This article throws light upon the five major effects of air pollution on our environment. The effects are: 1. Effects on Vegetation 2. Effects on Animals 3. Effect on Man 4. Effects on Materials 5. Global Climate Changes.
Air Pollution: Effect # 1.
Effects on Vegetation:
Air pollution can affect plants to varying degrees. At the lowest levels, i.e., below the ‘threshold’, there is no effect, such as visible damage, cumulative chronic effects, genetic effects or even gradual changes in the composition of the plant community. However, even at this level, air pollutants can be stored in the plants and introduced into the food chain, affecting animals which eat the plants.
The entry of air pollutants to plants may take place directly by gaseous diffusion or from the contaminated soil, acidic air pollutant in particular. The direct entry of gaseous air pollutants like SOX, NOX, CO2 etc.. may take place directly by stomata of the foliage’s.
Solid particulates are, however, adsorbed on the surface. In general, pollutants cause injury at lethal concentration on sensitive plants while tolerant plant species are capable of sinking the pollutants to a considerable extent without any injury. The air pollution induced injury on various plant species are given in Table 10.8.
Thus, various air pollutants have different types of injuries on exposed sensitive plants. Suspended particulates after deposition on foliage’s cause a number of damages to leaf functions, viz.,
(a) Changes in the sun’s energy falling on the leaf surface affecting the energy exchange due to dust layer;
(b) Decreases chlorophyll content;
(c) Interruption in gaseous exchange due to clogging of stomata by dust particulates; and
(d) Dust deposition causes changes in the soil properties that support the plant growth.
The oxides of sulphur, nitrogen and carbon are absorbed by the plants through gaseous exchange and then either assimilate in such a manner so that there is no detrimental injury to the plant parts or it causes appreciable injury to various plant organs.
In general, sensitive plant forms could be used for bio monitoring air pollutants. Several species of lichens and angiosperm plants are often used for bio monitoring of these pollutants.
Air Pollution: Effect # 2.
Effects on Animals:
The indirect effect of air pollutants has been observed for a considerable time. It tends to occur near smelters treating non-ferrous ores, and near factories, such as phosphate fertilizer works, brick kilns and aluminium smelters, where fluorides are emitted and are concentrated in the grasses in surrounding fields.
Identically, lead compounds from automobile exhausts are deposited near to roads, although the concentrations found in vegetation are much smaller than those near smelters and have so far been measured as below the accepted threshold for toxicity to animals.
But, with time, such metals accumulate in animal bodies through food chain and finally pose danger to animal health. The signs of heavy metal poisoning are diarrhea, anemia and stiffness.
Fluorosis is a more widespread problem, which affects ruminants—particularly dairy cows. Of course there are couple of reports of direct effect of gaseous pollutants on animal but considerable systematic studies have yet to be made.
Air Pollution: Effect # 3.
Effect on Man:
Air pollutants, along with breathing air, enters the nose, where fine hair filter out most particles greater than about 10 micro-meters diameter. The air is then warmed and humidified, and is then passed through the windpipe into the bronchial tubes which subdivide the air stream and pass it into the lungs where there are a multiplicity of air sacs.
From air sac through capillary diffusion gaseous pollutants enter into blood streams and particulates deposit in the alveolar sacs. The dangers of some small particles—such as silica and asbestos, which are common in mines, quarries and some industrial plants— are well-known over the years. They lead to specific occupational diseases such as silicosis or asbestosis.
In general, air pollutants mostly enter through the respiratory passages and thereby cause mostly various types of health disorders. Limits are set as to the maximum concentrations to which healthy persons are permitted to be exposed for periods of up to 8 hours per day. These are called Threshold Limit Values (TLV).
The WHO guidelines for such a threshold limit of exposure is given Table 10.9:
In the atmosphere, such high concentrations are seldom met, but, on the other hand, the exposure of a population is over 24 hrs, rather than 8 hours, and all members of that population, including the weakest, are involved. In addition, even at long term low level exposure, pollutants, as noticed in city environment, may lead to a number of slowly grown detrimental health effects.
An overall generalized health effect of various air pollutants are given in Table 10.10:
It was interesting to note the fact that low level exposure of air pollutants like NOX and SO2 on long term basis has significant health disorders. In general, an in-depth analysis with respect to SO2 was made in the past, which is primarily based on various kinds of urban studies.
It is most interesting to note that even at low SO2 concentration (0.01 ppm) exposure over a period of 1 year may lead to increased cardiovascular morbidity.
There are also possibilities of air pollution induced carcinogenesis in urban environment as urban air pollutants contain a number of carcinogenic elements. Extracts of atmospheric particulates showed the existence of polyaromatic hydrocarbons which are known to be potent carcinogen.
Air Pollution: Effect # 4.
Effects on Materials:
Air pollutants have a deleterious effect on materials:
Stone, paintwork, stained glass, fibre material and others. The soiling effect of particulate is obvious in industrial cities where building of light-coloured stones and bricks soon take on the characteristic black colour.
The erosion of the stonework on buildings of great historic and architectural value is very serious indeed, other results of air pollution are the faster deterioration of clothing, curtains and wood, the corrosion of metals and the soiling and subsequent cracking of paintwork.
The rapid deterioration of rubber acted on by ozone can be easily demonstrated in the laboratory. Silverware tarnishes rapidly due to hydrogen sulphide and sulphur dioxide in industrial cities.
Air Pollution: Effect # 5.
Global Climate Changes:
Over past couple of decades, it was realised that air pollutants cause a considerable change in global climate and associated processes, viz., greenhouse effects, ozone depletion, acid precipitation and El Nino effects etc.