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