Which term describes movement of pesticide in water or other solvent downward through soil or other planting medium?

• A. Leaching
• B. Runoff
• C. Drift
• D. Particle Drift

Answer: (A)

Leaching is the downward movement of pesticides through soil with water or another solvent. This happens when rainfall or irrigation infiltrates the soil and carries dissolved pesticides deeper toward the root zone or even groundwater. Pesticides that are highly soluble or not strongly bound to soil particles are more prone to leaching, especially in soils with low organic matter or coarse texture where water moves quickly. This is different from runoff, which is water moving across the soil surface and can wash pesticides away off-site, and from drift, which is movement through the air during or after application. Particle drift is the subset of drift that involves droplets carried by wind. Understanding leaching helps assess groundwater risk and informs how to adjust timing, application method, and formulation to minimize downward movement.