Long-Term Persistence of Encapsulated Facade Biocides and Their Transformation Products Is Associated with Shifts in Microbial Community Composition after Seven Years of Outdoor Weathering

Abstract

Encapsulated biocides are widely used in polymer-based facade coatings to decrease microbial colonization, yet their long-term persistence and ecological effects remain poorly understood. This study investigated the fate of encapsulated terbutryn (TER), 2-octyl-1,2-thiazol-3-one (OIT), and 4,5-dichloro-2-octyl-1,2-thiazol-3-one (DCOIT) and their influence on microbial communities during a seven-year outdoor field trial using realistic facade systems. High-resolution LC-MS/MS revealed substantial residual biocide concentrations after weathering, with recovery rates of 31–51% for TER, 23–28% for DCOIT, and 8–19% for OIT. Several transformation products, including TER–OH, TER-DesE, TER–OH-DesE, TER-SO, TBM, and n-octylamine, were detected, demonstrating ongoing degradation processes within the facade matrix. Amplicon sequencing showed diverse bacterial and fungal communities despite persistent biocide residues. Community composition was significantly associated with biocide and transformation product profiles, and several dominant taxa exhibited compound-specific correlations. These findings demonstrate that residual biocides and their transformation products are significantly associated with long-term microbial selection on building facades.