Persistent Organic Pollutants

Persistent Organic Pollutants are toxic synthetic organic chemicals that are used in industry and agriculture, as well as created unintentionally through chlorine combustion processes (EPA 2002). There are currently twelve of the most dangerous POPs under the scrutiny of the Stockholm Convention, a treaty signed by over one hundred countries and ratified by over fifty countries with the express purpose of eliminating these dangerous chemicals on a global scale. These twelve chemicals are adrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, toxaphene, polychlorinated biphenyls (PCBs), hexachlorbenzene, dioxins, and furans. (EPA 2002). POPs are particularly harmful because, by their nature, they are highly soluble in lipids, allowing them to accumulate in fatty tissues and thus biomagnify up the chain. This is why they are of particular threat to high level predators (including humans). They are also extremely resistant to biodegradation, and are able to travel through the atmosphere and be deposited far from their source regions (Ritter et al. 1995). POPs pose a particular threat to both wildlife and humans inhabiting Arctic and sub-Arctic regions because they are deposited in large quantities in polar regions as a result of global distillation (Ritter et al. 1995). Health issues associated with POPs in both humans and wildlife include immune dysfunction, thyroid and vitamin deficiencies, reproductive impairment, infant mortality, and deformities -- population declines in certain species have been observed as a result (Ritter et al. 1995).

What Are POPs?

Persistent organic pollutants are highly toxic synthetic organic (carbon-based) chemicals. These chemicals are fairly recent in their existence – it is only since the industrial boom following World War II that they have been produced on a large scale (EPA 2002).
There are three major reasons for the production of POPs:
1. Most are produced intentionally as commercial products, particularly pesticides. The most harmful pesticides include aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, and toxaphene (EPA 2002).
2. POPs are also produced for use in industrial processes, such as coolants for electrical transformers. This group includes polychlorinated biphenyls (PCBs) and hexachlorobenzene (EPA 2002).
3. The third category encompasses POPs that are produced unintentionally in industrial processes, as the by-products of the manufacture, use, or combustion of chlorine and chlorine-containing materials. This group includes dioxins and furans (EPA 2002).

These twelve chemicals in particular make up the “dirty dozen.” These are the most toxic known persistent organic pollutants, and pose the greatest threat to the global community. The dirty dozen have been targeted for the focus of the Stockholm Convention on Persistent Organic Pollutants. While many countries, including the U.S., have either banned or severely restricted the production and/or use of most of these chemicals, most of them are still in use in at least some countries. It is the goal of the Stockholm Treaty to reduce and eventually eliminate the use and production of these especially dangerous POPs on a global scale (EPA 2003).

