ES&T
Eisenreich and the Transport of Airborne Chemicals in Aquatic Systems BY
S T A N T O N
M I L L E R
early 1980s, when Eisenreich, an associate professor at the University of Minnesota, started saying that airborne chemicals are deposited in water bodies in important amounts, few scientists believed him because better sampling and analytical tools were needed to measure airborne chemicals, and environmental processes were poorly understood. In 1980 Eisenreich told the International Joint Commission (IJC) what was known and not known about how chemicals were getting into the Great Lakes and followed up -with a written report to the group. The IJC and the Canadian and U.S. governments were interested enough in his approach to begin funding research in this area. Eisenreich began the field experiments on the Great Lakes that he continues today. His research involves the collection of airborne, water, and sediment core samples for analysis on site and in the laboratory. Eisenreich set into motion, inspired, and led the research so that scientists everywhere could better understand what is happening in aquatic systems, and especially in the Great Lakes. One of his main goals was to develop a spatial and temporal record of deposition, leading to improved models and perhaps regulatory action. Effects of chemicals in the Great Lakes were hinted at earlier. Rachel Carson's Silent Spring called the nation's conscience to an awareness that pesticide chemicals, especially DDT, and polychlorinated biphenyls (PCBs) adversely affect birds, fish, and, potentially, humans; these chemicals were bioaccumulating in wildlife. Commercial fishing had been closed or restricted in all five Great Lakes at various times since the early 1970s because of toxic contamination.
Eisenreich and his students Steve Eisenreich chose to study the dynamics preparing for a dive in of PCBs in Lake Superior. Lake Superior in the Lake Superior, the largest of Johnson Sea Link II the Great Lakes and second submersible aboard the largest lake on Earth, pos- R/V Seward Johnson. sesses more than half of the The study was funded Great Lakes water volume, by the National makes up approximately 20% Undersea Research of the surface freshwater on Center/University of Earth, and has a large surface Connecticut and NOAA; area compared to its drainage both craft are owned area. PCBs were in the sedi- and operated by Harbor ment, water column, and air. Branch Océanographie The researchers wanted to Institute (Fort Pierce, know what was happening to FL).*> these chemicals in these media because the chemicals had been banned by the U.S. government, with certain exceptions, since 1972. PCBs are a class of compounds that are persistent in the environment and known to be toxic. Their range of physical-chemical properties represents thousands of chemicals in the environment. PCBs were industrial compounds manufactured by several companies and marketed worldwide under a variety of trade names. Approximately 1.5 million tons of PCBs have been produced worldwide. PCBs serve as a marker for other pollutants. When concentrations of PCBs in lake sediments and the overlying water column are measured, the core sample data are identical with the record of deposition to bogs. Isolated from any water source, bogs receive all their ingredients, including water, by deposition from the atmosphere. Because there was no manufacturer of PCBs near Lake Superior, the only way they could reach the lake was by transport through the atmosphere followed by deposition. Eisenreich found that atmospheric levels of PCBs over the lake have remained about the same from 1983 to 1993. At the same time core samples were showing decreases in PCBs. Eisenreich says there must be a reservoir of chemicals in Lake Superior and in the terrestrial environment in general. He now believes that the lake is losing past PCB accumulations via volatilization, about 10 times more important than loss to bottom sediments. What was needed was a mass balance of the movement of PCBs in the Great Lakes. Mass balance analyses
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0013-936X/94/0927-92A$04.50/0 © 1994 American Chemical Society
teve Eisenreich is the 1994 recipient of the ACS Award for Creative Advances in Science and Technology; his research provides an understanding of p o l l u t a n t s in water bodies. In the
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Environ. Sci. Technol., Vol. 28, No. 2, 1994
