My current research interests are directed at the fate, transport, and transformation of trace metals, especially mercury, but also cadmium, 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 and recent research is the important transformation processes, in the sediment, water and air, and at the interfaces (sediment/water and air/sea) for metals and how these impact bioavailability and bioaccumulation into aquatic organisms (http://mason.mercury.uconn.edu/research-projects/). 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, and as the links between inputs of inorganic mercury and accumulation of methylmercury in fish are complex, and involve many steps, these links have been the focus of much study.
The primary project focused on air-sea exchange and atmospheric chemistry of mercury, funded by NSF, is examining the factors influencing air-sea exchange and its seasonal variability in the North Atlantic near Bermuda on cruises and at the air sampling tower at Tudor Hill. The major objectives are to examine the variation in atmospheric and surface ocean Hg speciation and the primary mechanisms of mercury oxidation and reduction in seawater, and of mercury oxidation in air; to develop a more accurate assessment of the seasonal variability in the exchange of mercury and to provide better constrained flux estimates at the air-sea interface. Additionally, to use the data generated to constrain and improve ocean and global Hg models using the Harvard University GEOS-Chem modeling framework. To generate sufficient information for modeling requires the development and implementation of novel techniques and research is focused on improving the time resolution of measurement, and in the improvement of flux estimates. One current project funded through the NOAA CICEET Program is developing new techniques for estimating the dry deposition of mercury to coastal ecosystems.
A related NSF funded project is part of the international GEOTRACERS program, which is a newly initiated international oceanographic program and provides the necessary platform for a global measurement campaign to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions (www.ldeo.columbia.edu/res/pi/geotraces). One of the initial tasks is a thorough interacalibration exercise of techniques and approaches and my group participated in a cruise in June 2008 and there is a further cruise in 2009.
A focus on differences in concentration, fate and bioaccumulation in methylmercury and other metals across coastal ecosystems is through a collaboration with Dartmouth researchers, as part of a larger overall study funded through the NIH Superfund Program. Our project is aimed at examining the impact of different environmental conditions and levels of contamination on the bioaccumulation of methylmercury into aquatic food chains. The major goals are to characterize bioavailability and bioaccumulation in aquatic food webs across a gradient from forested to industrialized habitats that vary in levels of total mercury and organic carbon to determine the underlying mechanisms controlling differences between ecosystems. In addition, laboratory studies will examine specific aspects of the transformation and bioaccumulation processes to understand the impact of food type and quality, and growth dynamics and ecosystem functioning (betnhic versus pelagic food chains) on the extent of bioaccumulation.
The role of biota, primarily microorganisms, in mediating the chemical transformations of mercury and other metals in the environment has been a recent research focus. For example, recent investigations have examined the factors controlling mercury methylation and methylmercury degradation, as well as mercury redox chemistry in the Chesapeake Bay and mid-Atlantic Bight and in the Gulf of Mexico, with funding through the National Science Foundation (NSF). The primarily rationale for these studies was to improve our 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.
More details of the research programs, and of associated publications, of current and former students, and of other activities and are given at http://mason.mercury.uconn.edu/.
Air-sea exchange and boundary layer chemistry of mercury over the open ocean. – National Science Foundation
Collaborative Research: A GEOTRACES intercalibration of collection, handling and analysis methods for mercury species in seawater. – National Science Foundation
Developing global scientists and engineers through the study of mercury environmental issues in Southern Africa – National Science Foundation
Toxic metals in the Northeast: From biological to environmental implications. – National Institute of Health, Superfund Basic Research and Training Program
Brian DiMento – Ph.D. Student
Kathleen Gosnell – Ph.D. Student
Nashaat Mazrui – Ph.D. Student (Chemistry)
Emily Seelen – Ph.D. Student
Terill Hollweg – Ph.D. 2010
Udonna Ndu – Ph.D. 2011
Veronica (Roni) Ortiz – M.Sc. 2013
Amina Schartup – Ph.D. 2012
Susan Gichuki – Chemistry Ph.D. 2013
Papers and Book Chapters Since 2006. Total papers ~100
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.
