Turn off accessible linear format and redisplay the web page in it's original layout. TOXIC SUBSTANCES AND HUMAN HEALTH
Today, toxic chemicals overshadow all other problems in the Great Lakes and in many other water bodies in Canada. Although we are striving to solve this threat to water quality, we still have a long way to go before it is under control.
Like all other ecosystems, life in the Great Lakes Basin Ecosystem exists within an intricate web of interacting and interdependent relationships. When the web is in balance, the ecosystem is preserved; when the web is damaged, the ecosystem becomes unbalanced and parts of the ecosystem suffer or even fail to survive.
Human abuse of the Great Lakes ecosystem over the past 200 years has severely threatened this fragile balance. Perhaps the most destructive action has been the production, use and disposal of toxic substances.
WHAT IS A TOXIC SUBSTANCE?
Toxic substances are best defined by how they are used and their effects on living organisms. In the 1978 Great Lakes Water Quality Agreement between Canada and the United States, a toxic substance was defined as: "substance which can cause death, disease, behavioural abnormalities, cancer, genetic mutations, physiological or reproductive malfunctions or physical deformities in any organism or its offspring, or which can become poisonous after concentration in the food chain or in combination with other substances."
Toxics are often colourless and odourless. Their effects may be quite different, depending on their makeup, amount and how they enter the environment. Substances that appear to be harmless may become more toxic when they mix with other chemicals, or may degrade over time to levels that are not toxic.
When they are released into the environment, they may remain for days, years or even decades. The greatest threat is from those toxics that persist in the environment for a long time, called persistent toxic substances. Over time, these chemicals can mix with other chemicals and become more potent, or can harm large parts of the ecosystem.
WHERE DO TOXIC SUBSTANCES COME FROM?
Some toxics are found naturally in the environment, including heavy metals such as mercury, lead and cadmium. These metals become toxic at certain levels and can damage living organisms through large, one-time dosages or as a result of exposure to small amounts over an extended time. More often, toxic substances are synthetic and manufactured. Some 70,000 commercial and industrial compounds are now in use, and an estimated 1,000 new chemicals are introduced each year. These chemicals may be products, such as pesticides, insulating materials, household cleaners or paint varnishes, or may be by-products or wastes of a production process.
The synthetic chemical industry, developed during and after World War II, brought many new chemicals into the marketplace. As demand grew for chemicals such as pesticides, synthetic rubber and plastics, production increased. In the Great Lakes region alone, more than 30,000 chemicals are produced or used.
Toxic chemicals are released into the ecosystem from several sources. Industries and municipalities discharge them directly into the lakes when they do not have the technology to eliminate these toxins from their waste streams. Runoff from agricultural and urban land contributes pesticides, fertilizers and heavy metals, while leaking landfills add toxins through groundwater. Many chemicals also reach the Great Lakes through the air -- as much as 90-95 percent of certain toxic substances entering Lake Superior are, in fact, deposited from the atmosphere.
As consumers, we also contribute substantial amounts of toxic substances to the environment. Each time we buy and use a product containing toxic chemicals, we are contributing to the ecosystem's load of contaminants.
HOW DO PERSISTENT TOXIC SUBSTANCES AFFECT THE ECOSYSTEM?
Once these substances are in the Great Lakes environment, they do not disappear. Persistent toxic substances tend to accumulate and are consumed by many parts of the Great Lakes food chain. As organisms eat these substances, either with sediment, water or through other species, the toxics accumulate in their tissues and magnify, or bioaccumulate. Thus, concentrations of some chemicals can be one million times higher in fish than in water. Species at the top of the food chain, such as lake trout and fish-eating birds, suffer adverse effects from these high levels of persistent toxics in their bodies.
Researchers have found a number of serious impacts in Great Lakes fish, birds, reptiles and small mammals. In most instances, these effects include population declines, reproductive problems, eggshell thinning, severe changes in metabolism, gross deformities, tumours or behavioural changes. When almost entire populations of cormorants, herons and gulls living on the lakes started to die in the 1960s and 1970s, scientists realised that the devastating consequences of toxic chemical contamination had become a reality.
HOW CAN WE STOP TOXIC CONTAMINATION OF THE GREAT LAKES BASIN ECOSYSTEM?
Canada and the United States created the Great Lakes Water Quality Agreement in 1978 and a Protocol revising the Agreement in 1987, to control toxic substances. The Agreement requires the two countries to develop and implement programs to eliminate sources of persistent toxic substances, to remediate contaminated areas, and to complete research that will help both countries to prevent further introduction of all toxic chemicals into the ecosystem.
While it is estimated that over 1,000 chemicals are in the Great Lakes ecosystem, scientists have identified 362 toxic substances in quantifiable amounts in the lakes themselves. The effects of exposure on wildlife have been studied and documented in laboratory and field studies since the 1960s. Fourteen species, including lake trout, cormorants, terns, bald eagles, mink and snapping turtles, have suffered reproductive problems and their populations have declined.
Both Canada and the United States have banned or restricted some dangerous chemicals, like PCBs, DDT, mirex and mercury. Since then, contaminant levels in the Great Lakes have dropped dramatically and a number of species have started to repopulate the area. However, many toxic contaminants are extremely persistent, remaining in the environment for generations and continue to affect the ecosystem after their release.
GREAT LAKES HEALTH EFFECTS PROGRAM
The effects on human health of long-term exposure to metals and toxic chemicals are not as well understood as the impact on fish and wildlife. Although researchers have conducted numerous health studies, the lack of a comprehensive long-term monitoring program and a bank of human tissues has prevented scientists from drawing firm conclusions about human health. The Great Lakes Health Effects Program is designed to fill in these gaps.
Humans are part of the Great Lakes ecosystem, standing at the top of the food web. Scientists have established that 80 to 90 percent of human exposure to Great Lakes' contaminants comes from food, especially certain fish and wildlife, rather than from the air or water. Many persistent toxic substances are fat-soluble and accumulate in increasingly higher concentrations as they move up the food web. Exposure to toxic chemicals in individuals can be measured in concentration of a contaminant in tissue, particularly fat tissue.
Toxic contaminants have been found in tissue samples of people living around the Great Lakes, although levels are no higher than in people living in other industrial areas.
PROMOTING A HEALTHY ECOSYSTEM
We know that metals and toxic chemicals pose a threat to the entire ecosystem of the Great Lakes and that the levels of pollutants must be significantly reduced. The efforts of citizens, governments and businesses over the past 25 years have restored many parts of the Great Lakes. But the recovery has slowed and even stopped in some areas over the past decade, and greater efforts are needed from all sectors of society to reverse this trend. The toxic contamination issues facing the region are complex, and serious effects can occur before we can see clear symptoms of the degradation.
We must all work to achieve zero discharge of persistent toxic substances into our environment.
Source: Toxic Substances in the Great Lakes Basin Ecosystem published by International Joint Commission
