Soil Pollution
Dr. Saheli Pradhan Mitra
• Soil, the uppermost layer of the earth’s crust is
a mixture of many solid, liquid and gaseous
substances having both living and non-living
matter such as mineral particles, decaying
organic matter, microbes along with water and
air contained in pore spaces.
• Formation of soil is a very slow process
starting from weathering (Breakdown of bed rock
into mineral particles) to soil development i.e.
pedogenesis (modification of mineral matter
through interactions between biological,
topographic and climatic factors).
• It may take 200 to some thousand years to
form an inch of top-soil depending upon the
local conditions of the area.
• Thus, soil is an important natural resource,
formed over the centuries that supports the
variety of plants and provides habitat for various
microscopic and macroscopic life-forms apart
from other ecological functions.
SOIL POLLUTION
• Soil pollution is the contamination of the soil with pollutants, toxic chemicals or any
contaminant in such a quantity that reduces soil quality and makes it inhabitable to
organisms such as insects and other microbes.
• It can also be referred to as the addition of chemicals to the soil in quantities that
are toxic to the environment and its residents.
• This addition is mostly by human activities such as mining, modern practices in
agriculture, deforestation, indiscriminate dumping of human generated trash and
unregulated disposal of untreated wastes of various industries.
CAUSES OF SOIL 1. Industrial and Mining Activities:
POLLUTION
• Large numbers of Industries coming up
since the dawn of industrial era without
proper waste management systems are
the biggest contributor to soil pollution.
• Also, since the amount of mining and
manufacturing has increased, and
most industries are dependent on
extracting minerals from the Earth.
Whether it is iron ore or coal, the by
products are contaminated and they
are not disposed off in a manner that
can be considered safe. As a result, the
industrial waste dumped on the soil
surface for a long period of time
degrades it.
2. Modern Agricultural Practices:
• To increase the yield from limited land area, in
order to meet the increasing demand of food for
ever increasing population, synthetic chemical
pesticides and fertilizers are being used
rampantly in last few decades leading to
toxicity of the soil.
• They seep into the ground after they mix with
water and slowly reduce the fertility of the soil.
• Other chemicals damage the composition of
the soil and make it easier to erode by water
and air.
• Plants absorb many of these pesticides and
when they decompose, they cause soil
pollution since they become a part of the land.
3. Lack of proper Waste
Disposal:
Modern lifestyle, urban as well as
rural, produces huge amount of
waste and lack of waste
management procedures adds to the
problem of soil pollution. Urban
wastes comprise of both commercial
and domestic wastes consisting of
dried sludge and sewage, garbage
and rubbish materials like plastics,
glasses, metallic cans, fibres, paper,
rubbers, street sweepings, fuel
residues, leaves, containers,
abandoned vehicles and other
discarded manufactured products.
Plastic and other non biodegradable
wastes are the major cause of
concern.
4. Radioactive Pollutants:
• Radioactive substances resulting from explosions of nuclear testing laboratories,
radioactive fallout and industries giving rise to nuclear dust and radioactive wastes
penetrate the soil and accumulate giving rise to soil pollution.
• E.g. Nuclear reactors produce waste containing Ruthenium-106, Iodine-131, Barium-
140, Cesium-144 and Lanthanum-140 along with primary nuclides.
• Sr-90 with a half life 28 years and Cs-137 with a half life 30 years.
• Rainwater carries Sr-90 and Cs-137 to be deposited on the soil where they are held
firmly with the soil particles by electrostatic forces.
• All the radio nuclides deposited on the soil emit gamma radiations.
5. Biological Agents:
Soil gets a large amount of human, animal and bird excreta which constitute a major
source of land pollution by biological agents. E.g. Heavy application of manures and
digested sludge can cause serious damage to plants within a few years.
6. Accidental Oil Spills:
Oil leaks can happen during storage and transport of chemicals. This can be seen at
most of the fuel stations. The chemical present in the fuel deteriorates the quality of
soil and make them unsuitable for cultivation. These chemicals can enter into the
groundwater through soil and make the water undrinkable.
7. Acid Rain:
Acid rain is caused when pollutants present in the air mixes up with the rain and fall
back on the ground. The polluted water could dissolve away some of the important
nutrients found in soil and change the structure of the soil.
EFFECT OF SOIL POLLUTION
Impacts of soil pollution are not confined to soil and its biota but are carried over to every aspect
of the environment and affect every organism from the earthworm to humans. Some of the
adverse effects are as follows:
Human health
Since we are dependent on the land for our food, pollution from the soil is transferred to us in
this manner. Bio accumulation of toxins occurs in our bodies, causing chronic poisoning, and
leading to various diseases. Reproductive health, birth and developmental defects, neurologic
effects, malnutrition, and mutations in the cells of the body leading to cancers; all these are on
the increase today.
