As jokes go, it’s a bit of a groaner.
What does a lifeguard say if they catch you peeing in the pool?
As it turns out, the joke’s punchline could also serve as the title of a new University of Alberta study released Wednesday that employed a unique method to examine how often people might be polluting their local swimming pool.
The results won’t make you feel relieved.
Researchers behind the study estimated that in one 833,000-litre pool — a third of an Olympic-sized pool — swimmers had discharged about 75 litres of urine at the time it was sampled. That volume is roughly equivalent to 20 large milk jugs sold in the grocery store.
In another pool that was half as big, about 26.5 litres of urine was estimated in the water.
“Even though no one would admit to peeing in a pool, obviously somebody has to be doing it,” said study co-author Lindsay Blackstock, a PhD student of analytical and environmental toxicology. “There is no other explanation for that (substance) to be present in the pools.”
The substance Blackstock referenced was not urine specifically, but rather a compound called acesulfame potassium that is commonly present in urine.
Ace-K, as it is more commonly known, is an artificial sweetener widely consumed by people in sodas, baked goods and countless other processed foods. Companies use it as a calorie-free sweetener because it is resistant to decomposition by the human digestive system, and excreted through urine in the same form as it was ingested.
Ace-K and similar sweeteners are even resistant to wastewater treatment processes, meaning they often find their way into rivers, lakes and groundwater.
Previous research had used such sweeteners to get an indication of the level of human waste in environmental water bodies, but the U of A study was the first to employ the same idea for recreational waters, Blackstock said.
In total, the scientific team went to two undisclosed Canadians cities and collected samples from 31 different sites, including hot tubs, diving tanks, hotel pools and public pools — both outdoors and indoors — along with samples of tap water used to fill the pools.
Using a rapid, low-cost test developed in-house, the researchers found evidence of Ace-K in all of the samples, but in widely varying concentrations.
The researchers then decided to take a more detailed look at two pools in particular, finding the average concentration of Ace-K at those sites to be 150 to 200 nanograms per litre.
Blackstock noted that urine is considered sterile, and any bacteria or other pathogen that find its way into pools and drinking water is typically killed by chlorine.
Yet chlorine isn’t a perfect solution because recent studies have shown that urine and sweat can react with chlorine to form disinfection byproducts. These include tricholoramines, which can cause eye irritation and even respiratory problems with long-term exposure.
Still, Blackstock said the risk of any harm to swimmers is outweighed by the health benefits of using pools for exercise and recreation.
“I wouldn’t have any concerns about swimming,” she said. “I go swimming myself and my supervisor goes almost every day.”
The study, led by the U of A’s Xing-Fang Li, a professor of environmental health sciences, was published in the journal Environmental Science & Technology Letters.
Blackstock said testing results for hot tubs tended to be the most variable, with either really high or really low concentrations of the sweetener. She said this might be because health standards call for hot tub water to be replaced more often than other pool water. As well, one urination episode in a hot tub could have a more dramatic effect because the volume of water is smaller than in a swimming pool, she said.
Blackstock said she could not disclose where the samples were taken because anonymity was granted to the pool owners