Which process affects the movement of pesticides from soil to groundwater?

Leaching is the process that significantly affects the movement of pesticides from soil to groundwater. This occurs when water percolates through the soil, carrying dissolved substances, such as pesticides, downwards. As rainwater or irrigation water moves through the soil, it can dissolve these chemicals and transport them deeper into the soil profile, potentially reaching the groundwater aquifers. This is particularly concerning because it may lead to contamination of drinking water sources, which can have serious public health implications.

The other processes listed do not influence this movement in the same way. Evaporation primarily refers to the transition of water from liquid to gas, impacting surface water but not directly transporting substances downward into the groundwater. Adhesion, while relevant to the interaction of pesticides with soil particles, does not facilitate movement through the soil to groundwater. Precipitation involves the falling of moisture from the atmosphere, which can initiate leaching but is not the process through which pesticides themselves are transferred into groundwater. Thus, leaching is the key process of concern when discussing the movement of pesticides from soil to groundwater.