Soil Uptake and Emissions of Atmospheric Pollutants

Since the last century, soils (and sediments) have accumulated agricultural and atmogenic pollutants such as organochlorine pesticides, polycyclic aromatic hydrocarbons (PAHs) and polychlorinatedbiphenyls (PCBs). These compounds have been distributed in the atmosphere at global scale, and long-term fate depends on interaction with the top soils. Whether soils are sinks or sources of such diffuse pollutants depends on the input history, sorption and transformation capacity of the soils as well as on the aqueous leaching and (re-)volatilization rates of the compounds of interest. While soils may be regarded as sources for these legacy pollutants in industrialized regions, they still act as sinks in remote areas and in general they are sinks for emerging compounds such as flame retardants. For many compounds, substantial data exist to parameterize specific processes such as sorption mechanisms/isotherms and sorption/desorption kinetics at the grain scale. However, the interplay of the physical and biogeochemical processes which determines the long-term fate of such compounds is not clear. Several of these compounds (e.g. phenanthrene) are easily degradable under aerobic conditions, so that the reason for their persistence in biologically highly active top-soils exposed to atmospheric oxygen is not clear. Especially the rates of exchange of these compounds between soils and the atmosphere are not well understood, even though it is crucial for long-term fate and atmospheric spreading of diffuse pollutants.