Scott Fendorf - US grants

This Collaborative Research Activities in Environmental Molecular Science (CRAEMS) Award to Stanford University is supported by the Special Projects Office in the Chemistry Division. Gordon Brown, Scott Fendorf, and Alfred Spormann supported by this award will study the chemical and microbial interactions at environmental interfaces among solids, aqueous solutions, natural organic and plant matter, microorganisms and atmospheric gases. Support is also provided to Satish Myneni at Princeton University through a subaward. Model systems of increasing complexity will be studied with molecular-level probes to explore (1) geometric and electronic surface structures of environmentally relevant hydrated solids; (2) the structure of water at solid-aqueous interfaces and in the vicinity of nonpolar organic molecules absorbed on solid surfaces; (3) the mode of interaction of metal ion cations and oxoanions with these surfaces and with organic ligands and microbial organisms; (4) the structure and bonding of aqueous and surface complexes of these ions; (5) the rates of abiotic and biotic reaction pathways of redox-sensitive metalloids such as arsenic, selenium and uranium; (6) the hydrophobic interactions of polycyclic aromatic hydrocarbons with environmental solids at the molecular level; (7) the effects of microbial biofilm coatings on solids on the adsorption and transformation reactions of heavy metal and organic pollutants; and, (8) genomic-level interactions of microorganisms with mineral surfaces and organic and inorganic pollutants. Model studies will be coupled with laboratory studies of natural contaminated systems. Advanced spectroscopic methods, particularly those based on tunable synchrotron radiation, computational chemistry and molecular genomic technologies will be utilized.

This fundamental interdisciplinary research will advance our understanding of the role of sorption/precipitation/transformation at environmental interfaces in sequestering heavy metal and organic pollutants and will lead to the development of new remediation methodology. The affiliation with the Stanford Synchrotron Radiation Laboratory will also introduce environmental scientists and students to synchrotron-based studies in environmental chemistry.

0216458
Luthy
This proposal will create a modern analytical facility at Stanford University capable of accurately measuring emerging environmental contaminants at trace levels in aquatic systems. By building on the University's new campus-wide Environmental Initiative, this proposal represents a strategic opportunity to significantly impact environmental research and education at Stanford University among faculty and students in chemistry, biology, geological and environmental sciences, and environmental engineering. The proposed emerging contaminant analytical facility will create interdisciplinary research opportunities and promote the teaching on the fate, transport, and effects of emerging contaminants in aquatic systems.

0751701
Fendorf

This award supports a doctoral dissertation enhancement project between Dr. Scott Fendorf, his student and Dr. Michael Sampson, Director, Resource Development International in Phnom Penh, Cambodia. The project will involve deciphering Arsenic migration pathways within the Mekong Delta in Cambodia. Arsenic, a toxic and carcinogenic metalloid found throughout the earth's crust, is adversely affecting millions of individuals worldwide. Many individuals in Southeast Asia are exposed to drinking water contaminated with arsenic. Despite the widespread poisoning and resulting attention on subsurface arsenic sources, biophysicochemical processes leading to Arsenic groundwater remain unresolved. The researchers propose to define the processes responsible for releasing Arsenic into the aqueous phase within the sedimentary basins of Southeast Asia. The Mekong Delta of Cambodia will serve as a model system for the study. In accomplishing this project they will utilize a suite of field measurements, intact core leaching experiments, and sediment incubations with native microbial communities. Once completed, they will provide a specific illustration of arsenic release and transport within sediments, which will constrain predictions of where Arsenic is a problem contaminant. Such predictions are desperately needed to combat the current health crisis associated with the widespread ingestion of arsenic contaminated waters, especially in the developing nations of Southeast Asia.

The results of this study will provide a mechanistic description of Arsenic release from near-surface tropical sediments, inclusive of relevant biological, chemical, and hydrologic processes. The biochemical conditions with sediments conductive to Arsenic release will be constrained, and this disseminated information will be used to better predict locations which may be at higher risk of elevated Arsenic concentrations within Southeast Asia. The project will train the U.S. graduate student, as well as some young Cambodian scientists, to acquire and analyze field data, adding to the intellectual base now depleted by many years of the civil war. The project will also provide the U.S. graduate student with a global research experience. It is anticipated that the student will maintain scientific connections with his Cambodian collaborators for many years after the project is completed.

