Aerial Spraying Developments
During aerial pesticide application, some of the applied material is lost to the
atmosphere in the form of fine droplets moving off-target through the air stream by
a process called spray drift. Spraying pesticides through spray nozzles produces a spec-
trum of droplets of differing diameters. The smallest droplets will remain airborne
and become lost as spray drift. Larger droplets can be transported by the wind and
deposited some distance outside the target area. As droplets are transported, their di-
ameter decreases through evaporation. As they become smaller, they remain airborne
longer and can be transported over regional, continental, or intercontinental
distances.
Pesticides of moderate-to-high volatility sprayed above the soil surface form drop-
lets that rapidly enter the gaseous phase and can be carried in the atmosphere. A por-
tion of the pesticide that reaches the soil or plant surface also may evaporate over
time and move into the atmosphere through a process of volatilization. Once in the
atmosphere, a volatile pesticide can travel long distances. Loss during application
through spray drift depends largely on the application method, properties of the for-
mulation, and environmental conditions. Volatilization losses from soil or plants
depend largely on soil and environmental conditions, chemical properties of the
applied pesticide, and agricultural management after its application.
Once a pesticide is in the atmosphere, various atmospheric and chemical processes
control its movement and transformation. Pesticides can break down in the atmo-
sphere during photosynthesis or in reaction to other atmospheric constituents. Some
processes are particularly important in determining the ultimate concentration and
transport distance from the point of application, which affects the risk of contaminat-
ing sensitive ecosystems.
Source Reduction
Significant pesticide contamination is possible when pesticides are applied inap-
propriately or inefficiently or when accidentally spilled. Large quantities of applied
pesticides may be lost from aerial spraying during windy conditions, and pesticides
may drift onto adjacent fields or nearby ecosystems. Such conditions can cause signif-
icant atmospheric contamination.
Volatile pesticides are released into the atmosphere during and after application.
Large amounts of pesticides may be released from areas of heavy agricultural activity
for three to four days after application, causing increased pesticide concentrations in
the entire region. Lower concentrations persist throughout the remainder of the year
as the pesticide material is cycled within the plant-air-soil-water environment.
Potential impacts of pesticide loss to the atmosphere are 1) decline in air and water
quality; 2) loss of beneficial insects and plants through off-site drift; 3) regional and
long-range transport and degradation of soil, plant, and surface water quality; 4)
accumulation and transfer of pesticide residues to sensitive wildlife and potential
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