Growth of plants
Plants will not be able to adapt to sudden changes occurring in the soil. Fungi and bacteria
found in the soils cannot bind the soil due to chemical changes and this causes soil erosion.
Large tracts of land become barren; unable to support any life on it. Even the plants that do grow
on these lands will absorb the toxins and transfer to the food chain.
Main criteria that accentuate vulnerability to soil pollution
Main DNA damages caused by genotoxic agents
Radiation-induced DNA damage
and cell repairing mechanisms.
Microplastics accumulation in mice tissues after exposure for 28 days
CONTROL MEASURES OF SOIL POLLUTION
A. Prevention of soil erosion:
1.Conservational till farming or no-till farming:
Traditionally, land is ploughed to make a planting surface. This disturbs the soil and makes it
susceptible to erosion. The no-till farming method makes minimum disturbance to the topsoil
by making slits in the un-ploughed soil. Seeds, fertilizers and water are injected in these slits.
2. Contour farming:
In this method, crops are planted in rows along contours of gently sloped land. Each row acts
as a small dam to hold soil thereby slowing water runoff.
3. Terracing:
In this method, steep slopes are converted into a series of broad terraces that run across the
contour. This retains water for crops and reduces soil erosion by controlling runoff.
4. Alley cropping or Agro-forestry:
This method involves planting crops in strips
or alleys between rows of trees or shrubs that
provide fruits and fuel wood. Hence, when the
crop is harvested, the soil will not be eroded
as the trees and shrubs remain on ground
holding the soil particles.
5. Wind breaks or shelter belts:
In this technique, trees are planted in long
rows along the boundary of cultivated land
which block the wind and reduce soil erosion.
Wind breaks help in retaining soil moisture,
supply wood for fuel and provide habitat for
birds.
B. Sustainable Practices:
Number of sustainable practices can be applied in order to prevent spreading of desertification.
Checking overgrazing- Fewer animals in the same area will allow plants to grow back.
Integrated farming - Keep animals and grow crops. Use the manure from the animals to replace soil
nutrients where the crops grow. Swap the place where the crops grow and the animals graze from
time to time.
Plant more trees - These will protect the soil surface from the impact of rain and the effects of wind.
The roots will bind the soil together and trap water.
Build earth dams - These are small dams which follow the contours of the soil. When it rains, the
water does not run off the surface, but is trapped and infiltrates the soil
C. Remedies to correct salt affected soil
Deep Tilling:
Deep tilling can improve drainage for soils with high salt levels. This method works by breaking
up hard soils or rocklike soil layers that prevent the downward flow of water. But is usually
temporary, as some parts of the soil may harden and reseal.
Flushing Soil and Preventing Evaporation:
Flushing the soil is the process of irrigating the area with a low-salt water and washing the salt
below the root zone; provided soils have good drainage. When water evaporates on a dry soil
surface, it leaves salt behind. Mulching can help in retaining soil moisture.
Chemical remediation:
Modifying salty soils with sulphur, lime or calcium can help in removing or replacing the
sodium in the soil. But several factors like area's groundwater, soil condition, geological
factors etc. should be pondered before applying chemical remediation.
D. Ways to minimize the soil acidification process:
The use of less acidifying farming practices: Retain crop residue, no nitrate residue, less tillage
etc. Applications of agricultural lime: The addition of lime raises the soil pH to some prescribed
value (pH 6.0 to 7.0).
E. Production and use of natural fertilizers:
To prevent harmful effects of chemical fertilizers, biological routes of soil fertility are being
adopted. Organic farming should be practiced.
F. Education:
Education is an important tool that needs to be utilized in order to help people to understand the
best way to use the land. By educating them on sustainable practices, more land will be saved
from being getting polluted.
IMMEDIATE CONTROL MEASURES OF SOIL POLLUTION
While detailed investigations are being undertaken and the remediation strategy is being
developed, emergency risk reduction measures should be put in place immediately to safeguard
public health and the environment. These measures should be simple and quick to implement.
However, a risk assessment should be undertaken first to avoid risks of further exposure during
their implementation. Examples of such measures can include:
• stopping further release of the contaminant into the soil;
• covering the polluted area with an impermeable layer to prevent release of vapours and rain-
water runoff and leaching;
• briefing local communities about the risks of the site;
• erecting warning signage;
• securing the site for example with a fence, to restrict access to the public and livestock;
• restricting the use of the land to non-food production;
• warning public and restricting use of harvested crops or livestock products for food; and,
• providing an alternative safe water supply.
