Historical sediment record and distribution of polychlorinated biphenyls (PCBs) in sediments from tidal flats of Haizhou Bay, China. 
The spatial and temporal variations and sources of polychlorinated biphenyls (PCBs) in sediment of tidal flat from Haizhou Bay, China were investigated.  PCBs concentrations in surface sediments ranged from 1.33 to 6.27ngg(-1) dry weight.  Low-chlorinated PCBs, dominated by the tri-PCB homologs, were identified as the prevalent contaminate of surface sediments.  These results were in agreement with the fact that tri-PCB homologs are the dominant contaminants in China.  In surface sediment, the highest level appeared in the estuary, and it decreased with distance from the Linhong River estuary.  PCBs concentrations started to rise from the mid-1950s, and reached a maximum in 2005.  PCBs in sediment might originate from surface runoff and discharges of local source as well as slight atmospheric deposition, based on PCA.  Additionally, the PCBs levels in the sediments were considered to rarely pose hazard to the aquatic and human health, based on Sediment Quality Guidelines (SQGs).