What effects can the Environment have on Health?

Introduction.This brief account can address only a small part of a vast and expanding subject. The environment in which we live can be considered as having three fundamental sets of components:
Physical [energy of one form or another]
Chemical [matter i.e. substances whether natural or man-made]
Biological [living things]. Hazards can present themselves to us in various media e.g. air, water. The influence they can exert on our health is very complex and may be modulated by our genetic make up, psychological factors and by our perceptions of the risks that they present. The following deals with general environmental health hazards, and not extremes of climate, occupational hazards, hazards associated with food, most "accidents" or sexually transmitted disease. Health effects from economic and social consequences of environmental change are also not considered here.
Associations between an exposure and an adverse health effect do not, on their own, prove that the former is the cause of the latter. Many other non-causal associations could explain the findings. These concerns explain why the language in this context may well be "hedged" even though you might have formed impressions from other sources that some postulated causal associations had been proven.
Physical Hazards, and their Adverse Health EffectsAlthough you will have heard or read a great deal about the environmental consequences of global warming, man will probably be affected through famine, or war long before the health of the population as a whole is harmed to a serious degree by the temperature change. However increasing extremes of temperature, as a result of climatic change, could result in increased mortality even in temperate climates.
Important issues concerning physical hazards include those relating to health effects of electromagnetic radiation and ionising radiation. If one excludes the occupational environment, then noise and other physical hazards may present a nuisance to many inhabitants, and impair general well being. Environmental noise does not usually contribute to deafness but notable exceptions may include noisy discotheques and "personal stereos".
Electromagnetic radiation ranges from low frequency,relatively low energy, radiation such as radio and microwaves through to infra red, visible light, ultraviolet, X-rays and gamma rays. These last as well as other forms of radioactivity such as high energy subatomic particles (e.g. electrons - Beta rays) can cause intracellular ionisation and are therefore called ionising radiation. Exposure to ultraviolet (UV) radiation carries a increased risk of skin cancer such as melanoma, and of cataracts which are to an extent exposure related. Some pollutants such as chlorofluorocarbons (CFCs) used as refrigerants or in aerosol propellants or in the manufacture of certain plastics can damage the "ozone layer" in the higher atmosphere (stratosphere) and thus allow more UV light to reach us, and harm us directly. Ultraviolet light may also cause harm indirectly by contributing to an increase in ozone in the troposphere (the air we breathe) - see below under chemical hazards, or elsewhere in connection with air quality.
Radioactivity is associated with an exposure dependent risk of some cancers notably leukaemia. Contrary to popular belief however, most radiation to which the average person is exposed is natural in origin, and, of the man made sources, medical diagnosis and treatment is on average the largest source to the individual. A very important issue is the extent to which radon gas arising from certain rock types beneath dwellings can contribute to cancer risk. According to some estimates it could result in a few thousand cancer deaths per year in the U.K. (but still probably less than one twentieth of the cancer deaths alone caused by tobacco smoking).
Ionising radiation from the nuclear industry and from fallout from detonations contributes less than 1% of the annual average dose to inhabitants of the U.K. The explanation for leukaemia clusters around nuclear power plants is not yet resolved. Similar clustering can occur in other parts of the country. The effect of viral infections associated with population shifts may be important but requires further study.
Non ionising electrical, magnetic or electromagnetic fields are an increasing focus of attention. The scientific evidence of adverse health effects from general environmental exposure to these fields is "not proven". If there are adverse effects yet to be proven, the risk is probably likely to be very small.