Species- and tissue-specific profiles and potential risks of polychlorinated biphenyls (PCBs) and their metabolites in dogs and cats

In recent years, there has been growing concern about the long-term health effects of chemical exposure in pets, particularly dogs and cats, from sources such as pet food and house dust. Domestic cats (Felis silvestris catus) and dogs (Canis lupus familiaris) are continuously exposed to polychlorinated biphenyls (PCBs), with particular attention being paid to the toxicity of their metabolites, hydroxylated PCBs (OH-PCBs) and methylsulfonyl PCBs (MeSO₂-PCBs). However, the tissue distribution and species-specific differences of these PCB metabolites in domestic animals have not been fully elucidated. This study investigates the tissue-specific profiles of PCBs, OH-PCBs, and MeSO₂-PCBs by analyzing blood, brain, liver, and bile samples from dogs and cats. The analysis revealed that hexa- to octa-chlorinated OH-PCBs were the predominant congeners in the brain, liver and bile of dogs. In contrast, tri- to penta-chlorinated OH-PCBs were more prevalent in cats, with lower-chlorinated OH-PCBs tending to accumulate due to limited UDP-glucuronosyltransferase activity. In cats, OH-PCBs are more readily excreted in the bile than in dogs, probably because there are fewer higher-chlorinated thyroxine-like OH-PCBs, which are known to bind to and persist in proteins in the liver and blood. MeSO₂-PCBs were detected at lower concentrations than parent PCBs and OH-PCBs and primarily accumulated in the liver due to their lipophilic nature. The consistent concentrations of MeSO₂-PCBs across species, despite variations in parent PCB and OH-PCB levels, underscore species-specific differences in metabolic capacity and excretion pathways. In addition, some OH-PCB concentrations in both dog and cat brains exceeded levels known to affect neurons, suggesting the potential for neurotoxicity in these species. Therefore, continued biomonitoring and further investigation of the toxic effects of these compounds in pets is imperative.