What factors can lead to leaching or seepage of pesticides?

Leaching or seepage of pesticides occurs when pesticides move through the soil profile into the groundwater. The correct answer highlights the significance of applying pesticides before rainfall, particularly in sandy soil, which can facilitate this process. Sandy soils have larger particles and, consequently, larger pore spaces, allowing water—and any dissolved substances, such as pesticides—to move more quickly through them.

When pesticides are applied right before rainfall, the rainwater can quickly transport the chemicals downward, increasing the likelihood of leaching. This rapid movement is exacerbated in sandy soils, which do not retain moisture well, meaning water and any contaminants are less likely to be held in place and more likely to be washed away into deeper soil layers or groundwater.

In contrast, the other options do not effectively combine the right conditions for leaching. Application in dry conditions and clay soil would typically lead to less leaching because clay soil retains more moisture and has smaller particles, slowing the movement of water and contaminants. Applications made at low temperatures slow down the chemical reactions and the mobility of pesticides, reducing the risk of leaching. Similarly, using larger droplets for spraying means less fine spray that can be carried away by wind or water, which also minimizes the likelihood of leaching.