Figure 2. Aldrin (UNEP nd).	Aldrin is a pesticide used to control soil insects such as termites, corn rootworms, wire worms, rice water weevil, and grasshoppers, and has been used on corn, potatoes, and wooden structures. The most common route of exposure for humans is food, particularly meat and dairy products. It is easily metabolized into dieldrin by both animals and plants. Aldrin has been banned in many countries, including the U.S. (Ritter et al. 1995).
Figure 3. Chlordane (UNEP nd).	Chlordane is a pesticide used on a wide array of agricultural crops including vegetables, small grains, maize, potatoes, sugarcane, sugar beets, fruit, nuts, cotton, and jute. It is also used to control termites. The most common route of exposure for humans is through air, because it partitions to the atmosphere readily. Chlordane has been banned or highly restricted in many countries (Ritter et al. 1995).
Figure 4. DDT (UNEP nd).	DDT is perhaps the most well-known POP, due to the discoveries of its detrimental impact on predatory birds in the late 1960s and its possible link to cancer. DDT was widely used during World War II to protect soldiers from malaria and typhus (carried by mosquitoes), and has been used to some extent as an agricultural pesticide, particularly on cotton. The most common route of exposure is food. Although DDT has been banned in 34 countries, and highly restricted in 34 more, it is still widely used in many countries for disease vector control (Ritter et al. 1995).
Figure 5. Dieldrin (UNEP nd).	Dieldrin is a pesticide that has been used for disease vector control. Although this use of dieldrin has been banned in many countries, it is still used for control of soil insects in agriculture, and textile pests such as termites. Its primary route of exposure is diet, particularly meat and dairy products, and it was the second most common pesticide detected in a survey of U.S. milk. It should be noted, however, that because aldrin converts so readily to dieldrin, the levels of dieldrin detected likely reflect both chemicals (Ritter et al. 1995).
Figure 6. Endrin (UNEP nd).	Endrin is a foliar pesticide used mainly on cotton and grains, and also as rodenticide for mice and voles. Although it has a tendency, as do all POPs, to accumulate in fat tissues, it does not do so to the extent that similar compounds do, because it is more rapidly metabolized by animals. However, it is still quite persistent in the environment, and given to long-range transport. Endrin is particularly toxic to fish, and its use has been banned or restricted in many countries (Ritter et al. 1995).
Figure 7. Heptachlor (UNEP nd).	Heptachlor is a contact insecticide used in combating soil insects, termites, cotton insects, grasshoppers, and malaria. Heptachlor has been correlated to a decline in populations of wild bird species such as the Canada goose and the American Kestrel. In both cases, heptachlor epoxide (heptachlor’s break-down product) residues were found in the brains of dead birds and in eggs with low success rates. Humans are primarily exposed to heptachlor through food. Its use has been banned or severely restricted in many countries (Ritter et al. 1995).
Figure 8. Mirex (UNEP nd).	Mirex is an insecticide used against fire ants, leaf-cutters, termites, and mealy-bugs. It has also been used as a fire retardant in plastics, rubber, paint paper, and electrical goods. Mirex is one of the most persistent pesticides. It is especially toxic to crustaceans, and is also classified as a possible human carcinogen. The main route of exposure is through food, especially meat, fish, and wild game (Ritter et al. 1995).
Figure 9. Toxaphene (UNEP nd).	Toxaphene is a pesticide used primarily on cotton, cereal grains, fruits, nuts, and vegetables, and to control ticks and mites in livestock. It was the most widely used insecticide in the U.S. in 1975. The main route of exposure is through food, although residue levels detected are typically below the maximum limit allowed. Toxaphene has been banned or severely restricted in many countries (Ritter et al. 1995).
Figure 10. PCB (UNEP nd).	Polychlorinated biphenyls (PCBs) are mixtures of chlorinated hydrocarbons, and have been used for industrial purposes such as dielectrics in transformers and large capacitors, as heat exchange fluids, as paint additives, and in plastics. There are 209 different possible PCBs. Those containing higher levels of chlorine are most toxic. Exposure to PCBs has resulted in acute dermal conditions, liver problems, and suppressed immune activity in humans and wildlife, even affecting children born years after the exposure occurred. Exposure is typically through food, especially fish. PCBs have been banned or severely restricted in many countries (Ritter et al. 1995).
Figure 11. Hexachlorobenzene UNEP nd).	Hexachlorobenzene (HCB) is used in industrial processes to make fireworks, ammunition, and synthetic rubber (EPA 2002). It is also a fungicide used in seed treatment, as well as an unintentional byproduct of the manufacture of some industrial chemicals. Ingestion of HCB-contaminated seeds in eastern Turkey between 1954 and 1959 resulted in serious dermal afflictions, debilitation, and the death of 14% of those affected, while infants born to mothers that had been exposed developed “pink sore,” and experienced a 95% mortality rate. HCB has been banned in many countries (Ritter et al. 1995).
Figure 12. Dioxins and Furans (UNEP nd).	Dioxins and Furans are very similar to each other in their composition and properties. There are many different isomers of both dioxins and furans and, like PCBs, the toxicity varies depending on the amount of chlorine present. Dioxins and furans are both produced unintentionally as byproducts of chemical manufacture and chlorine combustion; there is no commercial use for either of them. Dioxins and furans are also emitted through the burning of municipal and hazardous waste, coal, peat, and wood (Ritter et al. 1995).

