A mixture of compounds having from one to ten bromine atoms attached to a biphenyl ring, analogous to polychlorinated biphenyls (PCBs). Manufactured as fire retardants, PBBs were banned after a 1973 Michigan incident when pure product was accidently mixed with cattle feed and distributed throughout the state. PBBs were identified as the cause of weight loss, decreased milk production, and mortality in many dairy herds. Approximately 30,000 cattle, 1.5 million chickens, 1,500 sheep, 6,000 hogs, 18,000 pounds (8,172 kg) of cheese, 34,000 pounds (15,436 kg) of dried milk products, 5 million eggs, and 2,700 pounds (1,225 kg) of butter were eventually destroyed at an estimated cost of $1 million. Although human exposures have been well-documented, long term epidemiological studies have not shown widespread health effects.