Persistent organic pollutants present environmental and health risks despite their effectiveness in their uses and applications. There is a strong international movement to ban them from food sources, but some countries still use them, and chemical manufacturing corporations still produce them for profit.
I. Why Are Persistent Organic Pollutants a Controversy?
II. Human Exposure
III. Disposal of POPs
IV. Do POPs Ever Degrade Naturally?
Why Are Persistent Organic Pollutants a Controversy?
These chemicals cause controversy because they last a long time in the environment. Their presence can be damaging to other parts of the soil and water. Since they persist, or last, in the environment, annual reapplication of pesticides increases cumulative exposures dramatically. Persistent organic pollutants (POPs) are several groups of chemicals. Polychlorinated biphenyls (PCBs) are industrial chemicals. The two remaining groups are dioxins and furans. POPs have one common characteristic: their persistence in the environment. Some early pesticide applications wanted this characteristic because it was presumed that stronger chemicals that lasted longer performed their task better. They last longer than required for their intended use, however, and it is always an issue as to exactly how long they do last. Over time, the accumulation of POPs eventually made the case that they do persist. All 12 POPs listed are chlorinated compounds, 9 of them having been developed as pesticides. Their use is decreasing, but controlling international use is controversial. Farm workers and others who live near POP applications can suffer from overexposure. This can cause acute poisoning. If acute poisoning occurs, no antidotes are available for the internationally banned POPs. POP exposure can follow other vectors of exposure because they are so persistent in the environment. They eventually reach the top of the food chain—humans.
The greatest part of human exposure to the listed POPs comes from the food chain. The contamination of food, including breast milk, by POPs is a worldwide controversy. In most of the world, breast milk is the sole source of food for most infants. Edible oils and animal products are most often involved in cases of POP contamination. Food contaminated by POPs can pose chronic health risks, including cancer. The long-term implications of low-level exposure are not known. There is controversy on this point within the scientific community. Some researchers are concerned that long-term low-level exposure to POPs may have more cumulative impacts because of their persistence. Others maintain that low-level exposures do not cause any risk, but these individuals do not engage the cumulative-risk concerns.
Vectors for food contamination by POPs occur through environmental pollution of the air, water, and soil or through the use of organochlorine pesticides. Food contamination by POPs can have a significant impact on food exports and imports. At the international level, limits for residues of persistent organochlorine insecticides have been established for a range of commodities. They are recognized by the World Trade Organization as the international reference in assessing nontariff barriers to trade. Because of this, international bodies are major players in the controversies over POPs.
Disposal of Persistent Organic Pollutants
Most countries are facing the problem of disposal of some remaining POPs. This is a large controversy because of the cost of such disposal and the environmental and public health risks of not implementing it.
The strict requirements for proper disposal of these chemicals create an enormous burden for a developing country and its industries, both economically and technologically. Legal aspects of transboundary movement of POPs are very specialized and timeconsuming. The temptation to dispose of POPs illegally can be strong.
Do Persistent Organic Pollutants Ever Degrade Naturally?
There have been recent claims that POPs can degrade naturally. Some say it is a type of bioremediation. If this is the case, the cost of cleanups decreases dramatically because POPs can be left to degrade in place. Environmentalists generally prefer bioremediation because it usually has lower environmental impacts.
The controversy over whether POPs can be naturally degraded by microbial action is a long-standing one. New research indicates that this occurs for DDT. Research also indicates that naturally occurring organisms in sediments play an important role in breaking down the chlorinated compounds. The finding that DDE, a toxic by-product of the pesticide DDT, can naturally degrade comes from laboratory experiments performed by researchers from Michigan State University’s Center for Microbial Ecology. They used marine sediments collected from a Superfund site off the coast of southern California. Their research samples came from the Palos Verdes Shelf, the subject of one of the largest Natural Resources Damage Assessment cases in the United States. More than 20 years after they were deposited, DDT compounds are still present in surface sediments at levels harmful to life. But according to the Michigan State University microbiologist, the experiments do not prove that dechlorination is taking place at a significant rate in the sediments at the site. They do demonstrate that there are sediment microbes that can dechlorinate what was previously considered a terminal product.
The EPA’s most likely plan for the Superfund site is to cover part of the ocean floor with a cap of thick sand, a project that could cost as much as $300 million.
The POPs list is likely to expand as our use and knowledge of them increases. So too will the list of potential alternatives to some POPs. Eliminating them from food chains and human breast milk will be a big first step when it eventually happens, but other more inclusive policy approaches will be more controversial. Waste disposal, bioremediation, cost of cleanup and who pays for it all remain debated and growing areas of environmental policy. The main front for the POPs controversy will remain the international environmental community in the form of treaties and international bodies like the United Nations. The issue of mandatory disposal is an emerging one and could shape the cleanup policies of hosting countries. Environmentalists fear an increase in illegal ocean dumping.
Robert William Collin
- Bargagli, Roberto, Antarctic Ecosystems: Environmental Contamination, Climate Change, and Human Impact. New York: Springer, 2005.
- Downie, David, Northern Lights against POPs: Toxic Threats in the Arctic. Montreal: McGill-Queen’s Press, 2002.
- Fiedler, H., ed., Persistent Organic Pollutants. New York: Springer, 2003.
- Hanson, Larry G., and Larry W. Robertson, PCBs: Human and Environmental Disposition and Toxicology. Urbana: University of Illinois Press, 2008.
- Harrad, Stuart, Persistent Organic Pollutants: Environmental Behaviour and Pathways of Human Exposure. New York: Springer, 2001.
- Johansen, Bruce Elliott, The Dirty Dozen: Toxic Chemicals and the Earth’s Future. Westport, CT: Praeger, 2003.
- Mehmetli, Ebru, and Bogdana Koumanova, The Fate of Persistent Organic Pollutants. Dordecht: Springer Science/Business Media, 2007.