The salient effects of some pollutants, in air, on the human system, or, otherwise, are, briefly, discussed as follows:
Sulphur Dioxide:
The effect of sulphur dioxide is mostly confined to the toxicity caused by the reaction of SO2 with moist air and the formation of acids. SO2 is an irritant to the eyes, nose, throat and lungs, and induces reflex coughing (5 parts per million); at higher concentrations, i.e., 200 parts per million, it is likely to induce rapid and severe toxic effects.
WHO (1972) has recorded that SO2 is a water soluble gas that acts as a powerful irritant to the mucous membranes of the eyes and the upper respiratory tract. It causes rapid and acute irritation of the eyes with tears and redness; its action on the upper respiratory tract causes cough, shortness of breath and spasms of the larynx.
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Oxides of Nitrogen:
Oxides of nitrogen can have biological and phytotoxic effects and they are intimately involved in the formation of photochemical smog. Nitrogen dioxide is far more toxic than nitric oxide.
The toxic action of nitrogen dioxide is primarily one of irritation of the lower respiratory tract, with pulmonary oedema developing in severe cases. In milder forms of poisoning, nausea, vomiting and vertigo, with cyanosis have been observed.
Methaemoglobinaemia may also be observed. Such severe symptoms are, however, unlikely to be caused by the concentrations normally found in polluted air. The Threshold Limit Value (TLV) for nitrogen dioxide is a concentration of 9 mg/m3. Damage to vegetation has been reported following a one-hour exposure to 1 mg/m3.
The formation of methaemoglobin in the blood, which inhibits its capacity to carry oxygen
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The concentration which can be inhaled for an 8-hour day 5-day week without Concentrations of nitrogen oxides (either as NO or NO2) as low as 0.2 mg/m3 can contribute to the formation of photochemical smog, a very unpleasant form of pollution, which is frequently experienced in the USA.
Fluorine:
In general, available evidence suggests that damage caused by atmospheric fluorides to vegetation and animals is much more wide-spread than its ill effects on man.
The acute effects of an increasing concentration of hydrogen fluoride have been listed as follows:
(i) 2.4 mg/m3 No immediate effects
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(ii) 8 mg/m3 Many persons experience discomfort
(iii) 24 mg/m3 All persons complain and object to staying in the environment
(iv) 48 mg/m3 Brief exposures cause irritation of eyes, nose pharynx, and upper chest
(v) 96 mg/m3 Not tolerable for more than one minute, all the above effects intensified, smarting of skin.
The first sign of chronic fluorosis is mottling of the teeth. Further symptoms include pains and stiffness in the joints. Radiological examination of workers, exhibiting these symptoms, has shown evidence of bone-thickening and gasification of the ligaments (osteosclerosis).
A survey of the literature, describing the exposure of workers to fluorides in industrial atmosphere, indicates that concentrations in the air were mostly less than 10 mg/ m3 (Hodge and Smith, 1970).
Although there were occasional complaints of the symptoms of irritation listed above, and radiography showed evidence of mild ostesclerosis in some individuals, only a few cases of crippling fluorosis have been authenticated. These occurred in a cryolite where fluoride concentrations of 30-40 mg/m3 were measured.
Ammonia:
Due to its alkaline properties, ammonia is irritating to the mucous membranes of nose, throat, eyes and high concentrations, and to skin. Mild irritation to throat is experienced at a concentration of 35 mg/m3 which is also the harmful effect directly.
The tendency mentioned earlier, for sulphur dioxide to be oxidized in the atmosphere to an ammonium sulphate aerosol, gives rise, however, to secondary effects, which can be a considerable nuisance. Where atmospheric conditions give rise to the formation of stable fogs, the presence of ammonium sulphate increases the density, persistence and extent of the fog.