(a)(i) Pollution; is the discharge of harmful/toxic substances into the environment in quantities which are harmful to life as a result of the activities of humans.
(ii) Pollutants of water: -
(i) Domestic waste/sewage/household waste.
(ii) Industrial waste/dyes/detergents/lead/mercury compounds.
(iii) Agricultural wastes/pesticides/insecticides/fertilizers.
(iv) Oil/oil spillage.
(v) Hot water/thermal plants.
(b) Effects of pollutants on aquatic organisms Domestic wastes:
(i) Bacterial breakdown of sewage reduces dissolved oxygen in water/eutrophication.
(ii) Aquatic animals suffocate and die.
(iii) Rapid growth of aquatic plants due to mineral rich sewage.
(iv) Reduces light penetration and photosynthesis.
(v) Contaminated sewage spread disease-causing organism.
Industrial wastes:
(i) They are poisonous to aquatic organisms.
(ii) Detergents form foam on the water surface tension causing floating animals to sink.
(iii) Phosphates cause rapid plant growth.
(iv) Dyes from textile factories reduce light penetration/photosynthesis.
Agricultural wastes:
(i) These may accumulate to toxic levels thereby poisoning aquatic organism.
(ii) Fertilizer residues stimulate growth of aquatic plants which form a dense mat on the surface of the water leading to depletion of oxygen/eutrophication reduction of light penetration resulting in decrease in the rate of photosynthesis and causing death of aquatic organisms.
Oil Spillage:
(i) Oil reduces surface tension of water causing floating animals to sink.
(ii) Animals die from lack of oxygen.
(iii) Coats feathers/fur of animals making them unable to fly/causing affected animals to freeze/starve to death.
(iv) Coats gills/filters of aquatic organism.
(v) Reduces light penetration and decrease photosynthesis.
(vi) Toxic to aquatic organisms.
Hot water:
(i) Kills living organisms.
(ii) Upsets the balance of the ecosystem.
(iii) Hot water increases the water temperature thereby reducing the oxygen content and leading to death.