Learn about the three fate processes for pesticides and earn a CEU toward the renewal of FDACS restricted-use pesticide license.
Those looking to renew their restricted-use pesticide licenses with the Florida Department of Agriculture and Consumer Services (FDACS) must accumulate continuing education units (CEUs). A recent Citrus Industry article shared information on the fate processes for pesticides, and “grants one continuing education unit (CEU) in the Core category toward the renewal of a Florida Department of Agriculture and Consumer Services restricted-use pesticide license when the accompanying test is submitted and approved.” See the details below.
Fate Processes for Pesticides
According to the article, “The fate processes for pesticides fall into three major types: adsorption, transfer, and degradation.
“Pesticide Adsorption. The adsorption process binds pesticides to soil particles, similar to paper clips sticking to a magnet. Adsorption often occurs because of the attraction between a chemical and soil particles. Positively charged pesticide molecules, for example, are attracted to and can bind to negatively charged clay particles.
Many soil factors influence pesticide adsorption. Soils high in organic matter or clay are more adsorptive than coarse, sandy soils, in part because a clay or organic soil has more particle surface area, or more sites onto which pesticides can bind.
Pesticides vary in their adsorption to soil particles. Some pesticides such as paraquat and glyphosate bind very tightly. Others bind only weakly and are readily released back into the soil solution.
One problem resulting from pesticide adsorption is reduced pest control. For example, weeds may not be controlled if a herbicide is held tightly to soil particles and cannot be taken up by the roots of the target weeds.
Pesticide Transfer. Five ways that pesticides can be transferred are through volatilization, runoff, leaching, absorption, and crop removal.
- Volatilization. The conversion of a solid or liquid into a gas is volatilization. Once volatilized, a pesticide can move in air currents away from the treated surface. The higher the vapor pressure, the more volatile the pesticide. To reduce pesticide volatilization, avoid applying volatile pesticides when conditions are unfavorable, such as on very hot, dry days or when soils are wet.
- Runoff. Movement of water over a sloping surface is runoff. Runoff occurs when water is applied faster than it can enter the soil. Pesticides can be carried in the water itself or bound to eroding soil particles. The severity of pesticide runoff depends on the slope or grade of an area. Over-irrigation can lead to excess surface water. It also can lead to pesticide runoff, especially when an irrigation system is used to apply a pesticide. Vegetation or crop residue tends to slow the movement of runoff water.
- Leaching. The movement of pesticides through the soil rather than over the surface is leaching. Leaching depends, in part, on the pesticide’s chemical and physical properties. For example, a pesticide held strongly to soil particles by adsorption is less likely to leach. Another factor is solubility. A pesticide that dissolves in water can move with water in the soil. Soil factors that influence leaching include texture and organic matter, in part because of their effect on pesticide adsorption. Soil permeability (how readily water moves through the soil) is also important. The more permeable a soil, the greater potential for pesticide leaching. A sandy soil is much more permeable than a clay soil. A certain amount of pesticide leaching may be essential for control of a target pest. Too much leaching, however, can lead to reduced pest control, injury of nontarget species and groundwater contamination.
- Absorption. The movement of pesticides into plants and animals is referred to as absorption or uptake. Absorption of pesticides by target and nontarget organisms is influenced by environmental conditions and by the chemical and physical properties of the pesticide and the soil. Once absorbed by plants, pesticides may be broken down or they may remain in the plant until tissue decay or harvest.
- Crop Removal. Crop removal transfers pesticides and their breakdown products from the treatment site. Most harvested food commodities are subjected to washing and processing procedures that remove or degrade much of the remaining pesticide residue. While we typically associate harvesting with food and feed products, it is easy to forget that pesticides potentially can be transferred during such operations as tree and shrub pruning and turfgrass mowing.
Pesticide Degradation. Pesticide degradation, or the breakdown of pesticides, usually is beneficial. Pesticide-destroying reactions change most pesticide residues in the environment to nontoxic or harmless compounds. However, degradation is detrimental when a pesticide is destroyed before the target pest has been controlled.
Learn more about pesticide degradation in the second part of our blog.
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