Occurrence and distribution of polycyclic aromatic hydrocarbons (PAHs) in an agricultural ecosystem

The concentration and distribution of PAHs were determined in soil, surface water, sediments, and groundwater of the experimental farm of the research network “Forschungsverbund Agrarokosysteme Munchen” (FAM), part of a rural region in Bavaria, Germany. Analytical procedures include ultrasonication, solid phase extraction, liquid-liquid extraction, HPLC and fluorescence detection. Fifteen common PAHs were usually found in low concentrations in the examined compartments. The distribution of total PAHs in surface soils of 15 sampling sites in the area was not uniform. It could be demonstrated that there were high concentrations in valleys and low concentrations on top of the hills, due to long-term transport of PAHs to the valleys by surface run-off. Subsurface soil was found to contain lower amounts. Tetra- to hexacyclic PAHs showed similar profiles in the subsurface soil and in the top soil, while profiles of bi- and tricyclic PAHs deviated significantly. Additionally, tetra- to hexacyclic PAHs were enriched in distinct zones in the subsurface soil and exhibited similar patterns in groundwater and aquifer material. These results indicate a transport of bi- and tricyclic PAHs mainly in the dissolved or gaseous state and a predominant particle-associated transport of tetra- to hexacyclic PAHs. This particle-bound transport increases the migration velocity of hydrophobic pollutants through the vadose zone and enhances the mobility in groundwater.