DePesto contamination of groundwater occurs primarily through which mechanism?

• A. Absorption
• B. Leaching
• C. Runoff
• D. Both B and C

Answer: (B)

Groundwater contamination from pesticides mainly happens when dissolved chemicals move downward with infiltrating water through the soil to the water table. This downward transport, called leaching, occurs after rainfall or irrigation drives water through the soil, carrying the pesticide with it. The likelihood of leaching depends on the chemical’s solubility, how strongly it adsorbs to soil particles (which keeps it in place), soil texture, organic matter, and how close the groundwater is. Runoff carries pesticides on the surface to surface water bodies rather than directly into groundwater, and absorption to soil particles tends to bind the chemical and slow or prevent downward movement. So the primary mechanism is leaching.