Michigan PBB Contamination Incident
Before the 1970s, PBBs were widely used commercially as a flame retardant. Michigan Chemical Corporation (owned by Velsicol Chemical Corporation) in St. Louis, Michigan was a major producer of the FireMaster range of PBB-based flame retardants. FireMaster BP-6 (a yellow-brown powder) is a mixture of many different PBB congeners with 2,2',4,4',5,5'-hexabromobiphenyl and 2,2',3,4,4',5,5'-heptabromobiphenyl being significant constituents by mass (60-80% and 12-25%, respectively). FireMaster FF-1 (a white powder) is FireMaster BP-6 with the addition of 2% calcium silicate as an anti-caking agent. Mixed bromochlorobiphenyls and polybrominated naphthalenes, as well as lower brominated compounds formed by incomplete bromination, have also been found as minor constituents of FireMaster products.
In 1973, several thousand pounds of FireMaster BP-6 were accidentally mixed with livestock feed that was distributed to farms in Michigan, USA. Some 1.5 million chickens, 30,000 cattle, 5,900 pigs, and 1,470 sheep then consumed this feed, became contaminated with PBBs and the carcasses were disposed of in landfill sites throughout the state. These events were portrayed in the 1981 film Bitter Harvest and in the book "The Poisoning of Michigan". A 1978 episode of Lou Grant ("Slaughter") portrays a similar, but fictionalized account. One year elapsed before the animals were culled. A study was undertaken on 4,545 people to determine the effects of PBBs on human beings. These include three exposure groups – all people who lived on the quarantined farms, people who received food from these farms and workers (and their families) engaged in PBB manufacture – as well as 725 people with low-level PBB exposure.
All were queried concerning 17 symptoms and conditions possibly related to PBBs. Venous blood was drawn and analyzed for PBB by gas chromatography. Mean serum PBB levels were found to be 26.9 ppb by weight (26.9 µg/kg) in farm residents, 17.1 in recipients, 43.0 ppb in workers, and 3.4 ppb in the low exposure group. No associations could be established between serum PBB levels and symptom prevalence rates.
To evaluate peripheral lymphocyte function, T and B cell quantitation and in vitro responses to three nonspecific mitogens were studied in 34 persons with highest PBB levels (mean: 787 ppb), and in 56 with low levels (mean: 2.8 ppb). Again, no statistically significant differences in lymphocyte function were noted.
Read more about this topic: Polybrominated Biphenyl
Famous quotes containing the word incident:
““It is of the highest importance in the art of detection to be able to recognise out of a number of facts which are incidental and which are vital.... I would call your attention to the curious incident of the dog in the night-time.”
“The dog did nothing in the night-time.”
“That was the curious incident.””
—Sir Arthur Conan Doyle (1859–1930)