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Fish consumption in the Great Lakes

Critical Contaminants
    in the Great Lakes

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Critical contaminants | Reducing exposure

Critical contaminants

Chlordane was used to control pests on crops (corn, grapes, strawberries, etc.), and to control fleas, ticks and mange on pets. It is a probable human carcinogen. The U.S. banned most uses in 1978 and all uses except termite control in 1987. Canada discontinued use in 1990. Chlordane has been detected in Lake Huron water, fish and wildlife.

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DDT and metabolites
DDT was used in large quantities in the 1950s and 1960s on cotton fields, orchards and other crops, and in unsuccessful extermination campaigns against the Japanese beetle, spruce budworm, gypsy moth, and Dutch elm disease bark beetle. DDT was also an ingredient in the pesticide Kelthane (Dicofol).

DDT breaks down into toxic metabolites, primarily DDE. DDT and DDE are probable human carcinogens and endocrine disrupters. The United States banned DDT (except for public health emergencies) in 1973, and banned Kelthane (unless it contained less than 0.1% DDT) in 1988. Canada discontinued DDT in 1985. DDT is still used in other countries, mostly for insect control. A major source of DDT in the Lake Huron watershed in the Pine River near St. Louis, Michigan at a now closed chemical processing plant. Remediation of contaminated sediment was initiated at the site in the spring of 1999. Also, some DDT has been stockpiled in the Lake Huron Basin, as it still shows up when agricultural pesticides are collected. DDT has been detected in Lake Huron water, fish and wildlife.

The development of the pesticide DDT in the 1940s was considered a major breakthrough in the battle against diseases, such as malaria, and in controlling crop pests. Highly effective and cheap to produce, DDT was the most widely used pesticide in North America and other countries from 1946 to 1972. Agricultural use of DDT has since been banned in North America following the discovery that DDT and its breakdown products were causing widespread reproductive failures in eagles and other wildlife species.

Although DDT continues to be used in other parts of the world, levels of DDT in the North American environment have decreased significantly since this pesticide was banned, and species impacted by DDT, such as the bald eagle, are recovering. DDT and its metabolites are identified as Lakewide Management Plan (LaMP) critical pollutants because they are responsible for wildlife consumption advisories and are identified as a potential problem contaminant for bald eagles once they re-establish their shoreline nesting territories.

The upper Great Lakes are the largest source of DDT and its metabolites to the Lake Ontario basin (96 kg/year). Atmospheric deposition and sources within the Lake Ontario basin contribute approximately 33.5 kg/year combined. Much of the tributary loadings likely consist of atmospheric fallout in the watershed given the banning of these materials from use in the watershed. The Niagara River basin does not appear to be a significant source of DDT. Approximately 143 kg/year of DDT leave Lake Ontario via volatilization to the atmosphere (141 kg/year) and the St. Lawrence River (2 kg/year), for a net loss from Lake Ontario of approximately 13 kg/year.

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Dieldrin is a formerly used pesticide that is now banned from use in the Lake Ontario basin and throughout North America. Aldrin, another formerly used pesticide, transforms into dieldrin through natural breakdown processes.

Dieldrin is identified as a Lakewide Management Plan (LaMP) critical pollutant because dieldrin concentrations in water and fish tissue exceed the U.S. Great Lakes Water Quality Initiative (GLI) criteria throughout the lake. The GLI criterion for water is 0.0000065 parts per billion (ppb) and Lake Ontario water averages 0.17ppb. The corresponding GLI fish tissue criterion is 0.0025 parts per million (ppm). Most Lake Ontario fish clearly exceed this criterion as dieldrin is detectable at concentrations ranging from approximately 0.005 to 0.030ppm.

Although the GLI criteria are being exceeded, dieldrin concentrations in the environment have been steadily declining. Between 1985 and 1995, dieldrin concentrations in the lake have declined from 0.35 to 0.17ppb based on information collected through Niagara River and Wolfe Island monitoring programs.