provide an essential framework for determining the relative importance of various input sources and output mechanisms in a water body, as well as a process for understanding the transport and distribution of pollutants in the water and estimating the time that a pollutant resides in any part of the ecosystem. Eisenreich published a mass balance of PCBs in Lake Superior for 1986. Based on Eisenreich's mass balance, PCBs appeared to be gradually moving from Lake Superior to the atmosphere. On the basis of an observed decrease in concentrations over the past 10—15 years, it is clear that PCBs stay in Lake Superior two or three years—much less time than the 170 years it takes for the water to flow through the lake. The majority of the decrease in PCB concentration is due to volatilization, which will slow down as the amount of PCBs in the water column continues to decrease. Eisenreich's mass balance calculations indicate that atmospheric deposition contributed 77-89% of the total input of PCBs to Lake Superior. These chemicals get there by wet and dry precipitation. Measurements of wet deposition are more reliable than those of dry deposition. Wet and dry deposition are responsible for PCBs in lakes as well as on land surfaces. For dry deposition, volatilization of the PCBs from lakes and land is responsible for their presence in the air. Today there are many examples of atmospheric deposition being the only process by which chemicals reach distant locations. Despite the remoteness of the Arctic,
PCBs and other pesticides are found there. European scientists have determined that persistent organic chemicals have been deposited from the air into the Baltic Sea from hundreds of miles away. PCBs from d i s t a n t s o u r c e s are present in the air above the open waters of all five Great Lakes. Studies of fish from Siskiwit Lake, a small lake on an isolated island in northern Lake Superior, have shown contamination with PCBs and toxaphene, which have no known source on the island. Toxaphene, a pesticide banned in 1982 but found in the Great Lakes, was heavily used in the U.S. Cotton Belt from the late 1960s to the early 1980s. In the late 1960s the discovery of synthetic chemicals in Antarctic snow provided strong evidence that air pollutants can travel long distances. A major concern is the tendency of toxic chemicals to be present in waters and to accumulate in the food chain. Chemical loading in waters of the Great Lakes has decreased, but atmospheric loading has remained at the 1970s level, so there needs to be another reservoir.
PCBs
and other
pesticides
are found even in
the Arctic»
Environ. Sci. Technol., Vol. 28, No. 2, 1994
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PCB Budget For Lake Superior, 1986 Other discharges -40 kg/year
Atmospheric deposition Wet 125 kg/year Dry 32 kg/year Total 157 kg/year
Particle settling -3000 kg/year
Atmosphere 200 kg
Volatilization -1900 kg/year
Water column -10,000 kg
Rivers r -110 kg/year
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Environ. Sci. Technol., Vol. 28, No. 2, 1994
Outflow r Recycling -2950 kg/year Burial -110 kg/year
-60 kg/year
Sediment -4900 kg
"Volatilization = inputs - outputs +1st order loss 1st order loss rate = -0.20 year 1 1986 1st order loss = -1800 kg 1992 1 st order loss = -400 kg Source: Jeremiason, J. D.; Hornbuckle, K. C ; Eisenreich, S. J. "PCBs in Lake Superior, 197892: Decreases in Water Concentration Reflect Loss by Volatilization"; unpublished ms.
Eisenreich warns that chemicals now banned in the environment may cycle among soil, air, and water for many years. The constant level of PCBs in the air over the Great Lakes suggests a continuous transfer between the atmosphere and the terrestrial reservoir of these contaminants. Because of this reservoir of persistent chemicals, recycling among media occurs and results in continued atmospheric deposition without new inputs. In November 1992, EPA submitted a report on atmospheric deposition as required by the Clean Air Act of 1990 (CAA). Entitled "Deposition of Toxic Air Pollutants to the Great W a t e r s , " the report said, "There is clear evidence of toxic chemical pollution and its adverse effects in the Great Lakes, Chesapeake Bay, and other U.S. water bodies, and pollutants deposited from the air appear to be an important contributor to the problem." EPA must submit a report of deposition to such areas as the Great Lakes and the Chesapeake Bay every two years under Section 112(m) of the CAA. The findings in this report are
largely the result of the pioneering studies of organic chemical fate and mass balance models published by Eisenreich and his students. For the past 19 years Eisenreich has been a professor at the University of Minnesota, where he was influential in developing an environmental engineering science program that is known internationally. Now he is director of the university's Gray Freshwater Biological Institute, where he performs atmospheric research and looks at the interaction of pollutants and the food web in lakes. He is beginning to provide data on emissions and the effects of urban industrial centers on water bodies. Eisenreich will receive the ACS award at the spring ACS meeting next month in San Diego, CA. He will lead a session there on the atmosphere and its role in deposition and chemical recycling in water bodies.
Stanton Miller is executive editor of ES&T.
