Minamata disease

• Caused by mercury poisoning. Characterized by crippling and death.
• The primary cause for this disease was a plastic industry which was started on the sea coast of Japan in 1905. From this factory a by- product called mercury was disposed into the sea. This mercury accumulated in marine animals.
• Later birds, cats, dogs and men receive mercury when they eat marine fishes and animals. The accumulation of mercury leads to crippling and death. Symptoms of minamata disease includes the numbness of limbs, lips and tongue, impairment of motor control deafness and blurring of vision. 

 

Diarrhoea- Caused by mercury, cadmium and cobalt.

Mortality of plankton and fish- Chlorine which is added to water to control the growth of algae and bacteria in the cooling system of power stations may persist in streams to cause the mortality of plankton and fish.

Reduction in productivity- Intensive agriculture increases the amount of silt in lakes and rivers. Silt prevents the penetration of light to depth and thus reduces primary production.

Siltation - Siltation is a phenomenon by which the gills of fishes are deposited with silt. This causes heavy mortality among fishes.

Poor Oxygenation - Oil present on the surface of water prevents water oxygenation. This reduces respiration and metabolism in aquatic organisms.

Poor Photosynthesis - Oil pollution prevents photosynthesis in phytoplankton.
Red Tide- When coastal waters are enriched with nutrients of sewage, dinoflagellates multiply rapidly and form bloom. These blooming dinoflagellates liberate into the water, produce toxic metabolic by-products which can result in a large scale death of marine fishes. This is called red tide.

Biochemical Oxygen Demand-Sewage enriches the water with nutrients. This causes rapid growth of plankton and algae. This leads to oxygen depletion in water. The oxygen depletion causes the death of algae. The decay and decomposition of algae consume more oxygen from water.

• Biochemical Oxygen Demand or Biological Oxygen Demand (BOD) is the amount of oxygen required by the microorganisms in water. BOD is higher in polluted water and lesser in drinking water. Increased BOD lowers the contents of dissolved O₂ in water causing the suffocation and death of aquatic flora and fauna.

Water-borne Diseases - Diseases like jaundice, cholera, typhoid, diarrhoea, etc. are transmitted through water contaminated with sewage.

 

Methaemoglobinema-The nitrate used in fertilizers enters the intestine of man through drinking water. In the intestine, it is converted into nitrite.

• Nitrate is absorbed into the blood where it combines with haemoglobin to form methaemoglobin. Methaemoglobin cannot transport oxygen. This leads to suffocation and breathing troubles, especially in infants. This disease is called methaemoglobinema.

 

Eutrophication-Domestic sewage and fertilizers add large quantities of nutrients such as nitrates and phosphates to the freshwater ecosystem. The rich supply of these nutrients makes blue green algae, green algae and other phytoplankton to grow abundantly. This increased productivity of lakes and ponds brought about by nutrient enrichment is known as eutrophication.

• As the algae use of the water for respiration, the O2 is depleted from the water. The rapid growth also consumes all the nutrients of the water. The depletion of O2 and nutrients lead to the death of algae and other phytoplankton.
• As other organisms, such as zooplankton and fishes of the water, depend on the blue green algae and phytoplankton for their food, they also die. Thus eutrophication leads to the complete depletion of the fauna from the ecosystem.