Research Interests

Dr. Dirk Baron
CSUB Department of Geological Sciences


 

Laboratories and Equipment


Toxic Trace-Elements in Natural and Contaminated Environments


One of the important long-term environmental issues that our society faces is the management of toxic trace metals and other harmful inorganic constituents in the environment.  Elevated levels of these substances are often the result of human activities but can also be naturally occurring.  My main research interests are to elucidate the processes that control the mobility and fate of harmful inorganic constituents such as heavy metals in aquatic and soil environments.   These processes include the formation of metal-containing solid phases, the formation of aqueous metal complexes, the adsorption of metals to soils and sediments and to aquatic particles, and reduction and oxidation reactions. 

Understanding these processes is crucial for the evaluation of human health risks and ecosystem effects of inorganic contaminants and for the development of rational and cost-effective remediation strategies for contaminated sites.  The scope of these research efforts ranges from spectroscopic investigations at the molecular level to bench scale experiments with natural materials and model systems to field investigations and numerical modeling. 

Two specific areas of research in this field are described below:


Sources and distribution of arsenic in sediments in the southern San Joaquin Valley 

Although the groundwater in the southern San Joaquin Valley is generally of high quality, there are isolated pockets where the concentration of the toxic element arsenic exceeds the drinking water standard.  In this study we examine water and sediments from two nearby wells, one with low arsenic, the other with elevated arsenic concentrations.

Analyses include sequential sediment extraction, examination of sediments by electron microscopy, and depth-resolved water sampling.  Groundwater has a mixed redox state with arsenic occurring as both As(III) and As(V).  Arsenic in the sediments is associated with pyrite grains which start to dissolve when the come in contact with oxygenated groundwater. (Boockoff et al., 2005; Negrini et al., 2008)

This work has been funded by the USDA and several grants from the state of California.




Iron-chromate precipitates in chromium-contaminated soils

Chromium-containing precipitates can affect the mobility of toxic Cr(VI) in the subsurface, control its concentration in groundwater, limit its bioavailability, and impede remediation of chromium contaminated sites.  These precipitates can be pure phases such as KFe3(CrO4)2(OH)6, the chromate-analog of the common sulfate mineral jarosite, or solid-solutions where chromate partially substitutes for another ion such as sulfate (e.g. Ba(SxCr1-xO4)).  In my research, we are measuring the thermodynamic properties of these solids.  These thermodynamic properties are the basis for determining the conditions under which these solids form and remain stable, as well as the chromium concentrations in water equilibrated with them. In addition to the practical applications, the thermodynamics of inorganic solid solutions is also one of the remaining theoretical frontiers in inorganic geochemistry. (e.g. Baron and Palmer, 2002; Drouet et al., 2003; Drouet et al., 2004).

 


 

Central California Climate History

Paleolimnology of Soda Lake, Carrizo Plain, California

We recently acquired 45 m of core from the Soda Lake basin in the Carrizo Plain National Monument of San Luis Obispo County, California. Initial analyses demonstrate that they contain a likely nonmarine counterpart to the well-known record of millennial-scale climate change from offshore Santa Barbara Basin. The Santa Barbara Basin record remains one of the most convincing pieces of evidence that the high-frequency, high-amplitude climate events shown in the ice core records are at least hemispheric in scale. Because the Soda Lake coring site is close to the Santa Barbara Basin locality and because the level of Soda Lake, a closed basin lake, should be very sensitive to changes in climate, the Soda Lake core should provide critical information on the impact of global climate change on nonmarine settings (e.g. Negrini et al., 2007). 

This work has been funded by the National Science Foundation.

 





Trace-Element Chemistry of Geologic Materials

Trace-element geochemistry of tephra, chert, and obsidian

Geologic materials such as obsidian, volcanic ash, and chert from different sources can be distinguished based on their trace-element composition.  We use ICP/MS and Laser Ablation ICP/MS to analyze various geological materials for stratigraphic and archaeological studies.  (e.g. Baron et al., 2008; Draucker et al., 2007; Remus et al., 2010; Remus et al., 2012)





References

Baron D., Negrini R.M, Golob E.M.*, Miller D., Sarna-Wojcicki A, Fleck R., Hacker B., Erendi A. (2008)
    Geochemical correlation and 40Ar/39Ar dating of the Kern River Ash and related tephra:  Implications for the
    stratigraphy of petroleum-bearing formations in the San Joaquin Valley, California. 

    Quaternary International. 176, 246-260.

Baron D. and Palmer C.D. (2002) Solid solution/aqueous solution interactions between jarosite
    and its chromate analog.
Geochimica et Cosmochimica Acta, 66, 2841-2853.

Baron D., Palmer C.D. and Stanley J.T. (1996) Identification of two Fe-chromate precipitates in
    a Cr(VI)-contaminated soil. Environmental Science & Technology, 30, 964-968.

Draucker A., Baron D., Yohe R., and Horton R. (2007) Geochemical characterization of obsidian subsources from
    the Coso Range, California, USA.  2007 Goldschmidt Conference, Cologne, Germany, August 19-24, 2007.

Drouet C., Pass K.L., Baron D., Draucker S., and Navrotsky A. (2004) On the thermochemistry of solid solutions
    between jarosite, natrojarosite, and alunite. Geochimica et Cosmochimica Acta, 58, 2197-2205.

Drouet C., Navrotsky A., and Baron D. (2003) On the thermochemistry of solid solutions between jarosite and its
    chromate analog.  American Mineralogist, 88, 1949-1954.

Negrini R., Rhodes D, Stephenson R., Noriega-Carlos G., Grant L., Baron D, Wigand P, and Rich F.(2007)
    Evidence of a long-lived Pleistocence lake, Carrizo Plain, California.  Annual Meeting of the Geological Society of
    America, Denver, CO, October 28-31, 2007, GSA Abstracts with Programs Vol. 39, No.6.

Negrini R., Baron D., Gillespie J., Horton R., Draucker A.*, Durham N.*, Huff J.*, Philley P.*, Register C.*, Parker J.,

   and Haslebacher T. (2008)  A middle-Pleistocene lacustrine delta in the Kern River depositional system: 

   structural control, regional stratigraphic context, and impact on groundwater quality. 

   Pacific Section of the American Association of Petroleum Geologists Publication MP48, 95-111D.

 

Remus J.J., Harmon R.S., Hark R.R., Potter I.K., Bristol S.K. Baron D., Haverstock G.*, and East L.J. (2012)

   Advanced signal processing analysis of laser-induced breakdown spectroscopy data for the discrimination

   of obsidian sources.  Applied Optics, 51, B1-B9.

Remus J.J., Gottfried J.L., Harmon R.S., Draucker A.*, Baron D. and Yohe R. (2010) Archaeological applications of LIBS:

   An example from the Coso Volcanic Field, CA using advanced statistical signal processing analysis. 

   Applied Optics 49, C120-C131.