In celebration of World Water Day, the University of Guelph welcomed a federal research scientist to share his work on tracing artificial sweeteners to detect water pollution and determine its source.
Environment and Climate Change Canada scientist John Spoelstra has been working with a groundwater team on the artificial sweetener portfolio since about 2008. Often hundreds of times sweeter than sugar, artificial sweeteners such as cyclamate, saccharin and sucralose, are not just used in soft drinks, but are part of a wide array of products such as medications, vitamins, toothpaste and yogurts.
The sweeteners can be used to reduce calorie intake in some dieting programs, blood sugar control for diabetics, and may also be used to reduce cavities in children, which is why they’re often present in children’s vitamins and toothpaste.
“So, the reason we don’t get calories from these artificial sweeteners is that our body doesn’t break them down into energy, like it does for sugar,” Spoelstra explained. “So, what ends up happening is the artificial sweeteners end up here. We end up flushing them down the toilet. They can also make it through the whole wastewater treatment process.”
Subscribe to our Newsletter!
The latest environmental engineering news direct to your inbox. You can unsubscribe at any time.
The durability of the sweeteners — much like caffeine and ibuprofen — makes them good candidates for determining where wastewater may be present, Spoelstra said. He focuses intently on acesulfame potassium as his tracing sweetener of choice. He considers this sweetener to be the hardest to degrade, and it can even survive septic tank treatment.
Sweeteners are also convenient for tracing because they occur in high concentrations and are detectable at very low levels. Spoelstra’s team uses ion chromatography and tandem mass spectrometry, which allows detection limits down to parts per trillion levels.
But the sweeteners have other uses too. Municipalities can trace sweeteners to evaluate leaky sewer systems and determine whether contaminants are being degraded or just being diluted. Or, farmers could figure out if the nitrate in their groundwater is from a septic system or from agricultural fertilizer. The artificial sweeteners map where the wastewater is going.
The sweeteners also have a negative charge when dissolving in water that makes them resistant to sticking to soil particles, Spoelstra said. For groundwater, they don’t get caught up in the soil, moving instead with the groundwater due to the negative charge.
“That’s another characteristic that we want in a tracer,” Spoelstra said, adding that wastewater is the major source for artificial sweeteners in the environment. “And, of course, if you crash a transport truck full of diet Dr. Pepper, that’s going to be a point source for a while too.”
Spoelstra’s first foray into tracing sweeteners was through a 2013 study into the Grand River, which he undertook in collaboration with the University of Waterloo. The area was selected because there are some 30 wastewater treatment plants that discharge into the river, allowing for a potentially large concentration of sweeteners to track. At the time, the treatment plants served some 800,000 residents. About 300 kilometres downstream is where the river discharges into Lake Erie.
At peak levels, the study found about 3,500 nanograms per litre of acesulfame potassium, with a detection limit as low as 2.
In looking at the City of Brantford, the study’s team was able to examine its tap water, which draws from the Grand River. Concentrations of acesulfame potassium were found up to 1,500 nanograms per litre in the tap water.
“So, hence the toilet to tap and back again,” explained Spoelstra, referencing the title of his World Water Day talk.
In rural Ontario, Spoelstra’s team has also detected artificial sweeteners that survived the septic tank treatment process and infiltrated groundwater. He said the sweeteners may survive for at least 15 years in groundwater based on travel times. In a study of about 59 domestic wells in the Alliston area, the team found one or more sweeteners present in about 30% of them.
“If you flush your toilet and it goes into your septic system, then that water percolates down to the groundwater table,” Spoelstra said. “What we’re finding with the sweeteners is that some of that water is then getting intercepted by the well and back up into the house. Possibly a worst-case scenario is you’re not getting your own septic effluent, but you’d be getting your neighbors.”
In another study published in 2020, Spoelstra’s team examined some 173 sites in southern Ontario expected to be impacted by septic systems. Artificial sweeteners were present in 91% of them, he said.
In terms of how much water was getting into nearby streams from septic effluent, the team found 80% of the samples had 0.01% to 0.14% of the water in that stream coming from septic effluent. They calculated that approximately 13% of all septic effluent reaches streams via groundwater.
