Soil pollution is the contamination of soil by harmful chemicals or substances,
often from human activities.
The root cause of soil pollution is often one of the following:
•Agriculture (excessive/improper use of pesticides)
•Excessive industrial activity
•Poor management or inefficient disposal of waste
What are the Pollutants that Contaminate Soil?
Some of the most hazardous soil pollutants are xenobiotics –
substances that are not naturally found in nature and are synthesized by
human beings. The term ‘xenobiotic’ has Greek roots – ‘Xenos’
(foreigner), and ‘Bios’ (life). Several xenobiotics are known to be
• Major part of global domestic and industrial waste
• Not easily biodegraded
• Waste plastic accumulates much thus adds to severe pollution
• Takes several years to disintegrate – 400 years to degrade mineral
• In USA, plastics are 7% in weight and 30% of the volume
• Use of biodegradable plastic solves the problem of pollution
Photodegradable or biodegradable plastic contains an element
sensitive to UV rays. In the presence of solar rays, the element
is activated and breaks polymeric chain into small fragments
that are easily digested
What is biodegradable plastic?
During the manufacture – 6% starch and Oxidizing agent
(vegetable oil) added to polymers
In case of metallic salts
Present in soil interact with oxidizing agent to form ferric
Attacks polymer bonds
Sets degradation of plastic in motion
Parallely, soil microbes break starch grains which results
in an increased attack surface
Finally accelerates auto oxidation process
• Starch present reduces water resistance of plastic
• Addition of fine protective layer to the starch based
plastic make it possible to obtain high degree of water
Plastics with 50% starch in the market
Biodegradable plastics offers solution to pollution
due to plastics
• Include pesticides, herbicides, fungicides
• Pesticides applied reach the soil ultimately
• Accumulation of pesticide residues in biosphere
creates ecological stress causing soil, water and
• Persisting chemicals are hazardous to human
• Total remediation is impossible
• Reduction of residue levels through redeeming
• Pesticides serve as nutrients (C,N,S) or substrate
for energy - many microorganisms
• Certain pesticides are metabolized but does not
serve as nutrient, transformation is by co-
• Many pesticides and their metabolites are toxic to
microorganisms – Mercuric fungicides are toxic to
Rhizobium, Nitrosomonas and Nitrobacter
• Continuous application – Deterioration in soil
properties, cultivated soils lose their characteristics
• Application of Amm. sulphate, Amm. chloride & Urea
reduce soil pH
• Crops – potato, grapes, citrus, beans – sensitive to
• Application of organic manures and biofertilizers reduce
the soil from pollution
Foreign and harmful substance or organism in a biological system
Derived from Greek Xeno meaning stranger and Bio means life
Life describes some toxic substances, parasites and
Drugs, Food and poisons when consumed in levels more than the
normal dose is linked to toxicity
Xenobiosis – In communities of species when two distinct species
share living space
At ecosystem level – toxic waste when bioaccumulation in the food
chain / food web we call it Xenobiotic
Arsenic Mercury Lead
Antimony Zinc Nickel
Cadmium Selenium Beryllium
Thallium Chromium Copper
The presence of heavy metals (such as lead and mercury, in abnormally high concentrations) in soils can
cause it to become highly toxic to human beings. Some metals that can be classified as soil pollutants are
These metals can originate from several sources such as mining activities, agricultural activities, and electronic waste (e-waste), and medical
Toxic Metals that Cause Soil Pollution
Polycyclic Aromatic Hydrocarbons
Polycyclic aromatic hydrocarbons (often abbreviated to PAHs) are organic compounds that
1.Contain only carbon and hydrogen atoms.
2.Contain more than one aromatic ring in their chemical structures.
Common examples of PAHs include naphthalene, anthracene, and phenalene. Exposure to polycyclic
aromatic hydrocarbons has been linked to several forms of cancer. These organic compounds can also
cause cardiovascular diseases in humans.
Soil pollution due to PAHs can be sourced to coke (coal) processing, vehicle emissions, cigarette smoke,
and the extraction of shale oil.
