They Call Me Mellow Yellow, or the Tale of PCB-11

 With apologies to Donovan, a few months ago there was a story in the popular science magazines about PCBs being found in yellow pigments used in a variety of products.  The stories often had that inflammatory tone reserved for announcing the latest environmental hazard.  Here are a few examples: 1, 2, and 3.  You should know that these three publications are among the better sources of science information intended to be publicly accessible.  But unfortunately that doesn’t mean that what they print is accurate.  So what is the real science here?  Just how serious a health/environmental problem is PCB-11 in yellow pigment?

More on PCB-11

What is PCB-11?  Let me start with what PCB-11 is not; it is not one of the PCB mixtures known as Aroclors that were used in electrical equipment and are now are present in sediments, our food supply and any number of Superfund sites.  The term “PCBs” (polychlorinated biphenyls) generally refers to a mixture of the 209 individual chemicals that together make up the PCB chemical group.  Each of the 209 slightly different chemicals that make up the PCB group are called “congeners”.

PCB-11 is the official designation for just one of these PCB congeners, specifically it is 3, 3’-dichlorobiphenyl (end of organic chemistry, I promise).  So PCB-11 is not a PCB mixture, it’s just one individual congener.  PCB-11 is a congener that contains only two chlorine atoms, and congeners with between 1 and 3 chlorine atoms are subject to a faster rate of natural degradation than are congeners with more chlorine atoms.  Note that the PCBs that are usually found in the environment have between 4 and 7+ chlorine atoms per congener, and this makes them much more environmentally persistent.

Another interesting quality of PCB-11 is that it is a non-Aroclor PCB congener; this means it is generally not present (or present only at very low concentrations) in the commercial PCB mixtures, known in the US as Aroclors.

Environmental and Health Significance of PCB-11

Because PCB-11 contains only two chlorine atoms, it is readily degraded in and excreted from the human body.  Because of its ability to biodegrade, PCB-11 does not bio-accumulate or bio-concentrate the way PCB congeners with four or more chlorines typically do.  While there have been few, if any, toxicity tests conducted on PCB-11, its chemical structure and the general toxicology of the dichloro-PCBs, suggest that its toxicity is low.

How Much PCB-11 is in Print Media and Pigments?

Concentrations of PCB-11 in print media with yellow coloring are reported to be in the mid-parts per billion range.  The highest reported concentration I have seen for PCB-11 in pure yellow pigment is around 50 parts per million (ppm).  While 50 ppm is the regulatory limit for the presence of Aroclors in consumer products in the US (40 CFR 761 regulations), it is a little known fact that this regulatory limit does not apply to PCBs consisting of only mono- or dichloro- congeners.  The regulatory limit for straight monochloro-PCB congeners is 2,500 ppm and the limit for straight dichloro–PCB congeners is 250 ppm.  This means that even the highest reported concentration of PCB-11 in pure yellow pigment falls well below the federal regulatory limits. 


The discovery of trace amounts of PCB-11 in yellow pigment, while interesting from an academic point of view, is pretty much without significance from an environmental or health perspective.  The dichloro-PCB congeners do not have the chemical properties to make them persistent in the environment; they do not bio-accumulate or bio-concentrate – these are the hallmark characteristics of the more highly chlorinated PCBs.

Earlier this week I received a good common sense article discussing PCB-11 in  my Google in-box written by Dr. Joe Schwarcz, a chemistry professor at McGill University, here is the link to the article.

So while Donovan may be “mad about Saffron”, when it comes to PCB-11, you can just call me Mellow-Yellow.