POLYCYCLIC AROMATIC-HYDROCARBONS (PAHS) IN SOILS OF THE MUNSTER (WESTFALIA) IRRIGATION FIELDS

From 1901 to 1975 municipal sewage waters with a daily amount of finally about 40.000 m3 were seeped in the irrigation fields of the city of Munster (Westfalia). Soil samples of former seeped sites and non-seeped neighbour sites have been examined with regard to 6 polycyclic aromatic hydrocarbons (PAHs) of the German ''drinking water regulation''. The irrigation caused an enrichment of PAH in the topsoils of the former irrigation basins up to an average concentration of 0,57 mg PAH/kg soil, while the topsoils outside of the irrigation fields show an average concentration of only 0.14 mg PAH/kg soil. Significant correlations between different soil properties, e.g. the organic matter content, and the concentration of PAHs are not evident. After termination die irrigation of sewage water, single irrigation bassins were filled with substratum, which is contaminated with scoriaceous materials. The average PAH concentration of such an area amounts to 7 mg PAH/kg topsoil. The PAH distribution in a soil profile shows a decreasing concentration by depth but a clear enrichment in oxidized gleyic horizons (Go) of different age. Probably the PAHs were leached under recent conditions by chemical bond to dissolved organic carbon (DOC) and finally adsorbed by Fe oxides. Since the end of irrigation Fluoranthene, the most mobile PAH compound, was leached down to 110 cm depth. A contamination of the superficial groundwater at such sites cannot be excluded.