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Title: In-situ subaqueous capping of mercury-contaminated sediments in a fresh-water aquatic system, Part I—Bench-scale microcosm study to assess methylmercury production

Bench-scale microcosm experiments were designed to provide a better understanding of the potential for Hg methylation in sediments from an aquatic environment. Experiments were conducted to examine the function of sulfate concentration, lactate concentration, the presence/absence of an aqueous inorganic Hg spike, and the presence/absence of inoculums of Desulfovibrio desulfuricans, a strain of sulfate-reducing bacteria (SRB) commonly found in the natural sediments of aquatic environments. Incubations were analyzed for both the rate and extent of (methylmercury) MeHg production. Methylation rates were estimated by analyzing MeHg and Hg after 2, 7, 14, 28, and 42 days. The production of metabolic byproducts, including dissolved gases as a proxy for metabolic utilization of carbon substrate, was also monitored. In all treatments amended with lactate, sulfate, Hg, and SRB, MeHg was produced (37 ng/g-sediment dry weight) after only 48 h of incubation and reached a maximum sediment concentration of 127 ng/g-sediment dry weight after the 42 day incubation period. Aqueous phase production of MeHg was observed to be 10 ng/L after 2 day, reaching a maximum observed concentration of 32.8 ng/L after 14 days, and declining to 10.8 ng/L at the end of the incubation period (42 day). The results of this study furthermore » demonstrates that, in the presence of an organic carbon substrate, sulfate, and the appropriate consortia of microorganisms, sedimentary Hg will be transformed into MeHg through bacterial metabolism. Further, this study provided the basis for evaluation of an in-situ subaqueous capping strategy that may limit (or potentially enhance) MeHg production. -- Highlights: • Hg methylation by SRB is limited by the depletion of sulfate and carbon. • Hg methylation is sensitive to competition by methanogens for carbon substrate. • In high lactate environment, all lactate was utilized in the microcosms within seven days. • In the absence of adequate metabolic fuel, MeHg levels decreased on the time scale of days to weeks. • Capping materials should sequester MeHg produced and not contribute to the production of MeHg.« less
Authors:
 [1] ;  [2] ; ;  [3]
  1. U.S. Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, 26 W. Martin Luther King Drive, Cincinnati, OH 45268 (United States)
  2. Geosyntec Consultants, 150 E. Wilson Bridge Road, Suite 232, Worthington, OH 43085 (United States)
  3. Battelle, 505 King Ave., Columbus, OH 43201 (United States)
Publication Date:
OSTI Identifier:
22246943
Resource Type:
Journal Article
Resource Relation:
Journal Name: Environmental Research; Journal Volume: 125; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 60 APPLIED LIFE SCIENCES; ABUNDANCE; CARBON; CONCENTRATION RATIO; DESULFOVIBRIO; DISSOLVED GASES; ECOLOGICAL CONCENTRATION; FRESH WATER; INCUBATION; LACTATES; MERCURY; METABOLISM; METHYLATION; METHYLMERCURY; MICROCOSMS; SEDIMENTS; SUBSTRATES; SULFATES