Befoul (verb)

1. To make something dirty or unclean.
2. To defile or desecrate something.

Origin:

From be- + foul, meaning to make something dirty or unclean.

Examples:

1. The industrial waste befouled the river.
2. The company was accused of befouling the air with their emissions.
3. The graffiti befouled the beauty of the building.
4. The oil spill befouled the coastline and killed marine life.
5. The criminal befouled the reputation of the organization.