Leaching of Biocides from Façades under Natural Weather Conditions

Abstract

Biocides are included in organic building façade coatings as protection against biological attack by algae and fungi but have the potential to enter the environment via leaching into runoff from wind driven rain. The following field study correlates wind driven rain to runoff and measured the release of several commonly used organic biocides (terbutryn, Irgarol 1051, diuron, isoproturon, OIT, DCOIT) in organic façade coatings from four coating systems. During one year of exposure of a west oriented model house façade in the Zurich, Switzerland area, an average of 62.7 L/m(2), or 6.3% of annual precipitation came off the four façade panels installed as runoff. The ISO method for calculating wind driven rain loads is adapted to predict runoff and can be used in the calculation of emissions in the field. Biocide concentrations tend to be higher in the early lifetime of the coatings and then reach fairly consistent levels later, generally ranging on the order of mg/L or hundreds of μg/L. On the basis of the amount remaining in the film after exposure, the occurrence of transformation products, and the calculated amounts in the leachate, degradation plays a significant role in the overall mass balance.

Modelling wind-driven rain on buildings in urbanized area using 3-D GIS and LiDAR datasets

“…Usually, typical average wall catch ratios range between 10% and 25% [27,38e40], which means high discrepancies with values simulated in this project. A recent study by Burkhardt et al [41] conducted on a West oriented facade under natural condition estimated a catch ratio of 6.3% after one year of exposure. But while comparing the different results, attention must be paid to measurements, simulations and boundary conditions.…”

Ten questions concerning modeling of wind-driven rain in the built environment

“…Moreover, the conservation of historic buildings, the design of new buildings and the development of new building materials rely on the correct prediction of moisture loads (Briggen et al 2009). The correct prediction of WDR is also significant in the assessment of environmental risks related to the leaching of harmful biocides and nanoparticles from buildings (Urkhardt et al 2012). WDR deposition in the built environment sees these mentioned effects propagating through different urban surfaces, including, in addition to building facades, roofs, vegetated areas and paved streets, pedestrian ways, etc.…”

Polyacrylate–water partitioning of biocidal compounds: Enhancing the understanding of biocide partitioning between render and water

“…Based on the determined polyacrylate-water partition constants the partitioning of the biocides into the water phase would be in the following order: isoproturon > diuron > carbendazim > N-octylisothiazolinone > iodocarb > cybutryn > terbutryn > propiconazole > tebuconazole > dichloro-N-octylisothiazolinone. During leaching tests from faç-ade render under natural weather conditions Burkhardt et al (2012) analysed seven biocides. Based on that study, the leaching ability could be sorted according to isoproturon > diuron > iodocarb > N-octylisothiazolinone > cybutryn > terbutryn > Table 2 Polyacrylate-water partition constants (log K AcW ) with 95%-confidence interval as well as coefficient of determination (R 2 ) from the non-linear regression model for the studied compounds; N number of data points.…”

“…Hence, the total content of biocides in render and exterior paints ranges from 5 to 10 g kg À1 (Burkhardt et al, 2011). Laboratory studies on constantly soaked material, dipping experiments with alternating wet and dry cycles, or forced rain experiments showed that the biocides leach out of the render material in considerable fractions (Schoknecht et al, 2003;Burkhardt et al, 2007;Schoknecht et al, 2009;Burkhardt et al, 2011Burkhardt et al, , 2012Wangler et al, 2012). The leaching process of biocides from render is assumed to be a multistep process: (1) removal from the surface layer which is itself (2) in equilibrium with the deeper layers of the render, from which (3) the surface layer is constantly refilled.…”