Pigments may be a new source of PCBs.
Hu, D and KC Hornbuckle. 2010. Inadvertent polychlorinated biphenyls in commercial paint pigments. Environmental Science and Technology 44(8):2822–2827.
Researchers at the University of Iowa have discovered that PCBs are present in many more kinds of paint pigment than previously known. While the U.S. Environmental Protection Agency knew about some of the contamination, the extent of the problem is a surprise.
The researchers suggest that the contaminated pigments used in a variety of paints, inks, cosmetics, plastics and other consumer goods are probably a source of ongoing exposures in humans.
PCBs are persistent and bioaccumulating toxic chemicals that have been largely banned from use in the United States since the 1970s. They can still be detected in air, water and people.
In the study, the scientists measured PCB levels in paints produced by Sherwin Williams, PPG and Vogel. The PCBs were only found in paints with certain kinds of colored pigments, belonging to two of the major classes of synthetic dye molecules. From that information, the researchers were able to pinpoint the mechanisms by which PCBs could be formed unintentionally during manufacturing.
PCBs contain the element chlorine. During manufacturing, PCBs could form from reactions involving raw materials or solvents that contain chlorine. The use of chlorobenzene solvents, for example, led to PCB contamination in pigments with no chlorine in their chemical structure.
From a green chemistry perspective, this information could be used to design a new manufacturing process free of chlorinated materials.
The researchers pointed out that the levels of PCBs found in the paint samples were below regulatory thresholds, but the ubiquity of pigments in urban areas and the ability of PCBs to bioaccumulate may increase exposures.
There are hundreds of possible structures for PCBs, and some are more toxic than others. The researchers detected a wide variety of structures, including some of the most toxic, dioxin-like PCBs.
The connection between modern pigments and global PCB pollution is suggested because some of the PCBs found in the paint samples were not produced on a large scale before bans took effect. Those PCBs have been found by other researchers worldwide in air and surface water as well as waste streams from pigment manufacturing.