Interactions of trace metals with authigenic sulfide minerals: implications for their bioavailability

Abstract

Abstract Trace metals that are mobilized during early diagenesis can be coprecipitated with and adsorbed on authigenic sulfide minerals in anoxic sediments. A major portion (generally > 60%) of the non-silicate bound fraction of potentially toxic metals, such as As, Cu and Hg, is commonly coprecipitated with pyrite near the sediment-water interface. Traditional methods (e.g. 1 N HCl or citrate dithionite extractions) for determining the concentration of potentially bioavailable metals in sediments do not include the pyrite bound fraction. However, pyritized metals can be potentially bioavailable if the pyrite is oxidized. Pyrite oxidation commonly occurs during sediment resuspension, seasonal migration of the redoxocline in sediments and when dredge spoils are dumped on land. Experimental measurements of metal release from pyrite, in initially anoxic sediments exposed to oxic seawater, indicate that a major portion (20% to over 90%) of the pyrite bound metals can be released in a day or less. The As, Cu and Hg released from pyrite usually exceeds the concentration of their potentially bioavailable fraction determined by traditional methods. Consequently, the pyritization-depyritization of trace metals is probably an important process in controlling the bioavailability of many important trace metals.