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 Insecticide 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 some fluorescent light fixtures. These should be assumed to contain PCB if manufactured before 1980 unless they are labeled otherwise. Most of the compounds in this class persist in the environment and are classified as persistent organic pollutants. They can cause immediate or delayed toxicity.
Exposure to the compounds may result from contamination of the indoor environment (especially house dust), atmospheric deposits on soil and plants, spreading sewage sludge and industrial wastes on farm fields, industrial accidents, and feed contamination. 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 have been considered the major sources of exposure. Indoor pets (and small children) may be exposed to household products with flame retardant and antibacterial additives. 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.
There is no known treatment for poisoning by halogenated aromatic compounds, but supportive care is recommended. If an animal has had known exposure during pregnancy, the offspring should not be allowed to nurse because the milk will be contaminated. Both the indoor and outdoor environments should be evaluated for the presence of these compounds, which is not always obvious.