What is a common source of surface water contamination by pesticides?

Runoff and erosion are significant contributors to surface water contamination by pesticides because these processes can carry pesticides from agricultural fields or treatment areas into nearby streams, rivers, and lakes. When it rains, water flows over the land surface, picking up pesticide residues that are present on the soil or plants. This runoff can transport not only the pesticide itself but also soil particles that have been coated with pesticide, leading to increased concentrations of contaminants in surface water bodies.

Once these pollutants enter surface waters, they can adversely affect aquatic ecosystems, drinking water sources, and overall water quality. The combination of runoff, which directly transports pesticides, and erosion, which can mobilize pesticide-laden soil, makes this process particularly impactful in agricultural areas where pesticide use is common.

Soil erosion is relevant but does not encapsulate the full process involved, as runoff specifically describes the movement of water and its contents. Atmospheric deposition refers to the way pesticides can settle out of the air but is not as direct in causing surface water contamination. Pesticide evaporation, while a noteworthy phenomenon in terms of pesticide loss to the atmosphere, does not typically lead to surface water contamination. Therefore, the most accurate answer that captures the full scope of the issue is the combination of runoff and erosion.