What are POPs: Definition, Examples, and Consequences of Their Use

In a world ravished by multiple environmental problems (one more challenging than the next), we have to be fully aware of the dangers that we face and the solutions we have to lower the threat for future generations and ourselves. We have covered the use of harmful pesticides before, but today we will focus on a larger, more threatening picture: POPs. What are POPs? We will answer that question in the article that follows, focusing on offering a clear picture on the issue. Yes, POPs include pesticides, but there is more to them than we imagine.

What are POPs: Definition

what are pops bioaccumulation and travel

According to the European Commission and the EPA, POPs (Persistent Organic Pollutants) are toxic chemicals that harmfully affect human health and the environment around the globe. The full definition of the concept is as follows:

  • Persistent organic pollutants (POPs) are synthetic chemical substances that persist in the environment, bioaccumulate through the food web, and pose a risk of causing adverse effects to human health and the environment. This group of priority pollutants consists of pesticides, industrial chemicals and unintentional by-products of industrial processes.

The EPA also issues warning regarding the free travels of POPs. In other words, because they can travel by wind and water, most POPs generated in one country/region can and do affect people and wildlife far from where we use and release them.

One might underrate the severity of the POPs global problem by thinking that one cannot have an industry or an agriculture without some sort of pollutants. In addition, if these pollutants get safe storage, away from the population, then what is the true harm?

In order to answer this question, we will dismantle the definition above, and explain its main concepts.

  • Synthetic organic chemicals: Despite the apparent contradiction in terms such as “organic” and “synthetic”, POPs are, in fact, man-made.
  • Persistent in the environment: This means that their lifespan is incredible. It can take them decennia or even centuries to degrade.
  • Food chain bioaccumulation: As we mentioned before about bioaccumulation, it represents the build-up gathering over time of a chemical in a living creature. Usually, this happens when the organism processes the chemical faster than it can use it. Moreover, the build-up of a chemical can occur when the organism cannot metabolize the chemical (the sun is incapable to break the chemical down for the organism to use it in a healthy manner). From this point of view, POPs enter the natural food chain, infiltrating (via water, land, air etc.) into small animals, which are then eaten by larger animals.
  • Long-range transport leads: Since the POPs can travel all over the planet, they lead to global pollution.

Other Concerns Related to POPs

One of the biggest problems concerning POPs is that we have difficulties to establish that specific illnesses or diseases are directly attributable to the exposure to a specific Persistent Organic Pollutant or to a group of POPs. According to specialists, POPs seldom occur as a single compound.  Moreover, we have still too few individual field studies to provide compelling evidence of cause and effect in their own right. What we can prove, however, is the fact that, if we make tests, we will usually find POPs in organic tissues or environmental samples from different parts of the world.

What Are POPs: An Entire World’s Fight for Containment

One of the first major global actions to contain and control the dangers of POPs can be traced back to the Stockholm Convention, in 2001. Back then, the United States joined forces with 90 other countries and the European Community in a United Nations treaty regarding POPs. These countries agreed to reduce or eliminate the production, use, and/or release of 12 key POPs.

From that point on, many of the POPs on what is officially called “The Dirty Dozen” is no longer produced in the United States and many have been banned from other countries as well. Under the same Convention, countries also joined forces to achieve a scientific review process that has led to the addition of other 4 new POPs of global concern to the initial list of twelve.

As we can all easily figure out, although most developed countries have taken powerful measures to control POPs, many developing nations are just now at the beginning of the production, use, and release restraint process and procedures.

Of course, all these efforts matter. However, the world is not cured of POPs. Since they can (and are) everywhere, the people and the environment of one continent, for instance, can suffer the damages of the POPs that traveled by air or water from another continent.

What Are POPs: Classification and Examples

We said something about POPs and pesticides, but, as we mentioned, things got a lot trickier as of late. Before we get into the details of what happens today in terms of POPs, let us all look at the original Dirty Dozen.

The 12 POPs that have been recognized by the Stockholm Convention as causing adverse effects on the environment and in humans can be placed in 3 categories:

  • Pesticides: aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, hexachlorobenzene, mirex, toxaphene;
  • Industrial chemicals: hexachlorobenzene, polychlorinated biphenyls (PCBs); and
  • By-products: hexachlorobenzene; polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/PCDF), and PCBs.

Since we are not all chemists, we will focus on each of the 12 initial POPs and see what they are and how they can harm us and the environment we share.


These are the original eight pesticides included on the Dirty Dozen list. Unfortunately, some trace amounts of them can be found today as well.

  1. ALDRIN: Soil pesticide against termites, grasshoppers, corn rootworm, and other insect pests. It can also kill birds, fish, and humans. It reaches human organisms mostly through dairy products and animal meats.
  2. CHLORDANE: Soil pesticide against termites and broad-spectrum pesticide for agricultural crops. It can kill several types of fish and birds. It can attack humans (as a carcinogen) as it is airborne.
  3. DDT: Residual DDT has even been detected in the Arctic, even if we do not use it anymore for more than 60 years. The infamous pesticide is one of the most toxic elements for animal and human life.
  4. DIELDRIN: It controls termites and textile pests and it is deadly to fish and aquatic beings. It was also found in milk and dairy products consumed by humans.
  5. ENDRIN: Pesticide for cotton and grains crops’ insect pests. Also used for rodent control. It is highly toxic to fish. It can enter the human body through food.
  6. HEPTACHLOR: Used to kill soil insects and termites, malaria mosquitoes, crop pests and more. It is believed to be responsible for the decline of several wild bird populations across Canada and the US. It is considered a human carcinogen and was found in cattle consumed in the US and Australia.
  7. MIREX: Fire ants killer. Also fire retardant in plastics, rubber, and electrical goods. Classified as a human carcinogen when consumed via food (mostly meat, fish, and wild game).
  8. TOXAPHENE: Pesticide used on cotton, cereal grains, fruits, nuts, and vegetables. Also used as ticks and mites control in livestock. Highly toxic to fish. Labeled a human carcinogen.

