Natural Cr(VI) contamination of groundwater in the Cecina coastal area and its inner sectors (Tuscany,Italy)

A detailed hydrogeochemical study of groundwater in the Cecina coastal plain (Livorno province, Italy) and its inner sectors was undertaken in 2008, as chemical analyses carried out on groundwater since 2006 have revealed Cr(VI) concentrations of up to 49 μg/L (well above the permissible limit of 5 μg/L). Ophiolite outcrops are present throughout the study area, and their fragments likely represent a significant portion of the existing multilayered aquifer skeleton. Waters delivered by the serpentinite outcrops have a typically Mg–HCO₃ composition, whereas those of the coastal plain are prevailingly of the Ca/Mg–HCO₃ type with significant Mg contents. Significant NO₃ contamination characterises the studied coastal plain, and an interesting negative correlation exists between Cr(VI) and both NO₃ and SO₄ deriving from the widespread use of (NH₄)₂SO₄ as a farm fertilizer. Chromium speciation calculations carried out using the EQ3NR code reveal that the prevailing Cr(VI) species in solution is CrO₄ ^2?; however, CaCrO₄° and MgCrO₄° neutral complexes represent significant percentages (up to 42 %). These findings suggest that the mobility and consequently the bioavailability of Cr(VI) can be significantly enhanced by these neutral complexes, which are not considered to be affected by adsorption/desorption processes. The Cr(VI) source, investigated by means of the Mg/SiO₂ molar ratio, seems to be represented mainly by Mg-bearing minerals of the chlorite group. Petrographic observations confirm the occurrence of this mineral group. The interaction between rainwater and the local serpentinite rock was simulated at different $P_{{{\text{CO}}_{ 2} }}$ and $P_{{{\text{O}}_{ 2} }}$ conditions by reaction path modelling using the EQ3/6 software package. $P_{{{\text{O}}_{ 2} }}$ was varied in accordance with the assumption that redox conditions are determined in part by NO₃. Results are in good agreement with experimental data on spring waters and subordinately with data on some coastal plain groundwater, which plot in a rather wide $P_{{{\text{CO}}_{ 2} }}$ and $P_{{{\text{O}}_{ 2} }}$ field. Although the dissolved Cr content is mostly of natural origin, fertilization may affect its fate.     

“The ESA XMM-Newton Science Operations Centre: Making Basic Space Science Available to the Whole Scientific World”

XMM-Newton is a major X-ray observatory of the European Space Agency (ESA). Its observing time is open to astronomers from the whole scientific community on a peer reviewed competitive basis. The Science Operations Centre, located at ESA’s premises in Villafranca del Castillo, Spain, is responsible for the instrument operations, as well as for all the tasks related to facilitating the scientific exploitation of the data which the mission has been producing since its launch in December 1999. Among them, one may list:

The formerly X-ray reflection-dominated Seyfert 2 galaxy NGC 6300

In this paper, a BeppoSAX observation of the bright Seyfert 2 galaxy NGC 6300 is presented. The rapidly variable emission from the active nucleus is seen through a Compton-thin     absorber. A Compton-reflection component with an unusually high reflection fraction     , and the comparison with a reflection-dominated spectrum measured by RXTE two and half years earlier suggest that NGC 6300 belongs to the class of 'transient' active galactic nucleus, undergoing long and repeated periods of low activity. The spectral transition provides support to the idea that Compton-thick and Compton-thin X-ray absorbers in Seyfert 2 galaxies are decoupled, the former being most likely associated with the 'torus', whereas the latter is probably located at much larger distances.     

