Encapsulated biocides in facade materials impact leaching and UV stability, resulting in lower aquatic toxicity of the eluates

In the construction or reconstruction of building facades, user-friendly, dispersion-based renders and paints, which contain organic polymers, are increasingly being used. These materials are susceptible to microbial colonization, potentially causing both esthetic and structural damages. To prevent this, biocides are often added, which in turn can have harmful environmental effects after leaching induced by wind-driven rain. To reduce leaching rates, biocides are widely utilized in encapsulated form. In this study, we investigated, using test facades and standardized leaching with and without sunlight irradiation, whether and to what extent sunlight-caused UV exposure additionally impacts the leaching of encapsulated biocides compared to unencapsulated biocides, and how this affects the chemical composition as well as the toxicity of the resulting eluates. Our results show that encapsulation significantly improves the UV stability of the biocides 2-Octyl-1,2-thiazol-3-one (OIT) and 4,5-Dichloro-2-octyl-1,2-thiazol-3-one (DCOIT), thereby extending their effectiveness in facade materials, while Terbutryn is only slightly affected. Furthermore, encapsulation leads to a reduction in the concentrations of the leached biocides, both without and especially with irradiation, along with a corresponding decrease in the toxicity of the eluates towards aquatic model organisms, luminescent bacteria, and green algae. These findings emphasize the relevance of encapsulation as an effective strategy for improving the sustainability and safety of biocides in facade materials, as well as the need to consider the influence of UV irradiation in toxicological evaluations of renders and paints.