Inspección de Paquetes de Intercambiadores

Contamination of surface waters has long been a recognized concern surrounding pesticide use. Such contamination can occur directly by drift or accidental application of pesticides into waters at the time of application. Extreme care must always be taken when making pesticide applications near water.

Pollution of water by pesticides may also occur from runoff following

irrigation or rainfall. Wind blown soil contaminated by pesticides may also enter surface waters. These problems are most severe if substantial erosion occurs shortly after a pesticide application. Site conditions that favor erosion (slope, exposure, etc.) greatly increase the potential of unwanted pesticide movement from erosion.

Recently, attention has shifted to groundwater contamination by pesticides and industrial chemicals. Groundwater is the water source for wells and springs. About one-half of the population of the U.S. relies upon groundwater for drinking; in rural areas 90% of drinking ♦

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water is from groundwater sources. Groundwater was long thought to be relatively protected from pollution sources and the discoveries of pollution have raised serious concerns. In addition, there has been increased awareness that groundwater and surface water resources are often interconnected.

Groundwater is maintained in an aquifer, a water saturated zone of soil, sand, gravel, or fractured bedrock. The upper layer of the aquifer is known as the water table. These underground water sources are maintained by percolating water, or recharge, that passes through soil into the water table.

When this downward percolating water contains dissolved chemicals the process is known as leaching. Leaching of soil salts has long been an important aspect of irrigation practice in areas of high salt content. Groundwater becomes contaminated when recharge water carries

pollutants with it to the water table. Once in the aquifer, water

travels in a more horizontal direction. These chemicals move with the groundwater, forming a region of contaminated water known as a

plume.

Once contaminated, groundwater may be prohibitively expensive or impossible to clean. Since pesticides degrade very slowly in

groundwater, results of contamination may last for many years. Clearly, the best solution is to keep pesticides and other chemicals out of

groundwater through careful use in application, storage, and disposal. A number of factors contribute to groundwater contamination. These include site conditions, characteristics of the pesticide, the method of application, and environmental conditions following application.

Site conditions associated with groundwater contamination potential include:

Soil texture is determined by the relative proportion of

sand, silt, and clay. Soils with more clay and organic matter hold water and dissolved chemicals longer than soils of low clay and organic matter content. Clay and organic matter also adsorb, or hold onto, many dissolved chemicals. Sandy soils increase risks of contaminated water moving into groundwater. Many Colorado agricultural areas, such as the

northeast part of the state, have very sandy soils.

Soil permeability is a measure of how rapidly water

is able to percolate through a soil. Highly permeable soils allow for greater downward movement of

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Pesticides can leach through the soil profi le

waterborne contaminants. Many Colorado areas, such as the San Luis Valley, have very permeable soils.

Soil organic matter - organic matter content infl uences how much

water a soil can hold and how well the soil can adsorb chemicals, including pesticides. Soils with high organic matter contents can retain water and adsorb chemicals better than soils with low organic matter contents. Low organic matter soils are common in Colorado.

Soil pH - the relative acidity or alkalinity of soil can be important in

the degradation of the pesticides. Most pesticides degrade more rapidly under alkaline conditions.

Depth of water table - water table depth infl uences the rapidity

with which dissolved chemicals can enter the underlying aquifer. Pesticides degrade slowly in groundwater since few microorganisms are present to break down the pesticide. In areas with high

water tables, such as parts of the San Luis Valley, groundwater contamination risks can be greatly increased. Areas along streams, rivers, and lakes are also at high risk of contaminating groundwater supplies through careless pesticide use.

Pesticide characteristics that affect groundwater pollution potential include:

Water solubility - solubility of a pesticide affects how the pesticide dissolves in and moves with water. Highly water soluble pesticides, such as many carbamate insecticides and triazine herbicides, are among the more readily leached pesticides.

Environmental persistence - this is a pesticides’ ability to resist

degradation. Pesticides which resist degradation are more likely to enter groundwater.

Electrical charge - affects how readily a pesticide binds to soil

particles. Since clay and organic matter are negatively charged, chemicals with a positive charge adhere to the soil and resist

leaching. Negatively charged pesticides, or soils with few negatively charged clay and organic matter particles, increase leaching

potential.

Pesticide uses and applications that can affect groundwater contamination potential include:

High use rates can increase the amount of pesticide available to

leach and contaminate water sources.

Excessive irrigation can increase water fl ow and leaching.

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Chemigation techniques pose special potential

hazards to groundwater. If power failure occurs during application, back siphoning of chemicals is possible. This draws large amounts of non-degraded pesticides directly into the well causing serious

groundwater contamination. Appropriate protective devices, such as check valves, and label instructions to prevent accidental back siphoning pollution of wells are required by law. The Colorado Chemigation Act is available from the CDA or at http://www.ag.state. co.us/DPI/rules/ chemigation.html.

Environmental conditions following pesticide application can infl uence the breakdown of the pesticide and groundwater contamination. For example, cold or dry conditions generally retard the breakdown of pesticides in the soil.

Carefully read the pesticide label each time a pesticide is applied. Some pesticides carry a Ground Water Advisory (GWA) statement on the label. This information will help the applicator to apply the pesticide in a manner that will minimize the risk for groundwater contamination. Examples of pesticides with groundwater advisory statements include atrazine and 2-4,D. In addition, many pesticide labels carry a Surface Water Advisory (SWA) statement on the label. This advisory statement informs applicators of the danger of surface water contamination. Metolachlor and sulfentrazone are examples of pesticides that carry a surface water advisory.

The pesticide applicator’s attitude is the most important factor in protecting the environment from pesticide hazards. Pesticides will remain viable pest control alternatives only if these chemicals can be applied accurately and responsibly.

Additional Resources

Colorado Department of Agriculture, Groundwater Program, 700 Kipling Street, Suite 4000, Lakewood, CO 80215-8000. Phone: 970- 223-7017. http://www.ag.state.co.us/CSD/GroundWater/Waterhome. html. Information on agricultural chemicals and groundwater

protection.

EPA Endangered Species Protection Program. http://www.epa.

gov/espp/. Information on how to protect endangered and threatened

species from harm due to pesticide use.

National Fish and Wildlife Service. http://www.fws.gov/endangered/.

National endangered species information.

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Spray Drift Task Force. http://www.agdrift.com/. Publications and

information on spray drift.

U.S. Fish and Wildlife Service Region 6. http://www.r6.fws.gov/ endspp/. Colorado endangered species information.

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Pesticide Storage, Disposal and