POPs tend to concentrate in colder climates such as Canada's North, as well as in the Great Lakes Basin and St. Lawrence River. As chemical compounds, POPs are very stable and consequently can last in the environment for years or decades. POPs are also bio-accumulative, meaning they can concentrate in living organisms and accumulate up the food chain through fish, predatory birds, mammals and humans. Aboriginal peoples, who rely heavily on such country foods, are particularly affected. Some POPs can be passed on from mother to child across the placenta, or through breast milk.
POPs can travel great distances around the globe through the atmosphere.
Touching down on oceans and freshwater bodies, they then evaporate into the atmosphere once again, and travel further to touch down in another spot until they ultimately gather in the colder climates. This is known as the grasshopper effect. The role of Canadian science Canada is a leader in the science of identifying and assessing past and current sources of POPs, and in predicting global movement through the atmosphere. Canadian scientists have improved the ability to detect POPs in rain and snow and have contributed to tracking the accumulation of these chemicals up the food chain and into humans. These developments are the basis for policy decisions and action both in Canada and on the international scene.