Contaminate (verb)

1. To make something impure or dirty by the presence or addition of a harmful substance or element.
2. To corrupt or pollute something morally or ethically.

Origin:

From the latin contaminare, meaning "to defile, pollute", from con- meaning "with" + taminare meaning "to soil, defile".

Examples:

1. The water was contaminated with chemicals from the factory.
2. The soil was contaminated by the oil spill.
3. He contaminated the sample with his own DNA.
4. She contaminated her reputation by her unethical behavior.
5. The food was contaminated with bacteria.