Legacy and current-use pesticides in indoor settled dust and association with building age and seasonality

Indoor pesticide exposure is increasingly recognized as a significant contributor to pollutant exposure in residential spaces. This study investigates concentrations of legacy organochlorine pesticides (OCPs) and current-use pesticides (CUPs) in settled dust from 116 homes in the Czech Republic, in the context of their seasonal variability, relationships with building characteristics, geospatial factors, and indoor dust bacteriome diversity and composition. CUPs were detected in dust in 93% of homes, with carbendazim (84.5%), propiconazole (49.1%), atrazine (24.1%), and tebuconazole (11.2%) detected most frequently. OCPs were found in all homes. Propiconazole concentrations were significantly higher in homes with adjacent gardens, potentially reflecting its use as a biocide in outdoor building materials. CUP concentrations had clear seasonal trends, with peak levels in spring and summer, corresponding to pesticide application periods, particularly in rural environments. OCP concentrations were substantially higher in houses over 40 years old, indicating the persistence of residues from past indoor uses. While pesticide presence was ubiquitous, exposure estimates for children, under both average and high-exposure scenarios, were well below U.S. EPA reference doses (RfDs) for individual compounds; however, most homes had 3-11 pesticides in dust, raising the possibility of mixture effects. No significant associations, using a Spearman rank correlation matrix, were observed between pesticide concentrations and indoor dust bacteriome diversity and composition. These findings highlight the presence of pesticides in homes, including those in urban areas, driven by both current and historical sources, and reinforce the importance of monitoring to better understand potential exposure pathways. • Current-use pesticides in dust in 93% of homes; most frequently carbendazim and propiconazole • DDT compounds detected in dust from all homes; higher in homes >40 years old • Homes closer to agricultural areas had higher current-use pesticide levels in dust in spring • No relationship between pesticide levels and composition of indoor dust bacteriome