Introduction

Persistent Organic Pollutants (POPs) are a group of toxic chemicals that can remain in the environment for long periods of time and travel long distances through the air and water. They are known to have negative impacts on human health and the environment. These chemicals were widely used in the past in agriculture, industry, and as pesticides, but their production and use has been restricted or banned in many countries due to their harmful effects. However, POPs can still be found in the environment due to their persistence and long-term effects.

What are the Sources of POPs?

There are several sources of POPs:

• Industrial sources: Many POPs were originally used as industrial chemicals, such as PCBs (polychlorinated biphenyls) which were used as coolants and lubricants in electrical equipment.
• Pesticides: POPs such as DDT (dichlorodiphenyltrichloroethane) and HCB (hexachlorobenzene) were used as pesticides in agriculture and for controlling pests in buildings.
• Incineration and other combustion processes: Dioxins and furans are produced as byproducts of certain industrial processes, such as the burning of certain types of waste.
• Natural sources: Some POPs can also be produced naturally, such as dioxins which are produced by forest fires and volcanic eruptions.
• Long-range transport: POPs can be transported long distances by wind and water currents, leading to their presence in remote areas far from their original source.
• Legacy sources: Even though their production and use have been banned, POPs can still be found in the environment due to their persistence and long-term effects, these chemicals can be found in soil, water and even in human blood and milk due to their accumulation in the food chain.

Health Impacts

Many POPs are fat-soluble, which means they can dissolve in fats and oils. Because of this property, they tend to accumulate in the fatty tissues of animals, including humans, rather than being excreted from the body. This is known as bioaccumulation.When animals consume food that contains POPs, the chemicals are stored in their fat cells. As the animal moves up the food chain, the POPs can accumulate in the fat cells of predators at higher levels than in their prey. This is known as biomagnification. This can lead to higher concentrations of POPs in animals at the top of the food chain, such as fish-eating birds, marine mammals, and humans who consume these animals as food.

The accumulation of POPs in the body can cause a range of health problems, including cancer, neurological disorders, and developmental problems. This is one of the reasons why POPs are considered to be so harmful to human health and the environment, and why efforts are being made to reduce and eventually eliminate their production and use.

Examples

Types of POPs

• DDT (dichlorodiphenyltrichloroethane) is a pesticide that was widely used in the past to control insects on crops and in homes. It was banned in many countries in the 1970s due to its negative impacts on wildlife, particularly birds of prey. DDT is a persistent chemical that can remain in the environment for long periods of time and can accumulate in the fatty tissues of animals, including humans.
• PCBs (polychlorinated biphenyls) are a group of industrial chemicals that were used in a variety of applications, including as coolants and lubricants in electrical equipment. PCBs are highly persistent and can remain in the environment for decades. They have been linked to a variety of health problems, including cancer and developmental disorders.
• Dioxins are a group of chemicals that are produced as byproducts of certain industrial processes, such as the manufacture of pesticides and the burning of certain types of waste. They are highly toxic and can cause a range of health problems, including cancer and developmental disorders.
• Hexachlorobenzene (HCB) is a fungicide and pesticide which has been banned in most countries, but it still present in the environment due to its persistence and long-term effects.
• Chlordane is a pesticide which was used in the past to control termites in homes and buildings. it has been banned in many countries, but it still present in the environment due to its persistence and long-term effects. All of these chemicals and many others have been identified as POPs, and international agreements such as the Stockholm Convention have been put in place to reduce and eventually eliminate their production and use. 

Transport of POPs

Some examples of the transport of POPs include:

1. Airborne transport: POPs can be transported through the air by wind and can travel long distances from their source. For example, DDT that was applied in agriculture in one country can be transported by wind and deposited in another country.
2. Waterborne transport: POPs can also be transported through water by rivers, oceans and currents. For example, PCBs that were released into rivers from an industrial facility can be carried downstream and deposited in the ocean.
3. Biomagnification: POPs can accumulate in the fatty tissues of animals and move up the food chain. For example, a bird that eats fish contaminated with POPs will have higher concentrations of POPs in its body than the fish did.
4. Long-range transport: POPs can be transported long distances by wind and water currents, leading to their presence in remote areas far from their original source. For example, POPs released in one continent can be transported by the jet stream and deposited on another continent.
5. Deposition: POPs can also be deposited on land and in water bodies, and can remain in soil and sediment for decades or even centuries.

