I.) Pesticides in the Environment Flashcards
Pesticides in the Environment
Pesticides are important and necessary pest management tools for agriculture, urban landscapes, forestry, and public health, but they must be handled with appropriate caution to minimize exposure and avoid risks to human health and the environment.
Pesticide residues get into the environment as a result of application or by accident and may be found in:
- ) Air
- ) Water
- ) Soil
The potential for a pesticide to contaminate the environment depends in large part on; the nature of the pesticide, application rates, frequency, and environmental conditions.
1.) Air
Pesticides become airborne in the following three main ways
A.)Volatilization
B.)Drift
C.)Dust-borne
1A.) Volatilization
Volatilization:
The process by which a pesticide changes from a liquid to a vapor.
1Ab) Although a pesticide’s chemistry is a determining factor of volatility: so is the environment into which it is applied.
Conditions such as air movement, relative humidity, temperature, all influence volatilization.
1Ac.) Pesticide Formulation and VOC’s
A number of pesticides, such as emulsifiable concentrates and fumigants are all classifies as volatile organic compounds (VOC’s) because they readily vaporize into the atmosphere.
In the presence of sunlight, VOC’s react with nitrogen oxides in the atmosphere to produce ozone. Accumulations of ozone in the lower atmosphere contribute to smog, which can irritate the human respiratory system and cause damage to the environment including the desired crops.
Regulatory restrictions have been placed on the use of VOC pesticides to reduce damage to the ozone layer.
1Aa.) All pesticides are volatile to a certain degree, but they differ greatly in this property.
Volatility is a useful property that helps disperse a pesticide in the target area thereby increasing its’ exposure to the pest.
This characteristic, however, can also lead to the exposure of non-target pests as well as traveling long distances (possibly into non-target areas) as vapors move up into the atmosphere.
The volatility of a chemical is measure by its ‘vapor pressure’; that is the pressure exerted by a material in its gaseous form.
- Compounds that vaporize or evaporate at low temperatures are referred to as ‘highly volatile’. (And low volatility in opposite instances).
- The ability of a pesticide to dissolve in water or be rapidly taken up by plants also limits volatilization. This partly related to a pesticides ability to be absorbed or adhere to treated surfaces (leaves, stems, soil, etc.)
1Ad.)
Practices that restrict movement of volatile pesticides include:
-Soil incorporations
-Tarping
-Evening applications (less heat and wind)
Practices that increase chances of pesticide volatilization include:
-Disking/Tilling after treatment.
Information about the vapor pressure or volatility of a pesticide is available on the manufacturer’s Material Safety and Data Sheet under “Physical Properties”.
1B.) Drift
The air-borne movement of pesticides away from the treatment site during application.
An important and costly problem is that it can illegally damage susceptible plants away from the application site, as well as cause environmental/water pollution.
1Ba.) Factors Influencing Drift
Pesticide
-Volatility of active ingredient
-Cormulation
-Carrier used to dilute pesticide in spray tank
-Droplet size:
~Small droplets fall through the air slowly and have a
greater potential to drift.
Adjuvants
-Deposition aids, thickners, and stickers (Reduce drift by making droplets larger or less volatile).
Application Equipment
-Sprayer type (e.g. conventional air blast vs. multifan, tower sprayer, or smart sprayers).
-Operating pressure of spraying system:
~Higher pressure create smaller droplet sizes.
-Nozzle type, orfice size
-Distance from nozzles to target surface:
~The further the distance the application is made from the
intended surface the greater probability of drift.
-Speed of travel of application equipment
-Application pattern and technique
Target Surfaces
-Size of target area
-Location of target area:
~*Buffer Zones: Increase the distance that drift must travel
in order to contaminate neighboring lots.
-Nature of target surfaces:
~Spraying in-line (parallel) to neighboring lots, as
opposed in the direction of (perpendicular) them, can
decrease probabilities of drift.
Weather Conditions
-Wind speed:
~Having some air movement, up to 5mph, can help with
dispersal.
~If winds exceed 7-10 mph, drift may become an issue. (variable with product)
-Wind direction:
~May be toward fields with differing crops.
-Air temperature:
~High temperatures increase drift.
~ When cool air is trapped beneath a layer of warm air
about 10-100’ above ground, an “inversion
layer” is created.
*Inversion layer: Causes the fine spray particles from
pesticide applications to become trapped, thus forming a
concentrated cloud that can then can move away from the
treatment site, depending on other conditions.
-Humidity:
~Lower RH’s increases drift.
1C.) Dust-borne:
Pesticides move around in the air on dust particles in several ways.
- Fine particles of pesticide dust formulations may be moved in the air during the application process.
- Liquid pesticide droplets may also adhere to soil particles after application and later be carried into the atmosphere by wind.
- The movement of dust-borne pesticides can be minimized by avoiding the use of dust formulations whenever possible and by incorporating pesticides into the soil, either mechanically or by irrigation.
- Irrigating as soon as possible after the application increases the ability of some material to adhere.
2.) Water
Another potential fate of pesticide residues in the environment is movement into water
A.) Persistence:
B.) Adsorption:
2A.) Persistence: Long persistence rate pesticides have greater potential for movement in water.
Persistence is measured by the ‘half-life’ of the pesticide.
Half-life: The period of time it takes for half of the pesticide to breakdown in the environment. The longer the half-life, the greater potential for movement of the pesticide through waterways before it degrades.
2B.) Adsorption: Is the tendency for the pesticide compound to attach itself to soil particles or H20 molecules and is measure in parts per million (ppm)
a. ) Pesticides with low solubilities (less than 1 ppm) are likely to remain near the soil surface. Such pesticides are more likely to be moved through run-off situations.
b. ) Pesticides with high solubilities (greater than 100 ppm) are more likely to dissolve with the water. Such pesticides are more likely to leach into ground water.
2Ba.) Pesticides in surface water run-off
Surface water contamination occurs through direct application (overuse), through drift, accidental spills or runoff.
It is illegal to spray a body of water (unless for control of aquatic organisms) or to drain spray equipment into or near water sources. The same procedures used to reduce drift discussed above help prevent drift onto water.
Runofff: is the movement of water and dissolved or suspended matter from the area of application into surface water or on neighboring land, that may also end in streams, rivers, and other water bodies through runoff in soil sediment.
-Runoff is also influenced by the extent of pesticide use, soil properties, climate, topography, land use, and management practices.
-Runoff is one of the most common ways that surface water can become contaminated. /it is likely to occur when heavy rainfall or irrigation takes place after an application.
~For example, during flood irrigation, if excess water reaches the end of the field, water can flow in the drainage system. where a pesticide (through chemigation practices) may be transported in the tailwater (rice production).
~In many urban areas, pesticides regularly contaminate storm drains, often at level that are toxic to surrounding wildlife.
-Runoff of organophophate or pyrethroid insecticides applied as dormant spray in orchards during heavy winter rains is a major concern in California orchards.
2Ba*.) Runoff prevention
Diligent monitoring and reduction of water use to prevent overflows into the drainage system can minimize tailwater runoff.
Recirculating water in which a pesticide has directly been applied or increasing the water0holding time before draining the field can assist in pesticide breakdown and decrease the amount released.
The use of buffer strips, if feasible, between the crop and the water source can help trap pesticides and sediment.
Choosing pesticides that are less likely to move or persist in water or nonchemical control methods may be the best solution in some circumstances.
Water pumps must be equipped with a shutoff device to stop pesticides from being injected into the system when using chemigation and irrigation stops.
-Safety valves are also installed in the irrigation system to prevent possible contamination of the water source by back-flow of irrigation water or pesticide.
