Banff National Park of Canada
Airborne Pollutants: our chemical heritage
From space, delicate sweeps of cloud swirl around earth. Tracing prevailing air currents, they are an important part of the global water cycle, linking ecosystems around the world. This link reveals itself in our mountain national parks. Invisibly, within those sweeping clouds and air currents ride toxic chemicals. Picked up from points around the world, they leave their chemical signatures in our pristine mountain lakes.
Released into the environment in far away countries, these chemicals evaporate and condense, touching down in fresh and salt-water bodies, travelling the world. Captured by sparkling snowflakes, they sink down into Arctic and mountain ecosystems and attach to dust and rock particles. They rest for years, if not decades in ice and glaciers.
As they melt out into alpine lakes, they begin another journey, this time through the food chain through tiny aquatic animals to fish and other predators. With each step up in the food chain, they concentrate in fatty tissue at ever increasing levels; they bio-magnify. This is the unfolding story of remote mountain ecosystems and their ties to distant agricultural and industrial activities the story of how the farm pesticide toxaphene got into lake trout in Bow Lake, high in Banff National Park.
Toxaphene is a persistent organic pollutant, or POP. A large and complex class of toxic compounds, POPs include pesticides and industrial chemicals. Their stable nature means they can persist for decades in the environment. Today, most are banned or severely restricted in Canada.
The dirty dozen
Pesticides : DDT, chlordane, toxaphene, mirex, aldrin, dieldrin, endrin and heptachlor
Industrial chemicals : PCBs, hexachlorobenzene
By-products and contaminants : dioxins and furins
Though a source persists in the environment from our own past use, by far the greatest sources of POPs entering Canada's environment today are foreign. Despite strong evidence of their harmful effects on wildlife, ecosystems and people, they continue to be produced, used and stored as waste in a number of other countries.
The presence of contaminants in the Arctic from distant sources first came to light in the late 1970s when pesticides were found in polar bear fat tissue. Since then, the reality of atmospheric POPs, their effects on wildlife and human health, and the need for international cooperation has crystallized. A well-known story in the Arctic, researchers have begun to look for evidence of air-borne POPs in other cold ecosystems, our mountain environments.
In the 1990s, research found that the largest lake trout in Bow Lake contain high levels of toxaphene. Since the lake supports only a small population of large lake trout (~ 2.5 kg) and people do not consume high amounts of fish from the lake, human health is not at risk; however, predators such as osprey, feed exclusively on fish.
Ospreys, a common breeding species in the west, are excellent "environmental indicators" since their fish diet exposes them directly to any aquatic pollutants. POPs are known to affect eggshell quality and the viability of developing chicks, which can result in population declines.
Pathway resulting in biomagnification of persistent organic pollutants in aquatic food web
As part of a larger study in British Columbia and the Yukon, Environment Canada is conducting research on ospreys in the mountain national parks to determine if they are being affected by air-borne contaminants. Initial results indicate that concentrations of POPs are fairly low. The research will also help determine if contaminant levels in osprey can be predicted from what is found in fish. If so, this would provide additional evidence that fish could be used for an effective environmental monitoring program for POPs.
Airborne POPs are 'caught' by snowflakes high in the atmosphere and deposit in cold, high-altitude environments like Bow Glacier in Banff National Park.
POPs bind to fine rock flour particles in snow and ice on the glacier. With spring run-off, water with suspended rock flour enters Bow Lake, giving it the classic emerald colour of a glacier fed lake.
The very fine rock flour particles remain suspended in the water for a time, gradually settling to the lake bottom.
While filtering water for food, tiny zooplankton take in rock flour and POPs.
The rock flour is excreted but the fat soluble POPs are absorbed and begin to accumulate in the fat cells of the zooplankton.
Lake trout eat the zooplankton and POPs accumulate at greater levels in their tissue.
Osprey eat lake trout.
Canadian research has provided the evidence needed to push for international controls on POPs. The way to evaluate domestic and international control agreements is long-term monitoring; we need to know if atmospheric deposits of toxic chemicals are increasing or decreasing to evaluate our controls and regulations, and international treaties.
In May 2000, 122 governments negotiated the Stockholm Persistent Organic Pollutants Convention, the first global treaty to focus on POPs. It targets an initial list of 12 POPs, known as the "dirty dozen" and will come into force once ratified by 50 countries. Canada was the first to ratify it. This process is expected to take 3-4 years. Other important chemical-related treaties also in the process of being ratified include:
- The Rotterdam Convention (1998) alerts governments as to what chemicals are banned or severely restricted, by which governments, and for what reasons;
- The Basel Convention (1992) aims to control the transboundary movement of hazardous wastes and promotes environmentally sound management and disposal;
- The 1996 Protocol to the 1972 London Convention on ocean dumping.
POPs are the ultimate recyclers, their persistence and mobility means that present-day, as well as previously released amounts will be on-going sources. Even small amounts can have harmful effects on ecosystems, wildlife and humans. We need to shut and lock the door on these toxic globe-trotters; ratified treaties provide the key.
What can you do to help?
Become an informed global citizen. Learn more about POPs and the international treaties that will help eradicate them. Check out these web sites: