Elina Aidona

Study of road dust magnetic phases as the main carrier of potentially harmful trace elements

Mineralogical and morphological characteristics and heavy metal content of different fractions (bulk, non-magnetic fraction-NMF and magnetic fraction-MF) of road dusts from the city of Thessaloniki (Northern Greece) were investigated. Main emphasis was given on the magnetic phases extracted from these dusts. High magnetic susceptibility values were presented, whereas the MFs content of road dust samples ranged in 2.2-14.7 wt.%. Thermomagnetic analyses indicated that the dominating magnetic carrier in all road dust samples was magnetite, while the presence of hematite and iron sulphides in the investigated samples cannot be excluded. SEM/EDX analyses identified two groups of ferrimagnetic particles: spherules with various surface morphologies and textures and angular/aggregate particles with elevated heavy metal contents, especially Cr. The road dusts (bulk samples) were dominated by calcium, while the mean concentrations of trace elements decreased in the order Zn > Mn > Cu > Pb > Cr > Ni > V > Sn > As > Sb > Co > Mo > W > Cd. MFs exhibited significantly higher concentrations of trace elements compared to NMFs indicating that these potentially harmful elements (PHEs) are preferentially enriched in the MFs and highly associated with the ferrimagnetic particles. Hazard Index (HI) obtained for both adults and children through exposure to bulk dust samples were lower or close to the safe level (=1). On the contrary, the HIs for the magnetic phases indicated that both children and adults are experiencing potential health risk since HI for Cr was significantly higher than safe level. Cancer risk due to road dust exposure is low.

First archaeomagnetic results and dating of Neolithic structures in northern Greece

Archaeomagnetism in Greece has continuously developed during the last decades. Numerous studies have provided high quality data and accurate secular variation curves for the direction and intensity of the geomagnetic field have been constructed. The Greek Secular Variation Curves (SVCs) cover the last 8 millennia for intensity and 6 millennia for direction. The coverage of the archaeological periods remains uneven, with several gaps, mostly in the directional dataset, with only two results for periods older than 2500 B.C. In the present contribution, the first archaeomagnetic results from Neolithic settlements in northern Greece are presented.For the present study, samples were collected from three different archaeological sites: burnt structures in Avgi (Kastoria) and Vasili (Farsala) and one oven from Sosandra (Aridaia). The natural remanent magnetization (NRM) grouping of all specimens indicated that the majority of the samples were burnt in situ, providing thus a reliable direction of the ancient field. Magnetic cleaning (both alternating-field and thermal) revealed the presence of one stable component of magnetisation. Rock magnetic experiments (acquisition of isothermal remanent magnetization (IRM), thermal demagnetisation of the IRM, thermomagnetic curves) have been performed on pilot samples indicating that low coercivity magnetic minerals such as magnetite or Timagnetite are prevailing. The mean directions (declination D, inclination I and parameters of the Fisherian statistics), which arose from the three sites are as follows: Sosandra: D = 343°, I = 55.6°, α95 = 4.8°; Avgi: D = 10.1°, I = 53.4°, α95 = 4.2° and Vasili: D = 357.5°, I = 43.1°, α95 = 4.1°. The obtained data are in a very good agreement with results from Neolithic Bulgaria. This study represents the beginning of an effort to fill the gaps of the Greek secular variation curves and their extension to the Neolithic period.

Palaeomagnetic and rock magnetic properties of sediment cores from Chalkidiki, Greece

Abstract A detailed palaeomagnetic investigation was performed on Eocene and Oligocene core samples from 4 deep boreholes (1–3.1 km) from the Chalkidiki peninsula. Both low field magnetic susceptibility and intensity of the natural remanent magnetization (NRM) indicate rather weakly magnetised materials. 134 samples have been subjected to either stepwise thermal or alternating field demagnetization. Both procedures indicate that the NRM is carried by magnetite. Isothermal remanent magnetization (IRM) acquisition curves suggest the dominance of magnetite. Finally, 12 thin sections were studied in order to more precisely characterise the magnetic mineralogy of the samples. This investigation reveals the presence of magnetite and pyrite. In general, the observed inclinations of characteristic remanence in these rocks are much lower than expected inclinations but converge with those obtained from formations on land.