Impacts of POPs

POPs have had a significant impact on the environment and human health:

1. Environmental impacts: POPs can have negative effects on wildlife, including birds, fish, and mammals. For example, DDT can cause thinning of bird eggshells, leading to decreased reproductive success. POPs can also accumulate in the food chain, leading to higher concentrations in animals at the top of the food chain.
2. Human health impacts: POPs can have a range of negative health effects on humans, including cancer, neurological disorders, developmental problems, and reproductive issues. For example, exposure to dioxins can increase the risk of cancer, while exposure to PCBs can cause developmental problems in infants and children.
3. Economic impacts: POPs can have significant economic impacts on industries that rely on natural resources, such as fishing and tourism. For example, the decline of fish populations due to POPs can lead to decreased income for fishermen and related industries.
4. Social impacts: POPs can also have social impacts, such as displacement of communities and loss of livelihoods. For example, if an agricultural community's crops are damaged by POPs, the community may be forced to move or to find new ways to make a living.
5. International impacts: POPs are not bound by national borders and can travel long distances through the air and water, which has lead to their presence in remote areas far from their original source. This makes it difficult to control and manage their impacts, and has led to the need for international cooperation and agreements, such as the Stockholm Convention, to reduce and eventually eliminate their production and use.

What is the Stockholm Convention?

The Stockholm Convention is a legally binding treaty that currently has 179 Parties (as of 2021), including the European Union. The Convention was adopted on May 22, 2001 and entered into force on May 17, 2004. It aims to eliminate or restrict the production and use of POPs, which are chemicals that remain intact in the environment for long periods, can travel long distances and can accumulate in the fatty tissues of living organisms, including humans.

The Convention includes a list of POPs that are banned or restricted for production and use, known as the "Annexes" of the Convention.

• Annex A includes chemicals that are banned for production and use, such as DDT, hexachlorobenzene, and polychlorinated biphenyls (PCBs).
• Annex B includes chemicals that are restricted for production and use, such as chlordane, dieldrin, and endrin.
• Annex C includes chemicals that are under review for possible inclusion in the future, such as PFOS (perfluorooctanesulfonic acid) and PFOA (perfluorooctanoic acid).

Under the Convention, Parties are required to take steps to eliminate or restrict the production and use of the chemicals listed in the Annexes, as well as to implement measures to manage and dispose of POPs that have already been released into the environment. The Convention also includes provisions for the sharing of information, technical assistance, and capacity building to help Parties meet their obligations.

The Convention is overseen by the Conference of the Parties (COP), which meets every two years to review and assess the implementation of the Convention and make decisions on any amendments or additions to the Annexes.

Specific World-Impacts of POPs

• DDT and birds of prey: The pesticide DDT was widely used in the past to control insects on crops and in homes. DDT is a persistent chemical that can remain in the environment for long periods of time and can accumulate in the fatty tissues of animals. DDT was found to cause thinning of bird eggshells, which led to decreased reproductive success and population declines in birds of prey such as the Bald Eagle, Peregrine Falcon, and Osprey in the United States and many other countries.
• Dioxins and Agent Orange: Dioxins are a group of chemicals produced as byproducts of certain industrial processes, such as the manufacture of pesticides. Dioxins were an ingredient of the defoliant Agent Orange, which was used during the Vietnam War. Exposure to Agent Orange has been linked to a range of health problems for veterans, including cancer and developmental disorders.
• PCBs and the Hudson River: PCBs are a group of industrial chemicals that were used in a variety of applications, including as coolants and lubricants in electrical equipment. PCBs were found to have been released into the Hudson River by two General Electric plants in the Hudson Valley. The PCBs have contaminated the river and its fish, leading to health advisories and restrictions on fish consumption.
• Chlordane and health problems: Chlordane is a pesticide which was used in the past to control termites in homes and buildings. It was banned in many countries due to its persistence and negative health effects. However, it can still be found in homes and buildings treated with the pesticide decades ago. Long-term exposure to chlordane can cause neurological effects, liver and kidney damage, and cancer.
• HCB and health effects: Hexachlorobenzene (HCB) is a fungicide and pesticide which has been banned in most countries, but it still present in the environment due to its persistence and long-term effects. Long-term exposure to HCB can cause liver and kidney damage, and cancer.