Which factor is NOT a concern when applying pesticides near water sources?

The surface tension of water is not a primary concern when applying pesticides near water sources. Surface tension refers to the elastic tendency of liquids which makes them acquire the least surface area possible. While it can influence how substances interact at the water's surface, its impact on the movement and behavior of pesticides in relation to aquatic environments is minimal compared to the other factors listed.

Drift during application is a significant concern because it refers to the unintended movement of pesticide particles through the air to non-target areas, potentially contaminating water bodies. Runoff from rain is also crucial because it can carry pesticides into nearby water sources after application, leading to contamination and harming aquatic ecosystems. Volatilization refers to the process of pesticides turning from liquid to gas, which can also pose risks of contaminating air or water through chemical movement away from the intended application site.

Understanding these factors helps in making better decisions regarding pesticide application to protect water sources and maintain environmental health.