Degradation rate is quantified in terms of degradation half-life, the time required for 50 percent of the pesticide to decompose to products other than the original pesticide. The EPA considers a pesticide with soil half-life of greater than 21 days as having a potential for causing water concerns due to the pesticide s longevity. A region within the earth that is wholly saturated with water. Dissolving and transporting of materials by the action of percolating water. The ability of a substance to remain in its original form without breaking down.
Permeability is a function of soil texture, structure, and pore space.
Highly permeable, coarse, sandy soils have large pores that allow water and pesticides to move rapidly between soil particles during rainfall or irrigation. Each layer of soil can have a different permeability, but the overall permeability is determined by the most restrictive layer. Soil permeability increases when there are macropores, large channels produced by plant roots, earthworms, soil cracks, and the burrowing of smaller animals. Soil organic matter. Soil organic matter helps to bind pesticides, especially those with high Koc values, and promotes degradation.