The Atlantic tomcod in the Hudson River has evolved immunity to the PCBs dumped in the river by General Electric.

http://news.nationalgeographic.com/news/2011/02/110217-hudso...

That is possible because the generation time of many bacteria can be measured in hours or minutes. The generation time in humans is ~25 years (possibly a bit higher in the western countries mentioned) So there could be hundreds of bacterial generations in a few days, but only ~2 human generations in the time period covered by this study. Selection would have to be extremely strong (the strongest ever observed by far) for the sperm count decrease to be primarily related to selection.