What is the primary mechanism by which pesticides leach into groundwater?

The primary mechanism by which pesticides leach into groundwater is through water movement through soil. When pesticides are applied to the soil, they can be dissolved in water. As water moves through the soil, particularly during heavy rains or irrigation, it can carry these dissolved pesticides along with it. This process, known as leaching, allows pesticides to infiltrate deeper into the soil profile and potentially reach the groundwater aquifers.

Water movement through soil occurs due to gravitational forces and capillary action, which can transport chemicals downward. Factors such as soil texture, structure, organic matter content, and the solubility of the pesticide all influence how readily pesticides can leach into groundwater. In contrast, evaporation, surface runoff, and rainfall absorption do not primarily facilitate the movement of pesticides into the deeper soil layers where groundwater resides.