Although banned in 2013 as a probably human carcinogen, a group of chemicals called polybrominated biphenyl ethers are still around— in soil, food, and in our blood.
PBDEs are a group of compounds that were used as flame-retardants mainly in plastics, and they were also used extensively in the latter part of the 20th century in electronic enclosures, business equipment, and foam cushioning in upholstery.But there was a problem. They don't chemically bond to plastics; they are just sort of mixed in, which means they can leach out. They are hydrophobic, meaning they don't get washed out of soil, and, when ingested or inhaled by humans, they dissolve in fat stores, making it difficult for our excretory systems to excrete them.
PBDEs biomagnify. What this means is that each time a smaller animal is eaten by a larger animal higher concentrations of the compounds accumulate in fat stores. This bioaccumulation increases as you move up the food chain until you get to the top predator — humans.
The International Agency for Research on Cancer determined, based on mechanistic studies, that PBDEs are probably carcinogenic to humans. A comprehensive epidemiological study recently appeared in JAMA Open Network that analyzed in detail the population-based NHANES data base (National Health Nutrition Examination Survey).
PBDE Outcome Analysis determined after adjusting for other variables that those with a high level of PBDEs in their blood had a 4.09 hazard ratio for cancer mortality compared to those with low levels of PBDEs. In other words, those with high levels of PBDEs are more than 4 times as likely to die from cancer as those with lower PBDE levels even though cancer deaths were rare in the studied cohort, and the hazard rate is a relative, not absolute risk. Nevertheless, the data are strongly suggestive of the carcinogenicity of PBDEs. The data, however, was not strong enough to determine the type of cancer.
What is the significance of this data if the chemicals have already been banned? It appears that the primary source in our environment is the food we eat due to biomagnification including high-fat fish, meat, dairy products, and fish oil supplements.
