Polybrominated Biphenyls (PBBs)
The Michigan Chemical Company in St. Louis, Michigan produced two chemicals, ok they produced more than two but this story involves only two. One day in early 1973, there was a shortage of preprinted paper bag containers which led to misidentification of materials. Ten to twenty 50-pound bags of polybrominated biphenyl, specifically BP-6, accidentally being sent to Michigan Farm Bureau Services in place of NutriMaster, a magnesium oxide cattle feed supplement. Of course these two chemical compounds look similar enough that the mix up was not discovered. Well it was not discovered until April 1974 and by that time PBB had entered the food chain through milk, other dairy products, beef products, and contaminated swine, sheep, chickens and eggs.
So what are PBBs?
They are a class of biphenyl compounds with one to ten hydrogen atoms replaced by bromine. There are 209 possible compounds, referred to as PBB congeners, which differ in the number and position of the bromine atoms on the two phenyl rings.
PBBs with three or more bromines are solids with low volatility and the volatility decreases further as more hydrogens are replaced. PBBs are very stable. They are insoluble in water but readily soluble in fat.
So what do these properties of PBBs mean for organisms that consume them?
Because PBBs are fat soluble, when PBBs are ingested, such as in the contaminated feed, the organism assimilates the PBBs in fat cells in the body. They are very stable and will remain in the fat cells.
What happens if an organism consumes another meal containing PBB contaminates?
Termed bioaccumulation, the organism now has two doses of PBB in its fat cells.
Let's say some mice ate contaminated feed. What would you predict about the barn cat that fed on the mice?
Termed Ecological magnification, organisms higher in the food chain will assimilate larger quantities of fat soluble toxins.
What concerns would you have for new mothers and their young? What would you recommend?
Breast feeding passes fat cells in the mother's milk along to the baby. Since these toxins are accumulated in fat cells, the toxins would also be passed along.
So what was the fallout from Michigan's accidental chemical switch?
Failure to identify the mix up early on resulted in widespread contamination of farm animals requiring the destruction of thousands of contaminated livestock cattle, hogs and sheep, millions of poultry. Approximately 865 tons of animal feed, 17,790 pounds of cheese, 2630 pounds of butter, 34000 pounds of dry milk and nearly 5 million eggs were destroyed. A large number of health problems have been reported by people consuming contaminated food. Tests on people in the area, livestock and livestock products, soil and water have been conducted on a regular basis to track presence and concentrations of PBBs. It has been found that this compound is persistent in fat tissue and soils, especially those high in clay. (Di Carlo)
From ChemPRIME: 8.8: Aromatic Hydrocarbons
EFSA Panel on Contaminants in the Food Chain (CONTAM); Scientific Opinion on Polybrominated Biphenyls (PBBs) in Food. EFSA Journal 2010; 8(10):1789. [151 pp.]. doi:10.2903/j.efsa.2010.1789. Available online: www.efsa.europa.eu/efsajournal
Di Carlo, Frederick, Joseph Seifter, and Vincent DeCarlo. "Assessment of the Hazards of Polybrominated Biphenyls." Environmental Health Perspectives 23. (1978): 351-365. Web. 28 Jul 2011. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1637487/pdf/envhper00480-0330.pdf>.