Heyes, A., R.P. Mason, E-H Kim and E. Sunderland. 2006. Mercury methylation in estuaries: Insights from measuring rates using mercury stable isotopes. Mar. Chem. 102: 134-147.
Mason, R.P., E-H. Kim, J. Cornwell and D. Heyes. 2006. The influence of sediment redox status on the flux of mercury, methylmercury and other constituents from estuarine sediment. Mar. Chem. 102: 96-110.
Mason, R.P., Heyes, D. and Sveinsdottir, A. 2006. Methylmercury concentrations in fish from tidal waters of the Chesapeake Bay. Arch. Environ. Contam. Toxicol. 51: 425-437.
Kim, E-H., R.P. Mason, E.T. Porter and H.L. Soulen. 2006. The impact of resuspension on sediment mercury dynamics, and methylmercury production and fate: A mesocosm study. Mar. Chem. 102: 300-315.
Kerin, E.J., C.C. Gilmour, E. Roden, M.T. Suzuki, J.D. Coates and R.P. Mason. 2006 Mercury methylation by dissimilatory iron-reducing bacteria. Appl. Environ. Microbiol., 72: 7919-7921.
Laurier, F. and R.P. Mason. 2007. Mercury concentration and speciation in the coastal and open ocean boundary layer. JGR-Atmos., Art# D06302.
Miller, C.L., R.P. Mason, C.C. Gilmour and A. Heyes. 2007. Influence of dissolved organic matter on the complexation of mercury under sulfidic conditions. Environ. Toxicol. Chem. 26: 624-633.
Conaway, C., J.R.M. Ross, R. Looker, R.P. Mason and A.R. Flegal. 2007. Decadal mercury trends in San Francisco Estuary sediments. Environ. Res. 105: 53-66.
Strode, S.A., L. Jaeglé, N.E. Selin, D.J. Jacob, R.J. Park, R.M. Yantosca, R.P. Mason and F. Slemr. 2007. Air-sea exchange in the global mercury cycle. Global Biogeochem. Cycles; 21: Art #GB1017.
Whalin, L.M., E-H. Kim and R.P. Mason. 2007. Factors influencing the oxidation, reduction, methylation and demethylation of mercury species in coastal waters. Mar. Chem. 107: 278-294.
Harris RC, JWM Rudd, M Amyot, C Babiarz, KG Beaty, PJ Blanchfield, RA Bodaly, BA Branfireun, CC Gilmour, JA Graydon, A Heyes, H Hintelmann, JP Hurley, CA Kelly, DP Krabbenhoft, SE Lindberg, RP Mason, MJ Paterson, CL Podemski, A Robinson, KA Sandilands, GR Southworth, VL St. Louis, and MT Tate. 2007. Whole-ecosystem study shows rapid fish-mercury response to changes in mercury deposition. Proceedings of the National Academy of Sciences of the United States of America 104(42): 16586–16591.
Sunderland, E.M. and R.P. Mason. 2007. Human impacts on open ocean mercury concentrations. Global Biogeochem. Cycles 21: Article # GB4022.
Krabbenhoft, D, D. Engstrom, C. Gilmour, R. Harris, J. Hurley and R.P. Mason. 2007. Monitoring and evaluating trends in sediment and water indicators. pp. 47-86. In: Harris, R., D.P. Krabbenhoft, R.P. Mason, M.W. Murray, R. Reash and T. Saltman. (Eds.), Ecosystem Responses to Mercury Contamination: Indicators of Change, SETAC, CRC Press, Boca Raton.
Harris, R., Krabbenhoft, D., R.P. Mason, M.W. Murray, R. Reash and T. Saltman. 2007. Introduction. pp. 1-12 In: Harris, R., D.P. Krabbenhoft, R.P. Mason, M.W. Murray, R. Reash and T. Saltman. (Eds.), Ecosystem Responses to Mercury Contamination: Indicators of Change, SETAC, CRC Press, Boca Raton.
