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.