PAH-concentrations and compositions in the top 2cm of forest soils along a 120km long transect through agricultural areas, forests and the city of Oslo, Norway

The top 2cm of forest soils were collected along a 120km long south-north transect running through Norway's largest city Oslo. Forty samples were analysed for their polycyclic aromatic hydrocarbon (PAH sub(1) sub(6) as defined by the U.S. Environmental Protection Agency) concentrations and compositions. Local variations in the PAH values are high and the reported concentrations are in general low (maximum sumPAH sub(1) sub(6): 2.6mg/kg). The transect shows distinct differences of sumPAH sub(1) sub(6) values from south to north. PAH concentrations are substantially lower in the less populated areas at the north end of the transect than at the urbanised and much more populated south end. Several high values occur in a forested area to the north of Oslo, used for recreation purposes. The PAH distribution patterns point towards a predominantly pyrogenic origin. Local Cambrian carbon-rich black shales can be excluded as sources for PAHs in the forest soils.