Polycyclic aromatic hydrocarbons of anthropogenic and biopedogenic origin in a colluviated hydromorphic soil of Western Europe

Soil samples from a colluviated soil profile in a rural area of Western Europe have been analyzed by HPLC for 15 polycyclic aromatic hydrocarbons (PAHs) in order to determine their total contents and distribution patterns. Stagnant water and reducing conditions prevail in a depth below 70 cm. The sum of the 15 PAHs varied between 11 and 200 μg kg−1. The highest total contents of PAHs were observed in the two uppermost horizons, but also in some deeper layers with relatively high contents of organic matter. The PAH distribution pattern differed considerably in the various layers in relation to their age and sources. The four most abundant compounds in the two uppermost layers were phenanthrene>fluoranthene≥benzo(b)fluoranthene=benzo(a)pyrene in 0–5 cm depth and phenanthrene>fluoranthene≥pyrene≥benzo(b)fluoranthene in 25–30-cm depth. In some deeper layers with reducing conditions, benzo(g,h,i)perylene or dibenzo(a,h)anthracene was the predominant compound. Naphthalene, acenaphthene, fluorene and phenanthrene also exhibited substantial contents at these soil depths. The results from the principal component and cluster analyses indicate that the group of benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene and indeno(1,2.3-c,d)pyrene represents PAHs of mainly anthropogenic origin. Acenaphthene, fluorene, pyrene, dibenzo(a,h)anthracene, naphthalene, and benzo(g,h,i)perylene form a group of predominantly biopedogenic origin due to reducing conditions in the soil layers with stagnant water. The group with fluoranthene, chrysene, and phenanthrene consists of PAHs of both anthropogenic and biopedogenic origin.