Under which soil conditions are pesticides more likely to leach through soil?

Under which soil conditions are pesticides more likely to leach through soil?

• A. A sandy soil, low in organic matter, where groundwater is shallow.
• B. Clay soil with high organic matter and deep groundwater.
• C. Loam soil with moderate organic matter and intermediate groundwater.
• D. Rocky soil with no groundwater.

Answer: (A)

Pesticide leaching depends on how easily water can move through soil and how well the soil can hold onto pesticides. Sandy soil has large pore spaces that let water—and whatever dissolved pesticides it carries—move quickly downward. If this soil also has low organic matter, there are few sites for the pesticide to bind to, so it stays in solution and moves with percolating water more readily. When the groundwater is shallow, the distance for the pesticide to travel before reaching groundwater is small, increasing the chance of contamination. In contrast, clay soils and soils rich in organic matter bind pesticides more strongly and slow downward movement, reducing leaching risk; loam with moderate organic matter is intermediate; and rocky soil with no groundwater offers little opportunity for leaching to groundwater. Therefore, the sandy, low-organic-matter soil with shallow groundwater is the scenario most prone to leaching.