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Rapporten viser, at sedimentet i regnvandssøer i byer spiller en væsentlig rolle for tilbageholdelsen af biocider, før regnvandet ledes ud i det naturlige vandmiljø.De konstruerede regnvandssøger og filterjorde er vigtige i forbindelse med afledning af regnvand fra byer, og de finder stadig større udbredelse i forbindelse med klimatilpasning og reduktion af byernes påvirkning af det naturlige vandmiljø. Rapporten viser i hvor stor udstrækning biocider tilbageholdeles og omsættes i regnvandssøer og filterjorde. Derudover blev det undersøgt, hvordan algesamfund i regnvandssøer påvirkes af biocider i afstrømmet regnvand. Rapporten peger endvidere på, at sedimentet i regnvandssøer bidrager væsentligt til en udligning af biocidkoncentrationer ved at tilbageholde biociderne under spidsbelastninger, og derpå igen frigive dem mere jævnt over en længere periode. Herved reduceres størrelsen af spidsbelastningerne med biocider til det naturlige vandmiljø, som regnvandet herefter udledes til. Der sker også en vis omsætning af biociderne i sedimentet, så der samlet sker en reduktion af biocidudledning til det naturlige vandmiljø. Alt i alt tydede undersøgelserne af alger i regnvandssøer på, at biocider i de undersøgte koncentrationer ikke førte til væsentlige ændringer i artssammensætningen. Regnvandssøer er dog påvirket af mange andre faktorer end biocider, så mulige effekter af biocider i afstrømmet regnvand kan derfor have været overskygget af andre typer af påvirkninger.

Biocides are common additives in building material. In-can and film preservatives in render and paint, as well as wood preservatives are used in order to protect façade materials from microbial spoilage. However, it is known that these compounds with fungicidal, bactericidal and algaecidal activity leach out of the material when it gets in contact with rainwater. While in city centers the total façade runoff drains on paved surfaces like streets and terraces and further into the sewer system, the runoff in residential areas drains to a certain amount to beds or the lawn surrounding the houses. Based on a monitoring study of stormwater runoff from a residential catchment as well as direct façade runoff analysis, the present study was assessing the pollution of urban soil to biocides from building material. The stormwater runoff of a residential catchment in Silkeborg (Denmark) was monitored over nine months. The catchment covered 140 single family houses with a total façade area of about 24000 m2. However, only 25% of the total façade area was expected to release biocides (render, painted wood). Median concentrations of 45 and 52 ng L-1 (7 and 8 mg event-1) have been detected for carbendazim and terbutryn, respectively. The other studied biocides were usually lower. However, in some rain events the concentrations reached concentrations up to 1.8 µg L-1 (77 mg event-1), possibly resulting from freshly rendered or painted façades. Emissions of freshly treated façades measured on artificial walls ranged from 1 to 10 mg m-2 event-1. Hence, the emissions of a freshly treated house with a façade area of 160 m2 might range from 40-400 mg event-1, since only one side of the house is exposed to the driving rain. Assuming the peak emissions of 77 mg in the stormwater monitoring to result from a freshly painted or rendered house, it is obvious that a huge part is actually draining directly to the soil and not to the sewer system. Consequently, the soil in urban areas is exposed to stormwater highly polluted by biocides which might affect the microbial community there.

