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On the sunny morning of August 14, 2001, UW-Madison chemist Jon Manchester and the crew of the 72-foot ship RV Neeskay stopped ten miles off the eastern shore of Lake Michigan on a special mission to dig up a little dirt. Grateful for the calm waters, the crew began its work by lowering a giant, spider-like device to the bottom of the lake, 80 meters below.
On impact with the lakebed, a box plunged down from the device, slicing through sodden lake silt. A set of jaws secured the box from underneath. Manchester eyed the box as it was hoisted, black and dripping, back to the boat. It held valuable records: undisturbed sediments.
The contents looked like muck to the untutored; for Manchester, the fine brown grains of dirt are history. "That's what is neat about sediment," he said. "It's a great little library of information about different contaminants."
Traces of contaminants seep into sediment as air, dust, soil and rainfall settle into the lake. As the sediments accumulate, they provide a distinct chronology.
"We can date layers so we know when the sediment was deposited, and we can generate nice core profiles," Manchester explained. "From the shape of those profiles, increasing or decreasing, we can talk about a history of inputs."
The profiles show changing concentrations of contaminants in different depths of the sediment. If we find more contaminants in the upper layer for instance, we will know that contaminant levels have been increasing over time; if the reverse were true, then contaminant levels would be decreasing from previous exposures. By analyzing the historical details, Manchester hopes to describe the life of an emerging group of pollutants: polybrominated diphenyl ethers (PBDEs).
PBDEs are a family of chemicals used as fire retardants in the plastic components of electronic circuit boards, carpeting, draperies, plastic TV housings, other electrical appliances, and the fabrics in auto and airplane interiors. PBDEs account for about 10 percent of the 600,000 metric tons of flame retardants used annually worldwide. Some scientists suspect the compounds leak or leach out into the atmosphere over the lifetime of products treated with flame retardants, then fall out in rain and enter surface water, air, and soil.
Manchester is working on a three-year study to determine the prevalence and sources of PBDEs in the Lake Michigan ecosystem. The exact pathway these compounds follow once they are released into the environment is unclear, though there is evidence PBDEs enter the food chain and eventually accumulate in the bodies of animals and humans.
Researchers are concerned about how PBDEs may act because the compounds are chemically similar to the banned industrial pollutants, polychlorinated biphenyls (PCBs), which stubbornly resist breaking apart in the environment. Theoretically – owing to their chemical structure – PBDEs may crumble faster than PCBs when exposed to air, water, sunlight, weather variations and microbes.
The levels of PBDEs that might prove detrimental to human health, their potential to accumulate in our bodies, and their persistence in soil and sediment need analysis. The detrimental effects and the underlying mechanisms that might cause problems demand further exploration.
Wisconsin DNR environmental toxicologist Elisabeth Harrahy expresses the urgency: "We can't do anything without scientifically defensible data. We are not sure what long-term effects these chemicals have. It's going to come down to determining the risks and comparing the risks with the benefits of these flame retardants." Wisconsin scientists are already on the move to get those answers.
Looking for evidence
Is PBDE exposure an issue in Wisconsin? Studies so far indicate PDBE levels in the environment are very low, but a growing number of researchers are monitoring those concentrations and investigating if PBDEs pose environmental and health hazards.
The Environmental Health Division of the State Laboratory of Hygiene was among the first to suspect the compounds moved through the environment. Tests run on chinook salmon, brown trout, and carp collected from inland waters, Lake Superior and Lake Michigan revealed low levels of PBDEs that rose slightly throughout the 1990s.
In 1996, a project to test the blood from people who regularly ate Lake Michigan fish hinted at a stronger presence of PBDEs. "We analyzed the blood samples for a wide variety of organic chemicals, not looking for any specific chemical," explained David Degenhardt, a chemist from the State Lab of Hygiene. "This testing showed low concentrations of PBDEs in the blood of Lake Michigan fish consumers."
Detectable levels were found in only a few samples, but the discovery was significant enough to prompt collaboration among Manchester, Stockholm University's Karlis Valters, and the director of the State Lab's Environmental Division, William Sonzogni, to look for signs of PBDEs in Lake Michigan salmon.
