⏳ Estimated Reading Time: 6 - 8 minutes

Describe the effects of persistent organic pollutants (POPs) on ecosystems.

Persistent Organic Pollutants

Approximately 70,000 chemicals are available for various uses and this number increases by about 1000 per year. About half, or 35,000, of these chemicals are classified as hazardous. Toxic wastes are categorized based on their ignitability, corrosivity, reactivity, or toxicity. Explore the chemical labels below. Have you ever seen any of these labels? Maybe in your school's chemistry lab?

There are three major categories of hazardous materials (HAZMAT): heavy metals, organic compounds, and radioactive products. All three of these types can persist in the environment for a very long time.

A person in full protective gear, including a white suit, goggles, and gloves, is spraying plants with a handheld device. — *Many first-generation pesticides were POPs*.

Persistent Organic Pollutants (POPs) are synthetic, carbon-based molecules that do not easily biodegrade (break down) in the environment. They are sometimes referred to as “forever chemicals” because they are resistant to environmental degradation through chemical, biological, and photolytic (light-involved) processes.

Before we get too far into this lesson, let’s break down the words used to label POPs. When you think of persistent organic pollutants, think of this:

Persistent - lasts for a LONG time in the environment without biodegrading
Organic - carbon-based compounds; can be synthetic (man-made)
Pollutant - an unwanted substance that can damage living organisms and/or the environment

Remember when we discussed the pesticide DDT? You know, the one that's also an endocrine disruptor? Yes, that one! Guess what? It's also a persistent organic pollutant! We've discussed several times how DDT can bioaccumulate in organisms and biomagnify up the food chain, causing a slew of effects in exposed organisms.

It turns out that this scenario was similar to many of the other “wonder chemicals” being used during the 1950s, 1960s, and 1970s.

Sources of exposure to Persistent Organic Pollutants (POPs):
Diet, Products, Work, Indoor, Air Water — *People can be exposed to POPs through all aspects of their daily life*.

Later, they were all found to be too dangerous to human health and ecosystems, so they were all banned, just like DDT. Pesticides such as aldrin, dieldrin, chlordane, endrin, mirex, heptachlor, toxaphene, and hexachlorobenzene were all banned due to their persistence and negative effects.

We also realized that some hazardous chemicals, such as dioxins and furans, are made when wastes are combined and/or through certain industrial processes.

Endocrine disruptors, like PCBs and hexachlorobenzene (HCB), are also POPs.

Essential Knowledge

Persistent organic pollutants (POPs) do not easily break down in the environment because they are synthetic, carbon-based molecules (such as DDT and PCBs).

Impacts of POPs

Below are a few of the impacts found to be associated with POPs. Open each tab to learn more about each impact.

🏥 Human Health (click to reveal)

The image features a doctor in a white coat and a patient engaged in a conversation. Clinical equipment and furnishings are visible in the background. — **POPs can cause a suite of negative health effects in humans.**

Persistent Organic Pollutants (POPs) can cause a myriad of health issues, such as...

- - - - cancer
      - immune system suppression
      - neurobehavioral impairment
      - endocrine disruption
      - reproductive disruption
      - increased risk of hypertension, cardiovascular disease, and diabetes

Phthalates have been linked to increased rates of preterm birth in non-white groups, likely caused by increased exposure to phthalates (Welch et al. 2023).

Studies indicate that children exposed to high levels of PFAS have a diminished response to vaccines (Grandjean et al. 2017).

Researchers have found that ordinary exposure to certain phthalates, as found in urine samples, was associated with ADHD-related behaviors in adolescence (Shoaff, et al. 2020).

🦅 Wildlife (click to reveal)

An osprey in mid-flight is captured with its wings spread, holding a large, silvery-scaled fish in its sharp talons. — **POPs can accumulate in organisms, magnifying up the food chain.**

POPs can accumulate in the bodies of animals, especially in their fatty tissues, causing...

- - - - reproductive disorders
      - developmental disorders
      - death

Researchers have found that male alligators in Florida lakes have been experiencing feminization, likely due to exposure to endocrine-disrupting contaminants (Guillette, et al. 2000).

In Silent Spring, Rachel Carson detailed how DDT caused a decrease in eggshell thickness in raptors, such as bald eagles and peregrine falcons (1962).

🥚 Environmental Persistence (click to reveal)

As discussed above, POPs can persist in the environment for long periods of time, resulting in long-term exposure risks.

🌎 Global Transport (click to reveal)

the movement of Persistent Organic Pollutants from various sources to the ecosystem. The sources labeled are Industry, Waste, Traffic, and Agriculture, which connect to three mediums: Air, Water, and Land. — *POPs can be transported to areas far away from where they originated through routes in air, water, or land*.

POPs can be carried for many miles and across many boundaries when they evaporate from water or land surfaces into the air, or when they adsorb to airborne particles. Then, they can return to Earth on particles or in snow, rain, or mist.

POPs can also travel through oceans, rivers, lakes, and, to a lesser extent, with the help of animal carriers, such as migratory species.

If these chemicals were not so persistent, they would break down quickly and not become transported by these processes. Because they ARE persistent, they have ended up in places where they have never been directly used, such as Antarctica.

This makes the issue with POPs a global issue.

Essential Knowledge

Persistent Organic Pollutants (POPs) can be toxic to organisms because they are soluble in fat, which allows them to accumulate in organisms' fatty tissue.

Persistent Organic Pollutants (POPs) can travel over long distances via wind and water before being redeposited.

Mitigating POPs

Needless to say, we have learned much about POPs since the 1950s. Perhaps because we were early manufacturers and users of POPs, the United States has taken the lead in trying to eliminate their use and release.

The Stockholm Convention on Persistent Organic Pollutants, adopted in 2001 and entered into force in 2004, is a global treaty whose purpose is to guard human health and the environment from highly harmful chemicals that persist in the environment.

One of the main reasons for the Stockholm Convention was the discovery of POPs in pristine areas of the world such as Antarctica. The reasoning was that if POPs could make it all the way to Antarctica, then they could clearly make their way all around the Earth. Studies show that native people who rely on aquatic species as their main source of food were especially at risk from exposure to POPs.

The Stockholm Convention is managed by the United Nations Environment Program (UNEP) and it prohibits trade in POPs chemicals for which involved parties have eliminated production and use. Such POPs may be exported only for environmentally sound disposal.

We have learned a lot through the production, use, and eventual banning of various POPs over the years. Chemicals used as insecticides and fungicides today are manufactured with the intent of biodegrading quickly after use. This quick biodegradation keeps them from biomagnifying in our food chain.

Hopefully, all POPs will eventually be banned from use all over the world.

AP Exam Tip

You should know that POPs have been found worldwide, far away from where they originated.

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