想问下关于WHILE的用法,是表"当"还是转折呢?

看到了两个不同的题目,一个是Industrialization and modern methods of insect control have improved the standard of living around the globe while at the same time they have introduced some 100,000 dangerous chemical pollutants, having gone virtually unregulated since they were developed more than 50 years ago.=====>这里说WHILE应该做的是表示"当",后面应当直接跟着INTRODUCING...

但是之前我看到一个题是说WHILE可以表示转折,当作连词那样用...

那么,WHILE到底需要前后平行对称么?什么样的用法呢到底?请高手指点下!谢谢

这里的while应该是“然而”的意思，表转折吧

然而与此同时它们带来了大约100,000种危险的化学污染物...