PCBs

Polychlorinated biphenyl compound

During class on Thursday, someone asked about the effects of PCB, or polychlorinated biphenyls. In true science-nerd fashion, I thought it would be interesting to look up the chemical and biological implications of this compound. Polychloronated biphenyls are organic molecules composed of, you guessed it, two phenyl groups with anywhere from 1 to 10 chlorines attached to the carbons. PCBs were introduced to industry in the 1920s largely due to their chemical stability, resistance to heat, low flammability, and high dielectric constant. They have been used in transformers capacitors, electromagnets, circuit breakers, voltage regulators, and switches. They are insoluble in water can withstand extremely high temperatures without degrading. These advantages are also unfortunately the reason why PCBs are so difficult to get rid of. They are large, heavy, lipophillic molecules that are very likely to bind to soils and sediments. The ring structure of these compounds makes them very stable, meaning that they will not react with most other compounds. So pretty much, those babies aren’t going anywhere anytime soon.

PCBs are highly toxic and have been found to cause a number of adverse effects in humans, including chloracne, skin discoloration, liver dysfunction, reproductive effects, development toxicity, and oncogenicity. Animal studies have shown that the compound is carcinogenic, and it is very possible that they affect humans in the same way. PCBs can enter the body through the lungs, gastrointestinal tract, and skin, circulate throughout the body, and be stored in adipose tissue. One scary fun fact that I found during my wanderings on Access Science: “The estimated percentage of the United States population with detectable levels of PCBs was nearly 100% in 1981.” Hopefully this estimate has decreased with the increase in awareness and cleanup of PCBs.

A few methods have been developed to destroy PCBs, including reacting them with various chemicals, but dumping gallons of sodium in a river is probably not environmentally sound. After looking up some information on these compounds, I can see why the scientific community at large supports dredging to physically remove these compounds. There does not appear to be an efficient and environmentally friendly way to neutralize these compounds while they are present in rivers.

Source:

Glenn Kuntz, "Polychlorinated biphenyls", in AccessScience@McGraw-Hill, http://www.accessscience.com, DOI 10.1036/1097-8542.534000, last modified: April 10, 2000.