The discharge of industrial waste into soils can result in soil pollution. Some common soil pollutants that can
be sourced from industrial waste are listed below.
•Chlorinated industrial solvents
•Dioxins are produced from the manufacture of pesticides and the incineration of waste.
•Polychlorinated biphenyls (PCBs)
The petroleum industry creates many petroleum hydrocarbon waste products. Some of these wastes, such
as benzene and methylbenzene, are known to be carcinogenic in nature.
What are the Negative Consequences of Soil Pollution?
Soil pollution harbours a broad spectrum of negative consequences that affect plants,
animals, humans, and the ecosystem as a whole. Since children are more susceptible to
diseases, polluted soil poses a greater threat to them. Some important effects of soil pollution
are detailed in this subsection
Effects on Human Beings
Soil contaminants can exist in all three phases (solid, liquid, and gaseous). Therefore, these contaminants can find their way into the human
body via several channels such as direct contact with the skin or through the inhalation of contaminated soil dust.
The short term effects of human exposure to polluted soil include
•Headaches, nausea, and vomiting.
•Coughing, pain in the chest, and wheezing.
•Irritation of the skin and the eyes.
•Fatigue and weakness.
A variety of long-term ailments have been linked to soil pollution. Some such diseases are listed below.
•Exposure to high levels of lead can result in permanent damage to the nervous system. Children are particularly vulnerable to lead.
•Depression of the CNS (Central Nervous System).
•Damage to vital organs such as the kidney and the liver.
•Higher risk of developing cancer.
It can be noted that many soil pollutants such as petroleum hydrocarbons and industrial solvents have been linked to congenital disorders in
humans. Thus, soil pollution can have several negative effects on human health.
Effects on Plants and Animals
Since soil pollution is often accompanied by a decrease in the availability of nutrients, plant life ceases to thrive in such soils. Soils
contaminated with inorganic aluminium can prove toxic to plants. Also, this type of pollution often increases the salinity of the soil,
making it inhospitable for the growth of plant life.
Plants that are grown in polluted soil may accumulate high concentrations of soil pollutants through a process known as
When these plants are consumed by herbivores, all the accumulated pollutants are passed up the food chain.
This can result in the loss/extinction of many desirable animal species. Also, these pollutants can eventually make their way to the
top of the food chain and manifest as diseases in human beings.
• Biological methods
Agronomic practices Contour farming
Retiring of land to grass
Impact of DDT
DDT – Organic chemical – Dichlorodiphenyltrichloroethane
Is a Chlorinated Hydrocarbon
Takes long time to break down in the environment
Half Life – 15 years
Toxic to insects but not very toxic to human
Used much during the World War II to protect US troops from
mosquito – borne malaria and to prevent the spread of lice and
lice borne disease among civilian population in Europe
Thereafter used as pesticides to protect crops and people from
insect borne disease
Since it was the first of its kind, it was overused and by the year
1960s, the problem related to bio magnification of DDT became
• These are the technologies that we will cover.
• There seems to be thousands of variations on a theme!
•Just for completeness the definitions:
Biostimulation - Stimulation of indigenous microbial populations in soils and/or groundwater; may be done in-situ or ex-situ
Bioaugmentation - Addition of bacterial cultures to contaminated medium; frequently used in bioreactors and ex-situ systems
Landfarming - Solid-phase treatment system for contaminated soils; may be done in-situ or in a constructed soil treatment cell
Composting - Aerobic, thermophilic treatment process in which contaminated material is mixed with a bulking agent; can be done using static piles, of continuously fed reactors
Bioreactors - Biodegradation in a container or reactor; may be used to treat liquids or slurries
Bioventing - Method of treating contaminated soils by drawing oxygen through the soil to stimulate microbial growth and activity
Biofilters - Use of microbial stripping columns to treat air emissions
Baker, K.H. and D.S. Herson. 1994. Introduction and overview of bioremediation, p. 1-7, In: (Baker, K.H. and D.S. Herson, eds.) Bioremediation, McGraw-Hill, Inc. New York.