How Sewage Plants Hurt Fish, And How They Can Help – Forbes

Deformities linked to estrogen-like chemicals decreased dramatically in fish after a wastewater treatment plant in Canada got an upgrade.


Something strange has been happening to fish in Ontario’s Grand River, which drains into Lake Erie. Male rainbow darters—colorful fish a few inches long—are growing eggs in their sex organs. The condition, called intersex, has been identified in fish around the world. It’s often linked to pollution, especially molecules that mimic the female sex hormone estrogen.

In one place downstream from a wastewater treatment plant along the Grand River, every single male fish researchers examined had the abnormality. When that plant, located about 60 miles west of Toronto, was upgraded to a cleaner process, ecologist Mark Servos and his group at the University of Waterloo saw an opportunity to test the effect it and other treatment plants have on fish.

The plant in Kitchener, Canada, was converted in 2012 from a carbonaceous activated sludge process to a nitrifying activated sludge process. Both use microbes to break down biological molecules and other compounds in sewage, leaving clean(er) water. The latter process uses different microbes that can eat some nitrogen-containing molecules like ammonia, which is linked to fish die-offs. Neither is perfect at getting manmade chemicals out of the water plants release into streams and rivers, though the nitrifying process is known to reduce the amount of estrogen-mimicking endocrine disrupting molecules.

These endocrine disruptors come from a range of sources that end up in sewage: plastics, food additives, pharmaceuticals, pesticides. BPA, the plastic additive that has largely disappeared from the market after public outcry, is one example. There’s still debate about the dangers and effects of BPA and other endocrine disruptors to humans. But research does link some of them to intersex fish.

Fortunately, the research Servos and his group reported this week in Environmental Science & Technology shows one way we might fix that.

After the upgrades to the treatment plant, rates of intersex male fish downstream dropped off over the next several years. At the site where 100% of male fish had the deformity before the conversion, the rate dropped to 29% the next year. At another site it was below 10% after three years, from a high above 80% in 2012, before the upgrade.

As a reference point, fewer than 10% of fish at another site, far away from any treatment plant outflow, were intersex. The researchers saw no corresponding reduction over the same time period below a nearby treatment plant that hadn’t been converted.


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