Issues
Some of the issues associated with the manufacture and use of chlorine compounds include:

· Mercury used in production
· Incineration of chlorine-containing materials
· Use of organo-chlorine products

Link each to appropriate sections below
Mercury

Currently about 60% of the chlorine manufactured in Europe uses mercury cells. In the 1970s levels of mercury in the environment were found to be unacceptably high, and mercury cells certainly made a contribution to this. Process improvements over the last 10 years have reduced mercury emissions by over 97%, and chlorine production now makes a very small contribution to mercury levels.

New chlorine production facilities are based on membrane cell technology, which does not use mercury and requires less energy. Mercury cells will be phased out as they reach the end of their working lives, or earlier if investment is available.

The chlorine producer Ineos Chlor makes 80% of UK chlorine at a plant in Runcorn, Cheshire. Over £50m is being spent on converting existing mercury cells to membrane technology.

Incineration

The presence of chlorine compounds in incinerated waste can result in the formation of highly toxic dioxins. Commercial incinerators operate under conditions that do not generate dioxins, but this is not true for accidental fires and bonfires. Research carried out in the UK has shown increased dioxin levels in the atmosphere of cities immediately following "Bonfire Night" (November 5th, a commemoration of the failed plot to blow up parliament in November 1605 celebrated with fireworks and the burning of an effigy of Guido "Guy" Fawkes, one of the conspirators).

diagram: dioxin structure

Disposal is a particular issue for poly(chloroethene) (PVC). Find out more about this by clicking here.

Organic Chlorine Compounds

Mercury and dioxins are associated with chlorine production and use. There are also several manufactured chorine compounds that have been regarded as potential sources of environmental problems. This includes the pesticide DDT, and chlorinated fluorocarbons (CFCs) used as a propellant and coolant Click the links to find out more.
Natural Chlorine Compounds

The oceans contain huge quantities of the element chlorine as the chloride ion, and it is an essential component in the human body. Up until very recently, however, it was a widely held belief (even among the scientific community) that all or most organochlorine compounds detected in the environment were the result of human activity ("anthropogenic" in source).

In fact some 2000 naturally occurring organic chlorine compounds have been identified, and many of these are produced by living organisms. Analysis of stored soil samples also shows that many of these were present in the environment before the chemical industry arrived.

This would indicate there must be a "chlorine cycle" and reactions by which these materials can degrade.

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