Polychlorinated biphenyl

Polychlorinated biphenyls (PCBs) are a group of chemical compounds that were once commonly used in many industrial and electronic products. They were used to make carbonless copy paper, as fluids that transfer heat, and as materials that prevent electrical shocks and help cool equipment. However, PCBs are very harmful to living things and can cause cancer.

Because of their danger to the environment and human health, the production of PCBs was banned in most countries. In the United States, the federal law stopping most uses of PCBs began on January 1, 1978. Even though they are no longer made, PCBs still exist in many places because they last a very long time.

Scientists have found that PCBs can cause cancer and harm the thyroid system and the brain. An estimated 1.2 million tons of PCBs were produced worldwide, and many of them still remain in soil, water, old products, and storage areas, continuing to cause health problems today.

Physical and chemical properties

PCBs are pale-yellow liquids that do not mix well with water but can mix with oils and fats. They do not easily evaporate at room temperature and can resist heat, acids, and other changes.

PCBs are made from a chemical called biphenyl, where some hydrogen atoms are replaced by chlorine atoms. There are many different types of PCBs, and they can be harmful to health in different ways. Some types act like harmful chemicals called dioxins, while others can affect nerves and hormones, especially in growing animals.

Mixtures and trade names

Commercial PCB mixtures were sold under different names in various countries.

Brazil used a mixture called Ascarel.

In the Czech Republic and Slovakia, the mixture was called Delor.

France used Phenoclor and Pyralène, both made by Prodolec.

Germany used Clophen, made by Bayer.

Italy used Apirolio and Fenclor.

In Japan, mixtures included Kanechlor by Kanegafuchi, Santotherm by Mitsubishi, and Pyroclor.

The Former USSR used Sovol and Sovtol.

The United Kingdom used Aroclor xxxx by Monsanto Company and Askarel.

In the United States, mixtures included Aroclor xxxx by Monsanto Company, Asbestol, Askarel, Bakola131, Chlorextol by Allis-Chalmers, Dykanol by Cornell-Dubilier, Hydol, Inerteen by Westinghouse, Noflamol, Pyranol/Pyrenol and Clorinol by General Electric, Saf-T-Kuhl, and Therminol FR Series by Monsanto, which stopped production in 1971.

Aroclor mixtures

The only producer in North America, Monsanto Company, sold PCBs under the name Aroclor from 1930 to 1977. These products had a four-digit number. The first two digits showed the product series, and the last two showed the percentage of chlorine in the mixture. For example, Aroclor 1260 is a 1200 series product with 60% chlorine. Aroclor 1016 was made by distilling 1242 to create a more biodegradable product. Different Aroclors were used for different applications and times. Before 1950, Aroclor 1260 and Aroclor 1254 were common in the US for electrical equipment. In the 1950s and 1960s, Aroclor 1242 was main but was replaced by Aroclor 1016 in 1971.

Production

One estimate from 2006 suggested that about 1 million tonnes of PCBs had been made. About 40% of this material was still being used. Another estimate put the total global production of PCBs at around 1.5 million tonnes. The United States was the largest producer, making over 600,000 tonnes between 1930 and 1977. Europe followed with nearly 450,000 tonnes up until 1984. It is unlikely that we will ever know the exact amount produced worldwide, as some factories in places like Poland, East Germany, and Austria made unknown amounts of PCBs. As of 2002, there were still 21,500 tons of PCBs stored in eastern Slovakia.

Although making PCBs on purpose is now banned by international agreements, research shows that about 45,000 tons of PCBs are still made each year in the US as part of certain chemical processes.

Commercial production of PCBs was banned in the United States in 1979, with the passage of the Toxic Substances Control Act (TSCA).

Applications

PCBs were useful because they are very stable and do not catch fire easily. They were used in many ways, especially in electrical equipment like transformers and capacitors, where they helped keep things cool and safe.

People also used PCBs in paper that made copies without extra carbon paper, in oils for machines, and in many products like paints, sealants, and finishes for wood floors. Even today, we can still find PCBs in old machines and electronic waste.

Environmental transport and transformations

PCBs have spread into the environment through how they were used and thrown away. Their journey around the world is very complex.

In water, PCBs mostly collect in the water world, the soil, and living things, including people. The oceans hold a lot of these chemicals, and as you go deeper, they become heavier and sink to the bottom.

A smaller amount of PCBs can be found all around the air we breathe. The air helps carry PCBs around the globe, especially certain types with fewer chlorine atoms. In the air, PCBs can break down due to sunlight or reactions with natural particles.

In living things, PCBs can be broken down by the sun, tiny living things, or cells in animals and plants, but how fast this happens depends on the PCB’s structure. They build up in living things over time, especially in animals higher up the food chain like humans or orcas, which can lead to big amounts collecting inside them.

