Pesticide residues have constituted a significant source of contamination of environments.

农药残留已经成为环境污染的一大重要来源.

It is well recognized that people are the major source of contamination in an aseptic processing filling operation.

这是一个很好的认识：人是无菌灌装操作过程中的主要污染物。

The bean sprout crop that was the source of the outbreak requires a warm and humid environment to grow, which increases the risk of contamination by E. coli and other disease-causing bacteria.

豆芽菜的生长需要温暖潮湿的环境，这正好也适应大肠杆菌的生长，增加了被污染的风险。