PCBs: When green paint isn’t ‘green’

NEW ORLEANS, Nov. 22. It seems we’re literally painting the air — from the Great Lakes to Antarctica — with persistent pollutants. Including at least one whose safety has never been studied.

Last year, University of Iowa scientists reported the discovery of a novel contaminant in urban air — a polychlorinated biphenyl, or PCB, that had never been intentionally manufactured. Especially perplexing: Despite having no known sources, it was the fifth most abundant PCB in Chicago’s air. At once, chemists began puzzling over where this PCB-11 might be coming from. The solution – or at least one answer – emerged today. It’s paint. The type we slather on interior walls and outdoor trim.

The first clue to PCB-11’s source was its idiosyncratic abundance, which Keri Hornbuckle described at the Society of Environmental Toxicology and Chemistry annual meeting, last year. While the pollutant could be found almost anywhere that her team had sampled in Chicago and Cleveland, concentrations varied. Indeed, their data identified a fairly large number of hot spots in each town. Data by others also turned up this unusual PCB in the waste water from a paint-manufacturing plant.

Over the past year, others have turned up the anomalous PCB-11 as well — polluting air from Philadelphia to Antarctica.

Hornbuckle’s team returned to SETAC this year with data that now firmly indicts paint. Not the base paint, actually – that can of goop to which tint is added. The PCB instead laces pigments: especially greens – but also some blues, yellows, oranges and reds.

This was a rather painstaking study, explains Dingfei Hu. There are 209 different species of PCBs. They tend to persist in the environment for long periods of time, allowing them to travel long distances from where they were released. The Iowa scientist collected various types of base paint and colors from several local retailers: Sherwin Williams, PPG Pittsburgh and Vogel. Every tint these companies offer is mixed from some combination of roughly 10 starting colors. Hu sampled all of those starting-ingredient colors from each company – 33 in all – and analyzed each for the presence of any and every PCB.

Fifteen pigments contained PCBs – yes, multiple ones — in concentrations ranging from 2 to 200 parts per billion. Where these pollutants turned up, PCB-11 was almost invariably present, often in the company of PCB-209 (which sometimes greatly dwarfed PCB-11’s concentrations).

Further probing showed that the PCBs’ presence was anything but random. Pigments belong to two general classes. The inorganic ones derive from minerals or are manufactured synthetically. None of the sampled inorganic pigments, including titanium dioxide, iron oxide, raw umber or carbon black contained PCBs. The unwanted contaminants did show up in two families of organic pigments, Hu found — the phthalocyanines, which impart a deep blue or green color, and the azo pigments, which are used to color some paints yellow, red or orange.

In a paper slated to come out in Environmental Science & Technology within a few months, the Iowa group will describe their findings and offer hypotheses on how the production of some pigments unwittingly cooks up PCBs along the way.

Of course, the burning question about these unusual airborne PCBs is: So what? Are they toxic? If they are, at what concentrations? Hu says there are no answers yet. Indeed, until now, there hadn’t really been a reason to investigate.

Now that we’ve learned these pollutants get out of paint and accumulate in the air, it’s time to start investigating whether they pose any risks to health. Fortunately, Hu says he’s got colleagues at Iowa who are just about to embark on such studies. (Some PCBs are suspected carcinogens, but those tend to be ones that – unlike PCB-11 and -209 – mimic the biological action of dioxins.)

As for tips to apply at the paint store . . . Hu recommends avoiding green, blue, red and orange paint. Actually, to play it safe, he says: “I would stay with white and black.”

Not me – I’m allergic to both. And that’s why I’m hoping green chemists will take an interest in formulating recipes for PCB-free tints.