Biochemical metabolism

PCBs are changed by the body to make them easier to leave the system. This process depends on how many chlorine atoms the PCBs have and where they are placed. Special enzymes in the body add oxygen to the PCBs, which helps them become more water-friendly and leave the body. Some types of PCBs are more likely to leave the body because of how their oxygen is added.

Different animals break down PCBs in different ways. For example, some sea turtles break down certain PCBs faster than others because of the enzymes they have. Temperature also affects how quickly fish like yellow perch can break down PCBs. In warmer water, they break them down much faster. Also, the gender of an animal can affect PCB levels, with females sometimes having lower levels because they pass PCBs to their young.

Health effects

The harm from these chemicals changes depending on the type. Some types act like a dangerous substance called dioxin and are among the most harmful. Because these chemicals are often found mixed together, scientists use a scale to help measure risk, with some types being more dangerous than others.

People mostly come into contact with these chemicals through food, especially fish, and it can also happen by breathing dirty air or touching contaminated soil. Once inside the body, these chemicals can stay for many years, building up in body fat. They can also move up the food chain, meaning animals at the top, like fish-eating birds, can have higher levels. Babies are exposed through their mother’s milk or while still inside the womb, placing them at the top of this chain.

High levels of exposure can cause skin problems and changes in blood and urine that suggest liver damage. One famous case happened in Japan where many people got sick after eating chicken fed with contaminated oil. Symptoms included skin sores, changes in menstrual cycles, weakened immune systems, fatigue, headaches, and unusual skin issues. Children born to mothers exposed to these chemicals may have trouble with thinking, learning, and controlling their movements. There is also concern that these chemicals can interfere with hormones, possibly leading to problems like certain cancers, though more study is needed. High levels have been linked to lower thyroid hormone levels, affecting many body functions.

History

In 1865, scientists discovered a chemical similar to PCBs as a byproduct of coal tar. Later, in 1876, a German chemist made the first PCB in a lab. Over time, a lot of these chemicals entered the environment, and we can still find them today in old museum bird feathers.

In 1935, a company called Monsanto Chemical Company began making PCBs for use in electrical equipment. They were used to cool and protect machines because they don’t catch fire easily. However, by the 1930s, people started to notice that PCBs could be harmful to health. There were reports of skin problems in workers and their families who came into contact with PCB-contaminated clothing.

In the 1960s, more information about the dangers of PCBs became known, but production continued. In 1966, a scientist in Sweden identified PCBs as a pollution problem. By the 1970s, many countries had stopped making PCBs because of concerns about their harmful effects on both people and the environment. Even though production stopped, PCBs still exist in some old electrical equipment and continue to be studied for their impact on our world.

Pollution due to PCBs

Belgium

In 1999, a problem happened when some old electrical equipment was added to animal feed. This affected farms in many places. The issue was thought to be one kind of chemical, but it was actually caused by another group of chemicals called PCBs. Many chickens and pigs had to be removed because of this.

Italy

A company in Brescia made these chemicals for many years. The area around the factory became polluted, with high levels of these chemicals in the soil and water. People living near the factory had higher levels of these chemicals in their bodies.

Japan

In 1968, a mix of harmful chemicals entered cooking oil in Kyushu, making many people sick. This was called Yushō disease. In Okinawa, very high levels of these chemicals were found at a military base.

Republic of Ireland

In 2008, Irish pork products were found to have very high levels of harmful chemicals. This was caused by contaminated feed used on some farms. The government asked that all pork products from Ireland be removed and disposed of.

Kenya

In Kenya, some people have been using stolen electrical equipment oil for frying food. This oil contains harmful chemicals and can be dangerous to health.

Slovakia

A chemical plant in Slovakia made these chemicals for many years, polluting a large area around it, especially a river and a lake.

Slovenia

A company in Slovenia made electrical parts using these chemicals. The area around the factory, including rivers, became very polluted. The soil and water there are still affected today.

Spain and Portugal

Some sea animals in the Mediterranean Sea and southwest Iberian Peninsula have very high levels of these chemicals in their bodies.

United Kingdom

A company in Newport, Wales, made these chemicals until the 1970s. Waste from the factory, including these chemicals, was dumped near Cardiff and is still being released into water.

United States

A company in the US stopped making these chemicals in 1977. In 2020, a court case involving this company and these chemicals continued.

Alabama

Chemicals from a factory in Anniston, Alabama, spread into local waterways. In the early 2000s, lawsuits were settled by local land owners affected by the pollution.

California

San Francisco Bay has been polluted by these chemicals, which are found in fish and shellfish. Signs warn people about which fish to avoid eating. Local governments are working to reduce these chemicals in runoff.

Connecticut

In New Haven, a closed factory has high levels of these chemicals in the soil and nearby river.

