Determination Of Polychlorinated Biphenyls And Polybrominated Biphenyls In Marine Sediments From The South China Sea

The South China Sea is the largest sea with extremely abundant resources.Marine sediments are the main sinks of various pollutants and secondary pollution sources.It is of great practical significance to study accurate determination of the contents of two kinds of persistent organic pollutants polychlorinated biphenyls(PCBs)and polybrominated biphenyls(PBBs)as well as their species distribution for scientifically and effectively protection and assessment of local marine ecological environment.At present,there is no standard method for determinating PCBs and PBBs in marine sediments in China unsatisfactory due to the methods have established are high cost,time-consuming,low sensitivity,poor stability and lackof PBBs species analysis.So we use the sediments of the South China Sea as the research object.A rapid,sensitive and low cost method was developed for simultaneous determination of PCBs and PBBs in sediments from South China Sea by accelerated solvent extractiongas chromatography electron capture detection(ASE-GC/ECD).The distribution characteristics of the contents of PCBs and PBBs species with different chlorine and bromine substituent numbers were analyzed.The main work and conclusions are as follows.(1)Based on the results of spiked blank experiments,the extraction effects of some pretreatment methods,including ultrasonic extraction,microwave extraction,accelerated solvent extraction(ASE)and so on,were systematically compared.It was found that ASE was best for the extraction of PCBs and PBBs.The extracted conditions of ASE for PCBs and PBBs were optimized and the best conditions were: extraction solvent-hexane;static extraction time-7 min;extraction temperature-85?;cycle times-2;percentage of flush-60%,N2 purge-75 s.(2)Two purification methods with concentrated sulfuric acid and silica gel column were compared.It showed that the concentrated sulfuric acid was better.PCBs and PBBs were effectively separated by silver nitrate silica gel column,with DCM-HX(2:98)being eluent for PCBs and DCM-HX(50:50)for PBBs,respectively.(3)PCBs and PBBs were determined by gas chromatography-electron capture detector(GC-ECD),and the optimized instrument conditions for PCBs were: the inlet temperature-280?,the detector temperature-305?;automatic splitless injection,the injection volume was 1uL;high purity nitrogen carrier gas,the flow rate-1.0 mL/min;the programmed temperature: maintaining 130? for 2min,10?/min to 200? for 6 min,8? /min to 228? for 3 min,12? /min to 300 ? for 4 min;the tail flow rate-30 mL/min;the flow rate of the column-1.0 mL/min;the purge time-0.75 min.PBBs instrument conditions were that the inlet temperature is 275?;that the detector temperature is 310?;that the injection volume of automatic splitless injection is 1?L;that the flow rate of purity nitrogen carrier gas is 1.5 mL/min;that the programmed temperature: initial temperature of 105? is risen to 305? at the rate of 8? /min and kept for 25 min;that the tail flow rate is 45 mL/min;that the flow rate of the column is 1.5 mL/min;that the purge time is 1.0 min.(4)PCBs and PBBs mixture are within their respective linear range,the ratio of different PCBs /PBBs monomer peak area and internal standard PCNB peak area is linearly related to the ratio of PCBs /PBBs concentration and PCNB concentration.The linear correlation coefficients R are 0.9953-0.9993 and 0.9960-0.9994,and the detection limits are 0.0011-0.0026 ng/L and 0.0015-0.0058 ng/L,respectively.After ten replicate determinations of mixing standards,the RSDs of instruments are 0.40-1.06 % and 1.62-4.85 %,respectively.After seven replicate determinations of blank samples,method detection limits were 0.0048-0.0114ng/g and 0.0087-0.0106ng/g,and the RSDs were 1.6-4.2% and 3.1-4.6%,respectively.(5)PCBs and PBBs in nine different sampling sites of South China Sea were determined by the proposed methods.The total contents of PCBs and PBBs were 0.626-1.278 ng/g and 0.220-1.062 ng/g and the recoveries of spiked samples were 68.5-102.1% and 65.9-100.2%,respectively.At different sampling sites,the proportion of chlorinated PCBs showed a little difference and a consistent trend of decreasing mass concentration:Pentachlorodiphenyl>Trichlorobiphenyl>Tetrachlorobiphenyl>Dichlorobiphenyl>Hexachlorobiphenyl>Heptachlorodiphenyl.The distribution of PBBs in different sampling sites showed a significant difference and a distribution characteristic of slightly decreasing mass concentration trends,but overall trendsare:Pentabromobiphenyl>Hexabromobiphenyl>Tetrabromobiphenyl>Monobromobiphenyl>Dibromobiphenyl>Tribromobiphenyl.The PCBs contents were assessed by the methods of environmental quality standards in Canada and the ecological risk value of EPA in the United States.The results show that the South China Sea area does not cause negative biological effects and is the low risk ecological zone.