Polybrominated Biphenyls (PBBs)
Polybrominated biphenyls (or PBBs) are chemicals used to make plastics flame retardant. In Michigan in the early 1970s one type of PBB was accidentally mixed into livestock feed and fed to farm animals, resulting in the sickening and/or death of tens of thousands of animals. A large portion of Michigan's nine million residents became ill as a result of eating contaminated meat or poultry.
Polybrominated biphenyls are made from a chemical known as benzene (sometimes referred to as "phenyl") which is derived from coal tar. Benzene contains six carbon atoms connected in a hexagonal ring formation with two hydrogen atoms attached to each carbon atom along the outside of the ring. Two benzene rings can be linked together to form a diphenyl molecule. When a bromine atom replaces one of the hydrogen atoms on the phenyl rings, the compound is said to be "brominated;" when more than one such replacement occurs the compound is "polybrominated." The term "polybrominated biphenyl" is somewhat imprecise since it does not specify how many bromine atoms are present or to which carbon atoms they are attached.
One specific type of PBB, hexabrominated biphenyl (which contains six bromine atoms), was developed for use as a flame retardant for plastics. This white crystalline solid is incorporated into the hard plastics used to make telephones, calculators, hair dryers, televisions, automobile fixtures, and similar other objects at risk of overheating. The advantage of using hexabrominated biphenyl in plastics is that when they are exposed to flame, the presence of the PBB allows the plastic to melt (rather than catch on fire) and therefore flow away from the ignition source. The primary disadvantage of this material is its high toxicity; in fact, similar compounds are used in pesticides and herbicides due to their ability to effectively kill insects and weeds at very low levels. Another negative side effect is its ability to persist in the environment for long periods of time.
In the early 1970s hexabrominated biphenyl was manufactured by a small chemical company in Michigan under the trade name Firemaster BP-6 (BP-6 stood for BiPhenyl,6 bromine atoms). BP-6 was sold to companies making various plastics and in 1973 alone, over 3 million lb (1.3 million kg) of this material were sold. The same company also manufactured magnesium oxide, another white crystalline solid material, which is used as an additive in cattle feed to improve digestion. Due to poor labeling procedures it is believed that thousands of pounds of Firemaster were mistakenly identified as magnesium oxide and shipped to companies which manufactured animal feed. As a result, tons of livestock feed were contaminated with hexabrominated biphenyl. When this feed was given to cattle and poultry they also became contaminated with PBBs.
Many of the animals developed minor symptoms such as disorientation. Others become severely ill, with internal hemorrhaging or skin lesions, while many others died. (Controlled animal feeding studies later showed that PBBs can cause gastrointestinal hemorrhages, liver damage, as well as well as birth defects like exencephaly, a deformation of the skull.) When their cattle began sickening and dying the farmers were understandably upset, but since they did not know the cause of the problem, they did not realize the tainted meat from these animals posed a health risk. Therefore, meat from some of the sick animals was incorporated into animal feed which in turn contaminated other animals. Worse still, meat from the healthier cows that were slaughtered was sold for human consumption. Also, poultry that consumed the contaminated feed laid eggs containing high levels of PBBs. A tremendous number of people in Michigan and beyond (estimated at greater than nine million individuals), unwittingly ingested health-threatening quantities of PBBs.
The symptoms of PBB ingestion in humans depend upon the concentration and varies with the individual but stomach aches, abnormal bleeding, loss of balance, skin lesions, joint pains, and loss of resistance to disease are common. Hundreds of farm families developed extended illnesses as a result of PBB contamination. All told, long-term contamination for many Michigan residents occurred and because the long term effects of PBBs are still not fully understood, it may be decades before the true impact of this crisis is known.