PCBs - the Preamble

A mere three letters may not seem like much, but it can be packed with plenty of meaning. In this case, PCBs are the three letters synonymous with a presently challenging world issue: environmental contamination.

PCBs – polychlorinated biphenyls – are organic compounds which had been infamously employed in a variety of household and industrial products, including flame-retardant fabrics, insulating fluids, electrical coolants, plasticizers, old lighting fixtures, and carbonless copy paper. Due to the later concluded toxicity of PCBs, production was banned in 1977.

PCBs may have disappeared from North American manufacturing plants thirty years ago, but they still exist in our environment today. The stable nature of PCBs is what allows them to continually persist in the air, water, soil, animals, and even in our own bodies.

This site will help you discover the rich history and chemistry behind this seemingly simple three-letter-named compound: what they are, what they had been used for, why they had been banned, and where they are prevalent now.

Intro

What exactly are they?

PCBs, as they are commonly abbreviated, are a group of synthetic chemical compounds which formally stand for polychlorinated biphenyls. They belong to a class of organic compounds called chlorinated hydrocarbons.

Above: the structural diagram of polychlorinated biphenyls

These compounds can ONLY be prepared synthetically, when chlorine atoms attach to a biphenyl molecule (two benzene rings). Since up to ten chlorine atoms can be added to a biphenyl molecule in different configurations, there are as many as 209 possible compounds — 209 possible PCBs!

Their general molecular formula is C12H(10-n)Cln.


Also known as...
From a worldwide industrial standpoint, PCBs are more commonly identified by their trade names. Trade names include: Aroclor (United States), Asbestol, Plastivar, Pyralene (France), and Santotherm (Japan).

Above: Monsanto, a U.S.-based chemical
company, manufactured PCBs under the
trade name, Aroclor, from 1935 to 1977

Physical and Chemical Properties

In commercial uses, PCBs are often mixed with organic solvents such as chlorinated benzenes. Other mixtures also combine differently chlorinated PCBs together; each unique PCB component in a mixture is called a congener.

Physical properties
- density at 30°C = 1.4 - 1.5 g/mL (denser than water)
- low water solubility, but high solubility in organic solvents
- invisible vapour
- bitter odour
- high heat capacity
- slippery
- average boiling point for solid PCBs = 340 - 375°C
- most are liquid at SATP




Chemical properties
- flash point = 141°C
- non-corrosive
- low flammability, making PCBs non-explosive
- low conductivity, making them electrically insulating
- chemically stable and resistant to decomposition
- high thermal resistance: a temperature of 1200 °C is required in order to completely destroy them


Patterns of PCB properties
Lower chlorinated PCBs are thin, light-coloured liquids. As more chlorine atoms are added to the compound, the liquid becomes darker and more viscous. The highest chlorinated PCBs are yellow or black waxy solids.

PCBs with fewer chlorine atoms exhibit higher water solubility and greater flammability. They are also less stable and lipophilic. Monochlorinated and dichlorinated biphenyls are less hazardous than those with a higher degree of chlorination.

Impact on Society, Environment, and Human Health

Upsides to PCBs
Ever since its inaugural commercial production in 1929, the production of PCBs in the early twentieth century boomed like the Klondike Gold Rush. According to an American chemical engineer in the 1930s, PCBs were "as perfect as any industrial chemical can be." Why? Because of its convenient physical and chemical properties. As previously noted, this alleged ‘Wonder Bread’ of chemicals exhibits low flammability, low reactivity, and low electrical conductivity. PCBs also have a high heat capacity.

This set of handy characteristics therefore makes PCBs useful for all kinds of products. Up until 1977, PCBs had been widely sought after for residential, commercial, and industrial applications.

Below: an electrical transformer

Before PCB production was banned, you would've found them:
- as insulating fluids and coolants in heavy machinery, like electrical transformers, motors, and hydraulic systems
- thermal insulation material for fiberglass, felt, foam, and cork
- as plasticizers in paints, plastics, and rubber - pigments and dyes
- in carbonless copy paper (shown on the right)
- in fire-retardant materials
- in adhesives and sealants

More specifically, Askarel is a PCB-rich electrical insulating material which generates non-explosive gaseous mixtures when decomposed. Vintage fluorescent light ballasts (the electrical components at the end of fluorescent light fixtures, shown in the image below) may still contain PCBs.

Without PCBs, technological development in the 1920s and 1930s would have trudged at a much slower pace.

Nowadays, the products listed above are made with PCB-alternatives. These alternative chemicals will be covered in the next section.

