Bacterial Methylmercury Degradation in Florida Everglades Peat Sediment

• Published in: Environmental science & technology Vol. 32; no. 17; pp. 2556 - 2563
• Main Authors: Marvin-DiPasquale, Mark C, Oremland, Ronald S
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.09.1998
• Subjects: Animal, plant and microbial ecology; Applied sciences; Bacteria; BIODEGRADACION; BIODEGRADATION; Biodegradation of pollutants; Biological and medical sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; Biotechnology; Decomposition; Environment and pollution; Environmental impact; Environmental protection; Exact sciences and technology; FLORIDA; FLORIDE; Fundamental and applied biological sciences. Psychology; Industrial applications and implications. Economical aspects; MERCURE; MERCURIO; MERCURY; Microbial ecology; PEAT; Pollutants; Pollution; SEDIMENT; SEDIMENTO; Sediments; Soil and sediments pollution; TOURBE; TURBA; Various environments (extraatmospheric space, air, water); USA, Florida, Everglades; Biodegradation; Surface water; Bacteria; Marsh; Mercury Organic compounds; Water pollution; Lake sediments; Peat; Eutrophication; Heavy metal
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es971099l

Methylmercury (MeHg) degradation was investigated along an eutrophication gradient in the Florida Everglades by quantifying 14CH4 and 14CO2 production after incubation of anaerobic sediments with [14C]MeHg. Degradation rate constants (k) were consistently ≤0.1 d-1 and decreased with sediment depth. Higher k values were observed when shorter incubation times and lower MeHg amendment levels were used, and k increased 2-fold as in-situ MeHg concentrations were approached. The average floc layer k was 0.046 ± 0.023 d-1 (n = 17) for 1−2 day incubations. In-situ degradation rates were estimated to be 0.02−0.5 ng of MeHg (g of dry sediment)-1 d-1, increasing from eutrophied to pristine areas. Nitrate-respiring bacteria did not demethylate MeHg, and NO3 - addition partially inhibited degradation in some cases. MeHg degradation rates were not affected by PO4 3- addition. 14CO2 production in all samples indicated that oxidative demethylation (OD) was an important degradation mechanism. OD occurred over 5 orders of magnitude of applied MeHg concentration, with lowest limits [1−18 ng of MeHg (g of dry sediment)-1] in the range of in-situ MeHg levels. Sulfate reducers and methanogens were the primary agents of anaerobic OD, although it is suggested that methanogens dominate degradation at in-situ MeHg concentrations. Specific pathways of OD by these two microbial groups are proposed.