What determines PCB concentrations in soils in rural and urban areas? Insights from a multi-media fate model for Switzerland as a case study

Abstract

Polychlorinated biphenyls (PCBs) are banned worldwide under the Stockholm Convention on Persistent Organic Pollutants. However, PCBs are still emitted in appreciable amounts from remaining primary sources in urban areas or landfills and are ubiquitous environmental contaminants, inter alia in soil and air. Concentrations of PCBs have been measured in various media by numerous studies worldwide. However, monitoring data do not always provide quantitative information about transport processes between different media, deposition fluxes to ground, or distribution of PCBs between environmental compartments. Also future trends in environmental contamination by PCBs cannot be predicted from monitoring data, but such information is highly relevant for decision-makers. Here, we present a new regionally resolved dynamic multimedia mass balance model for Switzerland to investigate the origin of PCBs in air and to investigate their long-term fate and mass balance in the environment. The model was validated with existing field data for PCBs. We find that advective inflow of PCBs from outside Switzerland into the atmospheric boundary layer is responsible for 80% of PCBs present in air in Switzerland, whereas Swiss emissions cause the remaining 20%. Furthermore, we show that the atmospheric deposition of the higher-chlorinated PCBs is dominated by particle-bound deposition, whereas the deposition of the lower-chlorinated PCBs is a combination of particle-bound and gaseous deposition. The volume fraction of particles in air is in both cases an important factor driving the deposition of PCBs to ground and, thus, contributing to the higher concentrations of PCBs generally observed in populated and polluted areas. Regional emissions influence the deposition fluxes only to a limited extent. We also find that secondary emissions from environmental reservoirs do not exceed primary emissions for all PCB congeners until at least 2036. Finally, we use our model to evaluate the effect of chemical regulation on future environmental contamination by PCBs.