Lake Geneva study exposes micropollutant risks

Lausanne residents bask in the spring sunshine at Vidy Bay Keystone

Highly resistant antibiotic micropollutants are accumulating in the sediment of Lake Geneva despite wastewater treatment, new research has revealed.

This content was published on April 6, 2012

Scientists say there is no need to be alarmed but warn of potential long-term risks. Some 15 per cent of Switzerland’s wastewater is discharged, after treatment, directly into lakes.

The Swiss Federal Institute for Environmental Science and Technology (Eawag) carried out the study, published on the Frontiers in Microbiology website, to learn more about multi-resistant bacteria in natural aquatic environments and how resistance genes are transferred in wastewater.

Researchers focused on Lake Geneva and the city of Lausanne in western Switzerland, home to 214,000 people, several small healthcare centres and the Lausanne University Hospital (CHUV).

Every day 90,000 cubic metres of treated sewage from the city are released into nearby Vidy Bay, some 700 metres off shore, at a depth of 30 metres.

Researchers were surprised to find that, while 75 per cent of bacteria were eliminated at the main city sewage plant, “elevated levels” of multi-resistant strains of bacteria still left the plant and were detected in the lake sediment and at the wastewater outlet.

The plant also seemed to act as an ideal place for the creation of micropollutant “cocktails”, they discovered.

While there is no ground for panic - water taken from the lake is also treated before being fed into Lausanne’s water supply – there are potential long-term risks, they claim.

“Nobody should worry about swimming in Swiss lakes at the moment. Our results certainly would not support any such warning,” Eawag researcher Helmut Bürgmann told

“We don’t think there is an acute risk – we have no indications of that. But there is a potential risk if there is a constant discharge of antibiotic micropollutants into natural environments which build up. In the long term this could play a role in the transfer of resistance back to pathogens.”

Not unique

The Eawag researchers say the Lake Geneva case is not unique. They have therefore started similar tests at 20 other lowland and alpine lakes across Switzerland to form a better national picture.

Michael Schärer, from the Federal Environment Office’s water protection department, welcomed the research.

“It’s important to monitor this study and if we find an increase in concentrations of multiresistance genes in the coming years, then the situation should possibly be carefully assessed by the responsible authorities,” he told

“You can’t generalise about Vidy Bay as it’s in a distinct location with special currents. But we know that in other Swiss lakes the situation is similar with large treatment plants that discharge water into lakes.”

Additional treatment processes

The Swiss authorities are developing strategies to reduce micropollutants in aquatic environments, including the introduction of additional treatment processes to remove micro-pollutants at 100 out of 700 selected treatment plants.

A consultation process is due to be launched before summer on changes to the water protection law. If all goes to plan, new measures could start to be introduced in 2015.

Lausanne’s sewage plant at Vidy, which carried out tests on treatment technologies in 2009-2010 for the federal authorities, is pushing ahead to upgrade its installation the same year.

Michael Casanova, responsible for water protection at the environmental group Pro Natura, described these plans as “a step in the right direction”.

“Water quality in Switzerland has improved over the past 30 years due to better wastewater treatment,” he said. “But today we have micropollutants that are not visible in rivers and lakes. There are thousands of substances and nobody really knows how they affect the environment.”


The introduction of new processes like ozonisation and UV treatment to target micropollutants from pharmaceuticals and pesticides should eliminate 80 per cent of micropollutants at the 100 biggest treatment plants, said Casanova.

Overall, 50 per cent of all micropollutants could be eliminated by applying new technologies.

“But we could and should do more if we applied the new technology to all wastewater treatment plants. But there is a big question of finance,” said the Pro Natura water specialist.

According to Schärer, the new measures at the 100 plants could take 20 years to implement and cost SFr1.2 billion ($1.3 billion), an amount which still needs to be agreed upon.

Casanova felt there should also be a separate treatment process for sewage from hospitals that might contain highly resistant antibiotic micropollutants. But Schärer and Bürgmann were not convinced.

“It’s not clear if it’s necessary or justified,” said Bürgmann. “We need more information to see if there is an extra risk.”

Apart from introducing new technologies, Casanova wants to see much more prevention at hospitals and at home.

“People flush expired drugs down the toilet which is not appropriate; they should really be returned to a chemist,” he said.

Dirty laundry

Greenpeace International released a report on March 20 claiming that hazardous chemical residues in clothing items sold by brands including Calvin Klein, Puma, Abercrombie & Fitch and G-star are released into public waterways when they are washed by consumers.

Greenpeace measured the percentage of the hazardous chemicals nonylphenol ethoxylates (NPEs) washed out during simulated standard domestic laundering conditions for 14 clothing items. Some 84 per cent of NPEs in a Puma Swiss national football shirt and 45 per cent in a pair of Calvin Klein pyjamas, both purchased in Switzerland, were washed out in one wash.

NPEs are chemicals used in textile manufacture. Even where wastewater containing NPEs is treated, this only speeds up their conversion into toxic hormone-disrupting chemical nonylphenol (NP).

The use of NPs and NPEs in clothing manufacture has effectively been banned within the European Union and similar restrictions are in place in the US and Canada.

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Micropollutants originate from consumer products (pharmaceuticals, detergents, toiletries, etc.) and from plant and material protection products. These substances enter the water through the urban wastewater management system or by other means (e.g. storm drains, agriculture run-off).

Micropollutant is a collective term for organic trace compounds or heavy metals which occur in the aquatic environment in tiny concentrations (billionth to millionth of a gram per litre).

Even at these low amounts, they can have adverse effects on aquatic life or affect drinking water resources. In Switzerland more than 30,000 such substances are used regularly in innumerable products.

Persistent compounds that are used in large quantities can be particularly problematic for surface waters. Substances can enter the water either dissolved or bound to suspended particles.

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