Polychlorinated diphenyl ethers—a review

Polychlorinated diphenyl ethers (PCDEs) have been identified as by-products formed in the synthesis of chlorinated phenols. Analytical surveys have shown that PCDE residues are present in sediments, fish, wildlife, and human tissues. The uptake and persistence of PCDEs in laboratory animals resembled that observed for the polychlorinated biphenyls (PCBs), however, in metabolic studies, ortho hydroxylation of the PCDEs was the dominant oxidative pathway. Studies indicate that PCDE congeners elicit a broad spectrum of toxic and biochemical responses in laboratory animals including the induction of several cytochrome P-450-dependent monooxygenase enzyme activities. In contrast with the coplanar PCBs which are significantly more toxic than their monoortho coplanar analogs, the coplanar PCDE congeners and their monoorthochloro-substituted analogs were equipotent. These data suggest that the PCDEs may contribute significantly to the toxicity of halogenated aromatics associated with chlorinated phenol-derived contaminated areas such as toxic chemical waste dumpsites.