What are Polychlorinated Biphenyls?

Polychlorinated Biphenyl (PCBs) are mixtures of various isomers based on biphenyl. There are 209 individual possible PCB variants (also known as congeners). PCBs belong to a group of harmful persistent organic pollutants (POPs) that are toxic and last a long time in the environment and animals. It bioaccumulates through the food chain and poses a risk of causing adverse effects to human health and the environment. They are listed under the Stockholm Convention on Persistent Organic Pollutants for phasing out and eventual elimination.

PCBs are odourless, tasteless, and range from clear to pale yellow in colour (highly chlorinated mixtures are more viscous and deeper yellow). They are produced by reacting biphenyl with chlorine gas. PCBs don’t dissolve well in water and don’t easily evaporate at room temperature, but they dissolve in organic solvents, oils, and fats. They are very stable, resistant to breakdown by chemical reactions, and have properties like high thermal conductivity and high flash points (170 to 380 °C). PCBs are also very dense, ranging from 1.182 to 1.566 kg/L. Other physical and chemical properties vary widely across the class. As the degree of chlorination increases, melting point and lipophilicity increase, and vapour pressure and water solubility decrease.

What are Polychlorinated Biphenyls used for?

PCBs were used as coolants and insulating fluids (transformer oil) for transformers and capacitors, like those in old fluorescent light ballasts. PCBs were also used as plasticisers in paints and cements and as stabilisers in flexible PVC coatings for electrical wiring and electronic components.

Other uses included:

Carbonless copy ("NCR") paper

Extending pesticides

Cutting oils

Reactive flame retardants

Lubricating and hydraulic oils

Sealants (for caulking in schools and commercial buildings)

Adhesives and wood floor finishes

Paints and de-dusting agents

Waterproofing compounds

Casting agents

Vacuum pump fluids

Fixatives for microscopy

Surgical implants

Polychlorinated Biphenyls Hazards

PCBs entered the air, water, and soil during their production, use, and disposal. They also leaked during transport from spills or fires in products containing PCBs. Even today, PCBs can be released from hazardous waste sites, improper disposal of industrial and consumer products, old transformers, and waste incineration. PCBs don’t break down easily, so they stay in the environment for a long time. They can travel long distances in the air and end up far from where they were released. In water, a small amount dissolves, but most PCBs stick to organic particles and sediments. PCBs also bind strongly to soil. They accumulate in small organisms and fish, which are eaten by larger animals, leading to high levels in the food chain.

Sources of exposure

• PCBs are no longer produced or used in new products, but air exposure comes from the redistribution of existing PCBs in soil and water. Small amounts can still be released from disposal sites, incineration, and improper dumping.
• PCBs have been found in indoor air, especially from older appliances like fluorescent light ballasts that contain PCB components.
• In the past, PCBs were released into wastewater. Today, they still persist in water, mainly bound to soil and sediments, slowly releasing over time and entering the food chain through aquatic organisms.
• PCBs have been detected in food, especially in fish, due to bioaccumulation through the food chain.
• PCBs are a pollutant of concern because they persist in the environment, build up in living organisms, and are toxic.

Routes of Exposure

The main ways people are exposed to PCBs are:

Skin or eye contact

• Inhalation
• Skin absorption
• Ingestion

Health Effects

Acute Effects

There are no reports of short-term (acute) effects in humans from PCB exposure. In animals, studies show that acute PCB exposure can affect the liver, kidneys, and central nervous system (CNS). Tests on rats show moderate acute toxicity from oral exposure to PCBs.

Chronic Effects

Long-term (chronic) exposure to PCBs in workers has been linked to respiratory issues like cough and chest tightness, digestive problems like weight loss, nausea, and stomach pain, mild liver effects, and skin or eye issues like chloracne, rashes, and irritation. The EPA has not set a Reference Concentration (RfC) for all PCB mixtures. However, for Aroclor 1016, the Reference Dose (RfD) is 0.00007 mg/kg/d, based on reduced birth weights in monkeys, and for Aroclor 1254, it is 0.00002 mg/kg/d, based on immune system effects in monkeys.

