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Mercury Speciation in Floodplain Soils and Sediments along a Contaminated River Transect

Frontier Geosciences Inc., 414 Pontius Ave. North, Seattle, WA 98109,

Madhukar V. M. Desai

Bhabha Atomic Research Center (BARC), Health Physics Div., Bombay-400 085, India,

Markus Spengler

GKSS Forschungszentrum GmbH, Institut für Physikalische und Chemische Analytik, Abteilung Organische Spurenanalyse, Max-Planck-Str., 21502 Geesthacht, Germany;

Rolf-Dieter Wilken

Johannes-Gutenberg-Univ., Inst. of Geosciences, Johannes-Joachim-Becher-Weg 21, 55099 Mainz, Germany,

^* Corresponding author (dirkw{at}frontier.wa.com).

ABSTRACT

A novel mercury-specific sequential extraction procedure (SEP) for the assessment of mercury (Hg) speciation in soils and sediments, with emphasis on studying the interaction between Hg and organic matter (OM), was developed and tested. It was applied to determine Hg speciation in floodplain topsoils and surface sediments along the Hg-contaminated part of the river Elbe, and to simultaneously derive some information on the (re)mobilization potentials for Hg from these matrices. The majority of the total Hg in the ecosystem today is bound in the floodplains, which also still geographically reflect the historic emission record. Most of the Hg in both matrices is bound strongly to OM, suggesting low availability. However, distinct differences between Hg speciation in the floodplain soils and sediments were also discovered. Mercury deposited in the floodplains shows speciation patterns that indicate stronger fixation compared with Hg in the sediments. This difference is attributed to the association of Hg with larger quantities of OM, which presumably also has higher molecular weight (MW). By comparison, Hg in the sediments was distributed among weaker binding forms, which are more likely to liberate Hg. Particularly, sediments showed a total lack of sulfidic binding forms for Hg. Pronounced geographical trends were detected in the Hg speciation along the river transect, with a general downstream shift from weaker to stronger binding forms, probably due to increased association with OM. These studies indicate that Hg speciation in riverine ecosystems is dynamic and reflects the chemical mechanisms underlying (bio)geochemical processes like distribution and transport.

previously at GKSS;

previously at GKSS;

previously at GKSS.

Received for publication September 8, 1997.

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