• Since March, an installation has been measuring the environmental impact of the runoff of urban paints directly in the soils of an eco-district in Schiltigheim, in the suburbs of Strasbourg.

  • This Franco-German university project aims to determine which biocides escape into the water table and their quantities.

  • Beyond the scientific aspect, the project includes a sociological component, with a survey of the inhabitants of the district but also of painting companies and painters.

There are toxic molecules that are better not to see in paint.

However, some of them still end up escaping urban paintings, building facades and plasterwork.

Carried away by rainwater, it then flows to the soil and the water table.

This is the observation made by several teams of researchers, as part of a Franco-German experiment started in March in the Adelshoffen eco-district in Schiltigheim, on the outskirts of Strasbourg.

The goal: to install, in two places in the district, devices equipped with sensors and bottles to collect rainwater.

The samples are then analyzed weekly until December.

"The objective is to try to understand what becomes of the biocides in the paints of buildings," explains Sylvain Payraudeau, professor of hydrology at the National School of Water and Environmental Engineering in Strasbourg (Engees ).

The problem is, to prevent algae and mold from appearing on facades, paint manufacturers add molecules that escape with each downpour.

And it only takes a little bit to contaminate the flowing water.

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"Even small, they can have a consequence in the water"

The first results were presented on Thursday. They are revealing: "With each episode of rain, we detect the presence of certain biocides, including terbutryne, which is most often found in paints," continues Sylvain Payraudeau. Tobias Junginger, doctoral student at the ITES (Earth and Environment Institute of Strasbourg), was responsible for analyzing the samples collected in the two devices. He puts the results into perspective: “In the case of terbutryne, we find a minimum concentration, of the order of 10 nanograms per liter. This is the equivalent of a lump of sugar immersed in a container the size of 1.5 million tubs. "

The researcher nevertheless indicates that other molecules, "produced by degradation of the paint and which can be toxic", are found in the samples.

“Even in minimal concentrations, they can have a consequence in the water.

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Field surveys

Originality of the project: the scientific aspect is coupled with a sociological aspect.

Guillaume Christen and Maurice Wintz, respectively postdoc and professor of sociology at Sage (Societies, actors, government in Europe), carried out for several months a field survey among residents, but also painters and paint manufacturers.

The feedback is revealing.

“For the painters interviewed, many believe that the biocides come directly from the facade,” explains Guillaume Christen.

There is a difference between the perception of risk and the risk analyzed.

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“Ultimately, the challenge is to know how we communicate about the risk and how the communities will appropriate the results,” explains Sylvain Payraudeau.

The problem has been known for years, but often there is a lack of quantified references.

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Our Planet page

Michaël Malfroy, engineer in charge of the technical monitoring of the water and sanitation service for the Eurometropolis, summarizes: “We will have to work with the paint trades and manufacturers to limit the leaching of micropollutants.

We will not be able to ban it, because it is still necessary that the paintings protect the facades!

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