Water pollution involves contaminated water, whether from chemical, particulate, or bacterial matter that degrades the water’s quality and purity. It can occur in oceans, rivers, lakes, and underground reservoirs, and as different water sources flow together the pollution can spread.
The causes of water pollution include the increased sediment from soil erosion, improper waste disposal and littering, leaching of soil into water supplies, and organic material decay in water supplies. The effects of water pollution include decreasing the quantity of drinkable water available, lowering water supplies for crop irrigation, and impacting fish and wildlife populations that require water of certain purity for survival.
Types of Water Pollutants
Water pollutants can be categorized into:
- Inorganic Pollutants
- Organic Pollutants
- Biological Pollutants
- Chemical Pollutants
1. Inorganic Pollutants
The inorganic pollutants include:
- Mercury: When mercury is found in fishes, it may enter the human food chain and causes Minamata disease. The occurrence of Mercury in the form of methyl mercury and dimethyl mercury in fishes in Minamata Bay of Japan in 1950 had caused disease, therefore it was named Minamata disease.
- Lead: It adds toxicity in the water.
- Phosphates: The sources of phosphates are sewage outflow and phosphate containing detergents. It causes an algal bloom in the water, which finally depletes the level of oxygen.
- Nitrates: The sources of nitrates are sewage outflow with fertilizers which was used in farming fields. It causes eutrophication which finally causes problems of biological oxygen demand.
2. Organic Pollutants
The organic pollutants include:
(i) Pesticides and herbicides
The pesticides include:
(a) Chlorinated Hydrocarbons like D.D.T., Heptachlor, etc.
(b) Organophosphates like Malathion which can be used in wheat to prevent pest while storing.
The herbicides include soil sterilants like Trifluralin, Dalapon (kill microbes in soil), etc.
(ii) Materials for common household use, e.g. organic garbage.
(iii) Materials for industrial use, e.g. Biotech industry, vegetable oil manufacturing units, etc.
3. Biological Pollutants
The biological pollutants include algal bloom, addition of pollen, an addition of undesirable microbes in the water, etc.
4. Chemical Pollutants
The chemical pollutants include biocides, polychlorinated biphenyls, inorganic chemicals like phosphates, nitrates, fluorides etc.
The water pollution can be further classified as:
- Municipal Wastewater: Liquid wastes from domestic activities such as kitchen, toilet and other household waste-waters are in most cases discharge directly into a river or into a large water body nearby.
- Industrial Wastewater: Most of the coastal water species are threatened by pollution from the effluents of coastal prawn-culture farms and fish processing industries. Most components of industrial effluents are toxic to ecological systems.
- Surface runoff from the land: The runoff from agricultural land is contaminated with pesticides and residues of inorganic fertilizers while the run off from urban areas mainly contains biodegradable organic pollutants.
- Oil spills are the accidental discharge of petroleum in oceans or estuaries by oil tankers, offshore oil mining and oil refineries.
- Since crude is one of the most complex mixtures of natural products with a degree of toxicity, the importance of controlling oil pollution at sea lies not only short term effect but also the long term effect on marine life and environment.
Short Term Effect
- The oil film forms a barrier to the transfer of 02 into the water to support marine life particularly planktons.
- These oil film known as oil slick gives unpleasant flavour to fishes and sea foods, which reduces market values of sea foods.
- It causes the death of birds through the effect on feathers because birds often clear their plumage by pruning and in the process, consume oil which leads to intestinal, renal and liver failure.
Long Term Effect
Once the oil is consumed by a particular marine organism, then hydrocarbons pass through many numbers of marine food chain without any alternatives, and finally, it affects humans through biomagnification.
Measures to Control Oil Pollution
- Mechanical barrier or booms should be placed around the oil slick to check its spreading to other areas.
- It can be scooped-up from the surface by vessels known as skimmers.
- Dispersant that breaks up oil film can be used to check its spread. Dispersants are similar to soap in their action on the oil film. It reduces the surface tension between oil and water and breaks up oil in smaller droplets.
- Absorbents like polystyrene, polypropylene, and polyurethane are often used to absorb the oil and prevent it from spreading.
- Microbial surfactants can be also used to check its spread. Microbial surfactants mix with oil and emulsify oil slick and disperse it. This speeds up the process of evaporation and degradation of oil through other natural means.