Environ. Sci. Technol. 2001, 35, 3608-3615
Chemical Fractionation of Metals in Wetland Sediments: Indiana Dunes National Lakeshore NANCY L. DOLLAR,† C A T H E R I N E J . S O U C H , * ,‡ GABRIEL M. FILIPPELLI,† AND MARIA MASTALERZ§ Departments of Geology and Geography, Center for Earth and Environmental Science, Indiana University-Purdue University, Indianapolis, Indiana 46202, and Indiana Geological Survey, Indiana University, Bloomington, Indiana 47405-2208
Tessier-type (1979) sequential extractions for heavy metals (Cd, Cr, Cu, Fe, Mn, Pb, and Zn) were conducted on sediments from two wetland sites, one inundated and the other drained, within the Indiana Dunes National Lakeshore (IDNL), NW Indiana, with the objective of (i) evaluating extraction techniques on organic-rich sediments, (ii) determining the geochemistry and mobility of potentially biotoxic trace metals in a contaminated environment, and (iii) considering the implications of different restoration strategies on the potential for heavy metal remobilization. Long and repeated extractions were needed to effectively degrade the organic-rich sediments (up to 75% of the sediment by mass). Analysis of sulfur fractionation revealed that it was predominantly sequestered along with the organically bound fraction (renamed oxidizable). Metal recovery was good with the sum of the extractant steps typically within 20% of the total metal concentration determined after total microwave digestion. Results showed metal fractionation to be both metal- and site-specific. The oxidizable fraction is dominant for Cu, Cr, and Fe (>65% of the nonresidual fraction for almost all samples) and overall is most important also for Cd and Pb. The iron/manganese oxide fraction is important for Pb, Mn, and Zn, particularly at the drained site. The carbonate bound fraction is relatively insignificant at both sites, except for Cd and Mn, although it is more important at the drained site. The exchangeable fraction is significant in the uppermost sediments at the drained site, particularly for Cd (3-24%), Pb (3-14%), and Zn (36-45%); whereas, for the inundated site, it ranged only from 0 to 1% Zn, with no detectable Cd or Pb. Chromium, Cu, and Fe exist in forms not likely to be remobilized, whereas Cd, Mn, Pb, and Zn are potentially mobile if drained wetland sites are reflooded (and pH and redox potential altered). Simple mass balance calculations illustrate the potential for the removal of ∼84 375 kg of exchangeable Zn if currently drained sites across the IDNL are reflooded, with concentrations in water draining into Lake Michigan as high as 5 ppm.
Introduction The development of wetland nature preserves near industrial areas presents special problems of management, remediation, and restoration that must take into account historical legacies of industrial metal contamination. While the magnitude of heavy metal contamination in many such sites is well-documented, only limited attention has been directed to the insight that sequential extractions can provide into the significance of bioavailable phases and the potential mobility of heavy metals should environmental conditions change, for example, associated with restoration. This study focuses on wetlands within the Indiana Dunes National Lakeshore and the adjacent Indiana Dunes State Park (hereafter referred to collectively as IDNL) (Figure 1) located just downwind of the heavily industrialized southern shore of Lake Michigan (the Chicago-Gary-Hammond urbanindustrial complex). Previous work at the IDNL (1) documented elevated concentrations of heavy metals in the wetland sediments, with differences both in terms of absolute concentrations and patterns with depth (a record of both the history of deposition and the post-depositional mobility) for sites with contrasting disturbance histories and hydroperiods. In this study, Tessier-type sequential extractions for heavy metals (2) were conducted on sediments from permanently inundated and drained wetland sites within the IDNL with the objective of: (i) evaluating extraction techniques on organic-rich sediments, (ii) determining the geochemistry and mobility of potentially biotoxic trace metals in a contaminated environment, and (iii) considering the implications of reflooding previously drained sites on the potential for heavy metal remobilization.
Methods Study Site. The wetlands of the IDNL lie in lowlands between three dune-beach complexes, former shorelines of Lake Michigan, which parallel the present day shoreline. The most extensive of the wetlands, the Great Marsh (GM), formed approximately 4000 yr B.P. (3). The IDNL dunes and wetlands are underlain by a complex aquifer system composed of unconsolidated glacial, lacustrine, and eolian sediments deposited on carbonates and shales of Paleozoic age. Regional and intermediate groundwater flow systems are recharged in coarse-grained uplands south of the dune-beach complexes and discharge by upward leakage through the unconsolidated sediments into Lake Michigan and the largest interdunal area, the GM (4). The net result is well-oxygenated surface water and groundwater in the GM, with mean oxidation-reduction potentials of ∼340 mV (4). Precipitation in this region is among the most acidic within the United States, averaging 4.2 since 1980 (the period for which measurements have been made; 5); however, acidity of the GM surface water is neutralized by groundwater discharge from underlying aquifers, resulting in pH ranging from 5.3 to 7.4 (4). Industrial development of the Lake Michigan shoreline in Indiana dates back to 1869. Steel production in the GaryEast Chicago area began in the 1890s, and an industrial * Corresponding author e-mail:
[email protected]; telephone: (317)274-1103; fax: (317)274-2347. † Department of Geology, Center for Earth and Environmental Science, Indiana University-Purdue University. ‡ Department of Geography, Center for Earth and Environmental Science, Indiana University-Purdue University. § Indiana Geological Survey, Indiana University.
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 35, NO. 18, 2001
10.1021/es0105764 CCC: $20.00
2001 American Chemical Society Published on Web 08/10/2001
FIGURE 1. Location of the Indiana Dunes National Lakeshore and the two core locations (GM2 and GM8). The industrial complex just to the west of the wetlands includes Northern Indiana Public Service Company (NIPSCO), Midwest Steel, and Bethlehem Steel. complex (Figure 1) located just to the west of the IDNL opened in 1929, with three additional facilities developed in the 1960s. However, the history of land ownership of the IDNL means the watersheds studied have remained almost exclusively natural areas (70%) (Figure 4). The calcareous marl underlying the peat deposit at site GM2 contains an iron/manganese oxide boundary, and this is reflected by the jump in percent contribution by iron/manganese oxide bound Cr and Cu (for which the carbonate bound fraction also increases) in the lowermost portion of the core. Cadmium, Mn, Pb, and Zn demonstrate important differences in speciation between sites (Figure 4). In core GM8, Zn dominates in the exchangeable fraction, with a range of 40-50% in the upper 22 cm of the core. The carbonate bound and iron/manganese oxide bound Zn fractions are similar in their contributions, with ranges of 12-30% and 14-27%, respectively, above 22 cm depth. Below 22 cm at GM8, the oxidizable fraction of Zn predominates. In GM2, however, the iron/manganese oxide (22-54%) and the
TABLE 3. Summary of Trace Metal Affinities in Nonresidual Fractionsa
a
fraction
GM2 (inundated >90% growing season)
GM8 (inundated only after rainfall events)
F1, exchangeable F2, carbonate F3, iron/manganese oxides F4, oxidizable
Mn Mn> Cd > Cr > Zn Zn > Mn > Cd > Fe > Pb > Cu Cu > Fe > Cr > Pb > Zn > Cd > Mn
Zn > Mn > Cd > Pb Cd > Zn > Mn > Pb > Cr Pb > Fe > Cd > Zn > Mn > Cr > Cu Cu > Cr > Fe > Pb > Cd > Zn > Mn
Contributions
