BLOOMINGTON, Ind. -- The elevated PCB levels in U.S. lakes and rivers that led to hundreds of U.S. Environmental Protection Agency fish consumption advisories in 2003 may be the result of not only the toxin's persistence underground but also its diffusion through the air.
To investigate the phenomenon, the EPA announced today (Sept. 27) that it would continue its collaboration with Indiana University Bloomington environmental scientists Ronald Hites and Ilora Basu to study the toxin's circulation between the air and the Great Lakes. What the scientists learn will help the EPA determine whether new PCB clean-up policies are needed.
"We saw a surprising trend a few years ago," said Hites, Distinguished Professor in IU's School of Public and Environmental Affairs. "The concentrations of PCBs began increasing at most sites and then started decreasing again. We still don't know why this happened, but we hope the next few years of data will provide us with some answers."
The EPA will give Hites and Basu $3.5 million to operate the U.S. portion of the Integrated Atmospheric Deposition Network for five more years. As part of their duties, the scientists will measure atmospheric levels of PCBs (polychlorinated biphenyls), PAHs (polycyclic aromatic hydrocarbons which result from incomplete combustion), PBDEs (polybrominated diphenyl ethers which are widely used as flame retardants), and chlorinated pesticides such as DDT. IU scientists have been running IADN with the EPA and Environment Canada since 1994.
The EPA released data last month showing that elevated PCB levels have led to fish consumption advisories for all five of the Great Lakes, and for many rivers and lakes in or near the Great Lakes Basin. Advisories do not necessarily prohibit fish consumption, but they usually caution consumers to severely limit their consumption of fish caught in tainted waters.
The Great Lakes Basin is inhabited by about 10 percent of the U.S. population and about 25 percent of the Canadian population. The lakes also account for 18 percent of the world's freshwater supply.
"Protecting the Great Lakes' water quality is an important goal in itself," Hites said. "The lessons we learn from IADN, however, will relate to the behavior of contaminants around the world."
Discoveries by IADN scientists and others have helped reduce toxins in and around the Great Lakes, and improved the quality and safety of the lakes in recent decades.
PCBs are semi-volatile, which means the toxins can easily alternate between liquid and gaseous states. Hites and other environmental scientists have found that some of these airborne PCBs waft toward the Great Lakes and dissolve into them.
"Input from the air is one of the main ways that these chemicals can get into the Great Lakes," said EPA scientist and IADN Program Manager Melissa Hulting. "PCBs do not break down easily and can remain in the environment long after they were initially used or released. Their persistence also allows PCBs to travel long distances, even around the globe, so the PCBs that get into the Great Lakes can be from nearby or very far away."
A previous study by Hites and Basu reported increased lake PCB levels at Sturgeon Point, N. Y., when winds blew southward from Buffalo, about 12 miles away.
A broader study of other locations around the Great Lakes has corroborated this "urban effect" in PCB levels. For example, PCB concentrations at the most urbanized study site, downtown Chicago (1,000 picograms per cubic meter of air), are about 10 times higher than PCB levels at the decidedly less urbanized study site at Eagle Harbor on Michigan's Upper Peninsula (100 picograms per cubic meter of air).
Air, water and precipitation samples are collected at five master sites and 10 satellite sites in the United States and Canada. Some of the study sites are located in or near the cities of Chicago; Detroit; Cleveland; Buffalo, N.Y.; and Toronto. Hites and Basu will be collecting data from air and precipitation samples at four master stations (near Lakes Superior, Michigan, Erie and Ontario) and two satellite stations (Chicago and Cleveland).
IADN will help determine how much of the airborne PCBs fall and dissolve into the Great Lakes. Once in the water, PCBs accumulate or "bioconcentrate" in some Great Lakes fish to concentrations that are thousands to millions of times higher than PCB concentrations in the water surrounding the fish. The bioconcentration of PCBs in Great Lakes fish has led to widespread consumption advisories issued by both the EPA and Environment Canada. Humans' main exposure to PCBs is the consumption of contaminated fish.
PCBs are classified as "probable human carcinogens" by the EPA and as "reasonably anticipated to be human carcinogens" by the U.S. Department of Health and Human Services. PCBs are known to be toxic to humans. PCBs also take a long time to degrade naturally. In spite of the fact that their U.S. production ceased in 1977, PCBs persist throughout the country.
"Their concentrations are indeed declining, but fairly slowly," Hites said. "In fact, it's only through the long-term IADN project that we've been able to establish any decrease of atmospheric PCB concentrations."
Hites, an expert on environmental toxins, co-authored a Science report in January that showed that PCBs and other toxins exist at high levels in much of the world's farmed salmon. The scientists found that wild salmon tended to be less contaminated.
Another study, published last year in the National Institutes of Health journal Environmental Health Perspectives and co-authored by Hites and IU School of Medicine scientist Robert Bigsby, showed that polybrominated diphenyl ether levels are elevated in the blood of mothers and their infants. These compounds are commonly used as flame retardants. The IU study has been referenced numerous times by legislators and lobbyists in California and Hawaii during those states' deliberations over whether to ban imported products that contain PBDEs.
"Understanding the behavior of these chemicals in the environment allows the scientific community as a whole to identify potential threats to human health and the environment and work to reduce or eliminate them," Hites said.
IU SPEA post-doctoral fellow Daniel Carlson and graduate students William Hafner and Eunha Hoh will also participate in this next phase of the IADN project.
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