Lake by lake
Resources and references
About the Great Lakes LaMPs study...
Glossary of terms
Contaminants are clearly bioaccumulating in Lake Erie biota on a continuum from benthos to fish to amphibians and reptiles, birds, and mammals. In addition, the filter feeding habits of the non-indigenous invasive zebra mussel are re-introducing contaminants not previously biologically available back into the water column and ultimately into the food web.
Benthic organisms spend most or all of their lifecycle in the sediment of the lake. Some fish are benthic feeders or spend most of the time near the bottom; others eat organisms that have spent part of their lifecycle as benthos. Finally, birds and mammals prey on these same fish. Each organism has bioaccumulated contaminants during its lifecycle, and the effect magnifies as one moves up the food chain (biomagnification). There are species used as indicators of this phenomenon (midges, mayflies, brown bullhead, bald eagle and herring gull) for which we have the most information. However, the list of species used to monitor contaminant impacts has grown in recognition of widespread bioaccumulation.
The critical pollutants and chemical pollutants of concern in Lake Erie include organochlorines and metals that are known to cause adverse health effects in animals and humans. These chemicals do not break down easily, persist in the environment, and bioaccumulate in aquatic biota, animal and human tissue; thus they are called persistent bioaccumulative toxic chemicals (PBTs). Organochlorines tend to accumulate in fat (such as adipose tissue and breast milk), and metals tend to accumulate in organs, muscle and flesh. Food is the primary route of human exposure to these PBT chemicals, and consumption of Great Lakes fish is the most important source of exposure originating directly from the lakes. Sources from air, soil/dust, and water constitute a minor route of exposure.
Since the 1970s, there have been steady declines in many PBT chemicals in the Great Lakes basin, leading to declines in levels in human tissue, for example, lead in blood and organochlorine contaminants in breast milk. However, PBT chemicals, because of their ability to bioaccumulate and persist in the environment, continue to be a significant concern in the Lake Erie basin. Although contaminant levels in the Great Lakes are declining in general, recent trends suggest that concentrations for some pollutants may be leveling off. However, health concerns from environmental contaminant exposures in the Lake Erie basin remain. Therefore, public health advisories and other guidelines should be followed to minimize contaminant exposures. Most of the health effects studies for Great Lakes PBT chemicals have focused on fish consumption.
The large surface area of Lake Huron, like the other Great Lakes, has made it particularly vulnerable to atmospheric deposition of contaminants. Lake Huron has a large surface area and relatively few local contaminant point sources. Loadings to Lake Huron from water sources are lowest of all the Great Lakes but air sources are highest.
From the late 1970’s to the early 1990’s, persistent, bioaccumulative substances (such as PCBs, DDT, dieldrin, dioxins, and furans) concentrations declined significantly in Lake Huron lake trout. However, while concentrations of DDT have continued to decline, PCB concentrations have not declined significantly since the mid-1980s. DDE trends in Lake Huron herring gull eggs show a marked decrease in concentration since the mid 1970s. As with other trends, concentrations decreased significantly in the late 1970s but have remained relatively stable since. Continuing sources of contaminants are primarily from sediments contaminated by historic discharges, airborne deposition industrial and municipal discharges and land runoff.
Originally, there were six Great Lakes areas of significant environmental contamination or Areas of Concern (AOCs) on Lake Huron. One of these, Collingwood Harbour, Ontario, was the first and remains the only AOC to be delisted. The St. Marys River is designated as an AOC because of contaminants from sediment, municipal discharges and nonpoint source pollution sources. Control of industrial point sources is progressing and pollution loads are being reduced. The St. Clair River is designated as an AOC because of the pollution problems on the eastern side of the river.
Two other Canadian Areas of Concern, Spanish River and Severn Sound are responding well to remedial actions and showing recovery. The only Area of Concern solely in Michigan, Saginaw River/Saginaw Bay, is designated as an Area of Concern primarily because of contaminated sediments and nonpoint pollution sources.
Historically, phosphorus has been a significant problem in the Great Lakes. To a great extent this has not been the case in Lake Huron, with the exception of Saginaw Bay and the southern Ontario shore. The United States/Canada Great Lakes Water Quality Agreement (GLWQA) identified target loads for all lakes to prevent phosphorus-related problems (over enrichment), and Lake Huron has generally maintained loadings below target loads. With the exception of 1982 and 1985, loadings have been below the target since 1981.
Food, including fish consumption, is the primary route of exposure to persistent, bioaccumulative and toxic chemicals, including PCBs and mercury. For the U.S. Great Lakes basin, measured levels of these persistent toxic chemicals in drinking water are below the Maximum Contaminant Levels (MCLs) and therefore they are not considered to be a human health concern for drinking water.
Although there have been sporadic outbreaks of illness related to the use of drinking water, the drinking water in the Lake Michigan basin is of good quality. However, continuing efforts must be made to inform health professionals and the public of the results of analyses of drinking water. Information on local water quality is available from several sources, including the state public health department and local water supplier.
The EPA requires public water supplies to be monitored for bacteriological, inorganic, organic and radiological contaminants. The chemical analyses of drinking water include physical and chemical characteristics of the water, as well as contaminants resulting from natural sources or human activities. Community water suppliers deliver high quality drinking water to millions of people every day, and a network of government agencies are in place to ensure the safety of public drinking water supplies. Our drinking water is safer today than ever but problems can, and do occur, although they are relatively rare.
It is extremely difficult to estimate critical pollutant loadings entering Lake Ontario via rivers, precipitation, sewage treatment plants, waste sites, agricultural areas, and other sources. The levels of contaminants entering the lake from these sources are constantly changing in response to many known and unknown factors. As a result, loadings data are often limited and rely on numerous assumptions. Although quantitative loadings information may be difficult to obtain, qualitative indicators provided by the environmental monitoring of water, sediment, and aquatic organisms can often provide sufficient information to identify those contaminant sources that need to be controlled. Improving the database on sources and loadings of critical pollutants is a high priority, as is determining effective ways to virtually eliminate these critical pollutants from Lake Ontario.
