Weathering of outcrops of ultramafic rocks (remnants of ancient oceanic crust) is a source of biologically toxic trace elements, particularly first rowtransition elements. The Cr and Ni concentrations of serpentinite and metabasite outcrops in the northern sector of the Pollinomassif (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. Themajor solutes in the spring waters fromthis region areMg-HCO3 and Ca-HCO3. TheMg-HCO3 typewaters are produced mainly through the interaction of meteoric waters with serpentinites, whereas the Ca-HCO3 type waters are produced through the interaction of meteoric waters with Ca-rich rocks (i.e., carbonate rocks, calcschists, andmetabasites). Thermodynamic evaluation indicates that in theMgO–SiO2–Al2O3–H2O 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 Mgvermiculite and further Mg-saponite. In the CaO–SiO2–Al2O3–H2O system, Ca-HCO3 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-HCO3 and Ca-HCO3 type waters). The Cr(VI)-rich Ca-HCO3 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 associatedwith exposure to Cr(VI) in drinkingwater, especially as Cr contamination is not limited to springs flowing through serpentinites.

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

MONGELLI, Giovanni;PATERNOSTER, Michele;
2012

Abstract

Weathering of outcrops of ultramafic rocks (remnants of ancient oceanic crust) is a source of biologically toxic trace elements, particularly first rowtransition elements. The Cr and Ni concentrations of serpentinite and metabasite outcrops in the northern sector of the Pollinomassif (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. Themajor solutes in the spring waters fromthis region areMg-HCO3 and Ca-HCO3. TheMg-HCO3 typewaters are produced mainly through the interaction of meteoric waters with serpentinites, whereas the Ca-HCO3 type waters are produced through the interaction of meteoric waters with Ca-rich rocks (i.e., carbonate rocks, calcschists, andmetabasites). Thermodynamic evaluation indicates that in theMgO–SiO2–Al2O3–H2O 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 Mgvermiculite and further Mg-saponite. In the CaO–SiO2–Al2O3–H2O system, Ca-HCO3 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-HCO3 and Ca-HCO3 type waters). The Cr(VI)-rich Ca-HCO3 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 associatedwith exposure to Cr(VI) in drinkingwater, especially as Cr contamination is not limited to springs flowing through serpentinites.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11563/18246
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