10. Coupling geochemical and geoanalytical techniques to study processes affecting exposure to potentially toxic species that negatively impact human health

The impact of exposure to environmental contaminants on human health is becoming an increasingly important topic of study. A variety of human health problems are related to exposures to airborne particulates, dust, and soils. Soils have been recognized for their potential to affect human health and where contaminated by human activities, they can cause acute and chronic toxicity through a variety of exposure pathways, including dermal absorption, inhalation, and ingestion. Although much research has been done in the areas of occupational exposure to toxic elements, research into potential sources of exposures to toxic elements from naturally occurring processes is an emerging field of study. As numerous toxicology studies have shown, knowing the total concentration of an element is not enough to be able to determine how an element may affect human health. Knowledge of the chemical form or species present (e.g. Cr⁺³ vs. Cr⁺⁶ or As⁺³ vs As+5 or Methyl-Hg versus Hg⁰) is critical to understanding and estimating the potential bioavailability and ultimate toxicity of an element. As the USGS works to better understand our environment through regional geochemistry studies, information on the species present or liberated by natural processes will have more impact in our endeavor to understand the impact of geochemical processes on human health. Although work has been done on the impact of toxic species in waters, determining the potential impact in solid samples, such as airborne particulates, sediments, dusts and soils brings with it new challenges. These include determining the optimal sample collection, storage, and extraction processes, which may impact chemical speciation, to what methods are best suited to determine species concentrations for particular extraction or processing conditions.

The USGS is seeking to better understand the interaction between soil geochemistry and human health. Projects such as the Geochemical Landscapes Project (http://minerals.cr.usgs.gov/projects/geochemical_landscapes/index.html) and other regional geochemistry studies will allow the USGS to map total element concentrations across the United States and North America. Knowledge of where the potential for human exposure to toxic elements might occur from total element concentrations will be useful in studying the potential impact of environmental concentrations on disease and human health. However, to fully understand the impact on human health speciation information is also needed, as some elements are toxic in a particular chemical form or oxidation state (e.g Cr⁺³ is an essential element, Cr⁺⁶ is carcinogenic). The study of solid materials such as soils, sediments, dusts and airborne particulates for species information can generally not be done directly on the solid material at the detection levels necessary. Some form of processing, such as leaching, is generally required. This opens the door on a whole new area of research in terms of determining what conditions are best suited to study the speciation in solid geochemical samples. Some elements of particular interest for solid sample speciation studies include arsenic, selenium, tungsten, uranium and mercury. We are particularly interested in addressing the following questions:

• How do the species interact in solid samples under environmental weathering conditions?
• Do the species interconvert? Is there a way to compensate or correct for this?
• What types of sample preparation procedures are appropriate for studying species of interest in solid samples? Examples include simulated rain water leaches, buffered rain water leaches, simulated bio-fluid leaches, and extractions to obtain total available concentrations.
• How do concomitant elements and species affect the species of interest?
• Do the leaching characteristics of the soils change when they are leached wet vs. dry?
• How do sample collection and storage procedures affect the species that may pose a threat to human and ecological health?
• How stable are the various types of leachates used to storage time and conditions?

The USGS currently has the necessary state-of-the-art analytical instrumentation and expertise in place and methods either developed or under development to provide the analytical support necessary to carry out a wide variety of geochemical studies that will answer the questions outlined above. The USGS is also involved in collaborations with organizations such as CDC and Duquesne University that have additional expertise in the areas of toxicity, elemental speciation, and advanced sample preparation methodologies.

Proposed Duty Station: Denver, CO

Areas of Ph.D.: Geology, geochemistry, analytical chemistry, hydrology, environmental science

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

(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 Human Resources specialist.)

Research Advisor(s): Ruth Wolf, (303) 236-2470, rwolf@usgs.gov; Geoffrey Plumlee, (303) 236-1204, gplumlee@usgs.gov; Martin Goldhaber, (303) 236-1521, mgold@usgs.gov; Paul Lamothe, (303) 236-1923, plamothe@usgs.gov; David Smith, (303) 236-1489, dsmith@usgs.gov; H. M. Kingston (Duquesne University), (412) 396-5564, Kingston@duq.edu

Human Resources Office contact: Kathleen Scheich, (303) 236-9581, kscheich@usgs.gov

Summary of Opportunities