According to new research, large populations of male fish are starting to exhibit female traits after being exposed to chemical substances found in sewage runoff.
The findings come from leading ecotoxicologist Professor Charles Tyler, who has discovered that many species of freshwater river fish in the United Kingdom are being “feminized” by human waste products.
Some of this waste comes from industrial processes, but the majority come from drugs, like Xanax and birth control, which enter rivers after passing through humans and into the sewage system.
“If you look in terms of what gets into a fish’s liver or gonad, the analysis of the chemicals it contains is a bit of a blueprint in terms of what’s flushed down the toilet,” he told the Independent.
“We’re starting to establish not just effects on gender, but that they can also affect other physiological processes in the fish as well.”
Tests showed that 20% of fish observed at 51 different river sites throughout the UK displayed feminine characters, most notably in the production of eggs in the testicles.
In some of these sites, all the male fish exhibited feminine characteristics to some degree, thanks to increased levels of oestrogen from birth control pills.
While Tyler admitted that the effects from these drugs aren’t actually killing the fish, they will reduce their populations over time.
“It all depends how feminized they become,” Professor Tyler said. “If they are moderately to severely feminized, they are compromised as individuals and they really struggle to pass their genes on.”
“If we get sufficient evidence indicating there’s a high likelihood of a population effect, perhaps we need to be more proactive about restricting… or banning these chemicals.”