There is a lot of controversy around the manufacture and use of poly(chloroethene), PVC. Some would argue it is a very versatile and robust plastic that serves many useful purposes to enhance the quality of our lives, and there are few suitable alternatives. Others would argue the opposite - that its manufacture, use and disposal will continue to cause damage to human health and the environment, and it should be phased out completely.

The health and environmental aspects of PVC have therefore been more closely examined than perhaps any other plastic.

The Issues
Some concerns are related to the high chlorine content of PVC, and the implications for this in manufacturing and final disposal. Other issues are concerned not with the polymer itself, but with the additives used, in particular plasticisers and stabilisers.

Use the links below to find out more about some specific issues.

Chlorine is manufactured by the electrolysis of sodium chloride - this is why the first PVC manufacturing plants were sited close to natural sources of salt. For more details on the issues around chlorine use and manufacture, see the chlorine section.

Uncontrolled incineration of PVC (for example a building fire) will release hydrogen chloride and highly toxic dioxins. This only occurs because chlorine is present in PVC.

The burning of any carbon-based material commonly produces toxic carbon monoxide - this will include timber as well as polymers - and this is a more common source of poisoning than either hydrogen chloride or dioxins (dioxins are in any case usually adsorbed onto soot particles). Many commonly used materials (including timber) produce dioxins and other toxic products - wool, for example, produces hydrogen cyanide in a fire.

PVC has the particular advantage that it does not itself burn, but is charred by the heat of a fire. If there are no other fuels present, it will self-extinguish. This is one of its strengths when used as cable insulation, and in building construction.

Other issues related to chlorine and end-of-life disposal of PVC are discussed in the disposal section. and in the chlorine story.

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The chloroethene monomer (often referred to as VCM, vinyl chloride monomer) is a known carcinogen, and release of the substance occurs during PVC manufacture. Unreacted monomer is present in the polymer and so will also be present in the final PVC products, from which it may be slowly released.
Many hazardous materials are used in manufacturing, and employers have a statutory responsibility to protect their employees. Anyone knowingly exposing workers to unacceptably high levels of toxins would not stay in business very long! The carcinogenic effects of VCM are the result of long-term exposure to very high levels, and this has not been an industry issue since the early 1970s.The monomer left in the resin is present at no more than 0.1ppm (parts per million), or 0.00001%. VCM in the final products made from the resin is below detectable levels.

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Stabilisers are added to PVC (click here to find out more about additives). Lead and cadmium compounds have often been used because of the durability they impart to PVC products exposed to the elements, but concerns over their toxicity have been raised. Both are known to have serious effects if absorbed in sufficient quantity. The use of lead compounds is a potential hazard to employees at the manufacturing stage, and leaching can occur from flexible PVC products after disposal. Incineration of PVC-containing waste may also produce ash with a high heavy-metal content.

The evidence is that the stabiliser does such a good job that very little leaches from the plastic, even when it is buried in the ground. Lead-stabilised PVC is considered perfectly safe when used for buried water pipes.

In response to concerns the European industry has, however, phased out the use of cadmium (since 2001) and lead stabilisers are also being phased out (zero by 2015). They are not used in applications with a short life, for example packaging materials. More rapid phase-out is not possible, as new alternatives must be thoroughly tested in products. Replacements include other metal compounds like barium and zinc, but organic alternatives are also now in use.

Plasticisers make the PVC flexible, and although they are part of the plastic structure small amounts may leach out. One of the commonly used plasticisers is DEHP, and tests on rodents produced damage to kidneys, cancerous tumours, and affected general and reproductive development. This resulted in DEHP being classified as "possibly carcinogenic to humans" in 1982 by the World Health Organisation International Agency for Research on Cancer (IARC).

Most of the compounds used belong to a chemical group called phthalates. DEHP, (di-2-ethylhexyl)phthalate, is the most widely used. In the case of toys for children under 3 years old (and which are therefore likely to be chewed and sucked) di-isononylphthalate (DINP) is used instead, and the non-phthalate DEHA (di(2-ethylhexyl)adipate) is used for food contact products.

The relevance of the rodent tests to humans has been questioned. Very high doses were used, and further studies on the way different species react to DEHP suggest the results cannot be directly applied to humans. In particular, the mechanism by which the tumours formed in rodents could not occur in people. In 2000 the IARC reclassified DEHP as "not classifiable as to carcinogenicity to humans", and its use in medical tubing, blood bags and many other medical and non-medical applications continues.

diagram: structure of phthalates
The amount leaching from the plastic is an important issue, too. This must be kept low or the PVC will lose its flexibility, and manufacturing methods are constantly being improved to reduce further the proportion of plasticiser lost during use.

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It is a commonly held view that the high proportion of additives makes PVC almost impossible to recycle. This is not the case, and much recycling of manufacturing and bulk-packaging waste takes place. Domestic waste can be more difficult to recycle because of the need for plastic separation. This problem is not exclusive to PVC, but PET and PVC can be difficult to separate as they have similar densities.

For additional information on polymer recycling, click here.
The Australian recycling company, Cryogrind, separates PVC and PET by freezing the flaked polymers with liquid nitrogen at -40°C, when the PVC becomes very brittle, but not the PET. Grinding the flakes reduces the PVC to a powder, but leaves the PET intact, and the two can be separated using a sieve.

Simply melting and reforming PVC can result in a lower quality product. Solvay (Ferrara, Italy) have overcome this problem using a process in which the used PVC is ground, dissolved, filtered to remove impurities, and precipitated as pellets ready to be used again.

Some PVC-u window frames are made from recycled PVC with a layer of fresh PVC on the outside.
image: cross section of PVC-u window frame
There is a considerable quantity of rigid PVC currently in long-life applications, particularly in construction. At some time in the future this will begin to enter the waste stream. Landfill and incineration are the two usual methods of waste disposal and in the UK landfill is most common.
Increasingly, however, PVC is being recycled. This will become more important as quantities of PVC from long-life applications (windows, underground pipes) enter the waste stream.
Stabilised PVC will remain resistant to decomposition for 50 to 100 years - probably longer than the linings of the landfill (which are often made from PVC sheet!) used to limit leaching of decomposition products into water systems. On disposal, the properties that make it useful become a problem - it does not easily biodegrade. Leaching of additives may release heavy metals used in stabilisers, phthalates used in plasticisers and other substances into the environment.

PVC is recognised as not being a source of problems in landfill. Under the conditions of landfill neither hydrogen chloride nor the monomer (VCM) can be produced. Some additive leaching may occur, but levels are extremely low, presenting no hazard.

It must also be added that for PVC, like many other materials, landfill disposal is not the best environmental option. Carpets, tyres, fridges, electronic equipment and vehicles are all now subject to directives to keep them out of landfill. In all these cases some form of recycling is a much better option, and several PVC and recycling companies are actively pursuing this more sustainable route.

Chlorine is chemically bound to carbon in the polymer, but when the structure is broken up during incineration the strongly acidic gas hydrogen chloride is produced, which will rapidly dissolve in any available water to make hydrochloric acid. The combustion of a combination of hydrocarbons and chlorine is also known to result in the formation of toxic dioxins.
Chlorine is present in mixed waste from many sources other than PVC, and dioxins are as likely to be produced from these. Where incineration is used for waste, the temperatures used are sufficiently high to limit the formation of dioxins. Combustion gases must be "scrubbed" to remove any acidic content, and strict monitoring is in place. Research has shown that increasing the proportion of PVC in mixed waste has little or no effect on dioxin emission levels. Generally dioxin levels have fallen considerably, even though more PVC is present in the waste stream.

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