SOIL POLLUTION
Composition of Soil
•Mineral Matter (40-45%): This consists of inorganic
particles derived from the weathering of rocks and minerals.
These particles are classified by size as: Sand (0.1 - 2 mm):
Large particles that provide aeration and drainage.
•Silt (0.002 - 0.1 mm): Medium-sized particles that retain
more water and nutrients than sand.
•Clay (< 0.002 mm): Very small particles with a large surface
area, allowing for high water and nutrient retention.
Organic Matter (5%): This includes decomposed plant and
animal residues (humus), living organisms (microbes, roots,
etc.), and their byproducts. It improves soil structure, water
retention, and nutrient availability. Water (25%): Occupies
the pore spaces between soil particles and is essential for plant
growth and nutrient transport. The amount of water varies
depending on rainfall, drainage, and soil type. Air (25%):
Fills the remaining pore spaces and provides oxygen for plant
roots and soil organisms. The proportion of air and water is
inversely related.
O Horizon (Organic Layer): This is the uppermost layer, dominated by organic
material. It's made up of decomposed or decaying plant and animal matter (like leaf
litter, humus). This layer is usually dark in color and rich in nutrients. You'll find it
particularly well-developed in forests.
A Horizon (Topsoil): This layer is a mixture of mineral material (sand, silt, clay)
and humus. It's typically darker than the layers below and is where most of the
biological activity occurs – think roots, earthworms, and microorganisms. This is the
crucial layer for plant growth.
E Horizon (Eluviation Layer): This layer is often lighter in color and found below
the A horizon. It's characterized by the leaching or eluviation of clay, iron, and
aluminum oxides down to lower layers. This process leaves behind a concentration
of resistant minerals like quartz. This horizon isn't always present and is most
common in older, well-developed soils in forested areas.
B Horizon (Subsoil): This layer is where the materials leached from the E horizon
(clay, iron, aluminum oxides) accumulate. It's often denser and richer in these
materials than the horizons above. The B horizon can have different sub-horizons
(like Bt for clay accumulation, Bo for oxide accumulation).
C Horizon (Parent Material): This layer consists of weathered parent material – the
original rock or unconsolidated material from which the soil developed. It shows less
evidence of soil formation processes compared to the horizons above. You might still
see recognizable fragments of the original rock here.
R Horizon (Bedrock): This is the solid rock layer beneath the soil profile. It's not
technically considered part of the soil but is the underlying material.
Causes of Soil Pollution
Industrial Activities:
•Discharge of untreated industrial wastewater
containing heavy metals and toxic chemicals.
•Leakage and spills of hazardous substances
during manufacturing and storage.
•Disposal of industrial solid waste in landfills or
open areas.
•Emissions from industrial processes settling on
the soil (e.g., heavy metals from smelting)
Agricultural Practices:
•Excessive and improper use of chemical fertilizers
leading to nitrate and phosphate buildup.
•Overuse of pesticides and herbicides that persist in the
soil and harm non-target organisms.
•Animal waste (manure) if not managed properly, leading
to nutrient overload and pathogen contamination.
•Soil erosion carrying pesticide and fertilizer residues into
other areas.
Waste Disposal:
•Uncontrolled dumping of household and commercial
solid waste (plastics, paper, metals, etc.).
•Leachate from landfills seeping into the soil and
groundwater, carrying pollutants.
•Improper disposal of hazardous waste (e.g., batteries,
electronic waste, medical waste).
Mining Activities:
•Release of heavy metals and acid mine drainage from
mining sites.
•Disposal of mine tailings containing toxic substances.
•Land disturbance and erosion leading to the spread of
contaminated soil.
Urbanization and Construction:
•Spills of oil, gasoline, and other chemicals from vehicles and construction
equipment.
•Disposal of construction and demolition waste.
•Leakage from underground storage tanks (e.g., fuel tanks at gas stations).
•Sewage leaks and overflows contaminating the soil with pathogens and
nutrients.
Accidental Spills:
•Transportation accidents involving chemicals and petroleum products.
•Pipeline leaks releasing oil and gas into the soil.
Atmospheric Deposition:
•Acid rain containing sulfuric and nitric acids, altering soil pH and leaching
nutrients.
•Settling of airborne pollutants (e.g., heavy metals, particulate matter) onto
the soil.
Soil Pollution Control
Control Method Description Examples
Avoiding the introduction of pollutants - Use of organic farming
Prevention
into the soil - Proper waste disposal
Using microorganisms to break down - Phytoremediation (plants absorb toxins)
Bioremediation
pollutants in soil - Composting
Applying chemicals to neutralize or
Chemical Remediation - Use of lime to neutralize acidic soils
immobilize pollutants
Removing contaminants by washing the
Soil Washing - Flushing out heavy metals
soil with water or solvents
Heating soil to evaporate or break down
Thermal Remediation - Thermal desorption systems
contaminants
Preventing the spread of pollution - Landfilling with liners
Containment
through barriers - Capping contaminated sites
Government policies and laws to regulate - Bans on certain pesticides
Legislative Measures
pollution - Environmental protection acts
Educating people about the causes and - School programs
Public Awareness & Education
effects of soil pollution - Community workshops
Reducing waste generation that - Composting organic waste
Recycling and Reuse
contributes to soil pollution - Reusing industrial by-products
