Water cycle
From Tardis Wiki, the free Doctor Who reference
According to Jack Harkness, by 2008, oestrogen entered the water cycle when people flushed their contraceptive pills down the toilet: sending the hormone "all the way up into the sky, [then] all the way back down on to me" via rain. Jack further claimed that this was "feminising" the fish. Nevertheless, he was happy enough to avoid another pregnancy. (TV: Everything Changes)