Preliminary estimates indicate that the volume of some contaminants leaving the lake, such as PCBs and DDT, may be greater than the amount coming in. One explanation for this may be that contaminants are slowly being released from sediments already present in the Lake Ontario system.
Estimates of atmospheric loadings of critical pollutants to Lake Ontario are developed by the International Atmospheric Deposition Network, who also provided estimates for the amounts of critical pollutants volatilizing to the atmosphere. Volatilization may be a significant process by which critical pollutants are leaving the Lake Ontario system. Estimating atmospheric deposition is difficult, and these estimates contain a significant degree of uncertainty.
The amounts of critical pollutants entering Lake Ontario via all of the Lake Ontario basin tributaries were based on representative point and non-point sources within each tributary’s watershed. Quantitative and qualitative monitoring techniques, as well as biological monitoring results, were used to estimate loadings or the relative presence or absence of critical pollutants within each of the 22 tributaries with the highest flow rate within the watershed.
Information on releases to the environment of critical pollutants and other contaminants is available to the public in publications developed and released on a regular basis by governmental agencies. For sources in the U.S., the annual Toxics Release Inventory (TRI) summarizes on an annual basis the emissions of approximately 650 pollutants from facilities nationwide. For sources in Canada, the National Pollutant Release Inventory (NPRI) provides information on the onsite releases to air, water, and land; on transfers offsite in waste; and on the three R’s (recover, reuse, and recycle) of 176 substances. The NPRI is the only legislated nationwide publicly accessible inventory of pollutant releases and transfers in Canada.
Based on the limited loadings data available, it appears that a significant load of critical pollutants to the lake originates outside the Lake Ontario basin. The upstream Great Lakes basin contributes the majority of the estimated loadings of PCBs (440 kg/year), DDT and its metabolites (96 kg/yr), and dieldrin (43 kg/year). Attention must also be focused on the Niagara River, since most of the mirex entering Lake Ontario originates in the Niagara River basin (1.8 kg/year) and it also contributes to the load of other critical pollutants into the lake. Atmospheric deposition is a source of critical pollutants and appears to be the largest known source of dioxins and furans, contributing approximately 5 grams per year.
Food, including fish consumption, is the primary route of exposure to persistent bioaccumulative toxic (PBT) chemicals, including the nine chemicals designated as zero discharge contaminants for Lake Superior. Previous assessments for the Canadian Great Lakes basin show the intake of PBT chemicals via drinking water is negligible (less than 1 percent of total intake from all sources). They are well below the Maximum Acceptable Concentration (MAC) listed in the Ontario Drinking Water Objectives and the Guidelines for Canadian Drinking Water Quality. For the U.S. Great Lakes basin including Lake Superior, measured levels of these persistent toxic chemicals in drinking water are below the Maximum Contaminant Levels (MCLs) in Lake Superior, and therefore they are not considered to be a human health concern for drinking water.
Public water systems use various processes in order to treat raw water. One process involves the addition of alum, an aluminum compound that is used for the coagulation of suspended solids. Subsequently, the use of alum in the treatment process can raise the levels of aluminum in drinking water if the process is not optimized. If the quality of the raw water is poor, it may affect the amount of aluminum that needs to be added. There is much debate as to the role aluminum may play in the development of Alzheimer’s Disease and other dementias.
Currently, the U.S. EPA does not regulate aluminum under its drinking water program but has a secondary, non-enforceable standard of 50-200 micrograms/liter. The U.S. EPA is working to determine if aluminum is of health concern and has placed aluminum on its Contaminated Candidates List (CCL). This list is the source of priority contaminants for the Agency’s drinking water program. Priorities for drinking water research, occurrence monitoring, guidance development, including the development of health advisories will be drawn from the CCL. The CCL also serves as the list of contaminants from which the Agency will decide whether of not to regulate specific contaminants.
Other processes commonly used by water treatment plants include the addition of disinfectants such as chlorine to inactivate or kill micro-organisms in the distribution system. However, chlorine and other disinfectants can combine with naturally occurring organic matter in the raw water to produce disinfection byproducts. Of the chlorination disinfection byproducts, trihalomethanes (THMs) are present in the highest quantities. Evidence from toxicologic and epidemiologic studies suggests a possible link between byproducts of the chlorination process and increased risk of some cancers (e.g., bladder and colon) and adverse pregnancy outcomes (such as miscarriage, birth defects and low birth weight).
The amount of chlorination required and resulting levels of chlorination disinfection byproducts are dependent upon the quality of the raw water, including microbiological quality and organic content. Zebra mussel control at drinking water intakes can also result in increased levels of disinfectants and disinfection byproducts in finished drinking water. Nutrient enrichment in source waters can cause algal blooms which contribute to total organic carbon levels. In the U.S., EPA is developing standards to address the issue of disinfectants and disinfection-by-products. In Canada, Health Canada re-opened the THMs guideline in April 1998 and established a multi-stakeholder Task Group to oversee a comprehensive update of health risk information on THMs and to develop recommendations for controlling the risks.
Some materials in soils are naturally-present (for example, arsenic and/or mercury) and can become dissolved or suspended in groundwater. Groundwater can also pick up materials of human origin that have been spilled or buried in dumps and landfill sites, or that have resulted from agricultural activities (for example, nitrates and/or atrazine). Contamination can therefore occur both in urban and industrial areas, as well as in rural and agricultural areas.
Last modified: May 20, 2005