The team analyzed fish flesh from 21 coho and chinook salmon collected in 1996 from the Kewaunee River and Strawberry Creek in Door County. The research, published in March 2001, reported that PBDEs were found in all the sampled fish at average concentrations of 80 ppb, six times higher than PBDE levels found in Baltic Sea salmon. Compared to other studies that have examined PBDE levels in fish, Manchester characterized the concentrations as "among the highest reported in the world for salmon in open waters."
The findings suggested PBDEs, like PCBs, accumulate in fatty tissues as fish age, and that PBDEs have been found in salmon for at least eight-10 years.
"We're used to dealing with the idea of trace levels of contaminants," said Manchester. "This turned out not to be that. We found lots of PBDEs. What we didn't know was that it was going to be as concentrated as it turned out to be. The levels were a little surprising."
In the air and on the wing
During the early stages of the Lake Michigan salmon study, Indiana University scientists received reports of sharply increasing amounts of PBDEs detected in Swedish women's breast milk. Those reports led to monitoring Great Lakes air for traces of PBDE from 1997 to 1999. In 2001, researchers reported detecting PBDEs in all air samples from different areas surrounding the Great Lakes. Even more revealing: Chicago's air had five to 10 times higher PBDE concentrations than air in nearby rural areas. These data suggest PBDEs may be emanating from cities.
Scientist Ronald Hites, one of the Indiana University researchers, gives cautionary advice: "These levels are low in terms of human risk from the air. But the levels indicate atmospheric deposition of PBDEs into the lakes is possible, the fish may accumulate these compounds, and people are eating the fish. PBDEs in the air are an indirect risk."
With salmon and air research at hand, the U.S. EPA and Great Lakes states recently agreed the risk of PBDE exposure is worth further assessment. Reports following a March 2001 workshop on monitoring Great Lakes fish concluded: "Due to their toxicity, widespread use, and demonstrated occurrence, PBDEs could reasonably be added to the fish monitoring list immediately."
Hites plans to measure PBDEs in air and sediment around the Great Lakes. Manchester and Sonzogni are in the middle of a three-year study in Lake Michigan. "We're going to try and understand how they move out into nature, the history of input into the sediment, how widespread they are in the aquatic food chain, and ways they are getting into the fish," said Manchester.
New data from the ongoing research provides a plausible explanation of how Lake Michigan salmon wound up with such high levels of PBDEs: the forage fish salmon eat contain PBDEs.
DNR Wildlife Biologist Mike Meyer is in the early stages of analyzing effects on another fish-eating predator high up on food chains – the bald eagle. Last June, the State Lab confirmed finding PBDEs in blood samples drawn from five bald eagles inhabiting the southwest bays of Lake Superior near Duluth and Superior. Canadian studies of herring gull eggs from around the Great Lakes report rises in PBDE concentrations between 1981 and 2000.
Such findings suggest PBDEs are widespread, although sources may be urban. Traces of these compounds have been found in other sources: Samples of recycled sludge taken from 50 municipal sewage treatment plants in Wisconsin were examined in the summer of 2000. According to DNR Residuals Coordinator Greg Kester, 11 of the 12 samples analyzed had detectable PBDE levels.
"Since the purpose of wastewater treatment is to remove pollutants, it is not surprising that a complex mixture of material winds up in the sludge," said Kester.
More projects are planned, including a study by DNR's Harrahy to examine PBDE toxicity to water fleas and a study by Wisconsin Chief Medical Officer and Environmental Epidemiologist Henry Anderson to look for correlations between PBDE concentrations and thyroid disease in people who frequently eat fish.
There are clear signs that PBDEs are present in Wisconsin's ecosystems. However, according to Degenhardt, it is difficult to draw concrete conclusions or determine the extent of the contamination in Wisconsin because a limited number of samples have been tested.
PBDE use and disposal are not currently regulated in the United States. Effective July 1, 2003, the European Union will ban one commercial form of PBDEs (penta-BDE, levels of which have been doubling every five years in tests of Swedish women's breast milk). "Much of the PBDE research to date has been conducted in Sweden, where findings indicated enough risk to justify a ban," Harrahy explained. "In North America, the majority of the research has been aimed at determining concentrations of PBDEs in air, sediment and fish tissue. Very little research has been aimed at determining toxicity. It will take more information on toxicity to justify a ban here."
Edna Francisco is an intern science writer at the Wisconsin Academy of Science, Arts and Letters.