'A substance, released in to an environment, that causes harm either to living organisms, or built structures. The substance may be man-made or natural, and causes harm when the receiving environment cannot easily assimilate the type or quantity of substance released.'
The Dictionary of Human Geography’

“The introduction by man into the environment of substances or energy liable to causes hazards to human health, harm to living resources and ecological systems, damage to structures or amenity, or interference with legitimate use of the environment' . Royal Commission on Environmental Pollution, 1984
Both definitions stress the human influence and separate it from naturally occurring events. It is also implied that pollution causes harm. If it does not cause significant harm or damage, it may be termed a contaminant.

There are three main objectives in assessing the impact of pollution, or environmental damage;
i.      To determine the thresholds at which harm or damage occurs.
ii.     To determine the relationship between the dose of pollutant ingested or released and the response (outcome) of this action.
iii.   To measure the total damage suffered by populations and communities from a pollution incident.
The distinction between a contaminant and a pollutant is made on these criteria. For example, aluminium sulphate is present at low concentrations in most water supplies. On 20th July 1988, 20 tons was accidentally added to the drinking water supply of Camelford, Cornwall. The resulting pH of 3.5-4.2 (instead of 7-8) was flushed in to the Camel, where it killed most of the fish. It caused rashes and ulcers.
(a)  Health Effects;
Nitrates Not toxic themselves, they are absorbed in to the bloodstream as a powerful oxidising agent, which can affect the distribution and uptake of oxygen in the bloodstream. This is particularly prevalent in young babies, causing a condition known as blue baby syndrome [methaemoglobinaemia]. Only 2000 cases have been recorded world wide since the 1940s. Only 10 cases have been recorded in the UK in the last 30 yrs, and only one was fatal. Data in each case is inconclusive, as dose and exposure are very hard to measure.
Lead The toxicity of lead has been known for a long time. Low concentrations in the body cause lethargy, whereas high concentration can cause kidney failure and irreversible brain damage. Lead enters the body more readily through breathing than ingestion, as the stomach does not accumulate well. Identification of the point at which it becomes dangerous is complex, since the mild symptoms may be confused with other things, and unnoticed. It is also hard because of the cumulative nature of lead, in which it builds up over time.
MercuryAn unusual substance for the body. If ingested (taken by mouth) an adult can tolerate up to 30g per day. If inhaled (as vapour), even small quantities are very toxic.
(b)  Environmental Effects;
Identification of environmental effects may be easier to establish through lab testing or long term monitoring. The effects, however, are complex, and require many years of work before the complete picture is revealed.
Acid Rain.Since the 1970s, debate has focused on increasingly acid rain, caused in part by nitrogen and sulphur compounds released in to the air by burning fossil fuels. The gases may dissolve in rain droplets which comprises solutions of nitric and sulphuric acids. Some areas, due to their geology, are more susceptible to the impact of acid rain. Some areas are said to be able to buffer the effects. Buffering of acids occurs by neutralisation with an alkali. Rocks with a large amount of carbonates, particularly calcium and magnesium, have a high buffering capacity, and therefore can neutralise acid inputs easier than other soils. This means that the soils and water are less likely to be acidic.

In the UK, areas like Dartmoor, North Wales, and the Lake District have little buffering capacity, so the soils there are acidic (mor) whereas areas like the Midlands, Hampshire and the Central Lowlands of Scotland have soils and rocks with a high buffering capacity.

Acid rain has many impacts, both directly and indirectly. For example, fish levels decrease with acidity. But this is not solely due to the acidity, it has more to do with the increased solubility of metal sulphates at low pH values (e.g. aluminium)
Eutrophication It is known that the addition of nitrogen and phosphorous and their derivatives increases productivity of farmland. Overuse results in a condition known as eutrophication. If the fertilisers leach in to the water table and end up in stagnant water (stationary) they change from oligotrophic to hypertrophic conditions as a result of increased nutrient content.
·       Oligotrophic - (unpolluted) - Clear deepwater habitats, good oxygenation, high species diversity, including trout and other white fish.
·       Hypertrophic - (polluted) - Water of poor visibility, low oxygen levels, rapid sedimentation, and the presence of only coarse fish like roach or bream.