The upper Great Lakes are the largest source of dieldrin to the Lake Ontario basin (43 kg/yr). Atmospheric deposition and point and non-point sources within the Lake Ontario basin are approximately equal (13 kg/year and 9 kg/year) (see Figure 3-5). Estimates for the rate of loss of dieldrin in Lake Ontario due to volatilization (320 kg/year) and the St. Lawrence River (43 kg/year) suggest that the volume of dieldrin in the lake is decreasing at a rate of 298 kg/year.

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Dioxins and furans
There is no known use of dioxins and furans (Chlorinated Dibenzo-p-dioxins, or CDDs); they are by-products of processes involving chlorine, organic chemicals and heat, including incineration, pulp and paper bleaching with elemental chlorine, and chemical manufacturing. Dioxins are extremely toxic. They are carcinogenic and may be an important endocrine disrupter. Concentrations from pulp and paper bleaching are dropping as mills switch to alternative technologies. Other processes, including incineration of medical and solid waste, continue to produce significant amounts.

Dioxins have been detected in Lake Huron fish and wildlife. Laboratory studies have shown some wildlife species to be extremely sensitive to the toxic effects of these contaminants. The potential impacts of the very low levels of these contaminants found in Lake Ontario fish, wildlife, and humans are poorly understood.

Steps have been taken to control and limit those processes that produce high levels of dioxins and furans, resulting in a significant decrease in environmental levels of these chemicals over the last two decades. Some of the processes that can produce dioxins and furans include the use of internal combustion engines, incinerators, and a variety of other chemical processes, which are part of our modern way of life and may be difficult to eliminate altogether. Forest fires and wood burning stoves also produce low levels of dioxins and furans.

Dioxins and furans are identified as Lakewide Management Plan (LaMP) critical pollutants because levels of these contaminants exceed human health standards in some Lake Ontario fish and because these chemicals may limit the full recovery of the Lake Ontario bald eagle, mink, and otter populations by reducing the overall fitness and reproductive health of these species. Despite this analytical limitation, data from other media (mussels, spottail shiners, and sediment cores) indicate that there are several sources of both dioxins and furans in the Niagara River and that the river is a source of these pollutants to Lake Ontario.

Atmospheric deposition appears to be the largest known source of dioxins/furans, contributing approximately 5 grams per year. Dioxins and furans have been detected in a number of Lake Ontario tributaries using qualitative water and biological sampling methods. No reliable estimates are available for the volume of dioxins/furans that may be leaving the lake via volatilization to the atmosphere.

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Mercury (Hg) and methylmercury
Mercury is widely used in batteries (its use in alkaline batteries has been banned in most batteries, limited in others), electrical equipment (switches), medical equipment, thermometers, thermostats, and preservatives -- even in the silver amalgam dentists use for fillings. Many former uses (as a fungicide, pesticide, and in latex paint) have been discontinued, but mercury is still needed in some products and processes. Historically, mercury was added to paints as an anti-mildew agent. Its largest U.S. use today is at chlor alkali plants that produce chlorine gas and caustic soda.

Small concentrations of mercury that exist in natural materials such as coal, wood and metal ore are released when these materials are processed; because such huge quantities of these materials are processed, much mercury is released. Mercury is also released when garbage is burned, and it vaporizes from landfills.

Mercury is not known to be a carcinogen, but it is toxic to the fetuses of humans and animals. Human poisoning has occurred. U.S. use dropped from 2,649 tons in 1980 to 690 tons in 1993. The last registered use of mercury as a pesticide in the U.S. was voluntarily cancelled by the manufacturer in 1994. Mercury in Lake Huron fish has caused fish consumption advisories and has been detected in Lake Huron water, sediment and wildlife. Also, dredging activities are impaired on the Ontario shoreline of the St. Clair River and Severn Sound.

