What is a primary environmental concern associated with pesticide runoff?

Contamination of water sources is a primary environmental concern associated with pesticide runoff because when pesticides are applied to agricultural fields, lawns, or other areas, rain or irrigation can wash these chemicals off the treated surfaces. This runoff can then carry pesticides into nearby rivers, lakes, and groundwater, leading to potential contamination of drinking water supplies and harming aquatic ecosystems. Pesticides can have toxic effects on non-target organisms, including fish, insects, and other wildlife, which can lead to a decline in biodiversity in these water bodies.

The significance of this issue lies in the fact that once pesticides enter aquatic environments, they can persist and accumulate, potentially affecting both ecosystem health and human health through contaminated water sources. This emphasizes why understanding and managing pesticide runoff is vital in the context of environmental conservation and public safety. Other options, like soil erosion, increased biodiversity, and reduction of soil pH, do not directly address the immediate impact of pesticide runoff in terms of water contamination.