We then use both of these values to determine the contamination potential of pesticide-soil combinations. Because the concern for leaching is greater in the coastal plain than in the piedmont or in the mountains of North Carolina, we focus on the soils of the coastal plain. When plant and animal material decomposes in or on the soil, a small part of the material remains in the soil as very slowly degradable organic matter. This soil organic matter binds most pesticides very effectively, so the more organic matter in the soil, the less likely a pesticide will leach through the soil. The percentage of sand, silt, and clay in a soil determines its texture.
Soil texture influences how fast water can move through soil.
Soil acidity, or pH, affects the chemical properties of many pesticides. As soil pH decreases, pesticides bind more to the clay in the soil and are filtered out of the percolating water. Also, pesticides are usually less soluble in water at lower pH values. Acidity is more important with some types of pesticides than others and is less important overall than organic matter and texture. Other geologic and environmental factors also affect pesticide leaching to groundwater.