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Metals: alkylated lead, nickel, copper, zinc, cadmium
Lead, nickel, copper, zinc, and cadmium are heavy metals common in hazardous waste. They can damage organisms at low concentrations and tend to accumulate in the food chain. These heavy metals are found in sediment in Lake Huron and are associated with degradation of benthos, and planktonic communities and result in restrictions on dredging in navigation harbors. In most cases, existing concentrations are due to historical discharges. Also, dredging activities are impaired on the Ontario shoreline of the St. Clair River and Severn Sound.

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The discovery of elevated levels of mirex in Lake Ontario fish during the 1960s triggered lakewide fish consumption advisories. Investigations determined that most of the mirex originated from a chemical production facility on the Niagara River. Use and production of mirex, also known as dechlorane and chlordecone, are now banned in North America. Mirex is identified as a Lakewide Management Plan (LaMP) critical pollutant because levels in some Lake Ontario fish continue to exceed human health standards; a number of fish consumption advisories exist.

Although mirex is most widely known for its use as a pesticide, approximately 75 percent of the mirex produced was used as a flame retardant in a variety of industrial, manufacturing, and military applications. Available sales records suggest that more than 50,000 pounds of mirex were used for industrial and manufacturing flame retardant purposes in the Lake Ontario basin. More than 75,000 pounds of mirex were used as a flame retardant in other Great Lakes basins.

Most of the mirex entering Lake Ontario originates in the Niagara River basin (1.8 kg/year) and an additional 0.9 kg/year enters via the Oswego River. Approximately 0.7 kg/year of mirex leaves Lake Ontario via the St. Lawrence River. No reliable estimates of atmospheric deposition or volatilization are available at this time.

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Nutrients: phosphorous and nitrogen
Nutrients such as phosphorus and nitrogen, in excessive quantities can case eutrophication problems. Sources of nutrients include municipal wastewater treatment plants, some industrial discharges, runoff from agricultural and urban area, and the atmosphere. Nitrates and nitrites are inorganic chemicals that are present naturally in the environment due to the nitrogen cycle. Potassium nitrate and sodium nitrate is commonly used and found in fertilizers.

Nitrates are nutrients and do not bioaccumulate. However, at higher concentrations they have been shown to cause effects to amphibians that are similar to those caused by toxic contaminants. Because less research and monitoring data are generally available for amphibian populations as a group, the mechanisms for the observed biological effects of nitrates are not as clearly defined as those for other organisms.

A review by Rouse et al. (1999) evaluated the risk of direct and indirect effects of nitrate on amphibian populations. This review used a simple comparison of known environmental nitrate concentrations in North American waters to nitrate concentrations known to cause toxicity in a laboratory setting to amphibian larvae and other species that play an important role in amphibian ecology.

Lethal and sublethal effects in amphibians are detected in laboratory tests at nitrate concentrations between 2.5 and 385 mg/L (Table 4.8). Amphibian food sources (such as insects) and predators (such as fish) are also affected by elevated levels of ammonia and nitrate in surface waters (Rouse et al., 1999). This may have important implications for the survival of amphibian populations and the health of food webs in general.

Environmental concentrations of nitrate in surface waters in agricultural watersheds in southwestern Ontario and U.S. states in the Lake Erie watershed ranged from 1 to 40 mg/L. Of 8000 water samples from rivers in the watersheds of Lake Erie and St. Clair in the Canadian Great Lakes and in US states in the Lake Erie watershed, 19.8% had nitrate levels above 3 mg/L. This concentration was known to cause physical and behavioral abnormalities in some amphibian species in the laboratory (Rouse et al., 1999). A total of 3.1% samples contained nitrate levels that would be high enough to kill tadpoles of native amphibian species in laboratory tests (Rouse et al., 1997).

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Polybrominated biphenyls (PBBs)
Polybrominated biphenyl (PBB), a flame-retardant material, was introduced into the food chain in Michigan in 1973 due to a manufacturing and distribution mistake. A major source of PBB in the Lake Huron watershed in the Pine River near St. Louis, Michigan at a now closed chemical processing plant.

