Thomas Bullen


I have been with the National Research Program of the USGS  Water Mission Area since 1990, and am the organization's resident expert in the analysis and application of metal and metalloid isotopes for hydrologic, biogeochemical and environmental research. My technical training is in the fields of fluid mechanics (B.A. degree) and igneous geochemistry (Ph.D degree), which combined with my diverse research experiences while at the USGS has resulted in a strong inter-disciplinary approach to my science. I have long-standing interests in the science of small watersheds, large aquifers, contaminant transport and fate, human health and biogeochemical tracing techniques in general. My current research is focused on developing novel metal stable isotope tracing techniques to understand hydropedologic processes in forested watersheds and to determine the sources, transport mechanisms and fates of metals deposited on those watersheds as dust.


I conduct laboratory and field-based research utilizing metal and metalloid isotope tracers together with other geochemical tools to further our understanding of hydrologic and biogeochemical processes at all scales, the interactions between liquids and solids, the origin and fate of inorganic contaminants in the environment, nutrient cycling in ecosystems, and isotope biogeochemistry in general. In carrying out this research, I develop and refine methods to determine the isotopic composition of metals and metalloids in natural materials, using thermal ionization mass spectrometry (TIMS) and multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). I have measured the isotopic composition of Sr, Ca, Cd, Pb, Li, B, Fe, Cr, Zn, Se, and Te in natural materials using these instruments. In many cases, my isotope data for environmental samples and the interpretations of observed variations are among the first reported in the literature. I develop isotopic approaches that can be used to address problems either posed by colleagues or that I recognize as being of importance to the advancement of environmental science. I collaborate with USGS Water Science Center, National Research Program and other scientists from the United States and abroad in the conceptualization, development and execution of inter-disciplinary studies that utilize isotope tracers in novel ways to address a variety of scientific issues. I broadcast the utility of these emerging isotopic tools by presenting lectures at universities and at meetings of national and international scope, and through publication in the peer reviewed literature. I oversee the Metal and Metalloid Isotope Laboratory in Menlo Park, CA, which houses two TIMS and a single collector ICP-MS, and a “clean” laboratory for sample preparation. I spend approximately 2/3 of my time in the laboratory accomplishing chemistry and complex mass spectrometry tasks. Through our unique analytical capability within WRD, we provide high quality isotope data and interpretive services to scientists from the USGS, universities, and other research organizations and regulatory agencies worldwide.

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Bullen, T.D., 2011, Stable isotopes of transition and post-transition metals as tracers in environmental studies. In Handbook of Environmental Isotope Geochemistry, Advances in Isotope Geochemistry (M. Baskaran, ed.), Springer-Verlag. Pp. 177-203. [Download File]

Bullen, T.D. & Walczyk, T.R., 2009, Environmental and biomedical applications of metal stable isotopes. Elements, v.5, pp. 381-385 (T.D. Bullen and A. Eisenhauer, eds). [Download File]

Bullen, T.D. & Bailey, S.W., 2005, Identifying calcium sources at an acid deposition-impacted spruce forest: a strontium isotope, alkaline earth element multi-tracer approach. Biogeochemistry, v.74, n.1, pp. 63-99. [Download File]

Bullen, T.D., White, A.F., Childs, C.W., Vvit, D.V. & Schulz, M.S., 2001, Demonstration of significant abiotic iron isotope fractionation in nature. Geology, v.29, n.8, pp. 699-702 [Download File]

Bullen, T.D., Krabbenhoft, D.P. & Kendall, C., 1996, Kinetic and mineralogic controls on the evolution of groundwater chemistry and 87Sr/86Sr in a sandy silicate aquifer, northern Wisconsin, USA.Geochemica et Cosmohimca Acta, v.60, n.10, pp. 1807-1821. [Download File]