What are PCBs
Polychlorinated biphenyls (PCBs) are synthetic chemical compounds consisting of chlorine, carbon and hydrogen. First synthesized in 1881, PCBs are relatively fire-resistant, very stable, do not conduct electricity and have low volatility at normal temperatures. These and other properties have made them desirable components in a wide range of industrial and consumer products. Some of the same properties make PCBs environmentally hazardous — especially their extreme resistance to chemical and biological breakdown by natural processes in the environment. PCBs are also know by their various brand names which include Aroclor, Pyranol, Interteen, and Hyvol.
PHYSICAL PROPERTIES
PCB mixtures are usually light coloured liquids that feel like thick, oily molasses. However, some PCB compounds form sticky, yellow liquids or a brittle gum ranging in colour from amber to black. PCBs are soluble in most organic solvents but are most insoluble in water, so when added to it they sink to the bottom.
Most PCBs are non-volatile at normal temperatures (i.e., below 40 C). However, overheating of electrical equipment containing PCBs can produce emissions of irritating vapours. PCBs are completely destroyed only under extreme heat (over 1100 C) or in the presence of certain combinations of chemical agents and heat.
Where do PCBs come from?
Polychlorinated biphenyls (PCBs) are a prominent group of chemicals within a class of synthetic substances known collectively as chlorinated organic compounds. All of the PCBs that were produced in North America came from a single manufacturer, Monsanto Company in the United States.
How were PCBs used?
Commercial production of PCBs began in the United States in 1929 in response to the electrical industry’s need for a safer cooling and insulating fluid for industrial transformers and capacitors. This has been the major use for PCBs in Canada. Until other uses were banned in 1977 and 1980, PCBs were also used as hydraulic fluids; as surface coatings for carbonless copy paper; as plasticizers in sealants, caulkings, synthetic resins, rubbers, paints, waxes, and asphalts; and as flame retardants in lubricating oils.
What is the history of the PCB problem?
For the first 25 years of their use, few concerns were raised about any negative impacts of PCB compounds. In the late 1960s, however, the discovery of PCBs in birds in Sweden and the poisoning of 1200 people by rice oil containing PCBs in Japan both focused public attention on the problem. By 1972, scientific evidence suggested that PCBs posed a serious potential hazard to the environment and to human health. While both the manufacture and most non-electrical uses of PCBs were banned in Canada in 1977, the 1985 accidental spill of PCBs being transported near Kenora, Ontario, has again raised public concern – this time over the safe transport and disposal of this hazardous material.
How have PCBs entered the environment?
Ironically, one of the properties of PCBs which most contributed to their widespread industrial use – their chemical stability – is also one of the properties which causes the greatest amount of environmental concern. This unusual persistence coupled with its tendency to accumulate in living organisms, means that PCBs are stored and concentrated in the environment. This bioaccumulation raise concern because of the wide dispersal of PCBs in the global environment and the potential adverse effects they can have on various organisms, including humans.
What are the health effects of PCBs?
While there have been many laboratory experiments and other studies which have tried to determine the full health effects of PCBs on humans, none has been definitive. As a result, even expert opinion varies significantly on this subject. Scientists generally agree it is unlikely that serious injury would result from short-term low-level exposure to PCBs. However, most are concerned about possible adverse health effects of long-term exposure to even low concentrations of these substances. PCBs can enter the body through skin contact, by the inhalation of vapours or by ingestion of food containing PCB residues.
The most commonly observed health effect from extensive exposure to PCBs is chloracne, a painful and disfiguring skin condition, similar to adolescent acne. Liver damage can also result. People who might be exposed to PCBs include those servicing some types of electrical equipment, maintenance workers who clean up spills or leaks of PCB fluids, employees of scrap metal or salvage companies, and waste collection workers.
What are the substitutes for PCBs?
Safer alternatives have been found to take the place of PCBs in all their previous applications. As PCB-filled transformers come to the end of their service life, they are being replaced either with dry-type transformers (for smaller sizes only) or with transformers containing an approved dielectric fluid, such as silicone oils or transformer-grade mineral oil.
What safe destruction technologies are available?
Virtually everyone agrees that the only long-term solution to the PCB problem is to destroy the remaining volume of the chemical not yet dispersed in the environment. The best, most widely used and proven technology for destroying PCBs is high temperature incineration (greater than 1200 C for two seconds dwell time). Properly done, this has been shown to destroy PCBs at an efficiency of 99.9999 percent, leaving an inorganic ash. Smoke stack “scrubbers” are used to remove the hydrogen chloride gas and other compounds which can be formed as by-products of combustion.
Alternatives to incineration include chemical treatment for mineral oils to destroy low levels of PCBs and bacterial treatment. Chemical treatment methods are well developed and used commercially.
Taken from “The PCB Story,” Canadian Council of Resource and Environment Ministers, Toronto, Ontario, 1986.
