My
current research interests are directed at the fate,
transport, and transformation of trace metals, especially
mercury, cadmium, and lead, and the metalloids (arsenic
and selenium) in aquatic systems and the atmosphere.
The scope of research includes marine and freshwater
systems.
The focus of current research is the important transformation
processes, in the sediment, water column and atmosphere
for metals and how these impact the fate and transport.
Studies are also focused on the exchange across interfaces,
such as the processes controlling air-water and sediment-water
exchange of metals.
The role of biota, primarily microorganisms, in mediating
the chemical transformations of mercury and other metals
in the environment is a current research focus. For
example, recent investigations have examined the factors
controlling mercury methylation and methylmercury degradation,
as well as mercury redox chemistry in aquatic systems
with funding through the National Science Foundation
(NSF) and the Environmental Protection Agency (EPA).
The primarily rationale for these studies is to promote
an understanding of the relationship between the input
of mercury from the atmosphere, and from other sources,
to aquatic systems and the amount of methylmercury in
fish.
Mercury
inputs come from both natural and anthropogenic sources
and it appears that man’s activities has exacerbated
the mercury problem globally and locally. Elevated levels
of methylmercury in fish are an important human and
ecosystem health concern. One project, in conjunction
with Cindy Gilmour of the Smithsonian Environmental
Research Institute (SERC), funded by the NSF Chemical
Oceanography Program, is aimed at examining the production
and fate of methylmercury in estuarine and coastal ecosystems.
Another project, also with Gilmour, and with Andrew
Heyes of the Chesapeake Biological Laboratory (CBL),
University of Maryland, has allowed our participation
in a large program (the METAALICUS Project) within the
Experimental Lakes Area in Northwestern Ontario, Canada
where mercury isotopes are being added to a lake to
track the rate of formation and fate of methylmercury
in a freshwater ecosystem. In addition, I am involved
in a project in collaboration with the USGS in California
investigating mercury dynamics and differences in methylmercury
fate in various parts of the San Francisco Bay delta
region, where elevated mercury levels in fish occur.
In terms of the atmosphere, studies in surface waters
and in the atmosphere are aimed at quantifying wet and
dry deposition of mercury, as well as gas evasion, in
both the coastal zone and the open ocean. We are currently
air sampling at Bermuda in collaboration with the Bermuda
Biological Station/Bermuda Government and are completing
a project in Maryland, funded by the MD Dept of Natural
Resources, looking at atmospheric mercury speciation
and mercury deposition at a site within the Washington,
DC-Baltimore urban corridor (Beltsville). The atmospheric
studies are probing the importance of chemical reactions
in the atmosphere and in surface waters in influencing
mercury transport and chemical form, and the rate of
input of mercury from the atmosphere.
Some
Representative Publications
Mason,
R.P. and G.-R. Sheu. 2002. The role of the ocean in
the global mercury cycle. Global Biogeochemical Cycles
16: Art. # 1093, Oct/Nov 2002.
Leaner, J.J. and R.P. Mason. 2002. Factors controlling
the bioavailability of ingested methylmercury in channel
catfish and Atlantic sturgeon. Environ. Sci. Technol.
36:5124-5129.
Conaway, C.H., S. Squire, R.P. Mason, and A.R. Flegal.
2003. Mercury speciation in the San Francisco Bay estuary.
Mar. Chem. 80: 199-225.
Benoit, J.M., C.C. Gilmour, A. Heyes, R.P. Mason, and
C.L. Miller. 2003. Geochemical and biological controls
over mercury production and degradation in aquatic systems.
pp. 262-297. In: Y. Cai and O.C. Brouds [eds.], Biogeochemistry
of Environmentally Important Trace Elements, ACS Symposium
Series 835, American Chemical Society, Washington, D.C.
Laurier, F.J.G., R.P. Mason, L.M. Whalin and S. Kato.
2003. Reactive gaseous mercury formation in the North
Pacific Ocean’s marine boundary layer: A potential role
of halogen chemistry. JGR-Atmos. 108: D17, Art. # 4529,
doi: 10.1029/2003JD003625.
Kim, E-H., R.P. Mason, E.T. Porter and H.L. Soulen.
2004. The effect of resuspension on the fate of total
mercury and methylmercury in a shallow estuarine ecosystem.
Mar. Chem. 86: 121-137.
Leaner, J.J. and R.P. Mason. 2004. Methylmercury uptake
and distribution kinetics in sheepshead minnows, C.
variegatus, after exposure to CH3Hg-spiked food. Revised
manuscript submitted to Environ. Toxicol. Chem. 23:
2138-2146.
Heyes, A., C. Miller and R.P. Mason. 2004. Mercury and
methylmercury in the Hudson River sediment: impact of
resuspension on partitioning and methylation. Mar. Chem.
90: 75-89
Laurier, F.J.G., R.P. Mason, L.M. Whalin and G.A. Gill.
2004. Mercury in the North Pacific Ocean - 20 years
of observations. Mar. Chem. 90: 3-19.
Sheu, G-R. And R.P. Mason. 2004. An examination of the
oxidation of elemental mercury in the presence of halide
surfaces. J. Atmos. Chem. 48: 107-130.
Mason, R.P., M.L. Abbott, R.A. Bodaly, O.R. Bullock,
C.T. Driscoll, D. Evers, S.E. Lindberg, M. Murray and
E.B. Swain. 2005. Monitoring the environmental response
to changing atmospheric mercury deposition. Environ.
Sci. Technol. 39: 14A-22A.
Mason, R.P. 2005. Air-sea exchange and marine boundary
layer atmospheric transformations of mercury and their
importance in the global mercury cycle. In: Pirrone,
Nicola; Mahaffey, Kathryn R. (Eds.), Dynamics of Mercury
Pollution on Regional and Global Scales: Atmospheric
Processes and Human Exposures around the World. Springer
Press.
Rearick, M.S, C.C. Gilmour, A. Heyes, and R.P. Mason.
2005 Measuring sulfide accumulation in diffusive gradients
in thin films by means of purge and trap followed by
ion selective electrode. Environ. Contam. Toxicol. (in
press).
Heyes, A., R.P. Mason, E-H Kim and E. Sunderland. 2005.
Mercury methylation in eastuaries: Insights from measuring
rates using mercury stable isotopes. Mar. Chem. (in
press).
Mason, R.P., E-H Kim, J. Cornwell and D. Heyes. 2005.
An examination of the factors influencing the flux of
mercury, methylmercury and other constituents from estuarine
sediment. Mar. Chem. (in press)
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