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There are also issues related to the fate, the transport, and the characteristics of POCs present in an aquatic environment. POCs are very bioaccumulative. Therefore, past and current trends may not be indicative of the residue levels in fish occurring in the near future. Some POCs like DDT and PCBs are reported to have been transported to remote sites where the chemicals have never been used (Matthies and Scheringer, 2001). In fact, PCBs have been banned or severely restricted in many countries since the late 1970s. At that time, their total amount produced worldwide was estimated as about 2 x 109 kg (~2 million tonnes). Yet of this total, about 90% was estimated recently to still remain in mobile environmental reservoirs (IPCS, 2003).