Environmental biology is one of the critical Biology Topics that involves understanding how humans impact the environment and how to address environmental issues.
Understanding the Different Types of Soil Pollutants – Environmental Impacts and Mitigation
Soil pollution is defined as the buildup in soils of persistent toxic compounds, chemicals, salts, radioactive materials, or disease-causing agents, which have adverse effects on plant growth and animal health. Soil is the thin layer of organic and inorganic materials that covers the Earth’s rocky surface. The organic portion, which is derived from the decayed remains of plants and animals, is concentrated in the dark uppermost topsoil. The inorganic portion made up of rock fragments, was formed over thousands of years by physical and chemical weathering of bedrock. Productive soils are necessary for agriculture to supply the world with sufficient food.
The different ways by which soil becomes polluted are as follows:
- Seepage from a landfill.
- Discharge of industrial waste into the soil.
- Percolation of contaminated water into the soil.
- Rupture of underground storage tanks.
- Excess application of pesticides, herbicides, or fertilizer.
- Solid waste seepage.
The most common chemicals involved in causing soil pollution are:
- Petroleum hydrocarbons
- Heavy metals
Causes of Soil Pollution
Soil pollution is caused by the presence of man-made chemicals or other alterations in the natural soil environment. This type of contamination typically arises from the rupture of underground storage links, application of pesticides, percolation of contaminated surface water to subsurface strata, oil and fuel dumping, leaching of wastes from landfills, or direct discharge of industrial wastes to the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead, and other heavy metals. The occurrence of this phenomenon is correlated with the degree of industrialization and intensity of chemical usage.
A soil pollutant is any factor that deteriorates the quality, texture, and mineral content of the soil or which disturbs the biological balance of the organisms in the soil. Pollution in soil has an adverse effect on plant growth. Pollution in soil is associated with
- Indiscriminate Use of Fertilizers
- Indiscriminate Use of Pesticides, Insecticides and Herbicides
- Dumping of Large Quantities of Solid Waste
- Deforestation and Soil Erosion
1. Indiscriminate Use of Fertilizers:
Soil nutrients are important for plant growth and development. Plants obtain carbon, hydrogen, and oxygen from air and water. But other necessary nutrients like nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, and more must be obtained from the soil. Farmers generally use fertilizers to correct soil deficiencies. Fertilizers contaminate the soil with impurities, which come from the raw materials used for their manufacture. Mixed fertilizers often contain ammonium nitrate (NH4NO3), phosphorus as P2O5, and potassium as K2O. For instance, As, Pb, and Cd present in traces in rock phosphate minerals get transferred to super phosphate fertilizer. Since the metals are not degradable, their accumulation in the soil above their toxic levels due to excessive use of phosphate fertilizers becomes an in-destructible poison for crops.
The overuse of NPK fertilizers has reduced the quantity of vegetables and crops grown on soil over the years. It also reduces the protein content of wheat, maize, grams, etc., grown on that soil. The carbohydrate quality of such crops also gets degraded. Excess potassium content in soil decreases Vitamin C and carotene content in vegetables and fruits. The vegetables and fruits grown on over-fertilized soil are more prone to attacks by insects and diseases.
2. Indiscriminate Use of Pesticides, Insecticides and Herbicides:
Plants on which we depend for food are under attack from insects, fungi, bacteria, viruses, rodents, and other animals, and must compete with weeds for nutrients. To kill unwanted populations living in or on their crops, farmers use pesticides. The first widespread use of insecticides that began at the end of World War II and included DDT (dichloro diphenyl trichloroethane) is gammaxene. Insects soon became resistant to DDT and as the chemical did not decompose readily, it persisted in the environment. Since it was soluble in fat rather than water, it biomagnified up the food chain and disrupted calcium metabolism in birds, causing eggshells to be thin and fragile. As a result, large birds of prey such as the brown pelican, ospreys, falcons, and eagles became endangered. DDT has now been banned in most Western countries. Ironically many of them including the USA, still produce DDT for export to other developing nations whose needs outweigh the problems caused by it.
The most important pesticides are DDT, BHC, chlorinated hydrocarbons, organophosphates, aldrin, malathion, dieldrin, furodan, etc. The remnants of such pesticides used on pests may get adsorbed by the soil particles, which then contaminate root crops grown in that soil. The consumption of such crops causes the pesticides remnants to enter human biological systems, affecting them adversely.
