This is the 3400th most frequent Japanese word.
汚染
Pollution; contamination.
汚染されています describes the state of the river being polluted due to an external cause, showcasing the word as a descriptor of environmental contamination.
この川は工場からの排水で汚染されています。
This river is polluted by wastewater from the factories.
大気汚染 here specifies a type of pollution (air pollution), emphasizing the word's use in categorizing various kinds of contamination.
大気汚染が都市部の健康に深刻な影響を与えている。
Air pollution is seriously affecting the health in urban areas.
汚染する in this context is used metaphorically to indicate that the statement negatively influenced the situation, demonstrating the versatile application of the word.