Persistent organic pollutants, commonly called POPs, are persistent, bioaccumulative, and toxic substances released into the environment primarily through a variety of human activities. POPs fell into three broad categories: pesticides such as aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, toxaphene, and hexachlorobenzene; industrial substance such as polychlorinated biphenyls; and chemical by-products and contaminants of various industrial processes such as dioxin, furans, and hexachlorobenzene. POPs transported across national boundaries through air and watersheds are widely recognized to be of global concern. In order to protect and improve the environment and to reduce risks to health, national and international actions have already been directed towards severe reduction, and in some cases elimination of the release of several POPs. This paper briefly describes, from a Canadian perspective, some national and international initiatives undertaken in the last 15 years that are designed to reduce levels of POPs. These initiatives include: (1) the Canadian Toxic Substances Management Policy, (2) the Canada-US Great Lakes Water Quality Agreement (1987), (3) the Canada-US Great Lakes Binational Toxics Strategy, (4) the North American Agreement on Environmental Cooperation, and (5) the United Nations Economic Commission for Europe POPs Protocol to the Convention on Long-range Transboundary Air Pollution. Negotiations are underway for a global agreement to control POPs.

The International Joint Commission was established by the 1909 Boundary Waters Treaty to assist the governments of the US and Canada in preventing and resolving disputes along their border. Since the signing of the Great Lakes Water Quality Agreement in 1972, the Commission and the two governments have had significant experience—from scientific, managerial, and public involvement perspectives—dealing with the problem of toxic chemicals in the Great Lakes Ecosystem. This paper examines the recommendations proposed by the Commission concerning persistent toxic substances. The author then identifies six fundamental dilemmas that society must face in dealing with persistent and bioaccumulative chemicals. These are: (1) the use of science in the debate on toxics, (2) how economics is factored into decisions about toxics, (3) long term costs versus short term economic and social values, (4) the concept of reverse onus, (5) social discontinuity as change occurs, and (6) the political will of governments. While the US and Canada have made progress in diminishing the quantities of the most egregious pollutants, there is still significant work to be done in the Great Lakes region, as well as in other areas along the Canada-US border and throughout the world.

Persistent, bioaccumulative, and toxic materials are a special group of chemicals and heavy metals that are both synthetic and natural in origin. As pesticides, industrial wastes, and mining byproducts, they have contaminated air, water, and land, and they are biomagnified. Recent national, regional, and international agreements have targeted approximately two dozen contaminants for evaluation, control and elimination from the environment. This paper is a review and evaluation of the current and future impacts of 27 toxic materials in the US-Mexican border region. Because of economic development, population growth, and unique environmental conditions in the region, concern about them should be much higher. Evidence from research conducted within 100 kilometers of the border shows that though the effort is ongoing, there are not enough data upon which to confidently conclude that efforts to reduce contamination have been successful. In a few cases, investigators have detected a reduction of some materials in some biota, but the paucity of information, particularly in Mexico, leaves little hope that the health and welfare of the borderland's occupants will be preserved. The environmental Practitioner can contribute by focusing efforts on cross-border collaboration, on coordinated ecosystem or watershed-based analyses, and on the development of methods to accurately identify sources of contaminants for locations that lack detailed accounting.