Air-soil exchange of SOCs in the UK.

Cousins, Ian T. and Jones, Kevin C. (1998) Air-soil exchange of SOCs in the UK. Environmental Pollution, 102 (1). pp. 105-118. ISSN 0269-7491

Abstract

This paper describes (1) a field experiment in which the air–soil exchanges of a range of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were measured and (2) the use of the fugacity quotient concept to provide information on the equilibrium partitioning of PCBs, PAHs and polychlorinated dibenzo-p-dioxins (PCDDs) between the air and soil in the UK. In the field experiment aluminium foil trays containing thin layers (5 mm) of spiked and unspiked soil were placed under custom-built shelters at a meteorological station and exposed to outdoor air for periods of up to 9 months (281 days). Soil and air samples were taken periodically throughout the 9-month period and analysed for PCBs and PAHs. The results from the experiment showed that the PCBs and PAHs in the soils were moving towards equilibrium partitioning conditions. Statisitically significant losses of the majority of PCB/PAH compounds occurred in the spiked soils. Volatilisation was hypothesised to be the dominant loss mechanism. The PCBs in the unspiked soils were close to equilibrium with the air at the start of the experiment and there was, therefore, little change in their concentrations during the 9 months of exposure. For the PAHs there was also only a small change in the concentrations in the unspiked soils during the experiment, although there was a statistically significant loss of acenaphthene, fluorene and phenanthrene. Soil/air fugacity quotients were calculated using the air and soil concentrations measured in the field experiment and also using our database of UK air and soil survey data. The calculated soil/air fugacity quotients, together with the findings of the field experiment, indicate that the soil and air are close to equilibrium for PCBs. However, this study provides evidence that the soil may now be a source of some lighter weight PAHs to the atmosphere, whereas it appears to be still acting as a long-term sink for the heavier weight PAHs and the PCDDs.