Which statement best describes leaching in pesticide movement?

• A. Movement through air
• B. Evaporation from leaves
• C. Runoff into streams
• D. Movement through soil

Answer: (D)

Leaching is the downward movement of a pesticide through the soil with infiltrating water, carrying soluble residues deeper into the soil toward groundwater. This describes transport that happens as rain or irrigation water moves through the soil and dissolves the chemical, allowing it to travel with the water down the soil profile. It differs from movement through air (volatilization), evaporation from leaves, or surface runoff into streams, which involve different pathways. Leaching depends on how soluble the pesticide is, how strongly it adsorbs to soil particles, soil texture and organic matter content, and the rate of rainfall or irrigation plus how deep groundwater lies. In sandy soils with high water movement and for highly soluble pesticides, leaching is more likely; in soils rich in clay and organic matter, adsorption can limit downward movement. This concept helps inform timing, soil type considerations, and pesticide choice to protect groundwater.