What Are Persistent Organic Pollutants (POPs)? Definition, Examples, and Environmental Concerns

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POPs, or persistent organic pollutants, are toxic chemicals that accumulate and poison the environment. They include commonly recognized names like the pesticide DDT and the large group of industrial chemicals known as PCBs. 

The “O” in “POP” stands for “organic.” However, in a chemical context, “organic” does not mean “natural” or “relating to living matter.” As explained by the American Chemical Association, “organic chemistry” is the study of carbon-containing compounds. So, in this context, “organic” merely refers to presence of carbon in the pollutant. All POPs are synthetic. 

The "Dirty Dozen"

In 2001, the Stockholm Convention on Persistent Organic Pollution of the United Nation’s Environment Programme named 12 POPs that it recognized as toxic to humans and the environment. It took until 2004 for all member countries to ratify the list. The banned “dirty dozen” POPs are:

  • 8 pesticides. Aldrin, dieldrin, chlordane, DDT, endrin, heptachlor, mirex, and toxaphene
  • Industrial chemicals: HCB and the 209 PCBs
  • 2 by-products of industrial processes or burning: Dioxins and furans.

In 2009 the Stockholm Convention added another nine chemicals and chemical groups to the list. Some are currently found in popular cosmetics, lotions, and perfumes sold in the United States and Canada.

POPs Definition

The Environmental Protection Agency (EPA) and the World Health Organization (WHO) describe three qualities of POPs, which have been documented in a broad range of scientific studies. 

  1. They’re toxic to animals and humans, damaging nerves and nervous systems and causing immune system and cardiovascular diseases and cancers. They are also endocrine disruptors, either mimicking or blocking natural hormones enough to cause reproductive and developmental disorders. 
  2. With long half-lives, POPs resist environmental and biological forces that might otherwise break them down quickly. 
  3. They accumulate in the fatty tissues of humans and of the fishbirds, and animals that humans eat. In humans and possibly other animals, they can cross into the placenta, harming fetuses and embryos.

They are transported by wind and water around the world. Xu Baiqing, an environmental scientist at the Institute of Tibetan Plateau Research in Beijing explained to Nature.com that, because POPs are volatile, they tend to evaporate, get blown on wind, and then condense where the air is cool. This seems to have led to an accumulation of POS near Mount Everest, across the Himalayas, and on the plateaus of Tibet.

POPs can be created either intentionally or unintentionally. Pesticides and industrial products are the results of intentional creation. Combustion and industrial processes can unintentionally create persistent organic pollutants.

POPs History

POPs were produced plentifully in the United States in the 1940s, 1950s, and 1960s. In her exhaustively researched 1962 book, "Silent Spring," marine biologist and science journalist Rachel Carlson alerted the world to the environmental destruction and health devastation that POPs were causing.

Even though Carson drew on a wealth of studies published in reputable scientific journals, the chemical industry fiercely combatted her indictment of their highly profitable products, and they personally vilified her. Not knowing whom to trust, President John F. Kennedy asked the Life Sciences Panel of the President’s Science Advisory Committee (PSAC) to investigate Carson’s claims. Her allegations held up to scrutiny. As a result of the PSAC investigation, the EPA was formed in 1970 and the United States’ environmental movement was ignited. Then, in 1972, the widely used and exceptionally harmful POP pesticide DDT was banned.

Persistent Organic Pollutants List

Plantation spraying
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In 1995, the United Nations Environment Programme (UNEP) commissioned an assessment of an initial list of 12 POPs that scientific studies had identified as especially threatening. Within a year, the UNEP had proposed the Stockholm Convention on Persistent Organic Pollutants, a treaty that was adopted in May of 2001 and that went into force in May of 2004.

The Stockholm Convention mandated banning or phasing out of all twelve POPs. It has since been ratified by 184 countries. The 12 POPs, also called the "dirty dozen," are:

Pesticides

Aldrin and dieldrin. Developed as insecticides, from the 1950s until 1970 aldrin and dieldrin were used extensively on crops. Although in 1970 the U.S. Department of Agriculture prohibited that use, in 1972 the EPA approved the use of both pesticides against termites. That continued until 1987.

The compounds are structurally similar. Indeed, in the environment and in animal and human bodies, aldrin converts to dieldrin, which has a half-life of five years. Unfortunately, both compounds are highly toxic to birds, fish, aquatic animals like frogs, and humans.

They have been banned from use in the United States since 1987, though dieldrin residues can still be found in air, water, and soil throughout the world and at between 1/8 and 1/5 of the United States' most serious waste sites. 

Chlordane. A white solid that is a mixture of many chemicals, chlordane is a broad-spectrum insecticide that, from 1948 to 1978, was used in agriculture and on home lawns and gardens. Until 1988, it was also widely used in homes to kill termites.

Chlordane is lethal to some fish and birds and may be a human carcinogen. It can persist in soil for 20 years. All use of chlordane in the United States was stopped in 1988. 

DDT (chemical name dichlorodiphenyltrichloroethane). The first synthetic insecticide, DDT was widely used in World War II through 1972 to defeat disease-carrying insects like malaria and typhus. It was also used as an agricultural pesticide, primarily on cotton crops. In buildings, it was used for termite control.

