Continuous intake of facade eluates affects active and total soil Microbiome

Urban surfaces such as building facades release chemical compounds into the environment through rain-induced runoff. Facade eluates typically consist of a mixture of biocides and heavy metals that can pose an environmental risk. Even though, leaching of these substances and their aquatic ecotoxicity is well determined, data regarding their terrestrial ecotoxicological effects on the soil microbiome are still scarce. In this study, we investigated the temporal effects of repeated facade eluate applications on the composition and function of soil bacterial and fungal communities. Facade runoff was collected under natural weathering conditions from facades without and with biocides and applied to outdoor soil microcosms over a two-month period. High-throughput amplicon sequencing and qPCR analyses revealed that facade eluate exposure significantly altered microbial community composition and reduced bacterial gene copy numbers, while increased fungal richness over time. Active (Bromodeoxyuridine labelled DNA) communities showed stronger and more distinct treatment responses than total communities. Functional profiling indicated increased prevalence of stress-associated traits such as ureolysis in bacteria and shifts in fungal trophic modes, including reduced plant pathogens and increased photoautotrophs, which were supported by indicator species analysis. Our findings highlight that repeated facade runoff applications and prolonged incubation can alter the soil microbial community. These results emphasize the ecological risks posed by facade eluate on the soil microbiome and the consideration of biocides from building materials as environmental risk.