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 the open ocean, the coastal zone and estuaries, as well as freshwater systems. The focus of current research is the important transformation processes, both in the sediment and in the water column, for metals and how these impact bioavailability and bioaccumulation into aquatic organisms. 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). 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 have 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. A number of cruises were completed in 2005/06 and currently the samples collected are being analyzed. Another project, in conjunction with Harvard University, also focused on the coastal zone, is examining the impact of hurricanes on mercury dynamics in the Gulf of Mexico. A further project, 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. These studies follow up on a long-term and extensive set of studies that have been done at CBL. 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.

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. E-H. Kim and J. Cornwell. 2004. Metal accumulation in Baltimore Harbor: Current and past inputs. Appl. Geochem. 19: 1801-1825.

Conaway, C.H., R.P. Mason, D.J. Steding and A.R. Flegal. 2005. Estimate of mercury emission from gasoline and diesel fuel consumption, San Francisco Bay area, California. Atmos. Environ. 39: 101-105

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.

Sveinsdottir, A. and R.P. Mason. 2005. Factors controlling mercury and methylmercury concentrations in largemouth bass (Micropterus salmoides) and other fish from Maryland reservoirs. Arch. Environ. Contam. Toxicol. 49: 528-545.

Whalin, L.M. and R. P. Mason. 2006. A new method for the investigation of mercury redox chemistry in natural waters utilizing deflatable Teflon® bags and additions of isotopically labeled mercury. Anal. Chim. Acta, 558: 211-221.

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)24: 3043-3047.

Heyes, A., R.P. Mason, E-H Kim and E. Sunderland. 20065. 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. 20065. 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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