(i)    Point and Diffuse Sources.
Pollutants enter the environment from a number of sources. They can be roughly divided in to two groups;
·       Point sources: those where a specific point of emission can be identified on the ground, e.g. a sewage outlet pipe, an industrial effluent, or a power station chimney.
·       Non-point sources are those where pollutants enter the environment through a diffuse means, e.g. the application of agrochemicals, like herbicides, insecticides and fertilisers, to soils and water courses. Other diffuse sources include domestic refuse and industrial and industrial wastes which often require reprocessing to reduce their harmful nature. This demands an infrastructure for collection, treatment and disposal. Many of the original pollutants which originate from a diffuse source are treated at discreet points in the environment, e.g. incinerators, land-fill sites or reprocessing centres like THORP at Windscale at Sellafield, Cumbria.
(ii)  The importance of time.It is possible to subdivide the two groups above with the introduction of time. Some point sources repeatedly release pollution in to the environment. Others are randomly located in space and time, or accidents. This latter includes accidental spillage of hazardous materials through transport, through road and rail events, or shipwrecks or fires breaking out at power stations or chemical factories.
(iii) Effects of transportationOnce released, pollutants may travel great distances. This is particularly apparent with a change in phase of pollutant transport. For example, acid rain derives from the liberation of waste gases (the gas phase) from point sources, like factory chimneys. Atmospheric reactions and solution of these gases in precipitation causes acid rain (the liquid phase). Acid rain is often diffuse and widespread. Many industrial atmospheric emissions also include fine dusts which may be deposited in a dry state (the solid phase), but may subsequently dissolve during subsequent rainstorms. Even dust which does not dissolve may be transported laterally by flowing water.
(iv) Effects of chemical reactionsA further factor is in the relationship between the pollutant and the environment in which it is transported. For example, many agrochemicals, e.g. nitrogen, are highly soluble, and may be carried away from fields in solution towards rivers and lakes. Other nutrients, e.g. phosphorous, are only slightly soluble under normal conditions, and are transported with soil as it is eroded from fields, and reaches streams with suspended sediment. Herbicides, fungicides and pesticides may be transported in sediment, in solution, or as a combination of the two.

(i)    Fixed Point Sources;
Acid Rain;Acid rain is related to the emission of nitrogen, sulphur and chlorine from power stations, car exhausts and combustion of fossil fuels. These chemicals undergo chemical reactions in the atmosphere to form nitric, sulphuric and hydrochloric acids. These augment naturally occurring carbonic acids to reduce the pH levels from 5.6 to as low as 2.0. the effects are not necessarily direct, and operate in conjunction with other environmental factors. Consequences so far identified include;
·       Destruction of forests; caused by liberation of heavy metal sulphates in to the soils by strong acids.
·       Deterioration of fish stocks; increasing acidity and liberation of heavy metal sulphates.
·       Accelerated chemical weathering of buildings and natural weathering processes.

