The World Health Organization has set new guidelines for the regulation of dioxins and coplanar PCBs, a group of toxic chemicals that have a similar chemical composition to dioxins but are currently unregulated in Japan.

Chemical experts gathered at a WHO-sponsored meeting in Geneva late last month concluded that the maximum daily intake of dioxins a person can tolerate is between 1 and 4 picograms per 1 kg of weight. The limit had formerly been set at 10 picograms per kilogram under a WHO guideline issued in 1990. One picogram is one-trillionth of a gram.

Sources at the meeting said recent studies on dioxins such as endocrine disrupters — chemicals that disrupt the working of hormones in animals’ endocrine systems — pushed WHO to set stricter regulations on dioxins. The new guidelines also apply to coplanar PCBs, a group of chemicals related to polychlorinated biphenyls, which fall into WHO’s definition of dioxins.

In Japan, however, coplanar PCBs are not included in the definition of dioxins, and there are currently no regulations on the chemicals, Environment Agency officials said. Like dioxins, coplanar PCBs are known to cause deformities and cancer in animals. Although the production of PCB was banned in Japan under a 1974 regulation, coplanar PCBs have still been detected in riverbeds, saltwater fish and mother’s milk.

Findings reported Thursday by researchers from Ehime University and Tokyo University showed fish caught in waters off Iwate Prefecture contain harmful concentrations of PCB, as well as DDT, BHC, and organic tin.

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