Which of the following is a source of surface water contamination by pesticides?

Runoff and erosion are significant contributors to surface water contamination by pesticides. When it rains or when irrigation occurs, water can carry pesticides that have been applied to agricultural fields or landscapes over the surface of the land. This process transports contaminants directly into rivers, lakes, and streams, leading to a dilution of concentrations but simultaneous spread of the chemicals into aquatic environments, which can harm aquatic organisms and disrupt ecosystems.

The importance of this understanding lies in recognizing how pesticide application practices should be managed to minimize environmental impact. Implementing buffer zones, proper timing of pesticide applications, and choosing less harmful substances can help mitigate such risks and protect surface water quality.

In contrast, while leaching through soil pertains to the movement of pesticides through the soil profile and biodegradation in soil involves the breakdown of pesticides, these processes primarily affect groundwater quality rather than surface water. Direct application to water bodies can also lead to contamination but is not as common a source as runoff from agricultural fields during rainfall events.