3. Dumping of Solid Wastes:
In general, solid waste includes garbage, domestic refuse or municipal solid wastes and discarded solid materials such as those from commercial, industrial and agricultural operations. They contain increasing amounts of paper, cardboards, plastics, glass, old construction material, packaging material and toxic or otherwise hazardous substances. Since a significant amount of urban solid waste tends to be paper and food waste, the majority is recyclable or biodegradable in landfills. Similarly, most agricultural waste is recycled and mining waste is left on site.
The portion of solid waste that is hazardous such as oils, battery metals, heavy metals from smelting industries and organic solvents are the ones we have to pay particular attention to. These can in the long run, get deposited to the soils of the surrounding area and pollute them by altering their chemical and biological properties. They also contaminate drinking water aquifer sources. More than 90% of hazardous waste is produced by chemical, petroleum and metal-related industries and small businesses such as dry cleaners and gas stations contribute as well.
4. Deforestation and Soil Erosion:
Soil erosion occurs when the weathered soil particles are dislodged and carried away by wind or water. Deforestation, agricultural development, temperature extremes, precipitation including acid rain, and human activities contribute to this erosion. Humans speed up this process by construction, mining, cutting of timber, over cropping and overgrazing. It results in floods and cause soil erosion.
Forests and grasslands are an excellent binding material that keeps the soil intact and healthy. They support many habitats and ecosystems, which provide innumerable feeding pathways or food chains to all species. Their loss would threaten food chains and the survival of many species. During the past few years quite a lot of vast green land has been converted into deserts. The precious rain forest habitats of South America, tropical Asia and Africa are coming under pressure of population growth and development (especially timber, construction and agriculture). Many scientists believe that a weather of medicinal substances including a cure for cancer and aids, lie in these forests. Deforestation is slowly destroying the most productive flora and fauna areas in the world, which also form vast tracts of a very valuable sink of CO2.
Pollution due to Urbanisation
Urban activities generate large quantities of city wastes including several biodegradable materials (like vegetables, animal wastes, papers, wooden pieces, carcasses, plant twigs, leaves, cloth wastes as well as sweepings) and many non-biodegradable materials (such as plastic bags, plastic bottles, plastic wastes, glass bottles, glass pieces, stone/cement pieces). On a rough estimate Indian cities are producing solid city wastes to the tune of 50,000-80,000 metric tons every day. If left uncollected and decomposed, they are a cause of several problems such as:
- Clogging of Drains: Causing serious drainage problems including the burst/leakage of drainage lines leading to health problems.
- Barrier to movement of water: Solid wastes have seriously damaged the normal movement of water thus creating problem of inundation, damage to foundation of buildings as well as public health hazards.
- Foul smell: Generated by dumping the wastes at a place.
- Increased microbial activities: Microbial decomposition of organic wastes generate large quantities of methane besides many chemicals to pollute the soil and water flowing on its surface.
- Hospital wastes: Solid hospital wastes may create many health problems as they may have dangerous pathogen within them besides dangerous medicines and injections.
Pollution of Underground Soil
Underground soil in cities is likely to be polluted by:
- Chemicals released by industrial wastes.
- Decomposed and partially decomposed materials of sanitary wastes.
Many dangerous chemicals like cadmium, chromium, lead, arsenic, selenium products are likely to be deposited in underground soil. Similarly underground soil polluted by sanitary wastes generate many harmful chemicals. These can damage the normal activities and ecological balance in the underground soil.
Effects of Soil Pollution
- Reduce soil fertility.
- Reduce nitrogen fixation.
- Increase erodibility.
- Larger loss of soil and nutrients.
- Deposition of silt in tanks and reservoirs.
- Reduce crop yield.
- Imbalance in soil fauna and flora.
- Dangerous chemicals entering underground water.
- Ecological imbalance.
- Release of pollutant gases.
- Release of radioactive rays causing health problems.
- Increase salinity.
- Reduce vegetation.
- Clogging of drains.
- Inundation of areas.
- Public health problems.
- Pollution of drinking water sources.
- Foul smell and release of gases.
- Waste management problems.
Control of Soil Pollution
The following steps have been suggested to control soil pollution. To help prevent soil erosion, we can limit con-struction in sensitive areas. In general we would need less fertilizer and fewer pesticides if we could all adopt thej three R’s: Reduce, Reuse, and Recycle. This would give us less solid waste.
