| The studies on the residue of Polycyclic Biphenyls (PCBs) in the sediment environments are of important scientific and practical significance in revealing their sources, transition modes,contamination history and potential threat on environments.In this study, PCBs in the sediments from the typical plateau lakes-Dianchi Lake in southwest area of China,then discussed the PCBs contaminating case of the whole basin,made a preliminary analysis of sources,meanwhile, made pollution risk evaluation.A method for simultaneous determination of the six indicative polychlorinated biphenyls (PCB28, PCB52, PCB101, PCB138, PCB153 and PCB180) in sediments of Dianchi Lake by microwave-assisted extraction (MAE), solid phase extraction (SPE) and gas chromatography-mass spectrometry (GC-MS) has been developed. Based on systematic optimization of MAE conditions, the most efficient extraction was achieved at 100℃for 30 min (heating for 15min and then holding for 15min), using hexane:DCM (1:1,ν:ν) of 30mL as the solvent for 5g sediment sample. Under the optimal conditions, linear range was 1-3000 pg·g-1 (dry weight) for PCB28, PCB52 and PCB101, while 5-3000 pg·g-1 (dry weight) for PCB138, PCB153 and PCB180. The correlation coefficient (R2) was above 0.98 for all the analytes, with the limit of detection (LOD) and the limit of quantification (LOQ) of 41.7-62.3 pg·g-1 (dry weight) and 139.0-207.7 pg·g-1 (dry weight), respectively. The proposed method was further verified by performing spiking experiments in sediment samples at 20 ng·g-1 (dry weight), with the overall recoveries were ranged from 75.1% to 93.9% with relative standard deviations (RSD) (n=3) of 3.9%-12.8% for the entire procedure.Six commonly occurring polychlorinated biphenyl congeners were measured in surface sediments and sediment core samples from ten monitoring stations across Dianchi Lake in Kunming, China to determine the distributions, historical trends, and sources of PCBs to this ecologically and regionally important water body. The summed total concentration of all six PCB congeners ranged from 0.6 to 2.2 ng·g-1 dry weight (d.w.) in surface sediment, and from non-detectable to 2.2 ng·g-1 d.w. in sediment core samples. The six PCB congeners were found to demonstrate similar distribution characteristics across water and surface sediment samples, with PCB28 and PCB52 accounting for more than 67% of the total summed concentration in both matrices. The concentration of individual congeners in each media decreased in the order of PCB28> PCB52> PCB101≈PCB138≈PCB153≈PCB180. In addition, the PCB homologue profile in Dianchi Lake was similar to that of the commercial Aroclors 1242, the diffusion calculation of the ratios of congener in Dianchi Lake to the ratios from the commercial Aroclors 1242 was much relativity. Therefore, the Aroclors 1242 mixtures should be the main source of PCBs contamination in this area. Analysis of PCB congeners in sediment core layers as a function of depth revealed two distinct peaks occurring in the top velocity layer and in the layer between 20 and 25 cm in depth (corresponding to 1970s). Core sediment analysis showed PCBs are currently being released to Dianchi Lake and showed the historical trends of PCB deposition into the lake sediment.Data from this multi-media exploration of PCBs can be used by researchers, regulators, and policy makers to understand the fate of PCBs in Dianchi Lake, and also to begin to identify current sources of PCBs to the lake. |
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