(a) Phosphorus and Nitrates from fertilizers and detergents contaminate surface waters where they act as nutrients and promote the growth of oxygen consuming algae which reduce the DO level of water, killing fish and other aquatic organisms.
(b) Industrial effluents result in the addition of poisonous chemicals such as Arsenic, Mercury, Cadmium, Lead etc., which kill aquatic organisms and may reach human body through contaminated food (i.e.
fishes etc.) (c) Domestic, commercial and industrial effluents (petroleum refineries, paper mills, breweries, tanneries, slaughter houses) contaminate the water with organic pollutants.
These provide nutrition for micro-organisms which decompose the organic matter and consume oxygen and reduce the DO level of the aquatic system thereby killing the aquatic organisms.
(d) Non biodegradable pesticides (especially organ chlorines) travel through food chains and ultimately reach humans where they accumulate in the fatty tissues and affect the nervous system.
(e) Waterborne infectious enteric diseases like typhoid, bacillary dysentery, cholera and amoebic dysentery are the predominant health hazards arising from drinking contaminated water.
(i) Radio-active pollutants (from mining and refining of Uranium Thorium and Nuclear power plants) enter humans through food and water and get accumulated in the blood, thyroid gland, liver, bones and muscles.
- In the news we hear about all the problems with water pollution in third-world countries, making the problem feel sort of foreign to us.
(f) Fluoride containing pollutants cause fluorosis i.e.
neuromuscular, respiratory, gastro intestinal and dental problems.