Spatiotemporal Trends Of Polyhalogenated Carbazoles In Coastal Sediments Along The Coastline Of China

Polyhalogenated carbazoles(PHCs)are a group of polycyclic hetero-aromatic contaminants,including chlorinated,brominated and mixed halogenated carbazoles.Like persistent organic pollutants,PHCs are persistent and accumulative.PHCs also possess dioxin-like toxicity because of their structural similarities with polyhalogenated dibenzo-p-dioxin.Recently,many PHCs were discovered in different environmental matrices,including soil,sediment,organism and atmosphere.Previous studies showed that concentrations of PHCs in some regions were high,implying potential ecological risks.To date,most researches on PHCs were concentrated in North America and Europe,but less in China.This study aims to investigate the distributions of PHCs in sediments from Yangtze River Estuary and its adjacent East China Sea,Bohai Sea and Yellow Sea,Jiaozhou Bay and Beibu Gulf in China.On the basis of our previous studies,comprehensive spatiotemporal distributions of PHCs in sediments from the coastal areas of China were analyzed.The main contents include:(1)PHCs were investigated in surface sediments from Yangtze River Estuary and its adjacent East China Sea.Concentrations of PHCs in surface sediments ranged from 0.19 to 2.49 ng/g(dw),with a median value of 1.03 ng/g(dw).Among the detected PHC congeners,3,6-dichlorocarbazole(36-CCZ)(51.9%)was the dominant compound,followed by 3-monocarbazole(3-CCZ)(18.3%).Spatial distribution patterns of PHCs revealed a clear PHC concentration decrease from coast to offshore.TOC content was the main factor affecting the distributions of PHCs in this area.Concentrations of PHCs in sediment cores ranged from 0.49?2.00 ng/g(dw),with a median value of 1.16 ng/g(dw).PHC congener composition profiles revealed 36-CCZ(54.2%)was the prominent compound,followed by 3,6-dibromocarbazole(36-BCZ)(14.6%)and 3?CCZ(12.0%).36-CCZ maintained a relatively low and stable concentration in deeper core segments dated from 1903 to 1951,followed by a continuous increase to higher concentrations extending through to the present surface sediment.In contrast with 36-CCZ,other detected PHCs featured stable low concentrations.(2)Concentrations of PHCs in surface sediments from Bohai Sea and Yellow Sea ranged from 0.10 to 2.00 ng/g(dw),with a median value of 0.38 ng/g(dw).36-CCZ and 36-BCZ were the major congeners among these detected PHCs,accounting for 48.5%and 18.9%respectively.Concentrations of PHCs in surface sediments from Beibu Gulf ranged from 0.24 to 1.11 ng/g(dw),with a median concentration of 0.40 ng/g(dw).36-CCZ,2,3,6,7-tetrachlorocarbazole(2367-CCZ)and 36-BCZ were the dominant congeners,accounting for 34.7%,18.1%and 16.9%respectively.(3)Carbazole and PHCs were studied in sediment cores from Jiaozhou Bay.The concentration of carbazole ranged from 0.75 to 6.98 ng/g(dw),with a median value of 1.42 ng/g(dw).The spatial and temporal trend of carbazole presented an increase from the deep core,followed by a decrease in recent years.Concentrations of PHCs ranged from 0.40 to 5.09 ng/g(dw),with a median value of 0.87 ng/g(dw).PHC congener composition patterns revealed a dominance of 36-CCZ,36-BCZ and 1,3,6-tribromocarbazole(136-BCZ),accounting for 31.5%,20.5%and 13.2%respectively.Concentrations of 36-CCZ were relatively stable over time,except some of high concentrations in some core segments.These relatively high concentrations may result from the transformations of carbazole and further halogenated or dehalogenation of PHC congeners according to the Spearman correlation analysis.The concentration of 36-BCZ and 136-BCZ was stable in deep layers but slightly increased in surface sediments,which needs further investigation.(4)The concentrations of PHCs in sediments from the coastal areas of China are generally low.The whole profile was less affected by human activity.Concentrations of PHCs in sediments from Bohai Sea and Yellow Sea,Beibu Gulf were lowest,followed by Jiaozhou Bay and the East China Sea.Concentrations of PHCs in sediments from South China Sea were slightly higher than those in the East China Sea.Concentrations of PHCs from surface sediments from Sanmen Bay,Minjiang River and Jiulong River were relatively higher.Some PHCs with low halogen substitution were widely distributed in sediments,36-CCZ and 36-BCZ were the main congeners.However,in some areas,the abundance of PHCs with a higher halogenation,such as 1,3,6,8-tetrabromocarbazole(1368-BCZ)(South China Sea),1,3,6,8-tetrachlorocarbazole(1368-CCZ)(Minjiang River)and 2367-CCZ(Minjiang River,Beibu Gulf,Jiulong River)were relatively higher.Further environmental monitoring and research are needed to trace the source of different PHC congeners.