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Polychlorinated biphenyls (PCBs)
PCBs were widely used in electrical equipment such as transformers and capacitors. For example, PCB oil-filled electric switches eliminated electric sparking problems that could trigger explosions at petroleum refineries. PCB oils were used in electrical transformers as a non-flammable electrical insulating fluid. PCBs were also used as industrial lubricating oils to replace earlier types of hydraulic oils that could more easily catch fire under conditions of high pressure and temperature.

PCBs were manufactured between 1929 and 1978. PCBs are carcinogens and probable endocrine disrupters. Human poisoning has occurred. Some 1.4 billion pounds of PCBs were manufactured in the U.S. before such manufacture was banned; Canada imported 0.9 billion pounds before this manufacturing ban took effect. PCBs in Lake Huron fish have caused fish consumption advisories; PCBs have also been detected in Lake Huron water, sediment and wildlife. Also, dredging activities are impaired on the Ontario shoreline of the St. Clair River due to PCBs.

The production of PCBs was halted following the discovery that PCBs released into the environment were bioaccumulating to levels of concern in a wide range of organisms. The hazards posed by PCBs were discovered in the 1960s when ranch mink, that had been fed a diet of Great Lakes fish, experienced reproductive failures. The investigations that followed determined that Great Lakes fish were contaminated with PCBs at levels that warranted human fish consumption advisories. Since that time, production of PCBs in North America has been banned, and the use of PCBs is being systematically eliminated. In Canada, old electrical transformers and other equipment that contain PCBs are being stockpiled until they can be safely destroyed. In the U.S., old transformers and equipment containing PCBs must be properly disposed within one year.

Levels of PCBs in the environment have decreased in response to the banning and phasing out of the various uses of PCBs. PCBs are identified as a Lakewide Management Plan critical pollutant because levels of PCBs in Lake Ontario fish and wildlife continue to exceed human health standards and because PCB levels in the Lake Ontario food chain may pose health and reproduction problems for bald eagles, mink, and otter.

The majority of these estimated PCB loadings to Lake Ontario originate outside the Lake Ontario basin. The upstream Great Lakes basins contribute the largest amount (302 kg/year), followed by the Niagara River basin (138 kg/year). Within the Lake Ontario basin, point and non-point sources contribute approximately 100 kg/year, 80 percent of which enters the Lake via streams and rivers. Atmospheric loadings contribute 64 kg/year directly to the lake surface. Some of the tributary loadings are no doubt due to atmospheric deposition within the watershed. When the loss of PCBs from the Lake basin via volatilization (440 kg/year) and the St. Lawrence River (411 kg/year) is considered, the total amount of PCBs within Lake Ontario appears to be decreasing at a rate of 250 kg/year, only to be transferred downstream, downwind, or buried in the bottom sediments.

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Sediment and suspended solids
Sediment is solid material, either suspended or settled and both mineral and organic, that has been deposited within a water channel or impoundment. Sediment is a pollutant originating primarily from non-point sources such as agricultural runoff, urban runoff or from stream banks. Sediment usually occurs due to human-induced changes to the landscape.

Sediment causes harm through a number of actions, including carrying pollutants downstream and, covering fish spawning and aquatic invertebrate habitat. Excessive sediment is a problem in many Lake Huron streams in that it impedes fishery restoration by degrade spawning habitat and lower or change food web productivity, both in Lake Huron (especially Saginaw Bay) and in the tributaries.

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Tritium is a radioactive byproduct of light-water and heavy-water nuclear reactor operation. In their coolants, these reactors produce about 500 to 1,000 and 2 x 10 Ci/year, respectively, for every 1,000 MW(e) of power. Tritium is a fission product within nuclear fuel, generated at a rate of 1-2 x 10{sup 4} Ci per year/1000 MW(e). Also, tritium occurs naturally in the environment. Reactions between cosmic radiation and gases in the upper atmosphere produce most of the world's natural tritium.

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