What is a true statement regarding the movement of pesticides from application sites?

The statement that runoff and erosion can contaminate surface water accurately reflects a critical aspect of pesticide behavior in the environment. When pesticides are applied to agricultural fields, they can be washed away by rainwater or irrigation. This movement to surface water bodies like streams, rivers, or lakes can lead to significant environmental impacts, including harm to aquatic life and disruption of ecosystems. Proper management practices can help mitigate these risks, such as using buffer strips and minimizing soil disturbance.

In contrast, the other statements do not reflect the nuanced understanding of pesticide movement. While some pesticides may evaporate, not all do so quickly, especially if they are heavier or are applied in cooler conditions. The notion that there are no sources of contamination contradicts observed realities where various pathways, including runoff and leaching, can lead to pesticide movement away from application sites. Lastly, stating that pesticides are non-mobile in soil overlooks the fact that many pesticide formulations can move through soil profiles, particularly in sandy soils or when there is sufficient moisture. This highlights the importance of understanding the physical and chemical properties of pesticides and their potential to move beyond their intended application areas.