1.1 Identification of the agent 1.1.1 Nomenclature

Polychlorinated biphenyls (PCBs) are a class of aromatic chemical compounds in which some or all hydrogen atoms attached to the biphenyl ring are substituted by chlorine atoms (m + n = 1–10) (Fig. 1.1). Synonyms for PCBs include chlorinated biphenyls, chlorinated diphenyls, chlorobiphenyls, or polychlorobiphenyls. The general chemical formula is C12H(10-m-n) Cl(m+n), where (m + n) is the number of chlorine atoms on the two rings. Depending on the posi-tion and number of the chlorine atoms, there are theoretically 209 individual PCB compounds (congeners). The carbon positions are numbered 1 to 6 on one ring, and 1 ′ to 6 ′ on the other. While positions 2,2′,6, and 6 ′ are called “ortho, ” posi