Environ. Sci. Technol. 1993,27,2367-2372
Measurement of Trace Metals Associated with Acid Volatile Sulfides and Pyrite in Organic Freshwater Sediments Mlguel A. Huerta-Dlaz,'it Richard Carlgnan, and Andr6 Tessier INRS-Eau, Universite du Quebec, 2700 rue Einstein, C. P. 7500, Sainte-Foy, Quebec, Canada G1V 4C7
The efficiency of density separation and of a number of different chemical extraction methods to extract pyrite and associated trace metals from sediments having high organic matter contents were investigated. All chemical extraction methods tested were suitable for pyrite determinations but overestimated the associated trace metal (Co, Cu, Mn, Ni, Pb, and Zn) concentrations presumably due to interferences produced by simultaneous extraction of trace metals associated with organic matter. Concentrations of trace metals associated to pyrite in the bulk sediment can best be determined from the pyrite-trace metal/pyrite-Fe ratios obtained by density separation and the total concentration of pyrite in the sediment obtained by the chemical extraction methods. The concentration of trace metals associated to acid volatile sulfides (AVS) in the bulk sediment can be estimated by combining the determination of AVS in the sediments with the ratio of trace metal to AVS measured in AVS spontaneously deposited in situ on Teflon sheets. Up to 9% of the reactive trace metals can be associated with pyrite or AVS. Introduction Sedimentary pyrite and acid volatile sulfides (AVS = amorphous FeS mackinawite + greigite) have recently received considerable attention from geochemists and biologists for many reasons. They constitute potentially important sinks for trace metals of geochemical and toxicological interest and contribute to the permanent burial of trace elements (1-9). Trace metals associated with AVS can potentially be released into the aquatic environment when reduced sediments are transported to oxic environments through bioturbation or dredging activities. AVS may also play an important role in controlling the toxicity of Cd and Ni toward amphipods, oligochaetes, and snails (10-13). Pyrite is one of the major authigenic minerals found in anoxic-sulfidic marine sediments (14)with typical concentrations of 150 pmol g-1 (15). Although quantitatively less important, acid volatile sulfides (AVS) may also represent a significant portion of the iron sulfide pool in a given sediment, with typical concentrations of AVS being normally around 5-20 pmol g-' (16). Significant concentrations of pyrite (up to 80 pmol g-l) and AVS (up to 312 pmol g-l) are also found in freshwater sediments (17-19). The importance of AVS in the geochemistry of trace metals in freshwater sediments is still largely unknown because selective determination of trace metals associated with AVS in sediment samples has proven difficult, if not impossible, due to the natural instability of this mineral phase and to the difficulty of finding chemical extractants selective toward trace metals associated with AVS.
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+Author to whom correspondence should be addressed at his present address: Instituto de Investigaciones Oceanol6gicas, Universidad Aut6noma de Baja California, Apdo. Postal# 453, Ensenada, B.C. 22830, MBxico. 0013-936X/93/0927-2367$04.00/0
0 1993 Amerlcan Chemical Society
Trace metals associated with pyrite can be determined selectively in sediments with low organic carbon content (
