Lecture 10 Causes, effects and control of soil pollution.
Soil Pollution
Soil is the loose and unconsolidated outer layer of earth’s crust that is powdery in nature and
made up of small particles of different sizes. Soil ecosystem includes inorganic and organic constituents,
and the microbial groups. Soil microorganisms are the active agents in the decomposition of plant and
animal solid wastes and said to be nature’s garbage disposal system. The soil microbes keep our planet
earth free of unwanted waste materials and recycle the elements (C, N, and P) through mineralization.
Soil microbes decompose a variety of compounds, cellulose, lignin, hemi cellulose, proteins, lipids,
hydrocarbons etc. The soil microbial community has little or no action on many man made synthetic
polymers. The persistent molecules that fail to be metabolized or mineralized have been termed as
recalcitrants.
Soil pollutants
Pesticide pollution
In modern agriculture the use of various agrochemicals is a common practice. These include
pesticides, herbicides, insecticides, fungicides and others. Pesticides applied on seed or foliage
ultimately reach the soil. Accumulation of pesticide residues in the biosphere creates ecological stress
causing contamination of soil, water, and food. Persisting chemicals may also be hazardous to human
health and should be eliminated. Persistent pesticides may accumulate in the bodies of animals and
over a period of time increase in concentration if the animal is unable to flush leading to
bioaccumulation. When an affected animal is eaten by a carnivore, the pesticide is further concentrated
in the carnivore. This phenomenon ie. Increasing in the concentration of a nondegradable substance
along the food chain is called Biomagnification.
Another problem associated with insecticides is the ability of insects become resistant. Most
pesticides kill beneficial predators and parasites. The short term and long term health effects to the
persons using the pesticides and public that consumes the food are the major concerns. Exposure to
small quantities for longer time causes mutations leads to cancer. Pesticides or their metabolites affect
many soil microbes and their activities. Seed treatment with mercuric fungicides are found to be
inhibitory to Rhizobium (nodulation and nitrogen fixation), Nitrosomonas and Nitrobacter (nitrification).
Fertilizer pollution
The agricultural production depends on chemical fertilizer application, as most of our high
yielding varieties are fertilizer responsive. Continuous application of chemical fertilizers alone lead to
deterioration of soil properties and cultivated soils loose their natural characteristics. Fertilizers like
ammonium sulphate, ammonium chloride and urea reduce the soil pH. Many crops, like potato, grapes,
citrus, beans are sensitive to chloride toxicity. In integrated nutrient management, to sustain the
productivity of our soils, organic manures and bio fertilizers are recommended as supplements to
chemical fertilizers.
1
, Nitrate pollution
Nitrogen occurs in many forms in the environment and takes part in many biochemical
reactions. The four forms of nitrogen that are of particular significance in environmental technology are
organic nitrogen, ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen. In water contaminated with
sewage, most of the nitrogen is originally present in the form of complex organic molecules (protein)
and ammonia (NH 3 ). These substances are eventually broken down by microbes to form nitrites and
nitrates.
Nitrogen, particularly in the nitrate form, is a basic nutrient that is essential to the growth of
plants. Excessive nitrate concentrations in surface waters encourage the rapid growth of microscopic
plants called algae and excessive growth of algae degrades water quality.
Nitrates can enter the ground water from chemical fertilizers used in agricultural areas.
Excessive nitrate concentrations in drinking water pose an immediate and serious health threat to
infants under 3 months of age. The nitrate ions react with blood hemoglobin, reducing the blood’s
ability to carry oxygen and this produces a disease called blue baby or methemoglobinemia.
• An illness that arises when an
infant’s blood is unable to carry
enough oxygen to body cells and
tissue
• An infant with moderate to serious
"blue baby syndrome" may have a
brownish-blue skin tone due to lack
of oxygen
• Child may be fussy, tired, have
diarrhea or vomiting
• Severe cases can cause death
Excess Salts and Water
Irrigation water helps to produce more yield than rain fed land. Irrigation water contains
dissolved salts and in dry season, water is in the form of saline solution evaporates leaving its salts such
as NaCl in the top soil. This saline soil causes stunted plant growth, lower yield. Flushing out salts
reduces the salinity but makes downstream irrigation water, saltier. Another problem is water logging.
Heavy metal pollution
Heavy metals include all metals with atomic numbers greater than 23 (with few exceptions) or
more than 5 gm per ml. (eg. Hg, 70 gm ml-1). Heavy metals are hazardous, not acceptable to biological
system. They are toxic to man and other life forms. Most of them are slow poisons as they accumulate
in the body and cause serious disorders. Mercury, lead, arsenic, chromium and cadmium are the five
most common toxic heavy metals and they have serious effects on human health .
