Trace element distribution and Cr(VI) speciation in Ca-HCO3 and Mg-HCO3 spring waters from the northern sector of the Pollino massif, southern Italy

Abstract Weathering of outcrops of ultramafic rocks (remnants of ancient oceanic crust) is a source of biologically toxic trace elements, particularly first row transition elements. The Cr and Ni concentrations of serpentinite and metabasite outcrops in the northern sector of the Pollino massif (Lucanian Apennines, southern Italy) are hundreds of orders of magnitude higher than those of the upper continental crust. In this region, exposed intermediate to lower crustal rocks are significantly enriched in Ni, Cr, and V relative to the average upper continental crust. We evaluate the levels and distributions of trace elements of environmental concern, including Cr (as total dissolved Cr and Cr(VI)), V, Mn, Fe, Ni, Cu, Zn, As, Pb, and U, in spring waters from the northern sector of the Pollino massif. The major solutes in the spring waters from this region are Mg-HCO 3 and Ca-HCO 3 . The Mg-HCO 3 type waters are produced mainly through the interaction of meteoric waters with serpentinites, whereas the Ca-HCO 3 type waters are produced through the interaction of meteoric waters with Ca-rich rocks (i.e., carbonate rocks, calc-schists, and metabasites). Thermodynamic evaluation indicates that in the MgO–SiO 2 –Al 2 O 3 –H 2 O system, waters flowing in serpentinites fall in the kaolinite field, close to the kaolinite–Mg-vermiculite phase boundary. This result arises because kaolinite is a relatively early reaction product, which is consumed to produce Mg-vermiculite and further Mg-saponite. In the CaO–SiO 2 –Al 2 O 3 –H 2 O system, Ca-HCO 3 type waters fall either in the field of gibbsite or kaolinite, depending on dissolved silica. Chromium (VI) contamination associated with local mineralogy and with maximum admissible concentration > 5 μg L − 1 was observed for nine springs (both Mg-HCO 3 and Ca-HCO 3 type waters). The Cr(VI)-rich Ca-HCO 3 springs are not located in serpentinites. However, some of these waters likely acquire their high Cr levels from interacting with serpentinite clasts, as in the case of springs flowing through conglomerates. In addition, Cr(VI) contamination is not limited to waters interacting with serpentinites or serpentinite clasts, because in one case weathering of garnet-rich gneiss is responsible for the release of significant amounts of Cr(VI) in solution. Finally, studies are needed to address the potential health risks associated with the observed high concentrations of Cr(VI) in waters from the Pollino massif area. A mode-of-action analysis is needed to evaluate adverse health risks associated with exposure to Cr(VI) in drinking water, especially as Cr contamination is not limited to springs flowing through serpentinites.

[1]  Luigi Marini,et al.  Irreversible water–rock mass transfer accompanying the generation of the neutral, Mg–HCO3 and high-pH, Ca–OH spring waters of the Genova province, Italy , 2002 .

[2]  J. Wiltse,et al.  US Environmental Protection Agency's revised guidelines for Carcinogen Risk Assessment: incorporating mode of action data. , 1998, Mutation research.

[3]  D. Banerjee,et al.  Oxidation of aqueous Cr(III) at birnessite surfaces: constraints on reaction mechanism , 1999 .

[4]  J. R. O'neil,et al.  The Relationship between Fluids in Some Fresh Alpine-Type Ultramafics and Possible Modern Serpentinization, Western United States , 1969 .

[5]  L. Toscani,et al.  Springs and streams of the Taro-Ceno Valleys (Northern Apennine, Italy): Reaction path modeling of waters interacting with serpentinized ultramafic rocks , 2008 .

[6]  Carmelo Monaco,et al.  Tectonic role of ophiolite‐bearing terranes in the development of the Southern Apennines orogenic belt , 1995 .

[7]  M. Komatina.  Medical Geology: Effects of Geological Environments on Human Health , 2004 .

[8]  E. Pera,et al.  Post-Oligocene Sediment-Dispersal Systems and Unroofing History of the Calabrian Microplate, Italy , 1998 .

[9]  R. Salminen,et al.  Arsenic and other toxic elemental contamination of groundwater, surface water and soil in Bangladesh and its possible effects on human health , 2000 .

[10]  Scott Fendorf,et al.  Genesis of hexavalent chromium from natural sources in soil and groundwater , 2007, Proceedings of the National Academy of Sciences.

[11]  Steven D. Knott,et al.  The Liguride Complex of Southern Italy —a Cretaceous to Paleogene accretionary wedge , 1987 .

[12]  Jean E. Delvigne,et al.  Atlas of Micromorphology of Mineral Alteration and Weathering , 1998 .

[13]  S. Fendorf,et al.  Chromium Transformations in Natural Environments: The Role of Biological and Abiological Processes in Chromium(VI) Reduction , 2000 .

[14]  A. Lima,et al.  Hydrogeochemical analysis on Italian bottled mineral waters: Effects of geology , 2010 .

[15]  E. Dinelli,et al.  Elemental mobility during the weathering of exposed lower crust: the kinzigitic paragneisses from the Serre, Calabria, southern Italy , 1998 .

[16]  I. Thornton,et al.  Mercury in Brazil , 1994, Nature.

[17]  Bernhard Welz,et al.  Determination of chromium(III) and chromium(VI) in water using flow injection on-line preconcentration with selective adsorption on activated alumina and flame atomic absorption spectrometric detection , 1992 .

[18]  F. Tateo,et al.  The use of pelitic raw materials in thermal centres : Mineralogy, geochemistry, grain size and leaching tests. Examples from the Lucania area (southern Italy) , 1998 .

[19]  M. Armienta,et al.  Natural chromium contamination of groundwater at León Valley, México , 2000 .

[20]  C. Neal,et al.  Hydrogen generation from mantle source rocks in Oman , 1983 .

[21]  S. Fendorf.  Surface reactions of chromium in soils and waters , 1995 .

[22]  L. Marini,et al.  Natural hexavalent chromium in groundwaters interacting with ophiolitic rocks , 2002 .

[23]  K. Ahmed,et al.  Mechanism of arsenic release to groundwater, Bangladesh and West Bengal , 2000 .

[24]  G. Brown,et al.  Environmental mineralogy – Understanding element behavior in ecosystems , 2011 .

[25]  S. M. B. Oliveira,et al.  Anomalous content of chromium in a Cretaceous sandstone aquifer of the Bauru Basin, state of Sao Paulo, Brazil , 2011 .