Environmental stressors are mentioned briefly in the summary above.   In some places drugs, including reproductive drugs, are dumped into rivers after being excreted.   After treatment, this often becomes drinking water.  

Local water authorities usually strain and chemically-treat into waste before dumping it into waterways.   But they have no way of filtering out drugs which pass through the body more-or-less intact.   River water, often the drinking water for millions of people, contains many drugs (pharmaceutical and recreational) that have previously been swallowed by up-river humans and animals.

Wouldn't this affect men's sperm count, for example?