2. When a pesticide is applied to a field, it gets distributed in the
environment
For example, parathion was aerially applied at 1 lb per acre (about 15
mg/cm²). The amount that was detected on the leaves directly after
application was little more than 0.1 mg/cm². About 98% didn’t reach
the leaves. The undetected amount went elsewhere in the
environment, being distributed in the different environmental
compartments
Where did the parathion go?
Answer can be explained with the help of “Law of
Conservation of Matter”
2
3. Law of conservation of matter
Parathion was being distributed throughout the environment and also
becoming mineralized to CO₂, H₂0 and phosphates.
3
4. Pesticide fate processes in the environment
• Transfer: The way in which a pesticide is distributed between
solids and liquids (e.g., between soil and soil water) or between
solids and gases (as between soil and the air it contains)
• Transport: The movement from one environmental
compartment to another, such as the leaching of pesticides
through soil to ground water, volatilization into the air, or runoff
to surface water
• Transformation: Biological and chemical processes that
change the structure of a pesticide or completely degrade it
4
6. Adsorption
• Phenomenon whereby the molecules of a fluid come up against a
solid surface and are retained on it at a given time, establishing a
partition balance
• Adsorption is the result of the electrical attraction between
charged particles, pesticide molecules (sorbate) and soil particles
(adsorbent)
• Pesticide molecules that are positively charged are attracted and
can bind to negatively charged particles of clay and organic
matter
• Decreased bioavailability
• Reduced toxicity
• Reduced leaching and other transport properties
6
9. • Process by which a
compound evaporates to the
atmosphere from another
environmental compartment
• Once volatilized, a pesticide
can move in air currents
away from the treated
surface- vapour drift
• Vapour drift differs from dust
or spray drift in that it
occurs after the pesticide is
completely deposited onto
treated surfaces
Volatilization
9
11. • Downward movement of
pesticide through soil profile
along with water
• Pesticides that readily leach
beyond the root zone of the
soil - greatest potential to
pollute ground water
• Pesticides are frequently
leached through the soil by the
effect of rain or irrigation water
• Pesticide must be sufficiently
soluble in water for leaching to
take place
Leaching
11
12. Factors affecting leaching
Chemical characteristics of the pesticides-
Water solubility
Degree of adsorption
Soil characteristics-
Texture and organic matter content
Volume of water flow
12
13. • Movement of adsorbed and
dissolved pesticides along
with surface water
• Occur when a heavy rainfall
or excessive irrigation takes
place shortly after a
pesticide is applied to the
soil surface
• Pesticide can enter rivers
and reservoirs
Run off
13
14. Factors affecting run off
Soil slope
Rainfall intensity
Pesticide characteristics
Degree of adsorption of pesticides
14
15. Pesticide movement ratings (Cecil Tharp, 2010)
Common name
Pesticide
movement
rating
Soil half life in
days(persistence)
Water
solubility
(mg/L)
Sorption
coefficient
(Kₒc)
2,4-D dimethylamine
salt
Moderate 10 796,000 20
Acephate Low 3 818,000 2
Aldicarb High 30 6,000 30
Benomyl Low 67 2 1,900
Bifenthrin Very Low 26 0.1 240,000
Captan Very Low 2.5 5.1 200
Carbaryl Low 10 120 300
Carbofuran Very High 50 351 22
Chlorpyrifos Very Low 30 0.4 6,070
Diazinon Low 40 60 1,000
Dimethoate Moderate 7 39,800 20
Endosulfan Very Low 50 0.32 12,400
Esfenvalerate Very Low 35 0.002 5,300
Glyphosate
isopropylamine
Very Low 47 900,000 24,000
Malathion Very Low 1 130 1,800
Methomyl High 30 58,000 72
Methyl Bromide Very High 55 13,400 22
Methyl Parathion Very Low 5 60 5,100
Picloram Salt Very High 90 200,000 16
Permethrin Very Low 30 0.006 100,000
Simazine High 60 6.2 130
Triclopyr amine salt Very High 46 2,100,000 20
Trifluralin Very Low 60 0.3 8,000
15
