Background

Pesticides have been used for decades to control agricultural pests and to ensure an adequate quantity and quality of food for the Nation. A pesticide= s toxicity is responsible for its effectiveness in controlling pests but may cause undesirable side-effects when the chemical moves from its intended location. Pesticide movement to the atmosphere depends upon complex interactions between the properties of the individual chemicals, the weather, the properties of the soil or plant tissue on which they are adsorbed, the way they are applied, and the management of the field or crop. Pesticides potentially can contaminate soil, water, and air. To protect our natural resources, research on pesticide movement and transformation must integrate the effects from all environmental systems.

The occurrence of pesticides in the atmosphere and water is an important national issue. Studies have documented that some of the pesticides found in the atmosphere and water have resulted from agricultural applications. Dissipation and accumulation of pesticide residues can limit the efficacy of some pesticide materials. Pesticides and transformation products in the atmosphere can be a major health concern and cause plant damage far from their sites of application. For example, methyl bromide, a widely-used soil fumigant, has been implicated in damage to the stratospheric ozone layer. It has been estimated that as much as 40-60% of the applied material may ultimately reach the atmosphere.

Many pesticides are volatile, and even those with low volatility can be transported in the atmosphere as residues bound to dust particles or as aerosols. Both the active ingredient and formulation constituents can become air contaminants. Volatile components and residues bound to dusts may rise high into the atmosphere, travel long distances, and be deposited far from the point of origin through various deposition processes. Raindrops have been shown to have pesticide components.

Sources of Emissions.  Pesticides are applied to the soil or to a crop. Many techniques can be used to apply a pesticide depending on type of formulation, timing of application, the pest to be controlled, and other soil environmental management considerations. The pesticide can be injected into the soil as a fumigant or into irrigation water; or ir can be sprayed onto the soil surface. Crops can be sprayed, for example, with boom sprayers or tunnel sprayers or by aerial application, or they can be treated with systemic pesticides. Seeds are sometimes treated with pesticides prior to planting. Pesticides also can be incorporated into other materials so that release of the active ingredient occurs over a longer period of time.

During aerial pesticide application, some part of 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 spectrum of droplet 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 diameter 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 droplets that rapidly enter the gaseous phase and can be transported in the atmosphere. A portion 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 application method, properties of the formulation, and environmental conditions. Volatilization losses from soil or plants depend largely on soil and environmental conditions, chemical properties of the pesticide, and agricultural management after application.

Once a pesticide is in the atmosphere its movement and transformation are controlled by various atmospheric and chemical processes. Pesticides can degrade in the atmosphere during photosynthesis or in reaction with 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 contaminating sensitive ecosystems.

Alternatives to Pesticides.  Alternatives to use of pesticides to control agricultural pests include biological control, genetically altered organisms, and various cultural and environmental practices (e.g., exposure to the sun, flooding, and crop rotations). Many issues need to be addressed before cultural and environmental practices will be suitable for replacing pesticides. For example, exposure to the sun can provide good pest control near the soil surface, but control diminishes with depth, and the effectiveness of the treatment is often variable.

Genetic engineering poses unique possibilities to end or limit the use of pesticides but also may involve unexplored risks to agricultural and ecological systems. Releasing genetically engineered organisms into the environment could devastate native organisms in a similar manner as the introduction of nonnative species.

A pesticide= s behavior in the environment is fairly well known and, with proper management, may involve smaller overall risks to agricultural and ecological systems than the use of biologically engineered organisms. Cultural and environmental practices offer ways to reduce pesticide use; however, these systems likely will require occasional treatment with pesticides. Therefore, improved pesticide management methods are needed to reduce emissions and off-target contamination to ensure that pesticides are used safely.

Source Reduction.  Significant pesticide contamination is possible when pesticides are applied inappropriately, 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 significant atmospheric contamination.

Soil fumigants are a special category of pesticides that are highly mobile in the soil-water-air environment. Because of environmental and health concerns, several fumigants have been banned during the last decade. Recently, methyl bromide emissions to the atmosphere have been found to deplete stratospheric ozone, and the use of methyl bromide is scheduled to be phased out in the U.S. by 2005. There is a general lack of knowledge of the mechanisms underlying the environmental behavior of these volatile pesticides.

Volatile pesticides are released to the atmosphere during and after application. Large pulses 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 disruption of the food chain; and (5) degradation of the global atmosphere and loss of natural protective zones such as stratospheric ozone.

An environment and society free of adverse effects from agricultural pesticides

Develop agricultural production systems that minimize unwanted emission and transport of pesticides

Component Problem Areas
State	Location	Measurement, Mechanisms, & Processes	Model Development & Testing	Source (Emission) Reduction & Improved Pesticide Management
CA	Riverside	X	X	X
IA	Ames	X
MD	Beltsville	X
MN	St. Paul		X
TX	College Station	X