Anti-fungal and anti-bacterial additives in house paint are present in
dangerous quantities in the Vauchère river basin in the city of Lausanne, says
a study to be presented at the American Geophysical Union (AGU) conference in
San Francisco. Chemicals engineered to kill microorganisms, called biocides,
are added to exterior paints in order to prevent molding and plant growth.
Washed off of building facades during heavy rains, however, these chemicals can
be wind up in soil, groundwater and river basins where they attack bacteria,
fungi and algae at the bottom of the food chain. Researchers at EPFL's
Ecological Engineering Laboratory have now modeled the flow of biocides from
building façades into river basins with surprising accuracy, which could lead
to stricter regulations for Switzerland and abroad.

In Switzerland, biocides are present in exterior paint on some 60 percent of
buildings and they are common worldwide. The global demand on all biocides for
use in industrial and consumer goods was estimated at U.S. $6.4 billion in
2008. Certain antifouling biocides have been phased out of use on boat hulls
after being proven toxic to marine life.



The mathematical tool developed by Sylvain Coutu at EPFL accurately predicts
peak concentration levels in a local river of three biocides commonly found in
industrial paint: DCMU, Terbutryn and Carbendazim. Coutu predicted the
concentration of these biocides after four rainstorms during the spring of 2011
and compared the numbers to actual measurements taken from the river. The model
proved accurate up to a couple of nanograms per liter, an impressive feat
considering the variety and complexity of variables. The model's strength comes
from its ability to simplify urban surface hydraulic behaviors-how water is
channeled down streets and gutters or lawns and gardens-and still remain
extremely accurate.



"A true toxicology report should include peak levels of concentration after
rainfall, and we have created the first model that takes them into account over
a period of time,"Coutu said.



Establishing a working model has the advantage of reproducibility as well as
reducing dependency on expensive testing. Once a reliable model has been
created it can be used in other regions, although the model needs to be adapted
to the specific geography, for example the surface area of contaminated façades
as well as the quick water drainage of urban surfaces. Once the input is
determined and the dynamics of the hazardous substances reacting to rainfall
are worked out, it is possible to estimate the concentrations of these
substances to see if they exceed acceptable levels.



The biocides that reached the river basin in Switzerland did so in extremely
small concentrations-30 nanograms per liter, or 30 parts per trillion, of the
chemical DCMU were present after heavy rains. DCMU is a common herbicide and
algicide developed in the 1950s in Germany and the threshold concentration
after which this substance is considered a threat for the environment is 20
nanograms per liter. DCMU is considered harmful and can potentially kill algae
and other plantlife by inhibiting photosynthesis and thus depriving the
organisms of energy. Biocides in general do not degrade easily, thus increasing
their risk of moving up the food chain and making their way, in higher and
higher concentrations, throughout the environment.



"While it may seem like a very small concentration, 20 nanograms is all that is
needed to have an impact on the ecosystem since these chemicals are engineered
to kill at very low doses," Coutu said. Furthermore, the study also proves that
water behavior in urban environments can be accurately modeled, opening the
door to further toxicology studies for city ecosystems.

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AplusA-online.de - Source: environmental protection