Tougher controls should be considered on chemicals that can feminise male fish and cause other ‘sub-lethal’ effects, a leading eco-toxicologist has said.
Nearly 10 years after he helped reveal how significant an effect human drugs were having on wildlife, Professor Charles Tyler warned scientists were becoming increasingly concerned about the effects of thousands of waste chemicals.
Some are from industrial processes, but others are drugs taken by people which then pass through them and into the sewers or are simply flushed directly into the toilet.
Professor Tyler, of Exeter University, will talk about the issue in a speech at the 50th Anniversary Symposium of the Fisheries Society in the British Isles.
He took part in a major study in 2008 which found nearly a quarter of male roach fish taken from 51 sites on English rivers showed signs of becoming female, such as having eggs in their testicles.
In some rivers, all the male roach were found to have been feminised to a degree because of the high level of oestrogen, which is used along with progestin in birth-control pills to prevent ovulation and is also present in other drugs.
Other chemicals can affect different parts of the fish’s body, such as the liver, heart and brain.
Professor Tyler told The Independent: “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.
“We’re starting to establish not just effects on gender, but that they can also affect other physiological processes in the fish as well.”
Humans now use thousands of chemicals and their effect on the natural world is poorly understood. However about 200 have been shown to have a feminising effect.
This can prevent the males from breeding successfully.
“It all depends how feminised they become. If they are moderately to severely feminised, they are compromised as individuals and they really struggle to pass their genes on,” Professor Tyler said.
He said such effects, which do not actually kill the fish but can reduce their, could be hard to spot.
“One thing scientists are becoming much, much more conscious of now … is wildlife populations are exposed to a combination of stresses,” Professor Tyler said.
“All we can say is we need to be a bit smarter … there’s no doubt in some regions of the global some of our activities, including chemicals, are producing even local extinctions.
“It’s blindingly obvious when you stick a poison out and it kills something. It’s an incredibly difficult challenge to understand sub-lethal effects and how these things affect behaviour.
“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.”