Three-dimensional slope stability analysis of South Peak, Crowsnest Pass, Alberta, Canada

South Peak is a 7-Mm³ potentially unstable rock mass located adjacent to the 1903 Frank Slide on Turtle Mountain, Alberta. This paper presents three-dimensional numerical rock slope stability models and compares them with a previous conceptual slope instability model based on discontinuity surfaces identified using an airborne LiDAR digital elevation model (DEM). Rock mass conditions at South Peak are described using the Geological Strength Index and point load tests, whilst the mean discontinuity set orientations and characteristics are based on approximately 500 field measurements. A kinematic analysis was first conducted to evaluate probable simple discontinuity-controlled failure modes. The potential for wedge failure was further assessed by considering the orientation of wedge intersections over the airborne LiDAR DEM and through a limit equilibrium combination analysis. Block theory was used to evaluate the finiteness and removability of blocks in the rock mass. Finally, the complex interaction between discontinuity sets and the topography within South Peak was investigated through three-dimensional distinct element models using the code 3DEC. The influence of individual discontinuity sets, scale effects, friction angle and the persistence along the discontinuity surfaces on the slope stability conditions were all investigated using this code.     

The influence of a new artificial structure on fish assemblages of adjacent hard substrata

Deployed for diverse purposes, artificial substrata can, theoretically, act as fish attractors or as fish producers. We tested these hypotheses by comparing fish assemblages on two artificial hard substrata, the Ca’ Roman and Sottomarina jetties, before (1994 and 2003) and after (2005 and 2006) the deployment of a new breakwater in the area. Our results support the fish production hypothesis. A remarkable increase in richness and abundance of sedentary species was observed on the extant substrata with the presence of the new barrier. More mobile species showed less definite trends. The net result has been a total increase in abundance and richness in the area. While fish assemblage showed important temporal variation in composition before deployment (Ca’ Roman, comparison between 1994 and 2003), clear trends of increasing abundance were concurrent with the presence of the new barrier. This increase in abundance, particularly of sedentary species, may be attributed to enhanced connectivity and/or an improvement in larval retention due to the changes in water circulation connected with the new breakwater, or to an increase in juveniles and/or adults promoted by changes in environmental conditions. Indeed, changes in benthic cover were recorded, with an increase of uncovered rock and the appearance of previously unrecorded algae after breakwater deployment.     

Spatial fluctuations in the spectral shape of the ultraviolet background at 2 < z < 3 and the reionization of helium

The low-density hydrogen and helium in the intergalactic medium (IGM) probed by quasi-stellar object (QSO) absorption lines is sensitive to the amplitude and spectral shape of the metagalactic ultraviolet (UV) background. We use realistic H  i and He  ii Lyα forest spectra, constructed from state-of-the-art hydrodynamical simulations of a Λ cold dark matter (ΛCDM) universe to confirm the reliability of using line profile fitting techniques to infer the ratio of the metagalactic H  i and He  ii ionization rates. We further show that the large spatial variations and the anticorrelation with H  i absorber density observed in the ratio of the measured He  ii to H  i column densities can be explained in a model where the H  i ionization rate is dominated by the combined UV emission from young star-forming galaxies and QSOs and the He  ii ionization rate is dominated by emission from QSOs only. In such a model the large fluctuations in the column density ratio are due to the small number of QSOs expected to contribute at any given point to the He  ii ionization rate. A significant contribution to UV emission at the He  ii photoelectric edge from hot gas in galaxies and galaxy groups would decrease the expected fluctuations in the column density ratio. Consequently, this model appears difficult to reconcile with the large increase in He  ii opacity fluctuations towards higher redshift. Our results further strengthen previous suggestions that observed He  ii Lyα forest spectra at z ∼ 2–3.5 probe the tail end of the reionization of He  ii by QSOs.     

On the Relationship Between the Jets from X-Ray Binaries and Agn

The scale invariance model (Heinz, S. and Sunyaev, R.A.: 2003, MNRAS 343, L59) can be used to derive robust scaling relations between the radio luminosity from accreting black holes and the black hole mass and accretion rate. These relations agree well with the recently found “fundamental plane” of black hole activity (Merloni, A., Heinz, S. and Di Matteo, T.: 2003, MNRAS 345, 1057). This relation provides a new, powerful tool for the comparison of jets from black holes of different masses and accretion rates. The regression coefficients of this relation contain information about the nature of the X-ray emission mechanism driving the correlation. We argue that X-ray synchrotron emission from the base of the jets is unlikely to be the dominant contribution to the X-ray spectrum in most of the sources.