A class of organic chemical compounds called halogenated aromatics includes polychlorinated biphenyls (PCB), polybrominated biphenyls (PBB), naphthalenes, benzenes, and diphenyl ethers (PCDE, PBDE), as well as a number of pesticides such as DDT (see Poisoning: Chlorinated Hydrocarbon Compounds). Triclosan is a PCDE commonly used in antibacterial household products, and PBDE are used as flame retardants in plastics and electronic components. Most PCB use has been discontinued, but common PCB-containing products still in use include electrical transformers and capacitors and fluorescent light ballasts. These should be considered to contain PCB if manufactured before 1980 unless they are labeled otherwise. Other compounds resulting in persistent PCB contamination around farms and other facilities include hydraulic and heat transfer fluids, epoxy paints, and construction adhesives.

How long the poisoning lasts, how much toxin builds up in the body, and the types of toxic effects vary considerably among the many different halogenated aromatic compounds.

Livestock feed and pet food contamination as well as fish and fish meal were previously considered the major sources of exposure. Airborne and forage exposures are nearly universal, although at considerably lower levels.

Most toxic effects of halogenated aromatics are subtle and delayed but may be additive. Effects may include weight loss not necessarily accompanied by decreased food consumption, skin disorders, suppression of the immune system, enlarged liver, hormonal disruption, reproductive disorders, and cancer. Many effects may not become apparent until the animal is stressed or reaches adulthood. None of these signs are specific for poisoning by a halogenated aromatic compound and so cannot point to a specific diagnosis. Initial diagnosis is based on a complete history, inspection of the premises for potential exposures, and elimination of more common causes. Confirmation of poisoning relies on results of laboratory tests suggested by the medical history. Halogenated aromatic compounds are readily detected in blood as well as in body fat, milk fat, liver, feed, and other suspected sources.

Treatment is most likely to help when started as soon as possible after exposure. The source should be eliminated, and the animals bathed gently with detergent and cool water after skin exposure. Repeated large doses of activated charcoal given by mouth or flushing of the stomach may help prevent some absorption into the body after exposure by mouth. It is important to minimize stress. If the mother encounters persistent halogenated aromatics while pregnant, the offspring should not be allowed to nurse because the milk will be contaminated.

Last full review/revision July 2011 by Barry R. Blakley, DVM, PhD; Cheryl L. Waldner, DVM, PhD; Rob Bildfell, DVM, MSc, DACVP; William D. Black, MSc, DVM, PhD; Herman J. Boermans, DVM, MSc, PhD; Cecil F. Brownie, DVM, PhD, DABVT, DABT, DABFE, DABFM, FACFEI; Raymond Cahill-Morasco, MS, DVM; Keith A. Clark, DVM, PhD; Gregory F. Grauer, DVM, MS, DACVIM; Sharon M. Gwaltney-Brant, DVM, PhD, DABVT, DABT; Larry G. Hansen, PhD; Safdar A. Khan, DVM, MS, PhD, DABVT; Garrick C. M. Latch, MASc, PhD; Gavin L. Meerdink, DVM, DABVT; Lisa A. Murphy, VMD; Frederick W. Oehme, DVM, PhD; Gary D. Osweiler, DVM, MS, PhD, DABVT; Mary M. Schell, DVM; David G. Schmitz, DVM, MS, DACVIM; Norman R. Schneider, DVM, MSc, DABVT