Which example best illustrates non-point source pollution?

Non-point source pollution refers to contaminants that originate from multiple diffuse sources rather than a single, identifiable point. The best example of non-point source pollution from the choices provided is the situation where pesticides leach through soil after rainfall. This scenario highlights how rainfall can wash away pesticides from agricultural fields, gardens, or lawns, distributing them over a wide area instead of a specific location.

Unlike point source pollution, such as runoff from a specific industrial facility or waste from a single pipe, non-point source pollution is characterized by its ambiguous origin. In this case, the leaching of pesticides is not attributed to a discrete source but rather to broader agricultural practices, making it a prime example of non-point source pollution. Additionally, the diffusion of contaminants from multiple locations contributes to the overall pollution in nearby waters, showcasing the broader impact of agricultural practices.