More than 1,400 treatment plants in the U.S. and Canada spew 18 billion litres of treated wastewater and sewage into the Great Lakes every day — enough to fill the Rogers Centre to the top 11.25 times.
While the material is filtered and treated before being released, the process doesn’t remove all contaminants: modern sewage-treatment plants are still unable to target some pharmaceuticals, chemicals, and personal-care products.
Emerging research warns that the contaminants that remain can be harmful to fish populations. According to a new study from McMaster University, fish that swim in streams of treated wastewater spend more energy processing such toxins, meaning they have to eat more and work harder, expending energy that should be used for survival.
Researchers gathered bluegill sunfish and caged them in three locations in Hamilton: two in the stream of the Dundas Wastewater Treatment Plant and a third in a neutral location to serve as a control group. The wastewater plant drains into Cootes Paradise, a marsh on the coast of Lake Ontario.
“The main important finding was that the fish that were exposed to wastewater effluent were having to burn a lot more energy just under routine conditions to stay alive,” said Graham Scott, senior author of the study, which was published in the journal Environmental Science and Technology. “If it's burning more energy just to stay alive, that means it doesn't have as much energy to devote to the things the fish needs to do. It also means it needs to find more food to support those energy demands.”
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Increased metabolic demands caused by wastewater contaminants could potentially leave fish too exhausted to engage in vital activities, like breeding, or lead them to seek out food in areas where predators might roam.
These findings build on existing research, also from McMaster, that has shown that wastewater effluent containing remnants of antidepressants can make fish bolder — and therefore more vulnerable to predators.
“Wastewater treatment plants are pretty good at getting rid of the things that they're designed to remove,” says Scott. “But there are a lot of emerging contaminants in wastewater that historically we haven’t really thought about, so things like pharmaceuticals and personal-care products … In many wastewater treatment plants, those things pass right through without being removed, or are removed very little.”
The study focused on treated wastewater, but some untreated waste also flows into the Great Lakes thanks to sewage bypasses. Many wastewater systems are designed with combined sewers, meaning that runoff from drains on streets and roads mixes with sewage from toilets and sink drains. When it rains, those sewers fill up: to avoid overloading their systems, water-treatment plants will occasionally release raw waste directly into the Great Lakes. It’s difficult to get a handle on just how much raw waste enters the system, as municipalities are not required to report on it.
Scott says we need to develop new technologies to deal with the wide range of contaminants we’re dumping down our drains and into our sewers.
“What we need to start thinking about is whether wastewater treatment plants in the future can be designed differently to remove those sorts of things,” says Scott. “We’re at the point now where we’re just starting to appreciate the various effects of these types of contaminants on animals and aquatic environments.”