Using Team Science to Understand Airborne Sources of PCBs

Keri Hornbuckle, Ph.D.

September 13, 2018

Keri Hornbuckle, Ph.D., is developing innovative methods to understand how polychlorinated biphenyls (PCBs) and other pollutants are released and transported through the environment. Working with a team of diverse scientists, she is also discovering previously unknown sources of PCBs.

As a group, PCBs are classified as human carcinogens, and their manufacture has been banned in the United States since 1979. However, they are still found in the environment because of widespread historical sources and inadvertent production as manufacturing byproducts.

Hornbuckle was recently named director of the University of Iowa Superfund Research Program (SRP) Center, which brings together different disciplines to understand how PCBs move through the environment and how they affect human health. “We are working to understand how people are exposed to PCBs and how to identify different sources,” Hornbuckle said. “If we can determine where PCBs are coming from, it will cost a lot less money to clean them up.”

Studying How PCBs Enter Air

Hornbuckle became interested in studying airborne sources of PCBs as a doctoral student at the University of Minnesota. “In a study on Lake Michigan, I was shocked to find higher levels of airborne PCBs directly over the water than levels on land,” Hornbuckle said. “Our results showed that decreased PCB levels in the water were due primarily to PCB emissions into the air, and not because PCBs were deposited into the sediment.”

In 2006, Hornbuckle and colleague Peter Thorne, Ph.D., a professor in the University of Iowa College of Public Health, began a study to compare PCB exposures of children and their mothers in two communities – in heavily industrialized East Chicago, Indiana, and in rural Columbus Junction, Iowa.

Ongoing analyses from this study has produced interesting findings. “We expected that the airborne PCB exposures would be much higher in the industrialized area, but our studies showed that this wasn’t true,” Hornbuckle said. They found that PCB levels measured in blood of children and their mothers were almost the same in East Chicago and rural Iowa. Although they found different levels of PCBs in outdoor air, indoor air concentrations were about the same for both groups. “Before this study, we were primarily thinking about airborne PCBs as an outdoor exposure, but this made us realize that we need to be thinking about PCBs as an indoor exposure as well,” she added.

More recently, they found that indoor PCB exposures could explain half of a child’s PCB exposure, and inhalation exposure at school was almost as high as exposures through diet.

Looking More Closely at PCB Mixtures

Hornbuckle and her team at the University of Iowa SRP Center have developed methods to accurately measure all 209 types of PCBs in indoor and outdoor air, water, human blood, and other environmental sources such as soils and sediments.

Use of these measurements has allowed them to identify unique PCB signatures in air, which can point to likely sources of exposure. They have identified new airborne PCB sources, including modern paint pigments and the finish on kitchen cabinets, which were likely inadvertently produced during manufacturing.

They have also linked sources of airborne PCBs in schools to a combination of outdated building materials, such as window caulking and light ballasts, and PCB-contaminated paint pigments. Hornbuckle says that these findings can help school leadership make decisions about appropriate action to reduce PCB exposures. Moving forward, they will look more closely at schools to determine room by room differences in PCB concentrations using methods they developed to account for ventilation and air flow.

Understanding Global PCB Transport

Hornbuckle and her team have also done extensive work to interpret outdoor PCB air concentrations based on local weather and passive sampler data. They collaborated with researchers at Environment Canada, who were using passive samplers to measure airborne contaminants all over the world.

“The method Environment Canada was using to estimate airborne PCB concentrations was difficult and failed almost 50 percent of the time when it was too cold, too windy, or for various other reasons,” Hornbuckle said. “We used results from thousands of the Environment Canada samples to recalibrate our model to more precisely link the uptake of the chemicals on the sampler with local meteorology.”

In a project led by graduate student Nick Herkert, the Hornbuckle lab published the model results and released a Web-based application that more accurately determines pollutant concentrations in air using passive air samplers. The model uses publicly available hourly meteorological data and the physical and chemical properties of target compounds to demonstrate how the sampling rate and volume of compounds is captured by a passive sampler. Although primarily a tool for examining the relationship between local climate and passive sampler function, it can be used to predict the sampling volume of air samplers deployed anywhere in the world.

Driving Innovation Through SRP Team Science

As a member of the Iowa SRP Center since 2006, Hornbuckle has worked with a diverse team of scientists to not only address the transport of PCBs, but to understand how that affects exposure and health. Through the Iowa SRP Center’s community engagement component, she has also learned about the needs of communities, which has helped shape research projects to address local concerns.

“When reporting our results to a community, the first question they ask is if the levels are dangerous and if they need to take immediate action,” said Hornbuckle. “Being part of the SRP Center makes answering that question so much easier because our team includes toxicologists, who can explain potential health effects.”

“I’ve learned over my career that the strength of the team is everything,” she added. “In research, questions always come up that require a variety of skill sets. In our Iowa SRP Center, we have a diverse team of scientists and engineers addressing the same questions, which promotes innovation and helps us translate discoveries into change.”