2. Unraveling Complex Organic Mixtures in the Environment: Applications in Fossil Fuel Geochemistry, Surface and Ground Water Contamination, Ecosystems, and Human Health

Natural and man-made organic substances present in the environment commonly occur as complex mixtures. These complex mixtures provide an analytical challenge to geochemists. Many compounds can be identified using conventional extraction/chromatographic/mass spectrometric analysis procedures, however, far more remain unidentified. The unresolved portions of these organic mixtures contain information crucial to the successful characterization of processes affecting organic matter transformations and environmental impacts. Information regarding these transformations is needed to improve our understanding of carbon cycling, energy resource generation and quality, and the effects of natural and man-made substances on ecosystem and human health.

The challenge associated with analyzing complex hydrocarbon mixtures is readily observed as the broad "humps" of unseparated, unidentified organic compounds present in gas chromatograms. For example, chromatograms of degraded and weathered oil samples from natural seeps commonly contain these humps as the most abundant feature, meaning that the majority of the compounds comprising the sample are unresolved. This challenge, however, is not solely restricted to analyses of natural samples. Many industrial organic chemicals are synthesized as mixtures of isomeric and homologous compounds that are not easily separated and identified. Some examples of these man-made congeneric mixtures include polychlorinated biphenyls (PCBs) and surfactants such as the alkylphenol polyethoxylates.

The chemical structure of an organic compound is often crucial in determining its mutagenicity or cancer promoting activity. Thus, identifications beyond lumping into a general compound class is important. For example, groundwater flowing through shallow lignite coals dissolves hydrocarbons that may cause human health problems such as Balkan Endemic Nephropathy (BEN) and renal pelvic cancer, when such waters are used for drinking water supply. Identifying the individual compounds in these groundwaters is crucial in etiological studies linking organic contaminants to BEN and other diseases.

In all these examples the key to evaluating the impact of these materials on human or ecosystem health is identifying and quantifying the specific toxic components of these mixtures. It is well known that the toxicity of compounds with similar structures can vary widely with rather minor changes in structure. Therefore, meaningful assessment of the impact of these organic mixtures on the environment requires the separation and identification of the individual compounds within these materials. Newly available analytical instrumentation, such as comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC x GC-ToFMS), provides us with the capability to separate and identify the individual components in complex mixtures of organic compounds. The ability to resolve these mixtures will assist in fingerprinting and matching highly degraded hydrocarbon residues collected at the surface with possible sources; providing insight into the reaction mechanisms by which hydrocarbons are generated from kerogen; and in resolution of complex mixtures of emerging environmental contaminants, such as endocrine disruptors and their metabolites, for which compound-specific information is lacking.

Proposals are sought from organic geochemists, environmental chemists, or analytical chemists for a postdoctoral research position that uses state of the art analytical approaches, including GC x GC-ToFMS toward a wide range of energy and water resource problems, environmental and ecosystem issues, and geochemistry related to human health issues. The postdoc will work with USGS scientists and collaborators in organic- and biogeochemistry, geology, and microbiology to examine complex mixtures of organic substances in environmental samples. The successful candidate will also have an opportunity to take part in one or more USGS field studies. Research would be conducted in conjunction with the following ongoing or planned USGS studies:

1. Toxic organic compounds derived from coal in natural waters and human disease (William Orem)
2. Organic contaminants in coastal sediments and natural waters (William Orem)
3. Transport and fate of endocrine-disrupting surfactant chemicals in aquatic ecosystems (Robert Eganhouse).
4. Transformation of crude oil during weathering, the persistent components (Robert Eganhouse).
5. Mobilization of organic compounds during sequestration of carbon dioxide in coal deposits (Robert Burruss)
6. Organic geochemistry of petroleum hydrocarbons, north slope, Alaska (Robert Burruss)

The USGS maintains extensive organic geochemistry laboratory facilities in Reston, VA. These facilities include organic wet labs with hoods, Soxhlet and microwave extraction capabilities, and liquid chromatography separation equipment. Instrumentation available includes gas chromatography, gas chromatography/mass spectrometry, liquid chromatography/diode array UV-Vis/mass spectrometry, C,H,N,O,S analyzer, ion chromatography, and other support equipment. The USGS is acquiring a GC x GC-ToFMS to enhance capabilities in the study of complex mixtures of organic compounds. Additional facilities include a microbiology/toxicology laboratory for studying the effects of organic substances on cell cultures, a variety of stable isotope ratio mass spectrometers, and compound specific isotope ratio mass spectrometry.

Proposed Duty Station: Reston, VA

Areas of Ph.D.: Bio/Organic Geochemistry, Environmental Chemistry, Analytical Chemistry

Qualifications: Applicants must meet one of the following qualifications: Research Geologist

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Personnel specialist.)

Research Advisor(s): Robert Burruss, (703) 648-6144, burruss@usgs.gov; William Orem, (703) 648-6273, borem@usgs.gov; Robert Eganhouse, (703) 648-5879, eganhouse@usgs.gov

Personnel Office contact: Rosetta Alexander, (703) 648-7468, ralexand@usgs.gov

Summary of Opportunities