Montreal major polluter of St. Lawrence as E. coli plumes drift to Trois-Rivières, study finds

High concentrations of E. coli bacteria colonies are entering the St. Lawrence River in the Montreal area and following the current as far as Lake Saint-Pierre and Trois-Rivières, a recent study found.

“In Montreal, in some places, there’s up to a million E. coli colonies per 100 milliliters of water. The current standard for swimming is 200 colonies per 100 milliliters,” said François Guillemette.

He’s an associate professor of environmental sciences at the Université du Québec à Trois-Rivières who specializes in the ecology of the St. Lawrence. The study was conducted aboard the school’s Lampsilis research vessel, and it found that Montreal is a major river polluter.

That’s because the city does only a preliminary treatment of sewage, removing the solids but not disinfecting the water before releasing it back into the river. 

Flowing plumes of E. coli can lead to beach closures, as swimming in high concentrations of the bacteria can lead to serious illness. 

But it’s not just the E. coli that’s of concern. The bacteria is usually an indicator that other microbial pathogens are present, Guillemette said.

These microbes, which include bacteria and viruses, can cause different infections and diseases, he explained.

“Swimming east is generally not recommended if you are downstream from the city of Montreal wastewater treatment plant outlet, as the concentrations are very high,” said Guillemette.

Swimming still safe in most areas

However, that’s not to say swimming isn’t safe.

“For the most part along the St. Lawrence, the water quality is really beautiful for bathing,” said Sarah Dorner, a water quality expert and professor at Polytechnique Montréal.

“But we definitely need to keep improving.”

Dorner has been involved in testing the water quality at the new beach in Montreal’s borough of Verdun, and the city was careful to close it when the bacteria was present in the area, she said.

Bacteria can be more readily found when the water levels rise, and near discharge points, she explained, but it moves with the current and will clear out with time. Like Guillemette, she says the concern is more about what else can be found around E. coli plumes.

The Verdun Beach occasionally closes temporarily because bacteria is found in the water, but the pollution clears out quickly, says Sarah Dorner of Polytechnique Montréal. (Ryan Remiorz/The Canadian Press)

“It does indicate the presence of fecal material, but most often there are other pathogens that we are more concerned about,” Dorner said.

Dorner says Montreal’s administration is, like other municipalities along the river, pushing for more access to the St. Lawrence — taking advantage of the waterway’s natural beauty.

At the same time, those cities and towns are aware of the risks associated with swimming in contaminated water and that is why there is increasing effort to protect the river. 

Montreal works to improve wastewater treatment

The Jean-R.-Marcotte wastewater treatment plant located on the eastern tip of the island of Montreal treats all sanitary wastewater, including collected rainwater, said Audrey Gauthier, a spokesperson for the city.  

On average, the station processes the equivalent of the Montreal Olympic Stadium’s indoor volume each day, she said.
The station began operations in 1984, greatly improving water quality in the area, after decades of rapid population growth and poor wastewater management.

The station uses an advanced process to reduce the presence of phosphorus and suspended particles in water, Gauthier said, noting it meets current environmental standards.

Back in 2016, Montreal dumped nearly five billion litres of untreated water into the St. Lawrence River and Quebec City dumped millions more that same year. (Ivanoh Demers/Radio-Canada)

“However, the city wishes to go even further to improve the quality of the water in the St. Lawrence River,” she said.

Montreal has been working to build an ozone disinfection unit for treated wastewater that will reduce the risks to human health while protecting wildlife and the environment, she said. 

“This new plant will make it possible in particular to eliminate more than 99.99 per cent of fecal coliforms as well as a very large proportion of pathogenic bacteria, viruses and other pollutants, thus allowing the practise of aquatic sports more than a kilometre downstream of the river,” Gauthier said.

Former mayor Gérald Tremblay first announced the city would disinfect its wastewater using ozone gas in 2008, but there have been some delays in the years since. The new facility, estimated to cost around $500 million, still won’t be ready for another couple years.

Until then, Dorner says people can swim in the river as long as it’s not too close to the wastewater treatment plant.

“I wouldn’t want people to think the St. Lawrence is really polluted and they shouldn’t go swimming,” she said.

However, she said, “it’s important to have good monitoring and let people know where the water is good for swimming.”

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