Polycyclic aromatic hydrocarbons (PAHs) in river bank soils

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous and found in the atmosphere, aquatic environment, sediments and soils. For environmental risk assessments and the allocation of the polluter it is important to know the PAH sources. PAH contamination sites are usually the result of anthropogenic processes. Three major sources are known: i) petroleum, including crude oil and its refined products and coals (petrogenic PAHs), ii) burning of organic matter (pyrogenic PAHs) and iii) transformation products of natural organic precursors present in the environment (diagenetic processes). In one case elevated PAH concentrations were found in river bank soils when building a retention area along the Mosel River. The source of the PAHs in this area was unclear and required the investigation of possible sources. To evaluate the PAH distribution along the Mosel River, a section of ~ 160 km along the river and a short section along the Saar River were investigated within this study. Concentrations of the Σ16 EPA PAHs were as high as 81 mg kg-1 dry weight (dw). Additionally, coal particles were identified in some soils, which originated from mining activities in the Saarland region. PAH distribution patterns of the 16 EPA PAHs suggest a mainly pyrogenic origin and in some cases a mixture of pyrogenic and petrogenic origin. For a comprehensive investigation five sampling sites were selected. Two sites were located before the confluence of the Mosel and Saar River, one site at the confluence and two sites after the confluence. The examination included typical forensic methods such as PAH distribution patterns of 45 PAHs (including alkylated PAHs), calculation of PAH ratios, determination of PAH alkyl homologues, n-alkanes, principal component analysis (PCA) and coal petrography. The results revealed a mainly pyrogenic source at sampling sites before the confluence of the two rivers. At and after the confluence, a mixture of pyrogenic and petrogenic inputs were present. With the help of coal petrography, coal derived particles could be identified in these soils. Therefore, coal was suggested to be the petrogenic source. It could be shown that sites with diffuse sources of contaminants, like the bank soils of the Mosel River, are difficult to characterize. As previously mentioned for detailed source identifications, the use of various forensic methods is essential. Determination of PAH alkyl homologue series, biomarkers and isotopes are often recommended. Source identification was evaluated using three different methods (i.e. PAH distribution patterns of an extended PAH spectrum, PAH ratios and analyses of n-alkanes). It was assessed if these methods were sufficient for the initial steps in identifying sources of PAHs in selected samples, and if they could be used for decision-making purposes. Point- and non-point sources were identified by applying the three methods and it could be shown that these relatively simple methods are sufficient in determining the primary source. In a last step of this study two soils (one before the confluence of the Mosel and Saar rivers and one after the confluence), and one sediment of the Mosel River were evaluated by investigating the mutagenic potential of the soils and the sediment with a fluctuation version of the Ames-test. The study showed that coal bearing soils at the Mosel River do not exhibit a greater mutagenic potential than other soils or sediments without coal particles.

Palaeotsunami imprints in the near-coast sedimentary records of the Gulfs of Lakonia and Argolis (Peloponnese, Greece)

From historical accounts it is well-known that the coasts of the Gulfs of Lakonia and Argolis (southern and eastern Peloponnese, Greece) have been repeatedly affected by tsunamis during historical times. It is assumed that these palaeotsunamis left sedimentological and geomorphological traces in the geological record which are still detectable these days. As both gulfs are located within one of the seismically most active regions in whole western Eurasia in particular the nearby Hellenic Trench is regarded as the main trigger for tsunami generation. Against this background, selected near-coast sedimentary archives were studied by means of sedimentological, geomorphological, geophysical, geochemical and microfaunal investigations in order to detect signatures of Holocene palaeotsunamigenic activity. The investigations revealed allochthonous sediment layers featuring distinctive sedimentary characteristics of marine high-energy event deposits in most of the investigated study areas. In order to differentiate between the geomorphodynamic driving mechanisms for the deposition of the associated marine high-energy event layers, a multi-method approach was used. The detected high-energy marine deposits are suggested to be of tsunamigenic origin. Radiocarbon dating results allowed establishing local event geo-chronostratigraphies and correlations on a local and regional scale as well as correlations with already described palaeotsunami findings on a supra-regional scale. The geochronological dataset attests repeated tsunamigenic activity at least since the 5th millennium BC up to the 17th century AD. For the studied areas in southeastern Lakonia up to four palaeotsunami event generations were identified, for central Lakonia three and for the investigated areas around the Argolis Gulf also up to four. Comparing the findings with literature data, chronological correlations were found with palaeotsunami deposits detected in near-coast geological archives of Akarnania, of the southwestern, the western and northwestern Peloponnese, with event deposits found on Crete and on the Ionian Islands of Cefalonia and Lefkada as well as with findings from southeastern Sicily (Italy) and Cesarea (Israel). By the identification of multiple palaeotsunami event layers, disturbing autochthonous near-coast sedimentary records of the Gulfs of Lakonia and Argolis during the last seven millennia, a significant tsunami frequency is attested for these regions.