou Bay Wetland And Wastewater Into The Sea

Polyhalogenated carbazoles?PHCZs?are new type of organic pollutants with dioxin-like toxicity,which have the characteristics of persistent organic pollutants in the environment,but the research on their distribution and environmental fate is still limited.Here,the content,distribution and environmental risk assessment of PHCZs in the sediments of the Jiaozhou Bay and the influent,primary settling tank effluent,final effluent and sludge of wastewater treatment plants?WWTPs?were studied by Soxhlet extraction,liquid-liquid extraction,solid-phase extraction and composite chromatography,and the correlation between PHCZs and total organic carbon?TOC?in the study area was analyzed.The main conclusions were summarised as follows:PHCZs were detected in all sediment samples of the Jiaozhou Bay wetland.Among the samples collected in 2014,the total concentration of the PHCZs ranged from 4.4 to26.9 ng/g dw,and the concentration of carbazole?CZ?ranged from nd to 0.4 ng/g dw.The concentration of PHCZs in the Dagu River wetland is higher than that in the Taoyuan River wetland,which indicates that the landfill is not the main source of PHCZs pollution.In the samples collected in 2019,the concentration of CZ was 1.1-3.2 ng/g dw,and the concentration of PHCZs was 7.1-20.5 ng/g dw.Compared with the results of samples collected in 2014,the CZ concentration increased,and the PHCZs concentration basically remained unchanged.The concentration of PHCZs in the study area?sites E-M?was significantly higher than that in the control area?sites A-D?,which confirms that the dye factory is an important source of PHCZs.Based on the analysis of the correlation between PHCZs congeners and the total organic carbon?TOC?in Jiaozhou Bay Wetland sediments,it is found that CZ has no correlation with?PHCZs.Correlation analysis showed no correlation between?PHCZ and TOC in sediments,indicating that TOC may not be the influencing factor of PHCZs pollution in this study area.1,3,6,8-tetrabromocarbazole?1368-BCZ?and 3,6-dibromocarbazole?36-BCZ?have significant correlation with3,6-dichlorocarbazole?36-CCZ?,indicating that 1368-BCZ,36-BCZ and 36-CCZ may originate from the same source,or the sediments have similar accumulation capacity for them,or they have similar pollution source-water-sediment transformation rates.The dioxin toxicity and inventory of PHCZs in the Jiaozhou Bay wetland were also estimated.The results showed that toxic equivalent of PHCZs(TEQ^PHCZs)in the Jiaozhou Bay sediments were ranged within 0.1-3.9 pg TEQ/g dw?2014,mean:1.1 pg TEQ/g dw?and 0.2-2.5 pg TEQ/g dw?2019,mean:1.0 pg TEQ/g dw?,lower than the TEQ value of safe sediment?20 pg TEQ/g dw?.It indicated that the risks to the environment are relatively low.The inventory of PHCZs in the study area was estimated to be 48.1 kg,which indicates that PHCZs are easy to accumulate in wetland sediments,causing serious environmental pollution.The research on the content of PHCZs in the WWTPs found that PHCZs were detected in all WWTPs influent samples.The concentration of?PHCZs in the influents in Shouchuang WWTP?phase I:528.6 ng/L,phase III:321.9 ng/L?was significantly higher than that of Maidao WWTP?405.3 ng/L?and Tuandao WWTP?424.3 ng/L?.In the effluent,the concentration of?PHCZs ranged from 211.9 ng/L to 304.0 ng/L,with an average value of 275.0 ng/L.No 1368-BCZ was detected in any effluent,indicating that1368-BCZ can be completely removed in the wastewater treatment process.By comparing the total concentrations of PHCZs in the influent and final effluent,the overall removal rate of each WWTPs were calculated to be 29.5%?Maidao WWTP?,42.5%?Shouchuang WWTP Phase I?,34.2%?Shouchuang WWTP Phase III?and 29.8%?Tuandao WWTP?,respectively.The mass loading of the influent and final effluent was estimated.Every day,a total of 30.1 g CZ and 311.8 g?PHCZs entered into the three WWTPs,then 26.8 g CZ and 198.8 g PHCZs were discharged into the bay,causing potential hazard to the receiving environment-Jiaozhou Bay.The toxicity equivalent of PHCZs in the effluent and sludge of WWTP were estimated.In the effluent,the estimated TEQ^PHCZsof Maidao WWTP was similar to Tuandao WWTP and Shouchuang WWTP Phase I.The order of TEQ^PHCZsHCZs in the dewatered sludge was Shouchuang WWTP?4.8pg TEQ/g dw?>Tuandao WWTP?2.3 pg TEQ/g dw?>Longquan WWTP?0.7 pg TEQ/g dw?.In general,the risk of this study area arse low,but more attention should be paid.