The word "contaminates" is a verb, and the word "contaminant" is a noun. Contaminate means to make something harmful, undesirable, polluted, or impure. It may also be used figuratively to demonstrate an imperfect character or thought. The past tense of contamination is contaminated.
The contaminant, on the other hand, is the actual substance that contaminates something. The contaminant is the impurity or some other undesirable element that spoils, infects, decays, or corrupts. A contaminant is a substance that makes a place, an object, or an environment no longer suitable for use.