Properties and Behavior of POPs in the Environment

There are three properties of persistent organic pollutants in particular that cause these chemicals to be so problematic in the environment. They are lipophilic, meaning they dissolve readily in lipids, and are not water soluble, causing them to accumulate in the fatty tissues of organisms (Ritter et al. 1995). POPs are also highly resistant to most forms of degradation, allowing them to persist in the environment for many years. The combination of these two properties allows POPs to biomagnify up the food chain; thus POPs pose an increased risk to top-level predators (Ritter et al. 1995). POPs are also often (though not always) halogenated – usually chlorinated. Organochlorines are a significant category of POPs, as this group contains nine out of the twelve POPs at the center of debate: dioxins, furans, PCBs, hexachlorobenzene, mirex, toxaphene, heptachlor, chlordane, and DDT (Ritter et al. 1995).

These halogenated chemicals are lighter in molecular weight than the other POPs, and are semi-volatile. This allows them to be transported through the atmosphere, far from their source regions (Figure 13). They often evaporate from hot equatorial regions (where they are used heavily in tropical agriculture and for disease vector control) and condense in cold regions. As a result, POPs are often found in unusually high concentrations in polar and sub-polar regions. This problem is compounded by the fact that environmental conditions in polar regions, such as the low level of biological activity, the lack of sunlight, and the cold temperatures, slow the breakdown of persistent organic chemicals even more (Ritter et al. 1995).

Effects on Wildlife

POPs have been associated with adverse health effects, particularly immune dysfunction, thyroid and vitamin deficiencies, reproductive impairment, infant mortality, and deformities, in a wide range of species at nearly all trophic levels (Ritter et al. 1995). Marine mammals such as the common seal, harbor porpoise, bottle-nose dolphin, and beluga whale of the St. Lawrence have suffered declines in population as a result of POP exposure (Ritter et al. 1995). Studies have also shown a direct cause and effect relationship between PCB exposure and health problems in minks and ferrets similar to those mentioned above (Ritter et al. 1995).

One specific area of concern is the Great Lakes region. Wildlife species in this region exhibiting an abnormally high incidence of tumors have, upon examination of carcasses, also demonstrated high concentrations of PCBs, mirex, chlordane, and toxaphene (Ritter et al. 1995). High levels of reproductive failure have been observed in many of the top-level predators of the Great Lakes. One example is the double-crested cormorant, which feed on fish from the Great Lakes. Having recently recovered from a disastrous population crash due to the effects of DDT, more subtle problems are now coming to light – chicks are being born with severe deformities, which begin in the egg; for instance, many cormorants are born “cross-billed” (Figure 14) and, unable to catch fish, die in several weeks. Other abnormalities include edema (swelling caused by excess fluid underneath the skin), missing eyes, dwarfed limbs, clubfoot, incomplete skulls, and internal organs developing on the outside of bodies, to name a few (Dunn 1998). The numbers of deformed chicks/embryos correlates directly to the levels of PCBs and dioxins found in the eggs (Dunn 1998).

Figure 14. Cormorant with cross-bill
syndrome (Dunn 1998).

Figure 15. Beluga whale (WWF 2004b).

As a result of global distillation (discussed in the Properties and Behavior section above, and illustrated in Figure 13), arctic wildlife is especially vulnerable to POPs contamination. Polar bears, residing at the top of the food chain and subsisting primarily on seal blubber, are more contaminated (especially by PCBs) than any other arctic species (Figure 16). The arctic fox, another top-level predator, is also highly contaminated as a species. According to data collected by the Norwegian Polar Institute, the levels of PCBs found in arctic fox carcasses in Svalbard spiked in 1991 and 1992, exceeding the levels found in polar bears (Figure 17). Arctic birds also contain high levels of pollutants, particularly PCBs and DDT. Birds that feed higher on the food chain, such as the Glaucous Gull, are more vulnerable to contamination than birds, such as the Eider duck, that feed on benthic organisms (Figure 18). These levels of contamination could have a serious impact on not only those species mentioned, but on the entire Arctic food web.

