Soil-Air Exchange Controls on Background Atmospheric Concentrations of Polychlorinated Biphenyls (PCBs), Organochlorine Pesticides (OCPs), and Polycyclic Aromatic Hydrocarbons (PAHs): A Case Study from Temperate Regions

The environmental fate of persistent organic pollutants (POPs) depends on their behavior and transport at local and global scale, and soil-air exchanges processes are believed to play a major role controlling POPs reservoirs and global distribution. Measurements of POPs fugacity gradients suggest that soils from lower latitudes and temperate regions, as those studied in the Ebro river watershed (Spain), are starting to be important secondary sources of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) to the atmosphere and that atmospheric background concentrations of PCBs, OCPs and polycyclic aromatic hydrocarbons (PAHs) are now controlled by temperature dependent re-emissions from soils. In contrast, regions where the soil-air partition coefficient (KSA) values are elevated due to higher soil organic matter content (SOM) or lower temperatures, as is the case of UK sampling sites, soils will act as important traps and accumulate more PCBs and OCPs. These regions will need more time to reach equilibrium and become significant secondary sources. The close coupling of POPs fugacities in soil and air suggest a strong control of the atmospheric occurrence of POPs in the lower atmosphere in rural regions.