Great Lakes

In 1976, these chemicals were found in a harbor on Lake Michigan. By 1982, a company was ordered to share data about the waste they released. Much of the Great Lakes area remained polluted with these chemicals in 1988.

Indiana

From the late 1950s to 1977, a factory in Bloomington, Indiana, used these chemicals. Waste was dumped in local landfills and sewage systems, spreading the chemicals to many areas. Over 1,000 tons of these chemicals were estimated to have been dumped in Monroe and Owen counties.

Massachusetts

A factory in Pittsfield, Massachusetts, released these chemicals into local waterways. The area, including a river, was designated for cleanup in 1997. Another area in New Bedford Harbor also had high levels of these chemicals and cleanup began in 1994.

Missouri

In 1982, a company in Holden, Missouri, began processing waste containing these chemicals. The company stored the waste instead of disposing of it properly and falsified reports to authorities. The site became one of the largest waste sites for these chemicals in the nation. Cleanup efforts cost an estimated $35 million.

Montana

In 2023, two missile facilities at Malmstrom Air Force Base showed higher than recommended levels of these chemicals.

New York

The Hudson River was polluted by these chemicals dumped by a company from 1947 to 1977. The river, from Hudson Falls to New York City, was designated for cleanup in 1984. Another area in Niagara Falls, called Love Canal, was heavily contaminated with waste including these chemicals. An area in Lockport, called Eighteen Mile Creek, is also contaminated. In Binghamton, a building was heavily contaminated after a transformer explosion in 1981, keeping it closed for 13 years.

North Carolina

In 1978, a large amount of oil containing these chemicals was illegally sprayed along highways in North Carolina. The waste was later buried in a landfill in Warren County, which caused strong opposition from local residents.

Ohio

In Clyde, Ohio, these chemicals were found in soil in a public park within an area known for childhood cancers. In Akron, Ohio, soil and air were contaminated by an electrical transformer operation from the 1930s to the 1960s.

South Carolina

From 1955 to 1977, a factory in Pickens, South Carolina, used these chemicals and dumped waste into a local creek. In 2011, the first of two dams on the creek began to be removed. In 2013, state regulators banned the use of sewage sludge on land because it contained very high levels of these chemicals.

Washington

As of 2015, several bodies of water in Washington state were contaminated with these chemicals, including the Columbia River, Duwamish River, Green Lake, Lake Washington, Okanogan River, Puget Sound, Spokane River, Walla Walla River, Wenatchee River, and Yakima River. A study found that stormwater and municipal discharges were major sources of these chemicals in the Spokane River.

Wisconsin

From 1954 to 1971, a river in Appleton, Wisconsin, received these chemicals from several paper manufacturing facilities. Cleanup of the Fox River is ongoing.

Pacific Ocean

These chemicals have been found in tiny animals living in the Mariana Trench in the Pacific Ocean, with levels as high as 1,900 nanograms per gram of tissue.

Regulation

Many countries took steps to stop the use of harmful chemical compounds called PCBs. In 1972, Japan stopped making, using, and importing them. In 1973, Sweden banned PCBs in certain products like paints and adhesives. The United Kingdom followed in 1981 by stopping their use in new equipment. In the United States, laws were passed in 1976 to ban making PCBs, and rules were created to safely handle and dispose of them when they were still in use. These actions were taken because these chemicals were found to be very harmful to the environment and health.

Methods of destruction

PCBs are hard to break down because they do not catch fire easily and stay stable under many conditions. However, there are ways to safely destroy them.

One way is by heating them very hot, at about 1000 °C, which turns them into water, carbon dioxide, and hydrogen chloride. Another method uses special chemicals like glycols or sodium to break them apart. Some tiny living things, called microorganisms, can also help break down PCBs in soil, especially when helped by a small electric current. There is also research showing that certain fungi can break down PCBs as well.

Bioremediation

Cleaning up PCBs from river and coastal sediments is very hard because of the water above and the chance that harmful chemicals could spread during cleaning. One common way to remove PCBs is to dig up the area and move the dirt to a special landfill, but this can disturb the chemicals and harm nature.

A safer and cheaper method is called bioremediation, which uses living things to help clean the dirt. Scientists found that a type of seaweed called Ulva rigida, common in many parts of the world, can remove PCBs from sediments. During a bloom in New Bedford Harbor, this seaweed forms a thick layer that touches the sediment and can take in large amounts of PCB. In just 24 hours, the seaweed absorbed up to 1580 μg kg⁻¹ of PCB. Living seaweed took in more PCB than dead seaweed, but both types helped clean the area.

Homologs

Polychlorinated biphenyls (PCBs) have many different types, called congeners. There are 209 different PCB congeners in total. Biphenyl, which does not have chlorine, is often talked about with PCBs even though it is not a PCB congener.