Chapter 50 Polychlorinated biphenyls, polybrominated biphenyls, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans

Polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) belong to a group of compounds known as organohalogens or halogenated organic chemicals (HOCs) that are structurally similar and are biologically and environmentally persistent, hence called “forever chemicals”.  These HOCs bioaccumulate and bio-magnify in the food chain including veterinary animals. Exposure to HOCs has been linked to a broad spectrum of adverse effects. Fetal and early developmental exposures are particularly sensitive and can have different outcomes than adult exposures. Latent effects of early exposures include, but are not limited to, depressed circulating thyroid hormone levels and abnormal thyroid cytology; developmental effects of the heart, palate, and kidney; delayed cognitive development; altered sensory and motor abilities; and reproductive impairment and compromised neuronal function. Although Aryl Hydrocarbon Receptor (AhR) activation has been attributed to the adverse effects of several dioxin-like coplanar compounds, some PCBs that are non-coplanar in nature seem to exert their toxic effects through different mechanisms including calcium/protein kinase C signaling, oxidative stress, thyroid hormone perturbations, and neurotransmitter imbalance.  The most significant problem by these HOCs involves accidental poisoning via food supply or consumption of contaminated food. Additionally, there are areas of the environment that are heavily contaminated by these chemicals because of past industrial activities. Animals and humans residing in or near contaminated locations are at risk of serious health effects. Efforts must continue to reduce HOCs exposure to protect wildlife, veterinary animals, and humans. The best way to accomplish this is to modernize technological processes to prevent the release of these chemicals into the environment.

Impact/Purpose

This book chapter has updated information from the last five years on PCBs, PBBs, PCDDs and PCDFs. This book chapter is a very informativbecause it emphasizes not only the environmental levels and routes of human exposure to these toxicants, but also the human and veterinaty animal health effects focusing on reproductive, endocrine, neuro, and developmental effects. Additionally, the mechanisms (both biochemical and molecular) that underlie the observed toxicities of these chemicals were given due consideration. Some of the key biochemical endpoints such as enzymes, metabolites and cellular macromolecule (protein, lipids and nucleic acids) changes serve as biomarkers of effect upon exposure to the above-mentioned toxicants. This book chapter provides valuable insights to employing these biomarkers for toxicity studies. This information will be of use when dose-response studies are carried out for risk assessment purposes. The revised narrative in this chapter is supported by recent literature to make the knowledge base current.

Citation

Kodavanti, P., B. Loganathan, M. Leon-Olea, AND M. Curras-Collazo. Chapter 50 Polychlorinated biphenyls, polybrominated biphenyls, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans. Chapter 50, Ramesh C. Gupta VETERINARY TOXICOLOGY. Academic Press, Cambridge, MA, 1:683-698, (2025).