The hazards imposed by arsenic on human health are well recognized and nowhere better exemplified than South/Southeast Asia where the consumption of arsenic contaminated ground water has resulted high incidences of skin disorders and various cancers. Arsenic is usually associated with iron oxide and other minerals in sediments. However, in the absence of oxygen, microbes can carry out iron and arsenic reduction reactions that result in arsenic release from sediments and accumulation in ground water. The contribution of iron vs. arsenate reduction to arsenic release, however, is unclear. Furthermore, our understanding of arsenic fate and transport within soils and sediments is limited by poorly understood biological and geochemical processes occurring within complex ground water flow pathways. Therefore, the overarching goal of this research is to determine how microbial metabolism impacts arsenic transport in sediments and soils. Specifically, researchers will investigate the expression of bacterial genes responsible for iron and arsenic reduction and commensurate biogeochemical processes responsible for controlling the partitioning and mobility of arsenic (along with their spatial distribution) within model systems that simulate the physical complexity of natural soils and sediments. The proposed research integrates biogeochemical and molecular genetic approaches aimed at developing a mechanistic understanding of the impacts of microbes on arsenic contamination of ground water. Because the nature of the arsenic problem is rooted in geomicrobiology, the intellectual merit of the proposed research is the generation of crucial information important to understanding the mechanism(s) leading to arsenic release or retention in sediments. The results will lead to a detailed conceptual model of how genetics and geochemical processes impact microbe-mineral interactions and arsenic fate. The broader impacts of the research will be to integrate research with teaching activities and community outreach by participating in a laboratory research mentorship program (called ACCESS) for community college students of under represented groups and a high school science summer program called COSMOS. Lastly, the collaboration will enhance and promote diversity through intercampus mentorship of minority graduate students at both Stanford and UCSC.

An estimated 100 million people living in floodplains in Asia are exposed to arsenic in groundwater that is derived from Himalayan sediments. Arsenic is a toxin linked to cancer and a variety of other serious ailments through direct ingestion of contaminated groundwater. Growing exploitation of these contaminated aquifers increases the number of people facing these health risks, and exposes still greater populations to the hazard of consuming agricultural products irrigated with arsenic-contaminated groundwater. Despite widespread awareness of the arsenic hazard, understanding of the relationship between groundwater exploitation and arsenic contamination remains limited, particularly in deep aquifers, which are increasingly providing a larger portion of total pumped groundwater.

In this work, we focus on the Mekong Delta, where we have obtained a comprehensive, unique, unanalyzed dataset consisting of >42,000 dissolved arsenic measurements from southern Vietnam showing widespread contamination (>1000 sq km) in deep aquifers (>200m) that are used extensively for water supply. One hypothesis is that deep pumping has induced shallow dissolved arsenic or arsenic-mobilizing solutes to move deeper. However, preliminary analysis does not support this mechanism in the Mekong Delta given the observed widespread deep arsenic contamination in the presence of thick clay deposits that serve as relative vertical flow barriers. We hypothesize a previously unrecognized deep arsenic source mechanism in which water containing arsenic is expelled from storage in clays that compact when overlying and underlying deep aquifers are exploited. This work combines spatial statistical modeling of groundwater arsenic observations, 3D aquifer flow and compaction simulation, and remote measurement of land subsidence using satellite radar imagery (InSAR). Our goal is to explore the notion that deep groundwater arsenic may be due to the release of pore-waters containing arsenic trapped in clay beds deposited millions of years ago.

This research has important implications to science and society. First, our formerly unrecognized contamination mechanism may be fundamental to understanding arsenic occurrence in aquifer systems and the associated health risks of deep groundwater exploitation. Our investigation will have implications for water resources development and human health in the arsenic-affected basins of Southeast Asia where some regions of planned deep aquifer exploitation may unknowingly expose people to deep-source arsenic. This work has consequences for analogous arsenic-affected aquifer systems in sedimentary basins around the world containing interbedded compressible clays that may harbor arsenic and other contaminants. Second, in terms of methods, the link between subsidence and arsenic release has significant potential as a reconnaissance tool, particularly in underdeveloped regions where the impacts of excessive pumping on land subsidence have not been recognized. The use of satellite radar to detect land deformation can serve as a means to identify areas where clay compaction and consequent arsenic release may be occurring.