Last July I received an email from someone at the American Industrial Hygiene Association (AIHA) asking if I would be willing to speak about PCBs at their June, 2015 conference in Salt Lake City. Over the past few years the AIHA has been developing reference materials about PCBs for their members, and one of the focal points of the conference was to be PCBs in the built environment, particularly PCBs in building materials and air. After reviewing the information AIHA had already assembled and developing a topic for my presentation I agreed to submit an abstract.
The conference took place the first week of June this year at the Salt Lake City Conference Center where I was one of seven presenters speaking about PCBs. Over the next couple of posts I’ll highlight parts of the presentations that I found particularly interesting; I’ll also highlight some of my side trips in the Salt Lake City area.
PCBs in Building Air
Since the late 1990s researchers have known that PCBs from building materials can often be detected in indoor air. The concentrations detected are low (low nanograms to low micrograms of PCBs per cubic meter of air) and this reflects the relatively low volatility of PCBs. A lingering question that scientists pose is: are these airborne PCBs present in a gaseous or particulate form? In other words, are these PCBs stuck on to fine particles floating in the air like dust? Or are they present as free PCB molecules in air the same way oxygen and nitrogen are? At the conference several academic researchers presented data on this subject that was contrary to the information I’ve seen from others.
In short, these researchers found that the dominant PCB detected in air samples was a congener (an individual type of PCB molecule) referred to as PCB-28 (also known as 2, 4, 4’-trichlorobiphenyl) a PCB congener with three chlorine atoms. PCB-28 is a major constituent of the Aroclor mixtures 1016, 1242 and 1248. It is a much smaller part of Aroclor 1254 and is essentially absent from Aroclors 1260 and 1268. In the indoor air testing I am familiar with PCB-28 is detected, but not as a major component.
Also, in my experience the 4 and 5 chlorine containing PCBs tend to dominate air samples. I have attributed this to the parallel observation that Aroclor 1254 is the PCB mixture most frequently detected in building materials. Aroclor 1254 is a predominantly 5-chlorine atom mixture; it contains approximately 53% penta-chloro congeners. It is reasonable to expect that even when Aroclor 1254 is the mixture present in a building material, it would be the lower chlorinated congeners within the mixture that would be more likely to volatilize. However, as described at the conference, the extent of the shift towards lower chlorinated congeners in air coming from higher chlorinated PCB mixtures in building materials, is much greater than I have experienced in my own work.
While this may seem way too academic to worry about, from a risk assessment perspective it can make a difference, here’s why:
1. It could be that much of the higher chlorinated congeners being detected are actually associated with particulate matter and therefore may be less likely to be retained in the lungs;
2. If the PCBs are not retained in the lungs, then they do not contribute to a person’s PCB dose from breathing the air; and
3. Generally the lower chlorinated PCBs are considered to pose less risk than the higher chlorinated PCBs.
There are no answers for this yet, but I’ll continue to follow the issue.
Utah Natural History Museum
I had no plans when I arrived in Salt Lake City early on the Saturday afternoon before the conference started. It was a beautiful day, too early to go the hotel and why waste a beautiful day in a hotel room anyway? On the side of the street coming into the city was a billboard advertising the dinosaur exhibit at the Utah Natural History Museum. Since I still have more than a little of my boyhood fascination with dinosaurs, I decided going to the museum was the perfect way to spend the afternoon; good decision!
The museum is set in the foothills on the eastern side of the city in an attractive modern building with fabulous views of the surrounding mountains and the Great Salt Lake basin. The museum exhibits are laid out intelligently, the displays flowing easily into each other in a logical sequence. In addition to the incredible display of dinosaur fossils and reproductions, the museum is actively engaged in research and fossil restoration, a process that can be seen by visitors through laboratory windows.
The diversity of fossil types was beyond anything I have seen before or could even imagine. As much as I have enjoyed exhibits of ancient animals in east coast museums, they really can’t compete with what I saw at the UNHM.
If you have science-nerd children that love dinosaurs and there is any way you can swing it, my advice is to take them to Utah to see this museum. It was even better than I might have hoped, the exhibits were painstakingly constructed with great variety and well written descriptions. Personally, I was glad to be on my own so I could dawdle at my own slow pace and revisit favorite sections. A must see.