(每日一词）impurity

impurity /ɪmˈpjʊr.ə.t̬i/ n. 纯度不高，杂质; 不纯洁，淫秽

meaning: the fact that a substance is dirty or lower in quality because it is mixed with another substance, or something that causes this 

1) 前缀：im-否定

2) 词根：pur- 纯洁

3) 后缀：-ity 名词后缀

e.g. The impurity of the water is a health risk. 不洁的水质对健康是个威胁。