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This thematic issue of Geofluids includes 11 papers representing the three main topics discussed in the 10th edition of the International Conference on Gas Geochemistry (ICGG-10): (i) gas in petroleum systems and seepage, (ii) gas in geothermal systems and volcanoes and (iii) gas, seismicity and geohazards. ICGG-10 was held in 2009 in Romania, a country extraordinarily rich in surface gas manifestations, that offers innumerable opportunities for innovative studies on gas geochemistry. We briefly describe the present knowledge on gases occurring both in petroliferous sedimentary basins and geothermal areas of Romania. The 11 contributions of this special issue, which include data from eight countries, are then summarised. Based on these papers and other works presented at the ICGG-10, we find that significant advances in analytical capabilities, data treating and interpretation have led to innovative insights into the origin, distribution and environmental impact of gases migrating to the Earth's surface. It is increasingly clear, in particular, that gas geochemistry can be more effective for petroleum exploration, volcano-tectonic, geodynamic and environmental studies, if multiparametric studies are performed and the data are interpreted in the geological context. [ABSTRACT FROM AUTHOR]

Gas seepage from petroleum basins is the second largest natural source of methane to the atmosphere, after wetlands. The uncertainty in global emission estimates should be reduced by extending the flux database which is fundamental for defining the emission factors and the actual area of seepage adopted for up-scaling. As a contribution to this goal, we report a new seepage data-set for the Transylvanian Basin, one of the largest natural gas producing regions of Europe, that is characterized by the widespread occurrence of natural leakages of gas at the surface, including at least 73 mud volcanoes and gas seeps. In this study, methane flux was measured using closed-chambers, from 12 seepage sites, in correspondence with focused gas vents (mud volcano craters, bubbling pools, and flammable gas leaks), in the soil surrounding the vents, and at 15 sites located far from macro-seep zones but close to gas fields. Fluxes from individual vents (macro-seeps) were found to reach orders of kg CH m day (up to 12 kg m day) and diffuse fluxes from soils (miniseepage) were found to be up to a few g CH m day. Far from seep zones, positive CH fluxes (microseepage) may occur locally, typically on the order of tens to hundreds of mg m day. The values, as well as the occurrence of seepage even far from vent zones and in mud volcanoes that are apparently extinct, are coherent with results obtained in other countries. Gas fluxes from macro-seeps and soils may change seasonally, but the interannual variation of the average emission factor was found to be minimal. The total CH output for Transylvania macro-seeps is estimated conservatively to be around 680 t year; the total geo-CH seepage emission from the Transylvania petroleum system could be approximately 40 × 10 t year, and at least 100 × 10 t year for all Romanian petroleum systems, that is roughly 10% of the total anthropogenic CH emission in the country. [ABSTRACT FROM AUTHOR]

In the present study, two of the major naturally occurring radionuclides (Ra and Rn) were analyzed in water samples from shallow, medium-depth, and deep geothermal aquifers, all of which are located in Bihor County, northwestern Romania. Here, the results of radon and radium measurements, performed from 2008 to 2009 in 50 locations, are reported. Radon proved to have a wide range of activity, with values from 4.5 to 110.8 Bq l for shallow aquifers, from 9.3 to 106.0 Bq l for medium-depth aquifers, and from 10.1 to 34.8 Bq l for deep geothermal aquifers. The shallow aquifers have lower radium concentrations (0.06 to 0.48 Bq l), compared to medium-depth aquifers (0.1 to 0.52 Bq l) and deep geothermal aquifers (0.27 to 1.8 Bq l). The principal aim was a thorough investigation into the possible correlations between the occurrence of radon and radium in different aquifers and the hydrogeological, hydrogeochemical, and geothermal features of the area. Besides the direct link between the occurrence of uranium and thorium and the Ra and Rn contents in groundwater, the measurements we performed have allowed us to identify a secondary control on radionuclide distributions caused by the adsorption of dissolved radium onto clay minerals in exchange for sodium (for the sandy clay aquifer of Săcuieni), the high competition for adsorption sites in aquifers with high concentrations of dissolved calcium and magnesium (for the limestone dolomite aquifer of Oradea), and the role of thermal processes. [ABSTRACT FROM AUTHOR]

The paper describes a case of a natural emission of methane from soil in an urban development area, generating a significant risk for the local population and buildings, due to gas explosiveness and asphyxiation potential. The site is located on the south-western margin of the East-European Platform in eastern Romania, in a hydrocarbon-prone area crossed by the Pericarpathian lineament and regional faults. Molecular composition of gas and stable isotopic analyses of methane (CH4>90%, δ13C1: −49.4‰, δD1: −173.4‰) indicate a dominant thermogenic origin, with significant amounts of C2-C5 alkanes (∼5%), likely migrating through faults from a deep reservoir. Possible candidates are the Saucesti and Secuieni gas fields, located in the same petroleum system. Two surface geochemical surveys, based on closed-chamber flux measurements, were performed to assess the degassing intensity and the extent of the affected area. Methane fluxes from soil reach orders of 104 mg m−2 day−1. Gas seepage mainly occurs in one zone 30 000 m2 wide, and it is likely controlled by channeling along a fault and gas accumulation in permeable sediments and shallow subsoil. The estimated total CH4 emission is about 40 t year−1 CH4, of which 8–9 t year−1 are naturally released from soil and 30–35 t year−1 are emitted from shallow boreholes. These wells have likely channeled the gas accumulated in shallow alluvial sediment but gas flux from soil is still high and mitigation measures are needed to reduce the risk for humans and buildings. [ABSTRACT FROM AUTHOR]

Excessive arsenic content in drinking water poses health risks to millions of people worldwide. Inorganic arsenic (iAs) in groundwater exceeding the 10μg/l maximum contaminant level (MCL) set by the World Health Organization (WHO) is characteristic for intermediate-depth aquifers over large areas of the Pannonian Basin in Central Europe. In western Romania, near the border with Hungary, Arad, Bihor, and Timis counties use drinking water coming partially or entirely from iAs contaminated aquifers. In nearby Arad and Bihor counties, more than 45,000 people are exposed to iAs over 10μg/l via public drinking water sources. However, comparable data are unavailable for Timis County. To begin to address this data gap, we determined iAs in 124 public and private Timis County drinking water sources, including wells and taps, used by pregnant women participating in a case-control study of spontaneous loss. Levels in water sources were low overall (median=3.0; range=<0.5-175μg/l), although higher in wells (median=3.1, range=<0.5-1.75) than in community taps (median=2.7, range=<0.5-36.4). In a subsample of 20 control women we measured urine biomarkers of iAs exposure, including iAs (arsenite and arsenate), dimethylarsinic acid (DMA), and methylarsonic acid (MMA). Median values were higher among 10 women using iAs contaminated drinking water sources compared to 10 women using uncontaminated sources for urine total iAs (6.6 vs. 5.0μg/l, P=0.24) and DMA (5.5 vs. 4.2μg/l, P=0.31). The results suggested that the origin of urine total iAs (r=0.35, P=0.13) and DMA (r=0.31, P=0.18) must have been not only iAs in drinking-water but also some other source. Exposure of pregnant women to arsenic via drinking water in Timis County appears to be lower than for surrounding counties; however, it deserves a more definitive investigation as to its origin and the regional distribution of its risk potential., (Copyright © 2015 Elsevier GmbH. All rights reserved.)