Sewage plant upgrade reverses 'feminized' male fish

A 10-year University of Waterloo study has found upgrades to Kitchener's wastewater treatment plant have reset the reproductive systems of male darter fish that had started to produce eggs after exposure to toxins in the Grand River.

University of Waterloo study found egg-producing male fish returned to ‘normal’ within three years

PhD candidate Patricija Marjan and University of Waterloo biology professor Mark Servos are seen in this provided photo collecting rainbow darter fish on the Grand River. (University of Waterloo)

Male fish in the Grand River that started to produce eggs after exposure to toxins in the water made a full recovery after Kitchener, Ont. upgraded its wastewater treatment plant, a new study from the University of Waterloo has found.

In 2007, biology professor and researcher Mark Servos started to track the number of intersex male rainbow darter fish in the Grand River ahead of planned upgrades by the Region of Waterloo to the Kitchener wastewater treatment plant.

"The male fish were being feminized," Servos said of what he and his team of graduate students found between 2007 and 2012.

"We were actually observing that most of the fish downstream of Kitchener – the Kitchener outfall from the wastewater – were actually showing up with eggs in their male tissues or their testes. In some cases, we could open up the fish and we could actually see the eggs developing in the testes. And this was a major concern."

Not so rainbow

There were other changes to the fish as well, he noted.

The rainbow darter fish – which were studied because they are extremely sensitive to estrogens and other hormone disrupters in the water – didn't develop the same colour, they didn't behave the same way and they didn't reproduce the way they should.
Rainbow darter fish. (University of Waterloo)

The problems were being caused by endocrine disrupters in the water – chemicals that interact with the body and change how hormones signal and interact with different organs.

In 2012, the region changed the aeration tank in its water treatment plant. Researchers found that helpful microorganisms used to remove toxic ammonia from the treated water being released into the river, also reduced the levels of those endocrine disrupters.

Servos, who is the Canada Research Chair in water quality protection, said over the 12 months following the upgrades, they noticed a big difference in the fish – the number of intersex males dropped from 100 per cent to 29 per cent.

"Within a few years, we've actually seen the impacts we're concerned about: primarily the eggs showing up in the male fish, has almost totally disappeared. It's gone back to normal, or upstream levels," he said.

"We thought that there might be a historical contamination and we thought that perhaps the fish that were exposed in their younger years would persist to have this response in later years," he said, noting this wasn't the case. "What we found was the response [happened] very, very quickly."

Do the 'right thing, good things happen'

The health of fish in the Grand River was an important issue for the Region of Waterloo, Servos said, but it's also a very big research concern globally.

Switzerland, he noted, has been doing extended and more expensive treatment at wastewater plants.

"I think what our research is showing is that with well-operated, conventional plants, we can do an awful lot about remediating these particular problems and perhaps we don't need to spend hundreds of millions of dollars to continue to reduce this, because we're seeing an effective response already," he said.

"It really shows that when we care and when we try to do the right thing, good things happen. The region did the right thing and more good things happened than they expected."

The study was published in the journal Environmental Science and Technology.


To encourage thoughtful and respectful conversations, first and last names will appear with each submission to CBC/Radio-Canada's online communities (except in children and youth-oriented communities). Pseudonyms will no longer be permitted.

By submitting a comment, you accept that CBC has the right to reproduce and publish that comment in whole or in part, in any manner CBC chooses. Please note that CBC does not endorse the opinions expressed in comments. Comments on this story are moderated according to our Submission Guidelines. Comments are welcome while open. We reserve the right to close comments at any time.

Become a CBC Member

Join the conversationCreate account

Already have an account?