Left: fluorescent light ballasts


But wait...
When something is described to be “perfect”, you know it’s too good to be true. The properties which make PCBs useful to society also make them dangerous for our health and the environment.

PCBs enter the environment in the form of landfill leachate, leakage from electrical transformers, or combustion gases during waste incineration.

The non-explosive properties of PCBs may work wonders for fire prevention, but their inability to biodegrade allows these compounds to spread through the atmosphere and waterways like forest fire. It’s estimated that 150 million pounds of it are dispersed in the natural environment. PCBs also last for a long period of time; their average half-life is eight to fifteen years.

If you also take into consideration the high solubility of PCBs in fats and oils, you’ll understand why they readily dissolve and settle in the fatty tissues of animals. Toxic effects on wildlife are the consequence.

In turn, when humans eat fatty foods like eggs, fish, and dairy products, bioaccumulation occurs, and PCBs end up being absorbed in our liver and adipose tissues. The provisional tolerable daily intake for PCBs, set by Health Canada, is 1 microgram per kilogram of bodyweight per day. In comparison, our average daily dietary intake of PCBs is just 0.5 micrograms, but there are still detectable traces of it in our bodies.


Human health effects
The International Agency for Research on Cancer ruled PCBs as “probably carcinogenic”. Significant research has also been conducted on the non-cancer implications of PCB exposure.

Here is a table I created to summarize the human non-cancer health effects:
One of the most notorious PCB-contamination incidents occurred in Japan in 1968; it’s now known as the “Yusho” incident. Rice bran oil contaminated with PCB fluids made 1,300 citizens ill. After ingesting 0.5 to 2 grams of this fluid, they developed severe skin eruptions, eye discharge, jaundice, and edema.

Although that incident happened halfway around the world over a century ago, the residents of the Great Lakes are facing a smaller scale of Yusho today. Research by the Great Lakes Centers showed that Great Lakes fish and their offspring have suffered health effects due to PCB-contamination. Thus, when residents at the top of the food chain consume fish such as carp and salmon, bioaccumulation occurs once again.

Right: chloracne, a severe skin
eruption associated with PCB
exposure

Above: bioaccumulation in the food chain

Now can't you see why PCBs had been banned?

Alternatives to PCBs

Replacement chemicals
PCBs had been on the market for over forty years before production had to cease. Since a total of 1.5 billion pounds of these compounds were produced in the U.S. alone, it was clear that many products relied on PCBs to run.

But don’t fret; manufacturers have been making use of the following chemicals as alternatives to PCBs. Alternatives vary depending on the products:
Limiting exposure to PCBs

The above alternatives may be critical in eliminating the future need for PCBs, but how do we deal with those already released into the environment or already made in products?

Unless your line of work requires you to deal directly with PCBs (shown on the left), you need NOT take such drastic measures as the person on the right!

Here are tips on how to reduce everyday contact with PCBs:
- never burn wood that has been treated or painted

- when consuming fish and other fatty foods, use cooking methods that retain as little fat in the animal as possible (baking or broiling)

- limit consumption of fish

- avoid going near transformers or capacitors as old ones may have remnants of PCBs

- when renovating your home, be informed about which chemicals are contained in your paints, sealants, and floor finishing

- access the external links on the left column for further information

The Verdict

I believe I speak for almost all of us when I say that it was a sound decision on the government’s part to ban this toxic chemical.

PCBs have certainly given rise to multiple technological advancements; their fluids initially served as plasticizers to thin paints and as dielectric fluids to generate transformers which provide us with power. But ultimately, what are the benefits to societal growth if it’s coupled with the decline of human health and the environment?

When PCB use became heavily controlled under Canada’s Environmental Contaminants Act, the world had already been hit hard by the effects of PCB contamination. You read about what had happened in Japan as well as the results from numerous medical studies (see the Impact section). What would a chemical as potent as that be doing in our everyday products?

If you still feel the industrial growth brought on by PCBs outweighs the damage that ensued, consider this: further developments in chemistry have ensured that PCBs could be replaced with less poisonous alternatives (see the Alternatives section). Banning this chemical will not affect technological progress - this family of organic compounds is now redundant in society.

Thankfully, production of PCBs has ceased, but it doesn't mean that we're shielded from their presence. In order to prevent further adverse effects on human health and the environment, we have to avoid (and in an ideal world, eliminate) the rest of the PCBs which still linger among us: the remnants of the early twentieth-century PCB boom.

Agree or disagree? Comment below.