Figure 16. Concentration of PCBs in Polar Bears (Norwegian Polar Institute 2003).

Figure 17. Concentration of PCBs in Arctic Fox and Polar Bear (Norwegian Polar Institute 2002 a).

Figure 18. Concentrations of DDT and PCBs in seabirds (Norwegian Polar Institute 2002 b).

Effects on Human Health

While acute effects from exposure to high concentrations of POPs over a short period of time are well documented, it is much more difficult to correlate POPs exposure with illnesses resulting from chronic low-level exposure over an extended period of time. One reason for this is the broad range of environmental exposure both humans and wildlife face everyday – it makes it hard to pick out an exact cause and effect relationship (Ritter et al. 1995). However, there is evidence that long-term exposure to most POPs may result in immune deficiencies, dermal effects, reproductive impairment, neurotoxicity, behavioral abnormalities, and cancer (Ritter et al. 1995). The most common route of exposure to most humans is food intake. Also, women who have accumulated POPs in the fatty tissues of their bodies often pass these chemicals onto their newborns through breast milk (Greenpeace 1999). Indigenous populations inhabiting Arctic and sub-Arctic regions, especially those that rely on Arctic marine mammals as a major food source, are one of the most at risk groups for long-term POP-related illnesses (Arctic Council 2004). Figure 19 illustrates the levels of DDT and DDE (DDT's breakdown product, also highly toxic) found in the maternal blood plasma of people inhabiting several Arctic countries. According to this study conducted by the Arctic Monitoring and Assessment Programme (AMAP), DDE levels were highest among those inhabiting Greenland and the Canadian Arctic, while DDT levels were highest among those inhabiting northern Russia (Arctic Council 2004). Acute effects are similar to the long-term effects mentioned above, although acute exposure is far more likely to be immediately fatal. Those most at risk for both acute and chronic exposure are workers in close contact with POPs, particularly those involved in waste management, as well as farmers in developing nations, where persistent organic pesticides are used heavily in tropical agriculture (Ritter et al. 1995).

Figure 19. DDT and DDE Levels in Arctic Populations (Arctic Council 2004).

The Stockholm Convention is the most current and most important global agreement on the ultimate elimination of POPs – but is not the first action in this direction. The following is a brief timeline of steps taken to regulate POPs, leading up to the Stockholm Convention.

v 1979 – Member countries of the United Nations Economic Commission for Europe (UNECE) sign the Convention on Long Range Transboundary Air Pollution (LRTAP), initially aimed at acid rain prevention, but later including POPs (EPA 2002).

v 1989 – The Basel Convention, with the goal of reducing cross-border movement of hazardous waste, including POPs waste, is adopted (EPA 2002).

v 1991 – The eight arctic countries meet and create the Arctic Monitoring and Assessment Programme (EPA 2002).

v 1995 – The Inter-Organization Programme for the Sound Management of Chemicals released the POPs Assessment Report. Also in this year, the Commission for Environmental Cooperation (CEC) passes a resolution on the sound management of chemicals (EPA 2002).

v 1996 – The Intergovernmental Forum on Chemical Safety (IFCS) holds meetings in Manila, Philippines to discuss global actions on POPs (EPA 2002).

v 1997 – The UN Environment Programme organizes workshops to develop international strategies for eliminating POPs. Also in 1997, the U.S. and Canada develop an agreement for the elimination of POPs in the Great Lakes (EPA 2002).

v 1998 – Member countries of UNECE sign the Persistent Organic Pollutants Protocol under LRTAP. Also in 1998, the Rotterdam Convention on the Prior Informed Consent (PIC) Procedure for Certain Hazardous Chemicals and Pesticides in International Trade is signed (EPA 2002).

v 2000 – The UNEP POPs negotiations reach an agreement in Johannesburg, South Africa (EPA 2002).

