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Factors Affecting Methylmercury Accumulation in the Food Chain


Methylmercury is produced in the aquatic environment by sulfur-reducing bacteria. The bacteria that methylate (chemically change) inorganic mercury into toxic MeHg thrive in low-oxygen, high-sulfur marsh sediments. Once taken up by organisms, it gets accumulated because of its high retention. On its way along the trophic levels of the food-chain it further biomagnifies, leading to high concentrations at the end of the food-chain. As a consequence of the biomagnification, human health risks from dietary MeHg exposure are significant.

New study:
The new study of researchers from the University of San Francisco sought to establish whether different types (and amounts) of dissoloved organic matter (DOM) collected from the San Francisco Bay-Delta might enhance or suppress MeHg accumulation in a resident species of phytoplankton.

Photo:  Cyclotella meneghiniana is one of the ecologically most important centric diatoms and easy to culture.

The general design of the experiment was to add phytoplankton cells to flasks with different DOM treatments, including treatments with no DOM and controls with no added algae cells.  Radiolabelled MeHg was added to each flask, and its concentrations were measured in the water and cells over time. The controls allowed scientists to quantify the amounts of MeHg stuck to the filters and walls of the flasks. To determine whether mercury accumulation was an active or passive cellular process, MeHg accumulation rates were compared for living and dead cells.

Live diatom cells accumulated two to four times more MeHg than dead cells, indicating that accumulation may be partially an energy-requiring process. Methylmercury enrichment in diatoms relative to ambient water was measured by a volume concentration factor (VCF). DOM significantly decreased accumulation of methylmercury (MeHg) by the diatom Cyclotella meneghiniana. At very high (20 mg/L) DOM, VCFs dropped 10-fold. Presumably, MeHg was bound to a variety of reduced sulfur sites on the DOM, making it unavailable for uptake by the diatoms. Although the DOM composition influenced the availability of MeHg to some extent, total DOM concentration was the most important factor in determining algal bioaccumulation of MeHg.

The original study:

A.C. Luengen, N.S. Fisher, B.A. Bergamaschi, Dissolved organic matter reduces algal accumulation of methylmercury, Environ. Toxicol. Chem., 2012, doi: 10.1002/etc.1885

Related studies (newest first):

C.A. Gerbig, J.N. Ryan, G.R. Aiken, The effects of dissolved organic matter on mercury biogeochemistry, in: Y. Cai, G. Liu, N. O’Driscoll, eds, Advances in Environmental Chemistry and Toxicology of Mercury, Wiley, New York, NY, USA, 2011, pp 259–292. doi: 10.1002/9781118146644.ch8

A.C. Luengen, A.R. Flegal, Role of phytoplankton in mercury cycling in the San Francisco Bay estuary, Limnol. Oceanogr., 54 (2009) 23–40. doi: 10.4319/lo.2009.54.1.0023

H. Zhong, W.X. Wang, Controls of dissolved organic matter and chloride on mercury uptake by a marine diatom, Environ. Sci. Technol., 43 (2009) 8998–9003. doi: 10.1021/es901646k

P.R. Gorski, D.E. Armstrong, J.P. Hurley, D.P. Krabbenhoft,  Influence of natural dissolved organic carbon on the bioavailability of mercury to a freshwater alga, Environ. Pollut., 154 (2008) 116–123. doi: 10.1016/j.envpol.2007.12.004

P.C. Pickhardt, N.S. Fisher, Accumulation of inorganic and monomethylmercury by freshwater phytoplankton in two contrasting water bodies, Environ. Sci. Technol, 41 (2007) 125–131. doi: 10.1021/es060966w

M. Ravichandran, Interactions between mercury and dissolved organic matter: A review, Chemosphere, 55 (2004) 319–331. doi: 10.1016/j.chemosphere.2003.11.011

M. Haitzer, G.R. Aiken, J.N. Ryan, Binding of mercury(II) to dissolved organic matter: The role of the mercury-to-DOM concentration ratio, Environ. Sci. Technol, 36 (2002) 3564–3570. doi: 10.1021/es025699i

A. Amirbahman, A.L. Reid, T.A. Haines, J.S. Kahl, C. Arnold, Association of methylmercury with dissolved humic acids, Environ. Sci. Technol., 36 (2002) 690–695. doi: 10.1021/es011044q

C.T. Driscoll, V. Blette, C. Yan, C.L. Schofield, R. Munson, J. Holsapple, The role of dissolved organic carbon in the chemistry and bioavailability of mercury in remote Adirondack lakes, Water Air Soil Pollut., 80 (1995) 499–508. DOI: 10.1007/BF01189700

Related EVISA Resources

Link database: Environmental cycling of mercury
Link database: Toxicity of Organo-mercury compounds
Link database: Research projects related to organo-mercury compounds

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last time modified: June 17, 2012

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