Magnetic Susceptibility and Radioactivity Changes of Aegean and Ionian Sea Sediments during Last Glacial/Interglacial: Climatic and Chronological Markers

Abstract AIDONA, E. and LIRITZIS, I., 2012. Magnetic susceptibility and radioactivity changes of Aegean and Ionian Sea sediments during last glacial/interglacial: Climatic and chronological markers. Five marine sediment boreholes from the Aegean and Ionian Sea have been measured here for their magnetic susceptibility and (in an earlier work) by alpha- and beta-particle radioactivity. The corresponding borehole cores cover the Holocene period and closely spaced data have been sampled from all cores. The obtained depth data series have been converted here to the time series by using appropriate conversions on the basis of sedimentation rates derived from dating of selected samples of each core. The spectral characteristics of the new statistical elaboration for the final time series exhibit a significant correlation of the magnetic susceptibility and radioactivity data. This correlation is prominent especially for intermediate periods (typically 1–10 ky) of the examined spectra and tends to disappear for higher frequency variations (<1 ky), suggesting that mainly long-period climatic and other changes are the ones that affect the examined quantities in a similar manner. This pattern is verified by the band-pass filtered time series for intermediate periods, which reveals well-correlated susceptibility and radioactivity changes. In addition, specific time markers are observed in the filtered time series, and comparison of their variation to certain climatic phases within the Holocene is recognized.

Seasonal and spatial variations of magnetic susceptibility and potentially toxic elements (PTEs) in road dusts of Thessaloniki city, Greece: A one-year monitoring period

A one-year sampling campaign of road dusts was carried out at 10 distinct sites in the broader area of the city of Thessaloniki, Greece and concentrations of heavy metals (HMs) along with magnetic susceptibility were evaluated. The concentrations of HMs in road dusts were higher than their local background values, while magnetic parameters indicated a significant anthropogenic load. Principal component analysis (PCA) identified non-exhaust vehicular emissions, oil/fuel combustion and industrial activities as major sources of heavy metals accounted for approximately 73% of the total variance. A significant seasonal variability for Cr, Cu, Mn, and χlf was observed with constantly higher values during summer. Moreover, variations among urban and industrial sites were more pronounced for Cr, Cu, Zn, and χlf, while they displayed insignificant variations across all urban sites. On the contrary, concentration peaks in the urban cluster were observed for Cd, Mn, and Ni coinciding with the port area. Based on multiple pollution indices, a severe polluted area was revealed, while potential ecological risk index (RI) indicated a high potential ecological risk with Cd being regarded as the pollutant of high concern. The health risk assessment model indicated ingestion as the major exposure pathway. For both adults and children, Cr and Pb had the highest risk values, mainly recorded in the urban cluster underscoring the need of potential measures to reduce road dust in urban environments.

Archaeomagnetic versus luminescence methods: the case of an Early Byzantine ceramic workshop in Thessaloniki, Greece

In this contribution, we present a combined archaeomagnetic and luminescence study of archaeologically dated structures. The investigated area is a ceramic workshop comprising several Early Byzantine kilns. Based on (a) the archaeological–anthropogenic stratigraphy of the site, (b) the structural characteristics of the kilns and (c) the few ceramic findings revealed within their context, the operation of this brick and tile factory is approximately dated between the middle of the fifth century until the first decades of the sixth century AD. Three of the well-preserved workshop kilns have been studied archaeomagnetically. The full vector of the geomagnetic field, accompanied by rock magnetic analyses of the studied material, has been defined. The archaeomagnetic study revealed similar directions among the three kilns indicating and confirming their contemporary use. Additionally, several luminescence measurements were obtained on material from the same kilns. The dating of the site was performed with both methods. The archaeomagnetic dating is convergent with the archaeological estimation only when its upper limit is considered. Concerning the luminescence dating, the calculated ages (corrected for anomalous fading and for the 40K content) with their standard deviations are convergent with the archaeological estimations for the first kiln, while for the other two, the results seem to be incompatible. The possible factors that provoked this divergence are thoroughly discussed.