The Stockholm Convention was finalized in Stockholm, Sweden on May 23, 2001, with 90 countries, including the U.S., signing the treaty (EPA 2002). After three years, it was finally announced in February of 2004, after France became the 50^th nation to ratify it, that the Stockholm Convention would become legally binding on May 17, 2004 (UNEP 2004). The key concepts and goals of the Stockholm Convention include:

1.) Eliminating intentionally produced POPs, beginning with the dirty dozen. Most of the pesticides on the list will be immediately banned once the treaty takes effect. Both PCBs and DDT will have a longer phase-out period. PCBs will be phased out by 2025, and DDT elimination will be determined by the availability of cost-effective, safe alternatives for disease vector control in certain countries (WWF 2004a).

2.) Ultimately eliminating by-product POPs. For now, member Parties will be called on to take measures to reduce emissions of dioxins, furans, and hexachlorobenzene, with the goal of eventual elimination (WWF 2004a).

3.) Transparency and public participation will be a major part of treaty implementation.

4.) Environmentally sound management of POPs wastes, including stockpiles, products, articles in use, and contaminated materials (WWF 2004a). See Tables 1 and 2 for more information about POPs waste disposal.

5.) Controlling POPs trade. Trade in POPs will only be allowed for the purpose of environmentally sound disposal, or in very limited special circumstances approved by the Convention (WWF 2004a).

6.) Allowing limited and transparent exemptions. Most exemptions will be country- and chemical-specific, although there are some broader exemptions for chemicals used in laboratory-scale research and closed-system uses (WWF 2004a).

7.) Funding for developing nations. The fulfillment of the Stockholm Convention will not be possible unless all nations have the resources to participate. Developing alternative technologies costs money; thus it is necessary for developed nations to fund transitional economies in achieving the obligations of the treaty (WWF 2004a).

8.) Adding new POPs to the treaty. The dirty dozen represent a starting point; new POPs will be evaluated based on rigorous scientific criteria by a POPs Review Committee. Chemicals found to be a global threat will be added to the treaty (WWF 2004a).

The Bush Administration

Although the Bush Administration signed the Stockholm Convention in 2001, Congress has still not ratified the treaty, and the U.S. has yet to become a Party to the treaty (over 50 other nations have already done so). Before Congress can ratify the treaty, it must first amend the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and the Toxic Substances Control Act (TSCA) to give the EPA the authority to ban or restrict domestic production, use, and export of POPs (WWF 2004a). Senators Chafee (R-RI) and Jeffords (I-VT) of the Environment and Public Works Committee proposed amendments to TSCA that would address the need for an effective adding mechanism for new POPs. The bill (S. 1486) was hindered by the Office of Management and Budget (OMB) and other officials of the Bush Administration (WWF 2004a). In addition, the Bush Administration, working with the House Agricultural Committee and chemical industry leaders, is in the process of drafting new FIFRA legislation that would make it harder, not easier, for the EPA to domestically regulate POPs and review new POPs for addition to the treaty. This new legislation would add cost-benefit analysis to the process, which would not only be cumbersome and time-consuming, but would also shift the basis for POPs regulation onto economics and profit, rather than environmental protection (WWF 2004a). The other nasty part of the Bush legislation is that it would forbid Congress from mandating the EPA or other agencies to act in response to international treaty events (WWF 2004a). This is a radical and unprecedented constitutional interpretation, and one that would have implications beyond just the POPs treaty.

Figure 20. President George W. Bush (BBC News 2003)

To view a list of signatories and parties to the Stockholm Convention, click here.

To visit the Center for International Environmental Law's POPs page, click here.

To view Greenpeace's map of toxic hotspots, click here, and then click the Toxic Hotspots button. The rest of the page is cool, too!

UNEP United Nations Environment Program, 2004. “Stockholm Convention on Persistent Organic Pollutants (POPs) to enter into force on 17 May 2004.” Retrieved 1 May 2004 from http://www.pops.int/.

USDA U.S. Department of Agriculture, nd. Online Photography Center Photo Research. "Pesticides." Retrieved 3 Feb 2004 from http://www.usda.gov/oc/photo/94cs3886.htm.