1. Reducing chemical fertilizer and pesticide use:
Applying bio-fertilizers and manures can reduce chemical fertilizer and pesticide use. Biological methods of pest control can also reduce the use of pesticides and thereby minimize soil pollution.
2. Reusing of materials:
Materials such as glass containers, plastic bags, paper, cloth etc., can be reused at domestic levels rather than being disposed, reducing solid waste pollution.
3. Recycling and recovery of materials:
This is a reasonable solution for reducing soil pollution. Materials such as paper, some kinds of plastics and glass can and are being recycled. This decreases the volume of refuse and helps in the conservation of natural resources. For example, recovery of one tonne of paper can save 17 trees.
Control of land loss and soil erosion can be attempted through restoring forest and grass cover to check wastelands, soil erosion and floods. Crop rotation or mixed cropping can improve the fertility of the land.
5. Solid waste treatment:
Proper methods should be adopted for management of solid waste disposal. Industrial wastes can be treated physically, chemically and biologically until they are less hazardous. Acidic and alkaline wastes should be first neutralized; the insoluble material if biodegradable should be allowed to degrade under controlled conditions before being disposed. As a last resort, new areas for storage of hazardous waste should be investigated such as deep well injection and more secure landfills. Anaerobic decomposition of biodegradable municipal and domestic waste is also being done and gives organic manure. Cow dung which releases methane into the atmosphere, should be processed further in ‘gobar gas plants’ to produce ‘gobar gas’ and good manure.
Contribution of Ramesh Chandra Dagar
Ramesh Chandra Dagar is a simple farmer who has made great revolution in farming. A visit to his farmland in Akbarpur Barota village, Sonipat district, Haryana can be quite an eye opener. The farmland resembles the laboratory of any agricultural scientist. Dagar says, “I am a simple farmer, who has studied only up to the 10th standard. I used to keep hearing claims of the govenment that small land holdings are not viable for agriculture. And that set me thinking. About four years back, I set aside 1 ha from my agricultural land and started experimenting on it. Today I am confident that this land can give a minimum income of Rs. 10 lakh per annum.”
Dagar follows what is known as integrated organic farming. “Such farming does not merely mean not using pesticides,” he says. “It also comprises many other practices such as bee keeping, dairy management, biogas production, water harvesting and composting. A good combination of all these practices is sure to make organic farming successful, both ecologically and financially,” adds Dagar.
Today he is busy spreading the message of integrated organic farming in his home state. With support of other farmers, he has set up the Haryana Kisan Welfare Club, which has branches in all districts in the state. Almost 5,000 farmers are active members of this club and they are fast spreading the word around. In states such as Rajasthan, Madhya Pradesh and Gujarat there are now efforts at replicating organic farming clubs.
Dagar’s farm pond is the site of yet another innovative cycle. Most farmers avoid having such a pond since that would eat away precious agricultural land. Dagar says, “We tell farmers to go in for water predicament set me thinking. And I decided to go in for water harvesting, which also gives immediate benefits.” His farm pond collects rainwater, which is used in the dairy to wash buffaloes. “I have also introduced fish into the pond; that fetches me about Rs. 30,000 per annum. So, I am not only recharging groundwater, but also making money out of it,” explains the organic farmer.
The most important element of Dagar’s farm practice is bee keeping; it increases his crop output by 10-30 per cent (bees are very effective in natural pollination). Also the honey produced has great demand. Dagar has about 150 bee boxes; each generates about 35-40 kg of honey. His total annual income from honey is Rs. 4 lakh. “Bee keeping is a very profitable business that can be undertaken by even a landless farmer. And one farmer can benefit an area of about 2-3 km, the normal area covered by one bee,” says Dagar.
Today Dagar is busy spreading the word of integrated farming throughout the country. Farmers from Haryana are playing a lead role in the mission. The Haryana Kisan Welfare Club gives hands-on training on organic farming. Since most farmers cannot come to the district clubs, workshops are organized at village level. In February this year, a gathering of about 4,000 farmers was organised at Sonipat. Apart from farmers, experts, agricultural scientists and bureaucrats were invited. But Dagar concedes that motivating government machinery towards integrating organic farming is a big task. “Jo sarak sarak kar chale who sarkar (The government is something that crawls along slowly),” he remarks casually.