It is already known from water monitoring that pollutants in urban areas enter the environment with rainwater in sometimes significantly increased concentrations. However, it has only been possible to identify which pollutants and from which materials in individual cases. The new study shows that the biocides diuron and terbutryn in facades, the root protection agents Mecoprop and MCPA in bituminous sheeting, and zinc in roofing and facades (window sills, roof structures, plasters and façade coatings) can enter the environment. The biocides diuron and terbutryn are used to protect against algal and fungal growth. The herbicides Mecoprop and MCPA prevent plant root growth into construction materials. The measured concentrations exceeded target values (environmental quality standards) for surface waters, in part significantly. Many further substances, however, were present in normal concentrations.
The biocides and herbicides detected can have toxic effects on living organisms such as aquatic plants (reduced photosynthesis), small crustaceans (diminished mobility) and fish (deformation of eggs). Chronic toxicity of zinc to freshwater organisms – e.g. impaired growth and mobility – has also been reported.
The study also examined how the emission of pollutants from construction projects can be minimised. The study found that by taking environmental concerns into account at an early stage of planning, the input can be reduced by more than 90 percent. For example, a wide roof overhang on all façades reduces contact with rainwater. If the façade remains dry, nothing or little can leach out. Biocide or herbicide-free building products can also often be used. For example, roots can be protected with roofing materials that are not planned as green roofs - making the use of herbicides superfluous. Façades with mineral plaster protect against unwanted growth without biocides: they have a high pH value which algae and fungi cannot tolerate. A guide by the German Environment Agency for building planning shows various sample solutions for environmentally friendly building planning of roofs, façades and properties.
Research took place in Berlin from summer 2018 to winter 2020 in two new build areas of similar size and type of structure. This included buildings with approx. 120 flats with plastered facades (thermal insulation composite system) and with and without green roofs. For a period of 1.5 years, samples of stormwater runoff from facades, roof and the entire area (storm sewer) were taken for each area and analysed for organic substances and heavy metals contained in the building products. The results of the measurements were then modelled and can thus be transferred to new construction projects of a similar scale.
The study results will flow into the award criteria of the Blue Angel ecolabel. UBA plans to propose new ecolabels and award criteria for roofing membranes, roofing tiles, exterior plasters and exterior paints to the Ecolabel Jury. The Blue Angel for roofing membranes is scheduled to be introduced as the first new product group by summer 2022. With the help of the Blue Angel, everyone planning construction and renovation work can volunteer to strengthen the demand for environmentally friendly building products and ease the burden on the urban environment.