2
Soil Pollution
Soil is the loose and unconsolidated outer layer of earth’s crust that is powdery in nature and
made up of small particles of different sizes. Soil ecosystem includes inorganic and organic constituents,
and the microbial groups. Soil microorganisms are the active agents in the decomposition of plant and
animal solid wastes and said to be nature’s garbage disposal system. The soil microbes keep our planet
earth free of unwanted waste materials and recycle the elements (C, N, and P) through mineralization.
Soil microbes decompose a variety of compounds, cellulose, lignin, hemi cellulose, proteins, lipids,
hydrocarbons etc. The soil microbial community has little or no action on many man made synthetic
polymers. The persistent molecules that fail to be metabolized or mineralized have been termed as
recalcitrants.
Soil pollutants
Pesticide pollution
In modern agriculture the use of various agrochemicals is a common practice. These include
pesticides, herbicides, insecticides, fungicides and others. Pesticides applied on seed or foliage
ultimately reach the soil. Accumulation of pesticide residues in the biosphere creates ecological stress
causing contamination of soil, water, and food. Persisting chemicals may also be hazardous to human
health and should be eliminated. Persistent pesticides may accumulate in the bodies of animals and
over a period of time increase in concentration if the animal is unable to flush leading to
bioaccumulation. When an affected animal is eaten by a carnivore, the pesticide is further concentrated
in the carnivore. This phenomenon ie. Increasing in the concentration of a nondegradable substance
along the food chain is called Biomagnification.
Another problem associated with insecticides is the ability of insects become resistant. Most
pesticides kill beneficial predators and parasites. The short term and long term health effects to the
persons using the pesticides and public that consumes the food are the major concerns. Exposure to
small quantities for longer time causes mutations leads to cancer. Pesticides or their metabolites affect
many soil microbes and their activities. Seed treatment with mercuric fungicides are found to be
inhibitory to Rhizobium (nodulation and nitrogen fixation), Nitrosomonas and Nitrobacter (nitrification).
Fertilizer pollution
The agricultural production depends on chemical fertilizer application, as most of our high
yielding varieties are fertilizer responsive. Continuous application of chemical fertilizers alone lead to
deterioration of soil properties and cultivated soils loose their natural characteristics. Fertilizers like
ammonium sulphate, ammonium chloride and urea reduce the soil pH. Many crops, like potato, grapes,
citrus, beans are sensitive to chloride toxicity. In integrated nutrient management, to sustain the
productivity of our soils, organic manures and bio fertilizers are recommended as supplements to
chemical fertilizers.
1
, Nitrate pollution
Nitrogen occurs in many forms in the environment and takes part in many biochemical
reactions. The four forms of nitrogen that are of particular significance in environmental technology are
organic nitrogen, ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen. In water contaminated with
sewage, most of the nitrogen is originally present in the form of complex organic molecules (protein)
and ammonia (NH 3 ). These substances are eventually broken down by microbes to form nitrites and
nitrates.
Nitrogen, particularly in the nitrate form, is a basic nutrient that is essential to the growth of
plants. Excessive nitrate concentrations in surface waters encourage the rapid growth of microscopic
plants called algae and excessive growth of algae degrades water quality.
Nitrates can enter the ground water from chemical fertilizers used in agricultural areas.
Excessive nitrate concentrations in drinking water pose an immediate and serious health threat to
infants under 3 months of age. The nitrate ions react with blood hemoglobin, reducing the blood’s
ability to carry oxygen and this produces a disease called blue baby or methemoglobinemia.
• An illness that arises when an
infant’s blood is unable to carry
enough oxygen to body cells and
tissue
• An infant with moderate to serious
"blue baby syndrome" may have a
brownish-blue skin tone due to lack
of oxygen
• Child may be fussy, tired, have
diarrhea or vomiting
• Severe cases can cause death
Excess Salts and Water
Irrigation water helps to produce more yield than rain fed land. Irrigation water contains
dissolved salts and in dry season, water is in the form of saline solution evaporates leaving its salts such
as NaCl in the top soil. This saline soil causes stunted plant growth, lower yield. Flushing out salts
reduces the salinity but makes downstream irrigation water, saltier. Another problem is water logging.
Heavy metal pollution
Heavy metals include all metals with atomic numbers greater than 23 (with few exceptions) or
more than 5 gm per ml. (eg. Hg, 70 gm ml-1). Heavy metals are hazardous, not acceptable to biological
system. They are toxic to man and other life forms. Most of them are slow poisons as they accumulate
in the body and cause serious disorders. Mercury, lead, arsenic, chromium and cadmium are the five
most common toxic heavy metals and they have serious effects on human health .
2
