Long-term spatial and temporal patterns of polycyclic aromatic hydrocarbons (PAHs) in Scottish soils over 20 years (1990–2009): A national picture

Abstract

Long-term spatial and temporal concentrations of polycyclic aromatic hydrocarbons (PAHs) in Scottish soils from four transects were measured in three national-scale surveys conducted between 1990 and 2009. Measured concentrations of 16 priority PAHs ranged from 15,690 to 83.7 ng g−1, with an average of 3659 ± 3131 to 727 ± 654 ng g−1, of which the high molecular weight (HMW) PAHs (4–6 rings) accounted for 73.9 to 89.6%. Overall, concentrations of PAHs in the soil have decreased over time, but the proportion of carcinogenic ∑PAH7 has increased. Concentrations of total PAHs correlated significantly with latitude (R = −0.345, p = 0.001). A significant correlation was found between concentrations of PAHs and soil organic carbon (SOC, R = 0.439, p = 0.000), which is an important factor, influencing the levels of PAHs in soils. Source apportionment analysis indicated that the emission sources of PAHs have evolved from coal and biomass combustion to more diverse sources during the two decades covered by the surveys. It is likely that this reflects societal development towards a lower carbon economy and less use of biomass buring for domestic space heating.