Lecture 4 Flashcards
SOIL POLLUTANTS
Plastics
Agro chemicals
Fertilizers
Heavy metals
Plastics
PlasticsMajor part of global domestic and industrial waste
Not easily biodegraded
Waste plastic accumulates much thus adds to severe pollution
problem
Takes several years to disintegrate – 400 years to degrade mineral
water bottles
In USA, plastics are 7% in weight and 30% of the volume
Use of biodegradable plastic solves the problem of pollution
biodegradable plastic
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
During the manufacture – 6% starch and Oxidizing
agent (vegetable oil) added to polymers
Degraded easily
biodegradable plastic In case of metallic salts
Present in soil interact with oxidizing agent to form ferric oxides
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 resistance
Agrochemical pollution
Include pesticides, herbicides, fungicides
Pesticides applied reach the soil ultimately
Accumulation of pesticide residues in biosphere
creates ecological stress causing soil, water and
food contamination
Persisting chemicals are hazardous to human
health
Total remediation is impossible
Fertilizer pollution
lose chara
reduce ph
crops
biofertilizers
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
chloride toxicity
Application of organic manures and biofertilizers reduce
the soil from pollution
Xenobiotics
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
Symbionts
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
Heavy metal pollution
Metals with atomic number greater than 23 or more
than 5 gm per ml (eg. Hg – 70gm
ml-1)
They are hazardous, not acceptable to biological
system
Toxic to man & other life forms
Most are slow poison, accumulate in the body and
cause serious disorders
Common toxic metals- Hg, Pb, As, Cr, Cd
Biological Transformation of metals
Is a detoxification mechanism by the action of microorganisms
As a result metals undergo changes in valency and or
conversion into organo metallic compounds
Transformations
Changes in valency and resulting in production of volatile or less
toxic compounds
Ex. Oxidation of As (III) to As (V) and Hg
ion to metallic mercury
Formation of organo metallic compounds by methylation
Ex. Pb & Hg
Soil conservation
Biological methods
Agronomic practices
Contour farming
Mulching
crop rotation
Strip cropping
Dry farming
Agrostological methods
Lay farming
Retiring of land to grass
Mechanical methods
Basin listing
Contour terracing
Other methods
Gully control
Afforestation
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
apparent
Bioremediation Treatment
Technologies
Biostimulation
Bioaugmentation
Biosorption
Bioaccumulation
Landfarming
Composting
Bioventing / air sparging
Phytoremediation
Soil ecosystem
organic, inorganic constituents &
microbes
Soil microbes
Active agents in decomposition of both plant and
animal wastes – Nature’s garbage disposal system
though they decompose a variety of compounds
they do
not act on many man made synthetic
polymers
recalcitrants
Persistent molecules that fail to be metabolized or mineralized
