Some of the most important sources of land or soil pollution are: 1. Domestic and Municipal Wastes 2. Industrial and Mining Wastes 3. Agricultural Wastes 4. Radioactive Materials and Biological Agents.
1. Domestic and Municipal Wastes:
One of the main causes of land and soil pollution is the growing quantity of domestic and municipal wastes. Household garbage includes food scraps, old newspapers, and a variety of plastic items, bottles, discarded papers, wood, lawn trimmings, glass, canes, old appliances, tyres, worn-out furniture, broken toys and a host of other items.
The total quantity of solid wastes is large and increasing. In the United States, municipal solid wastes averaged 1.2 kg per person per day in 1920. The quantity rose to 2.3 kg in 1970 and 3.6 kg in 1980 and now it is more than 4.5 kg. Urban wastes comprise both commercial and domestic wastes including dried sludge of sewage. In general, all the urban solid wastes are referred to as ‘refuse’.
The amount of sold wastes generated is directly related with prosperity. In contrast to the 3.6 kg per person per day in the United States, residents of Australia produce only 0.8 kg per person per day. The average person in India produces only about 0.2 kg per day.
The general composition of municipal wastes is as follows:
It has been estimated that in 45 major cities of India, the quantity of average per day municipal wastes is about 50,000 tonnes.
The National Environmental Engineering Institute (NEERI), Nagpur, has given details of the municipal wasters in Indian town as follows:
It becomes clear from the above table that in our cities 90 per cent wastes include ash, dust, mixed material and carbon, while in developed countries paper, plastic, glass, metal, etc., dominates.
The dumping of domestic and municipal wastes is a serious problem in cities because of its impact on environment and public health. Solid wastes may or may not cause diseases in man but are hazardous to health. Diseases such as dysentery, diarrhoea, plague, malaria and numerous others are the result of the indiscriminate dumping of wastes.
2. Industrial and Mining Wastes:
The disposal of industrial solid wastes is the major source of soil pollution by toxic chemicals.
The industrial wastes are mainly discharged from coal and mineral mining industries, metal processing industries and engineering industries. They contain toxic metals such as lead, copper and chemicals having acids and are responsible for soil pollution.
It has been reported that about 50 per cent of raw materials ultimately become waste products in industry and about 15 per cent of it are toxic. The chemicals discharged from the industries often enter the surface or groundwater or poison the soil or crops. The production of consumer goods also involved environmental problems, including land and soil pollution.
The following table lists some of the effects of the production of consumer goods:
The expansion of mining activities in many countries has now become a major cause of land pollution due to loss of soil and destruction of land. Mining has become a threat to the environment because it leads to the huge quantity of waste generally not useful to man and its reprocessing is not economical. Mining operations produce about 1.35 billion tonnes of debris each year.
3. Agricultural Wastes:
Agricultural practices also pollute the soil. According to an estimate, agricultural activities produce more than 1.8 billion tonnes of waste, each year.
About three-quarters of this is manure. Much of this manure is piled in dumps where it pollutes streams and waterways. Yet, at the same time, farmers across the continent are suffering from worn-out and depleted soils. Other agricultural wastes include branches and slash left over from logging apart from animal wastes.
In addition to fertilisers and pesticides, soil conditioners and fumigants are used in agriculture. Organic compounds containing lead, mercury and arsenic, when applied to a land, accumulate on the soil permanently and introduce these toxic metals into plant products.
4. Radioactive Materials:
The radioactive wastes produced by nuclear testing laboratories and industries reach the soil and accumulate there. Wastes from nuclear reactors contain ruthenium-106 and rhodium-106, iodine-131, barium-140, lanthanum-140, cerium-144, etc. All the radionuclides deposited on the soil emit gamma radiations, and are harmful to soil as well as for plant growth.
5. Biological Agents:
The excreta of humans, animals and birds are also a source of soil pollution by biological agents. Digested sewage sludge, which is used as manure, also causes soil pollution. In the developing countries, intestinal parasites constitute the most serious soil pollution problems. Faulty sanitation, waste water and wrong methods of agriculture also induce soil pollution.
There are three groups of pathogenic organisms that pollute the soil, viz.:
(i) Pathogenic organisms excreted by man, (ii) pathogenic organism excreted by animals, and (iii) pathogenic organisms found in contaminated soil.