Industrial Chemicals

Let us see the two industrial chemicals listed as the most dangerous POPs.

  1. HEXACHLOROBENZENE (HCB): This compound was used as an agricultural fungicide in the past. In 2001, when the Stockholm Convention gained effect, HCB was also a byproduct of the manufacture of certain industrial chemicals. In some parts, it still exists as an impurity in several pesticide formulations. It caused illness and death in humans (subsequent to grain consumption) in between 1954 and 1959. According to studies, it is still present in food of all types in trace amounts.
  2. POLYCHLORINATED BIPHENYLS (PCB): Compounds used in industry as heat exchange fluids, in electric transformers and capacitors, and as additives in paint, carbonless copy paper, and plastics. Toxic and lethal for fish and marine wildlife. PCBs also suppress the human immune system and are listed as probable human carcinogens.

Unintended Synthetic Byproducts

We finish our Dirty Dozen list with the last two items: the unintended industrial byproducts.

  1. POLYCHLORINATED DIBENZO-P-DIOXINS (PCDD): All 75 different dioxins are produced unintentionally as a consequence of incomplete combustion, as well as during the manufacturing of pesticides and other chlorinated substances. They come from the burning of hospital waste, municipal waste, and hazardous waste, and also from automobile emissions, peat, coal, and wood. Classified as probable human carcinogens and causing a wide area of human diseases.
  2. POLYCHLORINATED DIBENZOFURANS (PCDF): They come from the main sources of PCDD and the production of the PCBs mentioned above. There are 135 different types of PCDFs with variable toxicities. They are classified as possible human carcinogens. Found mostly in food (animal products).

POPs: A Newer List

what are POPs a newer list

As of six years ago, the Stockholm Convention list of POPs got new “dirty” members. The new dangerous chemicals added to the EU Regulation on POPs have already been subject to prohibition or severe restrictions in the EU. If the original POPs were mainly pesticides, today, some of the new substances include products that have been widely used in consumer items. For instance, perfluorooctane sulfonic acid (PFOS) is found in metal plating and firefighting foams but also in stain repellents. The new substances include wastes of modern industrial manufacturing processes and a wide variety of ether products. The amendments to the Stockholm Convention enlarged the list up to 22 POPs in 2011.

What are POPs: Consequences on the Environment and Human Life

When it comes to the environment, POPs are responsible for prolonged water, soil, and air pollution. Many of the POPs listed by the Stockholm Convention are still here, even if they were used decades ago.

According to EPA and EU studies, POPs exposures lead to the declines, diseases, or abnormalities in a number of wildlife species, including certain kinds of fish, birds, and mammals. It seems that aquatic wildlife is the most vulnerable population. When it comes to marine mammals, immune dysfunction seems to be a plausible cause for the increased mortality among this population. Seals that consume POPs contaminated fish experience vitamin and thyroid deficiencies, paired with increased susceptibility to microbial infections, reproductive disorders, and death.

Naturally, what impacts animals and crops, also impact humans. In people, the exposure to and indirect consumption of POPs may lead to reproductive, developmental, behavioral, neurologic, endocrine, and immunologic adverse health effects. As we described above, many of the old and new POPs are also on the list of probable human carcinogens.

Moreover, both in mammals and in humans, POPs travel through the placenta and breast milk to developing offspring. We should also note that some populations on the globe present more risks of being exposed to POPs than others are. We are talking about people whose diets include large amounts of fish, shellfish, marine animals, birds or wild foods that are high in fat and locally obtained (from this point of view, Alaska and many African regions present higher risk levels).

The Influence of Climate Change on POPs: A Current Perspective

When we talk about POPs nowadays, we cannot exclude climate change from the equation. Even if many of the substances discussed earlier were banned, the world still produces new POPs, while the old ones still exist in amounts that cannot be neglected. Given these premises, researchers began to study the impact of present climate changes on the transport and behavior of POPs.

According to studies conducted between 2008 and 2011, researchers found that environmental variables (temperature, wind speed, precipitation, and solar radiation) had a direct and indirect influence on POPs’ environmental fate and transport. Their conclusions do not have the power of reassuring us that everything was going to be fine. In fact, the bottom line is that

climate warming is likely to influence the environmental behaviour of POPs by enhancing the volatilisation from primary and secondary sources, by influencing their partitioning between soil, sediment, water and atmosphere, including air–surface exchange, wet/dry deposition, and reaction rates. Climate change also encompasses the alteration of other important processes that influence POPs’ fate and transport, such as snow and ice melting, biota lipid dynamics, and organic carbon cycling, changing chemicals’ fugacity capacity in environmental compartments. Moreover, climate variability may induce inter-annual variations of POPs’ re-volatilization that could undermine global efforts aimed at reducing environmental and human exposure to POPs.

What Can We the People do about POPs?

what are POPs conclusion

The easiest answer here is making an effort towards a cleaner, safer life. Using natural weed killers instead of chemicals can be one first step out of many. Replacing chemical pesticides with organic ones is the next. Recycling, switching to alternative fuels and being mindful and fully aware that everything we produce may harm our children. We can do a lot, in fact: study about POPs and their potential threats; recognize the importance of exposure to POPs for humans and the environment; advocate for the protection of future generations; learn and educate others.

What did you know about POPs until now? What measures do you take to prevent the damage they cause?

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William E. Eubanks

I'm one of the main writers on the site; mostly dealing with environmental news and ways to live green. My goal is to educate others about this great planet, and the ways we can help to protect it.

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