2. The Food and Agriculture Organization (FAO) has
defined pesticide as:
any substance or mixture of substances intended for
preventing, destroying, or controlling any pest, including
vectors of human or animal disease, unwanted species of
plants or animals, causing harm during or otherwise
interfering with the production, processing, storage,
transport, or marketing of food, agricultural commodities,
wood and wood products or animal feedstuffs, or
substances that may be administered to animals for the
control of insects, arachnids, or other pests in or on their
bodies. The term includes substances intended for use as a
plant growth regulator, defoliant, desiccant, or agent for
thinning fruit or preventing the premature fall of fruit.
Also used as substances applied to crops either before or
after harvest to protect the commodity from deterioration
during storage and transport.
4. Classification Of Pesticides:
Target Pest Group:
e.g., herbicides, insecticides, fungicides, rodenticides,
and pediculicides.
Chemical structure:
e.g., organic, inorganic, synthetic, or biological
(biopesticide)and physical state e.g. gaseous
(fumigant).
Plant derived or Botanicals:
pyrethroids, rotenoids,nicotinoids.
6. Effects On Ecosystems:
Over 98% of sprayed insecticides and 95% of herbicides reach a
destination other than their target species, including non-target
species, air, water and soil.
Pesticide drift occurs when pesticides suspended in the air as
particles are carried by wind to other areas, potentially
contaminating them. Pesticides are one of the causes of water
pollution, and some pesticides are persistent organic
pollutants and contribute to soil contamination.
Pesticide use reduces biodiversity, reduces nitrogen fixation,
contributes to pollinator decline, destroys habitat (especially for
birds) and threatens endangered species.
Chlorinated hydrocarbon pesticides dissolve in fats and are not
excreted, organisms tend to retain them almost
indefinitely. Biological magnification is the process whereby
these chlorinated hydrocarbons are more concentrated at each
level of the food chain. Among marine animals, pesticide
concentrations are higher in carnivorous fishes, and even more so
in the fish-eating birds and mammals at the top of the ecological
pyramid.
9. Effects On Ecosystems:
Global distillation is the process whereby pesticides are
transported from warmer to colder regions of the Earth, in
particular the Poles and mountain tops. Pesticides that evaporate
into the atmosphere at relatively high temperature can be
carried considerable distances by the wind to an area of lower
temperature, where they condense and are carried back to the
ground in rain or snow.
10. Pesticides also affect animal health in the
following ways:
Cattle readily eat arsenic compounds. They will eat grass sprayed
with monosodium methanearsonic acid (MSMA). Arsenic damages
small blood vessels, which affects the blood supply, to major organs.
Membranes of the digestive tract are inflamed causing diarrhoea,
abdominal pain, thirst, weakness and collapse.
Organochlorine insecticides include DDT, lindane, toxaphene, and
heptachlor. Residues can build up in the fat of livestock. Toxicity to
livestock resulted from effects on the nervous system. Muscle
tremors and twitches, seizures, and unusual behaviour were signs of
poisoning. Death is caused by respiratory failure during sustained
seizures and/or high body temperature.
Ingestion of concentrate or forages recently sprayed at rate of 12
pounds per acre with sodium chlorate herbicide is likely to cause
fatal poisoning. The toxic action is oxidization of haemoglobin in red
blood cell producing a brown pigment called methemoglobin. Red
blood cells are destroyed, the blood, muscles, and urine are brown
and inflammation of the intestines causes diarrhoea.
12. Pesticides also affect animal health in the
following ways:
Pesticides may impact wildlife through secondary poisoning when
an animal consumes prey species that contain pesticide residues.
Examples of secondary poisoning are birds of prey becoming sick
after feeding on an animal that is dead or dying from acute
exposure to a pesticide, and the accumulation and movement of
persistent chemicals in wildlife food chains.
Toxic levels of carbamate insecticides like methomyl and
carbofuran can cause seizures and respiratory arrest in dogs.
Organophosphate toxicity, meanwhile, may lead to chronic
anorexia, muscle weakness and muscle twitching which may last
for days or even weeks.
15. Elimination Of Pesticides:
Manual removal of weeds.
Covering weeds with plastic.
Placing traps and lures for pests like rodents.
Removing pest breeding sites.
Maintaining healthy soils that breed healthy, more resistant
plants.
Cropping native species that are naturally more resistant to
native pests.
Supporting biocontrol agents such as birds and other pest
predators.
Biotechnology can also be an innovative way to control pests.