The use of biocides as additives for building materials has gained importance in recent years. These biocides are, e.g., applied to renders and paints to prevent them from microbial spoilage. However, these biocides can leach out into the environment. In order to better understand this leaching, the partitioning of biocides between water and inorganic phases of render was studied. In this study the partitioning constants of benzoisothiazolinone, carbendazim, dichlorooctylisothiazolinone, diuron, iodocarb, isoproturon, irgarol, mecoprop, methylisothiazolinone, octylisothiazolinone, terbutryn, and tebuconazole towards minerals were studied. A mixture of biocides listed above was used to estimate partitioning constants between water and five different minerals, commonly used as fillers in renders: barite, calcium carbonate, kaolinite, mica and talc. The resulting Kd values for all minerals analysed were compared. The partitioning constants for calcium carbonate varied between 0.1 (isoproturon) and 1.1 (iodocarb) and 84.6 (dichlorooctylisothiazolinone), respectively. The results for barite, kaolinite and mica were in a similar range and usually the compounds with high partitioning constants for one mineral also had high values for the other mineral. From all minerals investigated, only talc showed high partitioning for all studied biocides. Partitioning constants for talc vary from 2.2 (benzoisothiazolinone), 778.1 (carbendazim) and 435.6 (dichlorooctylisothiazolinone), respectively. The obtained partitioning constants were compared with render-water distribution constants, which showed that leaching of biocides, might be estimated based on partitioning constants for individual components of the render.

During the project it could be shown, that the biocide emissions from stormwater and combined sewers lead to considerable concentrations of biocides in urbanized surface waters. These concentrations were highly dependent on the building structures in the catchment as well as on the weather. Regularly rainfall led to elevated concentrations in those waters that are heavily influenced by biocides.An assessment of a best case for stormwater contamination (separated sewers in a rural catchment with mostly brick surfaces) resulted in still high concentrations of biocides in water. High values for carbendazim and terbutryn where often detected. Cybutryn and terbutryn often exceeded the environmental target levels due to their high toxicity.Market survey: A study of the Danish market (as being also typical for the European market), showed that octylisothiazolinone, iodocarb, terbutryn, zinc pyrithion, and diuron are used in current building materials as film preservatives while benzalkoniumchloride is used for outside cleaning. The use as in-can preservatives (compounds to increase shelf life of formulated products) was not assessed in marked surveys. Some of these compounds were assessed in the environmental studies of this project. Especially Methyl-isothiazolinone and Benzyl-isothiazolinone originating from use as in-can preservatives were detected.Presence in stormwater: Some compounds (especially cybutryn, terbutryn and mecoprop) are present in stormwater in levels sometimes exceeding receiving water quality standards set in regulations such as the water framework directive or the surface water directive. Other compounds such as carbendazim, isothiazolinones (used as in-can preservatives), azole fungicides, mecoprop, that are used in connection with building protection were found in the stormwater studies with high concentrations as well. The discharge mostly occurs continuous thus there is no option of treating just the first flush as for other parameters (particulate matter or PAH).Presence in wastewater: It turned out that most of the biocides used in building protection are present in current dry weather wastewater as well as in rain weather combined sewer. It is assumed that a combination of washing tools and disposing residues of materials such as paints is mostly responsible for the findings at dry weather. However in some samples the concentrations (especially of propiconazole) were so high, that rather professional urban gardening (flower and greenhouses) than handling of biocides from construction materials seem to be able to explain the findings. While the use in agriculture is restricted, the use in greenhouses is currently considered legal in Denmark. Leaching/partitioning: Considering material properties, it was found out that, for all of the compounds the sorption (and leaching) is highly pH-dependent. It must be take into account that the pH in the porewater of the tested render materials is between 9 and 10 while the rainwater is around 5, thus making prediction difficult at this stage.For some of the compounds the sorption is dependent on the amount of polymer in the render, while it is only rarely of importance which polymer is used. Considering the interaction of weather with the leaching of biocides from real walls it turned out that a lot of parameters such as irradiation intensity, length of dry period, rain intensity etc. did not have a detectable influence on the leaching. Only the water amount that due to driving rain indeed reached the wall had an effect to the leaching of biocides from building materials. It turned out that for some compounds transformation is relevant on the wall surfaces, and transformation products should be included in future studies. Again a difference between silicone and acrylate based renders in concern of leaching of biocides was not detectable.Modelling biocide emissions: The developed model allows predictions on concentrations of biocides in other catchments. However, it craves essential input parameters such as treated surfaces areas, connection rate to stormwater system etc.