Harmful Effects of Soil Pollutants
It has already been stated that soil pollution is the result of the dumping of waste products - domestic, human, animal, industrial and agricultural. The harmful effects of various pollutants are described below:
9.3.1 Effects of Industrial Pollutants
(1) Industrial pollutants comprise of a variety of chemicals which are very toxic to living beings.
Industries like paper and pulp, textile, steel, fertilizers, pesticides etc. release metallic wastes, oils, greases, plastics, plasticizers, heavy metals most of which are non - biodegradable. So these pollutants or toxic materials are transferred to different organisms via food chain and are responsible for undesirable effects.(2) Industrial effluents if discharged in the sewage system, will hinder the biological purification mechanism of sewage treatment resulting in a number of soil and water bome diseases.
(3) The organic compounds particularly amino acids, albumins and gelatins if discharged in soil, undergo putrefaction by bacterial action releasing sulphur and phosphorus compounds. These compounds produce gases like hydrogen sulphide and sulphur dioxide which are responsible for the foul smell of soil.
(4) Metallic contaminants (e.g., Hg, Pb, Zn, As, Cd, Cr, etc.) destroy bacteria and beneficial micro organisms in the soil. These metals accumulate in the soil and are fatal to living organisms.
(5) Soluble salts in the soil make soil unfit for agricultural cropping. It is believed that about 45% of the agricultural land is damaged by soluble salts.
(6) The chemicals from industrial wastes turn the soil acidic or alkaline which becomes unfit for agriculture. It is estimated that about 30% of agricultural land is rendered unfit for further crops.
(7) Some of the industrial wastes contain pathogenic bacteria. For example, the wastes, from tanning industries contain pathogen Anthrax bacilli.
9.3.2 Effects of Urban and Domestic Waste Products
(1) Sewage which is an excellent medium for the growth of pathogenic bacteria, virus and protozoa, can cause cholera, bacillary dysentery and even typhoid. The chances of mixing with ground water even after the treatment of sewage are quite high. The ova and larva of many worms are parasitic to man and may be transmitted to soil through urine and faeces.
(2) Solid wastes are responsible for offensive odour and cause clogging of ground water filters.
9.3.3 Effects of Radioactive Pollutants
(1) These pollutants are the worst pollutants. The volatile materials are first released into the atmosphere and are then washed down by rain on to the soil and water bodies. This results in the soil getting radioactivity, which in turn is passed to plants and finally to the humans.
(2) In water bodies, the aquatic flora and fauna absorb radiations which are also ultimately passed on to the humans.
(3) Radioactive pollutants produce great human misery.
9.3.4 Effects of Agrochemicals
Agrochemicals like fertilizers, pesticides and biocides etc. are used to increase the soil fertility and crop production. However, excessive use of agrochemicals is disadvantageous as will be clear from the following effects:
(1) Fertilizer enriched soils do not support microbial flora.
(2) With the use of NPK fertilizers, there is about 25% decline in protein content in com, maize, gram and wheat crops. In fact, this practice leads to malnutrition.
(3) Use of potassium fertilizers decreases the content of carotene and vitamin C in vegetables and fmits.
(4) Though fertilized soil produces big size vegetables and fruits but such produces are more prone to pests, insects and diseases.
(5) Excessive use of nitrogenous fertilizers leads to accumulation of nitrate in the soil. These nitrates are passed on to humans. Being soluble, the nitrates enter in the ground water. Drinking nitrate rich water can cause diarrhoea and cyanosis (blue jaundice) in children.
In the human body, the nitrates are converted into nitrosamines and nitroso compounds which are suspected carcinogens and may be responsible for stomach cancer. In case the nitrate fertilizers are used beyond safe amounts, they affect children less than 2 months old who become susceptible to a fatal disease 'methemoglobinemia' or 'blue baby syndrome’. In this disease, the nitrates interfere with the oxygen carrying capacity of the blood. Children who drink water containing excessive amounts of nitrate harbour the wrong type ofbacteria which reduce nitrate to nitrite ions which damage the respiratory and vascular systems ultimately causing the death of the infants.(6) Phosphate fertilizer like diammonium phosphate (DAP) is considered detrimental to the crop production.
(7) Excessive fertilizers are drained off into water bodies causing eutrophication.
(8) Farmers use pesticides to increase yield. However, they are hazardous to humans, animals, fish and livestock and they also reduce the yield of the crops.
(9) The level of pesticide residues like DDT, dieldrin, etc. in fruits, milk, eggs, vegetables beyond the permissible levels are responsible for causing diseases like cancer, sterility and even death.
(10) Organo chlorine pesticides, e.g., polychlorinated biphenyls (PCBs) are very dangerous. These accumulate in the soil and plants which ultimately enter human bodies. PCBs cause deformities in foetus, nervous disorders, liver and stomach cancer in animals.
(11) Organo phosphate pesticides cause muscular weakness, tremors and dizziness in animals.
(12) Pesticide poisoning from soil is a global problem. Excess absorption leads to greater accumulation of acetylchloline in the body. Chronic absorption damages liver and kidney causing malfunctioning. It also causes cancer and deformation of brain tissues.
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