Possible natural formation of polychlorinated dibenzo-p-dioxins as evidenced by sediment analysis from the Yellow Sea, the East China Sea and the Pacific Ocean

Polychlorinated dibenzo-p-dioxins (PCDDs) and related compounds were analysed in sediment samples from the Yellow Sea, the East China Sea and the Pacific Ocean. Interestingly, PCDFs and PCBs were not found in any of the sediment samples, although PCDDs were detected. The concentration of PCDDs in the core sediments were in the range of 0.13–1.9 ng g−1 on dry weight basis for octaOCDD, while low level of hexaCDDs and heptaCDDs were also found. These observations suggested that some of the PCDD isomers have been distributed widely in the marine environment since the ancient age (1–10 million years old). PCDD residues in marine sediment cores indicated the natural formation of these toxic chemicals on the surface of the ocean. However, generation of PCDDs by natural combustion on land and their long-range transport to the marine environment still remain to be elucidated.