The fate of iron in waters from a coastal environment impacted by metallurgical industry in Northern Italy: hydrochemistry and Fe-isotopes

The source and cycling of Fe in groundwaters from the phreatic aquifer which characterizes a site impacted by metallurgical activity in a coastal area of northern Italy (Adriatic Sea) have been investigated by Fe-isotope analyses, H-O-Sr stable-isotope systematics and major and trace element chemistry. Waters are characterized by circum-neutral to alkaline pH and dissolved O-2 zoning, and range from a low-salinity Ca-Mg-HCO3 type to a brackish Na-Cl type resulting from seawater intrusion. The O-H isotopic data indicate that the Ca-Mg-HCO3 waters originate from meteoric precipitation that infiltrated at elevated altitudes, and that a variable seawater fraction, in some cases exceeding 90%, characterizes the Na-Cl type waters. The Fe content ranges from 0.48 to 9.99 mg/L and from 2.50 to 43.8 mg/L in low-salinity and brackish waters, respectively. The delta Fe-56 value varies over the wide range from +0.87 parts per thousand to -5.29 parts per thousand in low-salinity waters and between +2.15 parts per thousand and -2.34 parts per thousand in brackish waters. The isotopically lighter compositions are interpreted as reflecting isotopic fractionation during repeated cycling of Fe precipitation. Positive delta Fe-56 values might indicate either a higher solubility of oxyhydroxides, which during diagenesis preferentially incorporated the isotopically heavier fraction of Fe, or the leaching of the foundry landfill disposal which characterizes the site. (c) 2013 Elsevier Ltd. All rights reserved.