Soil pollution –sources and its impact on environment and management techniques

Soil pollution is defined as the build-up in soils of persistent toxic compounds, chemicals, salts, radioactive materials, or disease causing agents, which have adverse effects on plant growth and animal health

Major sources

1. Agriculture

a.    Accumulation of animal manures:-Undecomposed cowdung, Poultry litter etc

b.   Excessive input of chemical fertilizers: As, Pb and Cd present in traces in rock phosphate mineral 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 indestructible poison for crops. Eventually, these fertilizers seep into the soil and poison groundwater supplies. Rain and irrigation may also cause runoff that directs these chemicals to local waterways, or deposits them in the soil at other locations.

c. Illicit dumping of tainted crops on land:- Wide C:N ratio

d. Indiscriminate use of pesticides:- organo chlorines viz., DDT, BHC, endosulphan. 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. An infamous herbicide used as a defoliant in the Vietnam War called Agent Orange (dioxin), was eventually banned. Soldiers' cancer cases, skin conditions and infertility have been linked to exposure to Agent Orange.

e. Deforestation:- removal of top soil

f. Unhealthy soil management:- Improper tillage of soil results in the deterioration of soil structure. Use of straight fertilizers, avoiding micronutrient fertilizers, Avoiding organic and green manures, excessive use of non biodradable synthetic fertilizers, improper maintenance of soil acidity, sodicity, poor drainage,

2. Mining and quarrying
• using of explosives to blow up mines
• using of machineries which emits toxic byproducts and leaks to the ground
• toxic mine tailings
3. Sewage sludge
• improper sanitation system causes sludge to leak at surrounding soil or rupture of underground storage tanks,
4. Dredged spoils
• improper method of dredging at fertile land causes soil infertility, leaving the soil more prone to external pollution
5. Household/urban activities  
• improper waste disposal system causes waste accumulation
• improper sanitation system
6. Demolitions and constructions

o    non biodegradable rubbles or debris which are not cleared settled in the soil undergo chemical reactions and increase soil toxicity

7. Industrial

Solid wastes oils, battery metals, heavy metals from smelting industries and organic solvents 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

• poisonous/toxic emissions of gases which are not filtered or neutralized
• 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.

Effects

1.    Ecosystem

a)    Reduced soil fertility by accumulation of heavy metals, undecomposed animal manures

b)   Increased salinity due to water logging

c)    Quality reduction in crops

d)    Reduced nitrogen fixation

e)    Increased erodibility

f)     Larger loss of soil and nutrients

g)    Deposition of silt in tanks and reservoirs

h)   Reduced crop yield

i)     Imbalance in soil fauna and flora

j)     Accumulation of toxins in food chain

k)   Dangerous chemicals entering underground water

l)     Release of pollutant gases

m)  Acid mine drainage

n)   Reduced vegetation

o)    Radical soil chemistry changes

p)   Alteration of metabolism of endemic microorganisms and arthropods resident in a given soil environment.

q)    virtual eradication of some of the primary food chain

r)    Biomagnification

s)    Potential extinction of species

t)     Increased soil erosion

u)   Ecological imbalance

2.    Health effects

Health consequences from exposure to soil contamination vary greatly depending on pollutant type, pathway of attack and vulnerability of the exposed population. Chronic exposure to chromium, lead and other metals, petroleum, solvents, and many pesticide and herbicide formulations can be carcinogenic, can cause congenital disorders, or can cause other chronic health conditions. Industrial or man-made concentrations of naturally-occurring substances, such as nitrate and ammonia associated with livestock manure from agricultural operations, have also been identified as health hazards in soil and groundwater.

Chronic exposure to benzene at sufficient concentrations is known to be associated with higher incidence of leukemia. Mercury and cyclodienes are known to induce higher incidences of kidney damage, some irreversible. PCBs and cyclodienes are linked to liver toxicity. Organophosphates and carbamates can induce a chain of responses leading to neuromuscular blockage. Many chlorinated solvents induce liver changes, kidney changes and depression of the central nervous system. There is an entire spectrum of further health effects such as headache, nausea, fatigue, eye irritation and skin rash for the above cited and other chemicals. At sufficient dosages a large number of soil contaminants can cause death by exposure via direct contact, inhalation or ingestion of contaminants in groundwater contaminated through soil.

Control of soil pollution

The following steps have been suggested to control soil pollution.

Prevent soil erosion

Soil erosion, which leads to the depletion of nutrient-rich topsoil, harms ecosystems and leads to the contamination of underlying layers of soil. Vegetation is a key factor in preventing erosion. People should retain native plants, especially grasses and trees. They should replace trees that are cut down. Farmers can prevent erosion by following agricultural practices that reduce erosion damage, such as minimizing tillage and rotating crops

 

 

Manage Livestock

Manures like polultry manure has to be composted using suitable technology.

Reducing chemical fertilizer and pesticide use

Applying bio-fertilizers, pesticides and manures can reduce chemical fertilizer and pesticide use.

Application of 3 R concept

Concepts like reuse, recovery and reduce will be useful. Reusing of materials such as glass containers, plastic bags, paper, cloth etc. can be reused at domestic levels rather than being disposed, reducing solid waste pollution. Recycling and recovery of materials 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.

Reforestation

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

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. Burying the waste in locations situated away from residential areas is the simplest and most widely used technique of solid waste management. Environmental and aesthetic considerations must be taken into consideration before selecting the dumping sites.

Incineration of other wastes is expensive and leaves a huge residue and adds to air pollution. Pyrolysis is a process of combustion in absence of oxygen or the material burnt under controlled atmosphere of oxygen. It is an alternative to incineration. The gas and liquid thus obtained can be used as fuels. It is an alternative to incineration. The gas and liquid thus obtained can be used as fuels. Pyrolysis of carbonaceous wastes like firewood, coconut, palm waste, corn combs, cashew shell, rice husk paddy straw and saw dust, yields charcoal along with products like tar, methyl alcohol, acetic acid, acetone and a fuel gas.

Anaerobic/aerobic 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.

Cleanup options

·         Excavate soil and take it to a disposal site away from ready pathways for human or sensitive ecosystem contact. This technique also applies to dredging of bay muds containing toxins.

·         Aeration of soils at the contaminated site (with attendant risk of creating air pollution)

·         Thermal remediation by introduction of heat to raise subsurface temperatures sufficiently high to volatize chemical contaminants out of the soil for vapour extraction.

·         Bioremediation, involving microbial digestion of certain organic chemicals. Techniques used in bioremediation include land farming, biostimulation and bioaugmentating soil biota with commercially available microflora.

·         Extraction of groundwater or soil vapor with an active electromechanical system, with subsequent stripping of the contaminants from the extract.

·         Containment of the soil contaminants (such as by capping or paving over in place).

·         Phytoremediation, or using plants (sesame, sunflower) to extract heavy metals

Dendroremediation, using of trees (such as willow))to extract heavy metals