The city is using our wastewater to detect Covid, but how does it work? We asked this expert

The city is using our wastewater to detect Covid, but how does it work? We asked this expert

We’re more than two years into this, and just when it seemed like everything was going back to normal, with the province eliminating mask and passport requirements, we started hearing about an uptick in Covid infection rates in our wastewater. It had everyone thinking, Wait, wastewater? We’re now using poop to track the virus? The whole thing felt confusing (and extremely icky). So to find out more, we called Elizabeth Edwards, co-lead of the team of scientists at U of T who are examining our excrement and giving data to public health officials.

When did all of this Covid wastewater analysis stuff start happening in Toronto?
Early efforts in Ontario started in Ottawa and Waterloo. Right after the pandemic started, I got calls from colleagues in Ottawa who were saying, “Hey, I think we should do this.” I was skeptical at the time because I didn’t believe we would get accurate data. Everything gets flushed down the drain—it’s not just the toilet waste—so fecal matter gets diluted. And I thought it just wasn’t going to be sensitive enough to be the early warning signal that people hoped for. The researchers in Ottawa and elsewhere in the country decided to go ahead anyway.

How did your team at U of T get this job?
The province started funding some academic institutions, because they recognized that wastewater treatment would be useful, but they didn’t want to take away from the clinical testing capacity. Universities have the same quantitative PCR systems used in clinical testing, so the province reached out to us. My U of T colleague Hui Peng was also interested, so we teamed up together. It was right before Christmas in 2020 so we had to ramp up capacity really quickly and learn the techniques from Ottawa and Waterloo. Since January 2021, we’ve been sampling the three big plants in Toronto—Ashbridge’s Bay, Highland Creek and North Toronto. Our colleagues at Ryerson are analyzing the Humber River plant.

Does it actually work?
Yes, wastewater testing tracks clinical cases really well. The original thought was that maybe wastewater would provide an early warning alerting us when cases go up. And you can get that—you can see that the wastewater signal does increase before clinical cases. The trends are mirroring each other in the peaks and dips very well. Wastewater gives the public health units that confidence and knowledge of what’s happening at the population scale. They really love it. And they’re relying on it right now, because unlike earlier waves, clinical testing is at an all-time low. Wastewater offers an unbiased perspective, and we see if it responds to changes in public policy, for example, to understand what’s happening now that mask mandates are off.

So do you just go over to the plant and collect the samples yourself?
The treatment plant operators collect the samples from what’s called “head works,” where all the main sewer lines converge on one huge pipe. Then the samples from all of the treatment plants go to a lab on Commissioner Street, right by Ashbridges Bay. We have a driver who goes down there three times a week, collects the samples and brings them to Ryerson and to us at U of T. So we get 500ml plastic jugs with cruddy-looking water in it.

Gross. How bad does it smell in the lab? 
It doesn’t smell bad because we do everything in the fume hood. It’s like a canopy over your stove, and it sucks up all of the air. We have a UV light hanging over the work area that helps to disinfect, and we wash all surfaces with bleach often.

So what happens next?
We extract a sample from the fecal matter, put it into a polymerase chain reaction (qPCR) machine, then we count how many cycles we need to detect the virus. The fewer the cycles, the more virus we had to start with.

Do you have a cool lab outfit, like a scientist in the movies?
We wear lab coats and safety glasses. And gloves. Lots of gloves—you change them often. The Covid virus is actually no longer infective in wastewater. However, there are all kinds of other viruses and bacteria that could be, so we are very careful. That’s why everything gets bleached every day.

Don’t you find this whole process kind of nasty?
Well, if you’ve ever changed poopy diapers, it’s not as bad as that. Occasionally you find surprises in the wastewater, but you get immune to all of that. It’s fun to take students on tours of wastewater plants to see what ends up there. I think everyone should go on a tour, just so they think twice before throwing something inappropriate down the toilet.

Do you have a degree in wastewater analysis or something?
My degree is in chemical engineering. Groundwater remediation is what my research is in. I also teach about wastewater treatment.

What else can wastewater analysis tell us?
You can detect chemical signals and biological signals as well. There’s a lot you can tell. From caffeine to sugar substitutes, you can tell a lot about diet. You can measure estrogen from birth control pills, and all kinds of illicit or legal drugs. Alcohol is harder because it degrades. You can also measure infective particles like polio, hepatitis, flu, and others.

Wait, is the city secretly analyzing our wastewater all year!?
No! The operators work hard just cleaning the water before it flows into Lake Ontario. Wastewater is unforgiving. It never stops all year round. It’s relentless. You can’t turn off the tap and take a break to fix things.

And who funds the Covid analysis? 
The province funds it. Our universities have contributed hugely, needless to say. They have contributed the time and salaries of the professors, space and equipment.

Are other countries doing this?
Yes, many. But I think Ontario has the most comprehensive effort on the planet right now. We’re monitoring 75 per cent of the population of a big province. I think it’s a model. It may seem like a lot of money and it is a lot of work, but it’s still cost effective when you realize that it provides reliable data for an entire region.

What’s your favourite part about the job?
Getting to look at all of this data, trying to figure out what it all means, and plotting it out and making sense of it all. It’s what drove me into research in the first place: you have a problem and you’re trying to figure it out so that you can help people.