Question

What is biological magnification?

Answer 1

Hint: Biological magnification is one of the effects of water pollution.It leads to the increase in toxicity in aquatic life.

Complete answer:
Biomagnification or biological magnification is a gradual increase in the concentration of toxicants at successive trophic levels. Certain toxic substances present in industrial waste undergo biomagnification.

This happens because a toxic substance accumulated is not metabolised or excreted by the organism and is passed on to the next higher trophic level. Phenomenon of biomagnification is well known for mercury and DDT. It is characterised by accumulation of fat-soluble pollutants in plants and animal tissues.
Effects of biomagnification
>DDT interferes with calcium metabolism in birds.It causes thinning of egg shells and their premature breaking leading to decline in bird population.
>Biomagnification of mercury into fishes through the food chain was responsible for minamata disease in Japan in 1952. Mercury compounds in waste water are converted by bacterial action into extremely toxic compounds, methyl mercury, which causes numbness of limbs, lips and tongue, deafness, mental retardation, blurred vision.
>Selenium accumulates in plants growing on selenium-rich soil. Through the food chain, such plants cause stunted growth, loss of appetite, gastro-intestinal disorders, etc. in animal grazing in such plants.
>Chlorinated hydrocarbons are known to effect CNS, softening of brains, cirrhosis of liver, cancer, malformation of sex hormones etc therefore, use of DDT and other pesticides is banned in agriculture.

Note:The various causes of biomagnification are,
>Industrial activities - Industries and factories release high amounts of toxic substances which are then released into the soil, rivers, and oceans.
>Agriculture - Farming leads to increase in nutrients and heavy metals because of high use of fertilizers, fungicides and insecticides.
>Organic contaminants - Manures and biosolids which are processed industrially contain various contaminants.