The key point is to show that the fluctuations in acidity is not a naturally occurring cycle. This has been done by reconstructive analysis of lake sediments, with particular reference to certain species of diatom (cyclotella meneghiniana). The increasing acidity occurs at the same time as soot particles begin to be found, dating about the time of the Industrial Revolution, and settling the blame with combustion of fossil fuels.
Metal Sulphates;Atmospheric pollution from manufacturing and waste incineration processes, as well as fossil fuel combustion, liberate a range of substances, including gases and lead, cadmium, copper, nickel, and zinc, some of which are known to be toxic. They can be transported long distances as dust. Sediment cores of lake beds show industrial pollution in the Scilly Isles. Urban areas show far more evidence of pollution than rural areas, from atmospheric sources only.
(ii)  Random Point Sources;
Pollution incidents which could be categorised under this heading include;
·       Accidents in chemical plants;
̃   Seveso, Italy, 1976; Accidental release of dioxin in to the environment. Vegetation affected, and a large number of animals dies shortly afterwards. By June 1977, there were 135 reports of chloracne, a skin disease, and a new outbreak occurred in December 1977.
̃   Bhopal, India, 1987; another accidental release of dioxin. Largest litigation cases in history brought against the factory.
·       Accidents in nuclear plants;
̃   Windscale Fire, October 1957; first major atmospheric release of nuclear waste from a commercial rather than a military installation. A radioactive cloud moved across to Scandinavia. National Radiological Protection Board (NRPB) calculations suggest that a statistically insignificant increase in thyroid cancers may result.
̃   Three Mile Island, Pennsylvania, 31st March 1979; similar event occurs, but at a power station, as opposed to a reprocessing plant. No fatalities were recorded, but a survey in the following year recorded higher numbers of miscarriages and babies with deformed thyroid glands.
̃   Chernobyl, 1986; later case study.
·       Accidental spillage of oil (waste) at sea;
̃   Transport accidents; many examples which are instantly recognisable to most people, e.g. Braer, Amoco Cadiz. The most detailed is the Exxon Valdez, which happened on Good Friday, 1989. The tanker hit an iceberg in Prince William Sound, discharging 11 million gallons of crude oil over 1000 square miles. Response to the accident did not occur until 36 hours later, and the clean up was struck by legal, technical and political difficulties. Economically, 2000 fisher people have had their livelihoods seriously affected. At least 10,000 seabirds died, and the clean up operation was estimated to have cost between £60-120 billion. By April 1989, only half a million gallons had been recovered.
̃   Exploration accidents. The most well known of these is the fire aboard Piper Alpha, in July 1988, which killed all 150 workers aboard. In the Ekofisk oil field (Norwegian North Sea), in April 1977, the Bravo rig experienced a blow out, releasing 20 000 tons of crude oil.
(iii) Non point sources.
·       These provide different challenges for control and management than point sources. The best example is the UK agricultural practices, in terms of artificial fertilisers.
·       Nitrates and phosphates are the principal components of fertiliser. They may also include to a lesser extent; nitrogen, phosphorous, potassium, calcium, magnesium, sodium, sulphur and chlorine. The effects of nitrates and phosphates on eutrophication is similarly known.
·       Factors affecting the use of the chemicals include the solubility of the chemical, since if it drains away, more will be needed.
·       Long term changes in river nitrate levels have been brought about by agricultural management factors, including, but not limited to, industrialisation, mechanisation of agriculture, the increasing use of agrochemicals, and the influence of the Common Agricultural Policy.
·       Following extreme meteorological conditions, pollution incidents may occur. After the drought of 1976, widespread crop failure resulted in the accumulation of unused fertilisers in the soil. The accumulations were rapidly flushed in to the water system when the rains returned in September.
·       Since the Food and Environment Protection Act of 1985, details of applications and types of pesticides in use must be registered with MAFF.
·       The agrochemical industry has expanded since WW2, producing 50 new chemicals in 1968.
·       Another development is the aerial spraying of crops; over 200,000 ha of crops were treated in 1987 from the air.

Environmental pollution poses risk of potential disaster to either health or the environment. In some cases action is taken before the risk is known, like the widespread use of DDT. Such chemicals may harm those who have not chosen to accept the consequences of their use, and do not know of their application. It is important that a regulatory authority is given powers to act on behalf of individuals to minimise potential risk.
Often, individuals may take calculated risks, e.g. smoking. Despite the hazard being well known (1 in 4 regular smokers die from it), many still smoke. Institutional and governmental response may and must be different. However, both groups have their own self interest at heart. This argument is relevant to all industrial processes where environmental pollution results directly from a manufacturing base and the implementation of stronger pollution controls may result in a loss of competitive edge, and unemployment.
Attempts have been made in the UK to assess pollution. In Greater Manchester, six measures of pollution were aggregated to give an index of pollution. High pollution often occurred in areas of low socio-economic status.

It is very difficult to asses hazards arising from pollution. Often the data is unavailable, or too complex to be measured. Risk calculation assumes that we can (1) Identify, (2) Estimate, (3) Evaluate and (4) Control the risk. This may be acheived by prediction based on experience, or transferring experiences from a similar situation.
This can be flawed in a new type of industry. The 1975 Rasmussen Report of the Atomic Energy Commission concluded that the risk of nuclear reactor core meltdown would be in the region of 1 in 200 million years. Following Three Mile Island, the Ford Foundation concluded that the risk of core meltdown before the year 2000 was as much as 1 in 4.

We are also at risk from nature. Natural radiation accounts for 87% of all received in the UK in 1987. Of the remainder 92% came from medical sources.We can see that there is uncertainty in assessing risk or hazard from pollution events. Events leading to accidents continually surprise us, and are impossible to predict.