Structure elucidation of some minor components of the polybromobiphenyl mixture, Firemaster

The polybrominated biphenyl known as "Firemaster" is a flame retardant that accidentally became mixed with cattle feed in Michigan in 1973. The resulting toxicosis to animals and humans prompted extensive study to determine Firemaster's toxic components. Although 4 of 12 major Chromatographic peaks of Firemaster produce mixed enzyme induction, they do not account for the total toxicity. By capillary gas chromatography, it was observed that Firemaster FF-1, lot FH 7042, consisted of at least 60 compounds. We have isolated or otherwise determined the structure for 10 minor components of Firemaster: 3,3′,4,4′-tetra-,2,2′,3,5′, 6-penta-,2,2′,4,4′,5-penta-,3,3′, 4,4′,5-penta-,2,3,3′, 4,4′, 5-hexa-,2,3,3′,4,4′,5′-hexa-, 3,3′,4,4′,5,5′-hexa-, 2,2′, 3,3′,4,5,5′- hepta-,2,3,3′,4,4′,5,5′- hepta-and 2,2′,3,3′,4,5,6′- hepta-bromobiphenyl. All of these polybromobiphenyl congeners except 2,2′,4,4′,5-pentabromobiphenyl are in the latest eluting (most polar) fraction by normal-phase high-performance liquid chromatography of Firemaster. This fraction exhibits biological activity. Hyperkeratosis induction tests were carried out on rabbit ears with 3,3′,4,4′-tetra-,2,2′,3,5′, 6-penta-, 2,3,3′,4,4′,5-hexa-, 3,3′,4,4′,5,5′-hexa-, and 2,2′,3,3′,4,5,6′-heptabromobiphenyl, but only 3,3′,4,4′-tetra- and 3,3′,4,4′,5,5′-hexabromobiphenyl gave positive responses. Apparently, these two compounds and 3,3′,4,4′,5-pentabromobiphenyl are significant contributors to the hyperkeratotic activity of Firemaster.