During its decades of high use, DDT so effectively contained malaria outbreaks that its inventor was awarded a Nobel Prize. Meanwhile, however, birds of prey feeding on fish swimming in DDT-poisoned water began laying eggs with exceptionally thin shells that couldn’t hold and protect developing chicks. As a result, the bald eagle population quickly plummeted so much that the species was in danger of extinction

DDT is exceptionally effective in controlling the mosquitoes that transmit malaria. That is why, even though it was banned in the United States in 1972, in some countries it continues to be used.

Endrin. This is a close chemical relative to dieldrin and was used as an agricultural insecticide as well as a pesticide that killed rodents and birds. It is highly toxic to fish and persists in the environment for about 12 years. It has not been produced or used in the United States since 1986

Heptachlor. This is an insecticide with uses similar to those of DDT. Many scientists suspect that eating seeds contaminated with heptachlor decimated the Canadian geese and American kestrel bird populations in the United States. Most uses of heptachlor were banned in the United States by 1978, though until 2000 the insecticide was still being used to control fire ants in underground cable boxes.

Mirex. This is a broad-spectrum insecticide (fire ants, yellow jackets, termites, and mealybugs) that was also used as a fire retardant in household products. Having a half-life of about 10 years, it easily persists in soil and water, and can still be found in aquatic wildlife. The United States banned its use in 1977.

Toxaphene. A mixture of over 670 chemicals, toxaphene was first produced in the United States in the 1940s and was commonly used as an insecticide in the 1960s and 70s. It was even put into lakes to kill unwanted fish.

After DDT was banned in 1972, toxaphene became very popular. Though it was banned in the United States in 1990, some developing countries still manufacture and use it. Depending on the soil type and climate, the half-life of toxaphene ranges from 1-14 years. 

Industrial Chemicals

PCBs (polychlorinated biphenyls). This is a group of 209 industrial chemicals that were once intentionally produced and widely used as coolants. They were also integrated into certain paints and copy papers. They have proven toxic to fish and some mammals. In 1979, domestic manufacturing and use were banned. Still, some PCBs are inadvertently generated as byproducts of other manufacturing processes.

HCB (hexachlorobenzene). It was used in the United States until 1966 as a fungicide on seeds and to make fireworks, ammunition, and synthetic rubber. HCB is no longer manufactured or used in the United States but it remains a byproduct of the manufacture of some pesticides and solvents. It’s been classified as a possible human carcinogen.

Unintended Byproducts

Dibenzodioxins and dibenzofurans (dioxins and furans) are byproducts of combustion, chlorine bleaching of pulp and paper, and of the manufacturing of pesticides and some other chemicals. They are chemically similar to PCBs, and so have similar toxicity.

Efforts to Eliminate POPs

In 2009, the Stockholm Convention added another nine chemicals and chemical groups to the dirty dozen list. According to the Reuters news agency, some continue to have wide use as pesticides, as flame retardants, and in industrial processes. One, lindane, is used to treat head lice, though now it can only be purchased by prescription. Another is perfluorooctane sulfuric acid (PFOS), a flame retardant that is also used in making flat screens and semiconductors, and in ant and termite control.

Some of the new POPs can also be found in many popular cosmetics and personal care products. A June 2021 article by the Green Science Policy Institute described a study in which investigators found organic fluorine in 52% of 231 personal care products purchased in the United States and Canada.

Organic fluorine is an indicator of a class of chemicals called PFAS, which is persistent, organic, and toxic—and on the new dirty dozen list. According to the article, most of the waterproof mascaras, liquid lipsticks, and foundation products tested had significant concentrations of organic fluorine. For almost none of those cosmetics did the label clearly state that an organic fluorine was one of the product’s ingredients. The paper did not name specific manufacturers, brands, or product names.

Even without those names, the paper’s publication got the ball rolling on useful legislation. Very shortly after various news outlets started reporting the dangers that the Green Science Policy Institute article exposed, U.S. Senators Susan Collins (R-ME) and Richard Blumenthal (D-CT) introduced the “No PFAS in Cosmetics Act.” If passed by the Senate and House and signed into law, it would require the Food and Drug Administration (FDA) to ban the use of PFAS chemicals in cosmetics products and would also require websites selling cosmetics to include full labeling and product warnings. 

Swift action, however, may not be forthcoming. Since at least 2015, Senator Diane Feinstein (D-CA) has been introducing various pieces of legislation requiring cosmetics companies to register their facilities with the FDA and to clearly label their products. So far, her bills have not been signed into law.

In 2020, Governor Gavin Newsom of California signed legislation making California the first state to ban the use of PFAS and other toxic chemicals in cosmetics. Unfortunately, that law won’t go into effect until 2025. In June of 2021, Maryland banned the manufacture and sale of cosmetics and personal care products containing toxic ingredients.

According to the website of the nonprofit Environmental Working Group, an advocacy group of scientists, policy experts, lawyers, and communications and data experts, the United States as a whole is far behind Japan and countries of the European Union in banning harmful chemicals from personal products. “More than 40 nations—ranging from major industrialized economies like the United Kingdom and Germany to developing states like Cambodia and Vietnam—have enacted regulations specifically targeting the safety and ingredients of cosmetics and personal care products. Some of these nations have restricted or completely banned more than 1,400 chemicals from cosmetic products. By contrast, the U.S. Food and Drug Administration has banned or restricted only nine chemicals for safety reasons.”