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Great Lakes Monitoring |  |
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Lake Michigan Mass Balance
Pollutants StudiedThe LMMB study focuses on four particular pollutants: These pollutants were selected from a list of chemicals of concern for Lake Michigan to represent a broad range of pollutants from a variety of sources. Most are persistant in the environment (they do not readily break down) and/or are bioaccumulative (they amass in living tissue). Thus, they pose a threat to the ecosystem's food web, as well as precious wetlands, wildlife, and fisheries. These substances are four of twenty-eight toxic substances referred to as bioaccumulative chemicals of concern (BCCs). The behavior of these chemicals in Lake Michigan will be analyzed via mass balance modeling. The summaries of the pollutants were adapted from the Lake Michigan Lakewide Management Plan and the EPA's Nonpoint Source News Notes Issue #12 1. Polychlorinated Biphenyls (PCBs) are industrial compounds once widely used in a variety of products, including electrical transformers and capacitors, carbonless copy paper, plasticizers in plastic and rubber products, and hydraulic fluids. Their high stability contributed to both their commercial usefulness and their long-term detrimental environmental and health effects. In May 1979, EPA banned the use of PCBs except in totally-enclosed systems. In 1982 these regulations were revised to restrict uses of PCBs in electrical equipment. PCB transformers posing a risk to food were banned in 1985. In limited access areas, PCB transformers and large capacitors can be used until the equipment is worn out. Small PCBs capacitors can continue to be used. PCBs are a family of products that can be mixtures of up to 209 different compounds. It is estimated that annual production between 1971 and 1977 averaged 40 million pounds. PCBs are present in some types of Lake Michigan fish at concentrations exceeding US FDA tolerances. Such elevated PCB levels have resulted in closure of some commercial fisheries and issuance of fish consumption advisories for sports fishing. PCBs contribute to reproductive problems and deformities in fish and wildlife (Mac 1988, Gilbertson, 1988). PCB congeners (specific types of the variety of substances known as PCBs) cover a wide range of physical and chemical properties, are relatively resistant to degradation, and are ubiquitous. These characteristics make them ideal representatives for many of organic compounds from anthropogenic (human-originated) sources (Eisenreich, 1987). 2. Trans-Nonachlor -- Chlordane is a chlorinated hydrocarbon originally registered as a pesticide in 1948. Chlordane had been released into the environment primarily from its application as an insecticide. It is estimated that prior to 1983, 3.6 million pounds were used annually in the U.S.. All commercial use of chlordane has been canceled by the USEPA since 1988. Technical grade chlordane is a mixture of at least 50 compounds; the major constituents are cis- and trans-chlordane, heptachlor, cis- and trans-nonachlor, and alpha-, beta- and gamma-chlordane. In the aquatic environment, chlordane is very persistent in the adsorbed state. Based on the high bioconcentration factor (BCF) values ranging between 7,240 and 20,000 chlordane is expected to have a high potential for bioconcentration. Trans-nonachlor is the most bioaccumulative of the chlordanes exceeding human health guidelines in fish tissue. As a chlordane constituent, it is also one of the chemicals addressed by the Great Lakes Initiative. In the Lake Michigan Mass Balance, trans-nonachlor will serve as a model for the cyclodiene pesticides. 3. Mercury occurs naturally in coal and mineral ores. About 3x10-6 percent of the earth's crust is made of mercury mostly in combination with sulfur to form more than 25 different minerals. It is used in battery cells, barometers, thermometers, switches, fluorescent lamps, mercury arc lamps producing ultraviolet light, and as a catalyst in the oxidation of organic compounds. Global releases of mercury in the environment are both natural and anthropogenic (caused by human activity). It is estimated that about 11,000 metric tons of mercury are released annually to the air, soil, and water through anthropogenic sources. These sources include combustion of various fuels such as coal; mining, smelting and manufacturing activities; wastewater; agricultural, animal and food wastes. As an elemental metal it is extremely persistent in all media. Mercury is readily sorbed to soil organic matter, clays and some hydrous metal oxides. Mercury also bioaccumulates with reported bioconcentration factors in fish tissues in the range of 1,800 to 85,000. BCF values for inorganic mercury range from 1,800 to 5,000, while BCFs for organic mercury are higher (10,000 to 85,000). Evidence from inland lakes indicates a trend of increasing fish tissue concentration (Sorensen et al., 1990), and increases over time in sediments. Sampling and modeling will provide new information on loads and fate of the combination of all forms of (e.g., "total") mercury. 4. Atrazine is the most widely used herbicide in U. S. corn and sorghum production. It was first marketed to U.S. farmers in 1959. In 1991, 51 million pounds of active ingredient of atrazine were applied to 40 million corn acres (62 percent of the U.S. crop). The average application rate was 1.3 pounds per acre. Approximately 4.1 million pounds of atrazine were applied to 67 percent of the 3.8 million sorghum acres in a Midwest study area. Unlike PCBs and trans-nonachlor, the manufacture and use
of atrazine has not been banned or put under strict controls. Atrazine has been reported
at elevated concentrations in Lake Erie tributaries (Baker et al, 1988), in the
open waters of the Great Lakes, and the atmosphere over the lakes (Steven Eisenreich,
personal communication, 1990). Its inclusion in the LMMB study will provide a model
for the more reactive, biodegradable compounds in current use. The model will not include
a food chain component, since atrazine does not appreciably bioaccumulate. EPA currently
classifies atrazine as “not likely to be carcinogenic to
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