Pesticides are most likely to leach in which scenarios?

Leaching refers to the process by which pesticides dissolve in water and move through the soil, potentially reaching groundwater. The correct choice highlights that leaching is more likely in heavily treated areas because a higher concentration of pesticide is present, increasing the risk of these chemicals being washed away by rain or irrigation water.

In heavily treated areas, the application of large amounts of pesticides raises the likelihood that they will be present in the soil in significant quantities. As precipitation occurs, these soluble compounds can dissolve and migrate vertically through the soil profile. This process is amplified when the concentration of pesticides increases, as there is more substance available to be mobilized.

In contrast, low quantities of pesticides would logically reduce the potential for leaching due to limited availability. Areas with heavy rainfall do contribute to leaching, but without the context of having pesticides in sufficient concentrations, the likelihood is not as pronounced as in heavily treated areas. Approaches or situations that involve just sandy soils would also be limited, as leaching can occur in a variety of soil types depending on pesticide concentration and other factors such as soil moisture and type. Therefore, while these factors can influence leaching, the significant determinant remains the amount of pesticide present in heavily treated zones.