Water is another important media of pollution. Pollutants find themselves in water and become sources of danger to human health and the environment. The significance of water in relation to pollution cannot be overemphasized given to its importance in our day to day living.
Indeed, man cannot survive without water, however, again polluted water can be very inimical to human health and hence the need for study of the media and the pollution that comes through it.
Water is in fact the commonest compound on earth and is not only essential for life but has become interwoven with human livelihoods in various inextricable ways. As compound water is made up of two elements- Hydrogen and oxygen (H2O) Water is found on land, in the oceans and in the atmosphere, and comes in different forms: as a liquid, as a solid (ice and snow) and as a gas. In free form it may be totally pure
There are many specific causes of water pollution, but it is important to first understand two broad categories which are point and non-point or diffuse sources.
The point sources of water pollution include wastes generated by human settlement, domestic, commercial and industrial activities including those of petroleum related industry, energy utilization activities and the precipitation of atmospheric pollutants.
The non-point sources of water pollution include run-off from agricultural lands treaded with fertilizers and pesticides, which cause nutrient enrichment and Eutrophication of surface water.
Water pollutant types may be categorized into:
Physical pollutants – include silt, clay, discarded objects, decaying organic matters which generally affect the aesthetic quality of surface waters.
Chemical pollutants – include non-biodegradable, toxic heavy metals such as lead, cadmium and mercury, as well as persistent and hazardous organic pollutants such as pesticides, phenols and polynuclear aromatic hydrocarbons (PAHs).
Biological pollutants – arising from the discharge of effluents from energy and manufacturing industries into surface waters – weeds, micro-organisms, etc.
Radioactive pollutants – include radioactive, substances or effluents carrying such substances, containing radioisotopes such as Radium 226, Strontium 90 and Cesium 137.
Types of Water Pollution
Below are the types of water pollution:
1. Precipitation Pollution
Wet precipitation such as rainfall is not exempted from pollution. This is so because the processes leading to the formation of precipitation can be initiated by dust particles from any sources, ranging from salt particles from the field, ash emitted from volcanic eruption, toxic dust particles such as chromium or asbestos, particulates from smokestacks, crystals of salt evaporated from sea spray, or pollens in air, or combustion by- products of coal or fossil fuel.
The increasing concentration of greenhouse gases containing carbon dioxide, oxides of nitrogen and sulphur, beyond threshold levels, are responsible for acid rain which adversely affects forestry and agricultural soil fertility.
2. Surface Water Pollution
Natural sources of surface water pollution in streams, lakes, ponds, etc., include silt and clay, decaying algae (some algae release toxic compounds) dead leaves during leaf fall and other organic matter. The flow of some streams originates from springs which may contain large concentration of salts.
Disposal of untreated industrial, municipal and domestic waste into stream, lake and rivers has been the major anthropogenic source of surface water pollution. In addition, effluent from municipal treatment plants, with unknown and unusual chemicals contained in the industrial process because of trade secrets, find their way into water courses.
Agricultural activities have been known to contribute to surface water quality deterioration. Evaporation has also been known to consume much of the water applied during irrigation thus concentrating the salts present into the water and soil. The remaining may either infiltrate, where it becomes more highly mineralized or flow across the surface into streams, lakes and rivers.
3. Ground Water Pollution
Ground water is generally not pure since dissolution of substances take place in the course of percolation of water through geological formations. In fact, chemical composition of ground water is normally considered on the basis of its intended use such as domestic, industrial, irrigation or other uses.
The principal inorganic chemicals in water are the cations magnesium, calcium, sodium and potassium, while important anions are carbonates, bicarbonates, sulphates and chlorides.
In conclusion, Water as a medium for pollution is very important in environmental health practice. Often we have our sources of water polluted through our activities or through some natural events. Water pollution is a phenomenon that can be responsible for illnesses in man and cause a lot of damage to the ecosystem.
The prevention and control of water pollution has become so important that governments all over the world are laying emphasis on it and making necessary policies in that connection.
Water pollutants are of different categories such as chemical pollutants, biological pollutants, radiological pollutants etc. Water pollution again is of different types and sources. For example precipitation, surface and ground water pollution and anthropogenic and natural sources respectively. In the next unit we are going to consider another important media of pollution; which is soil.