Reproductive/Developmental Effects

A study of women exposed to high levels of PCBs at work suggested a possible link between PCB exposure and lower birth weights and shorter pregnancies, though the study had limitations. Two studies on women who ate fish contaminated with PCBs showed possible developmental effects in their children, such as motor issues at birth, impaired memory, and reduced visual recognition. Evidence of PCBs affecting reproduction in humans is inconclusive. One study found no fertility issues in men exposed to PCBs at work, while another linked high PCB levels to reduced sperm motility in men with low sperm counts. In animals, PCB exposure has led to developmental issues like learning problems, immune impairment, liver damage, and thyroid changes. Reproductive effects, including decreased fertility and prolonged menstruation, were also noted in animal studies.

Cancer Risk

Human studies suggest a possible link between PCB exposure and liver cancer, but the evidence is inconclusive due to other factors and limited data. Animal studies show an increase in liver and thyroid tumours in rats and mice exposed to PCBs. While no animal studies have examined PCB inhalation effects, PCBs can be absorbed through inhalation, raising concerns about this exposure route. The EPA has classified PCBs as Group B2, meaning they are probable human carcinogens.

Polychlorinated Biphenyls Safety

First Aid Measures

Eyes: Rinse eyes with lots of running water for at least 15 minutes if liquid or solid PCBs get in them.

Skin: Remove contaminated clothing and wash skin thoroughly with soap and water. Hot PCBs may cause burns.

Inhalation: Move to fresh air. If a rash or breathing problems continue, see a doctor. (PCBs may release hydrochloric acid if electrical equipment arcs over.)

Ingestion: See a doctor. Do not induce vomiting or give oily laxatives. (If large amounts are swallowed, gastric lavage may be necessary).

Polychlorinated Biphenyls Safety Handling

Prevent PCBs from leaking, spilling, or evaporating into the environment. Avoid breathing vapours or mist and avoid contact with eyes and skin. Follow all local, state, and federal regulations.

Other Precautions

PCBs, PCB-containing items, storage areas, transformer vaults, and transport vehicles must be properly labelled according to federal regulations.

Ventilation

Use natural or mechanical ventilation to keep PCB exposure levels below safety limits.

Personal Protective Equipment

Respiratory Protection

Use OSHA-approved equipment if exposure levels are too high. Full-face equipment is recommended and can replace the need for chemical splash goggles or face shields. Follow the manufacturer’s guidelines for respirator use.

Protective Gloves

Wear chemical-resistant gloves to avoid skin contact.

Eye Protection

Use chemical splash goggles and ensure eye wash stations are available.
Other Protective Gear

Wear protective clothing and provide safety showers where skin contact is possible.

Regulations

United States

EPA: The Environmental Protection Agency limits PCBs in drinking water to 0.0005 mg/L. Any spill or release of 1 pound or more of PCBs must be reported to the EPA.

FDA: The Food & Drug Administration limits PCBs in infant food, eggs, dairy products, fish, poultry, and red meat to 0.2–3 parts per million (ppm). Many states also have advisories on consuming fish and wildlife due to PCB contamination.

OSHA: The Occupational Safety & Health Administration has established a permissible exposure limit (PEL) for PCBs of 0.5 mg/m3.

NIOSH: The National Institute for Occupational Safety & Health has set a recommended exposure limit (REL) for PCBs of 0.001 mg/m3.

Australia

Safe Work Australia: The eight-hour time-weighted average (TWA) exposure limit for PCBs (with 54% chlorine) is 0.5 mg/m³. A 15-minute short-term exposure limit (STEL) is 1 milligram of PCBs per cubic meter of air.

Drinking Water Guidelines: Australia has no established drinking water guidelines for PCBs.