Kim, E-H. and R.P. Mason. 2008. A modeling study of methylmercury bioaccumulation and its controlling factors. Ecol. Model. 218: 267-289.
Dabrowski, J.M., P.J. Ashton, K. Murray, J.J. Leaner and R.P. Mason. 2008. Anthropogenic mercury emissions in South Africa: Coal combustion in power plants. Atmos. Environ. 42: 6620-6626.
Chen, C.Y., N. Serrell, D.C. Evers, B.J. Fleishman, K.F. Lambert, J. Weiss, R.P Mason and M.S. Bank. 2008. Methylmercury bioavailability in marine ecosystems: Implications for environmental and human health. Environ. Health Perspect. 116: 1706-1712.
Holmes, C.D., D.J. Jacob, R.P. Mason and D.A. Jaffe. 2009. Sources and deposition of reactive gaseous mercury in the marine atmosphere. Atmos. Environ. 43: 2278-2285.
Evers, D.C., R.P. Mason, N.C. Kamman, C.Y. Chen, A.L. Bogomolni, D.L. Taylor, C.R. Hammerschmidt, S.H. Jones, N.M. Burgess, K. Munney and K.C. Parsons. 2009. An integrated mercury monitoring program for temperate estuarine and marine ecosystems on the North American Atlantic coast. Ecohealth 5: 426-441.
Liu, B., L. A. Schaider, R.P. Mason, M.S. Bank, N.N. Rabalais, P.W. Swarzenski, J.P. Shine, T.A. Hollweg and D.B. Senn. 2009. Disturbance impacts on mercury dynamics in northern Gulf of Mexico sediments. JGR-Biogeochem. 114: Art # G000C07.
Hollweg, T.A., C.C. Gilmour and R.P. Mason. 2009. Methylmercury production in Chesapeake Bay and mid-Atlantic continental margin sediments. Mar. Chem 114: 86-101.
Mason, R.P. 2009. Mercury emissions from natural processes and their importance in the global mercury cycle. In: Pirrone, N. and R.P. Mason (Eds.), Mercury Fate and Transport in the Global Atmosphere: Emissions, Measurements and Models, Chapter 7, Springer, pp.192-220.
Leaner, J.J., J.M. Dabrowski, R.P. Mason, T. Resane, M. Richardson, M. Ginster, G. Gericke, C.R. Petersen, E. Masekoameng, P. J. Ashton and K. Murray. 2009. Mercury emissions from point sources in South Africa. In: Pirrone, N. and R.P. Mason (Eds.), Mercury Fate and Transport in the Global Atmosphere: Emissions, Measurements and Models, Chapter 5, Springer, pp. 113-130.
Pirrone, N., S. Cinnirella, X. Feng, R.B. Finkelman, H.R. Friedli, J. Leaner, R.P. Mason, A.B. Mukherjee, G. Stracher, D.G. Streets and Kevin Telmer. 2009. Global mercury emissions to the atmosphere from natural and anthropogenic sources. In: Pirrone, N. and R.P. Mason (Eds.), Mercury Fate and Transport in the Global Atmosphere: Emissions, Measurements and Models, Chapter 1, Springer, pp. 3-49.
Sprovieri, F., N. Pirrone, R.P. Mason and M. Andersson. 2009. Spatial coverage and temporal trends of over-water, air-surface exchange, surface and deep sea water mercury measurements. In: Pirrone, N. and R.P. Mason (Eds.), Mercury Fate and Transport in the Global Atmosphere: Emissions, Measurements and Models, Chapter 11, Springer, pp. 232-380.
Kading, T.J., R.P. Mason and J.J. Leaner. 2009. Mercury contamination history of an estuarine floodplain reconstructed from a 210Pb-dated sediment core (Berg River, South Africa). Mar. Pol. Bul. 59: 116-122.