Air pollution refers to the introduction of chemicals, particulate matter or biological substances that cause harm or discomfort to human beings, other living organisms and the natural environment into the atmosphere. Air pollution mainly arises from solid particles and chemicals. It may arise from natural processes that impact the atmosphere such as volcanoes, biological decay and dust storms.
There are two types of air pollution; primary and secondary pollution. The former happens when pollution occurs directly in the air, for example through smoke and car exhaust fumes while the later forms in the air when chemical reactions change the primary pollutants. An example of secondary pollution is the formation of tropospheric ozone. Since the atmosphere is a complex, dynamic and fragile system, there is a growing concern about the global effects of air pollution especially in matters regarding climate change (Ward 2006, p.1).
There are two major sources of air pollution which are classified into two major categories: anthropogenic sources and natural sources. The anthropogenic sources are those caused by human activities and they are mostly related to the burning of different kinds of fuel. Examples of such sources include: smoke stacks from power plants, factories and waste incinerators. On the other hand, natural sources of air pollution are those that don’t result from human activities and they include dust from large areas of land, methane emitted by digestion of food by animals, sulphur and chlorine that is produced by volcanic activities (Dade 1997, p. 71).
Total suspended particulates (TSPs) refer to the total number of particles of solid or liquid matter that are found in a sample of ambient air. Examples include soot, dust, aerosols and fumes. The TSPs are usually less than 100 micrometers and they constantly enter the atmosphere from various sources. There are two sources of total suspended particulates; the human sources and the natural sources.
The human sources (anthropogenic) include motor vehicle use, combustion products from space heating, industrial processes and power generation. The natural sources of TSPs are soil, bacteria, viruses, fungi, moulds, yeast, pollen and salt particles from evaporating sea water.
Total suspended particulates are known to be associated with some health effects and over 99% of the inhaled particulate matter is either exhaled or trapped in the upper areas of the respiratory system after which it is expelled. The remaining particulates enter the windpipe and the lungs where some particulates known as inhalable particulates, cling to the protective mucous and are removed from the body.
Mechanisms like coughing also filter out or remove the total suspended particulates and collectively, these pulmonary clearance mechanisms protect the lungs from the majority of the inhalable particles. Some of the smallest particles called the respirable particles can lodge in the lung capillaries and the alveoli to cause the following health effects:
(i)Slow down the exchange of oxygen and carbon dioxide in the blood hence causing shortness of breath (ii) Straining of the heart because it has to work extra hard to compensate for the oxygen loss.
The most susceptible people to these conditions are those with heart problems, respiratory diseases like emphysema, bronchitis and asthma. The adverse health effects that result from exposure to particulate matter are not noticed immediately after the encounter. Therefore, particulates can accumulate in the lungs after repeated, long term exposure causing respiratory distress and other health problems.
The ambient air standard qualities for total suspended particulates are: PM 10(150mg/m3) -2.5(15ug/m3) yearly mean and 65ug/m3 over 24 hours by US EPA, PM25 (10ug/m3) annual mean and 25ug/m3 by WHO (NRC 1998, p.61).
Heavy metals refer to metals with a specific gravity which is greater than about 5.0 and is poisonous. Examples of heavy metals include; lead and mercury. Excessive levels of heavy metals are hazardous to man, plants and animals hence it’s important to regulate their levels in waste application sites. Zinc is an essential trace mineral which occurs in greater amounts than any other trace mineral except iron.
The best natural sources of Zinc include oysters, meats, wheat germ, hard cheese, poultry, spinach and eggs among others. The anthropogenic sources of Zinc are greater than the natural sources and the most important anthropogenic source comes from discharges that come from smelter slags and wastes.
When zinc is taken at doses of 20mg and above, it’s more likely to cause stomach upsets and nausea hence it should always be taken with regulated amounts of food. Long-term zinc supplementation above 50mg has been shown to increase total cholesterol due to an induced copper deficiency. Similarly, large doses of zinc may also promote folate deficiency (Selim 2009, p. 109). The ambient air standard quality for zinc by the European commission is 5ngm-3. Little data is available on the standards of zinc in air from EPA, WHO and UK.