污染(wū rǎn) - pollution, to pollute in Mandarin

污染 (wūrǎn) means "pollution" as a noun and "to pollute" as a verb, the same way English "pollution" nouns and the less common "to pollute" share one idea. 污 (wū) means "dirty, filthy" and 染 (rǎn) means "to dye, to stain", so the compound pictures contamination spreading like a dye through something clean.

As a noun it takes a describing word in front, the way most Mandarin nouns for problems do: 空气污染 (kōngqì wūrǎn), "air pollution", and 水污染 (shuǐ wūrǎn), "water pollution", are the two you will meet constantly in news and environment articles.

As a verb it takes a direct object: 工厂污染了河流 (gōngchǎng wūrǎn le héliú), "the factory polluted the river". Context, not the word itself, tells you which role 污染 (wūrǎn) is playing in a given sentence - much like English "pollution levels are rising" versus "factories pollute rivers".