RESEARCH INTERESTS

Work in my group involves lab and field experiments on natural soils, estuarine sediments and constituent phases in aqueous systems in order to better understand their role in controlling biogeochemical cycles and environmental quality. Primary focus areas presently include (i) organic chemistry of soils and sediments, (ii) macromolecule-surface interactions in bacterial adhesion, (iii) reactivity of radioisotopes (137Cs and 90Sr) in the vadose zone, and (iv) soil weathering (age and climate) sequences in Hawaii.

Professional Experience:

07/05-present: Professor of Environmental Chemistry, Department of Soil,
Water and Environmental Science, University of Arizona.
9/01-6/05: Associate Professor of Environmental Chemistry, Department of Soil,
Water and Environmental Science, University of Arizona.
5/01-9/01: Associate Professor of Environmental Soil Chemistry, Department of
Agronomy, Pennsylvania State University, University Park, PA
1/95-5/01: Assistant Professor of Environmental Soil Chemistry, Department of
Agronomy, Pennsylvania State University, University Park, PA.
12/93-12/94: NSF Postdoctoral Research Fellow, Department of Chemistry, University of
Geneva, Switzerland

Courses Taught:

I have taught classes in Environmental Soil Chemistry, Soil Physical Chemistry, and Biogeochemistry.

Research Interests:

Work in my group involves lab and field experiments on natural soils, estuarine sediments and constituent phases in aqueous systems in order to better understand their role in controlling biogeochemical cycles and environmental quality. Primary focus areas presently include (i) organic chemistry of soils and sediments, (ii) macromolecule-surface interactions in bacterial adhesion, (iii) reactivity of radioisotopes (137Cs and 90Sr) in the vadose zone, and (iv) soil weathering (age and climate) sequences in Hawaii.

(I) Environmental Organic Chemistry of Soils and Sediments. The aim of this work is to better understand reactions that occur between mineral particles, natural organic matter (NOM) and xenobiotic compounds in soils and estuarine sediments. Adsorption and transformation of NOM at mineral surfaces is an essential part of the global C cycle. It also strongly affects the bioavailability of NOM and "surface active" environmental contaminants. We have been studying NOM fractions in soils and estuaries to (1) assess fractionation and transformation of NOM that occurs when it reacts with major mineral phases, (2) determine how NOM coatings on mineral surfaces affect the sorption/desorption of organic pollutants, and (3) examine how contaminant sorption to dissolved and mineral-bound NOM affects its bioavailability to microorganisms. Mechanisms of interaction between organic contaminants and both dissolved and mineral bound humic substances are being studied by nuclear magnetic resonance (NMR) and fluorescence spectroscopy.

(II) Macromolecule-Surface Interactions in Bacterial Adhesion. A macroscopic-level examination of bacterial adhesion in aquatic systems has so far been insufficient to understand the factors that control the initial events in microbial attachment to environmental surfaces. A central reason is the lack of a molecular-level understanding of the chemical and physical interactions of colloidal-sized bacteria with surfaces. In natural systems, bacterial adhesion is controlled by the interaction of cell-surface biopolymers (exopolymers, including EPS), natural organic matter and mineral surfaces. We are working with researchers at Penn State and Yale University on a collaborative project (funded by NSF, Collaborative Research Activities in Environmental Molecular Sciences, CRAEMS) that involves the use of molecular-level surface chemistry techniques (e.g., atomic force microscopy, attenuated total reflectance FTIR spectroscopy) and molecular modeling to observe directly the behavior of bacterial polymers and their interactions with mineral surfaces in the presence of dissolved and solid-phase NOM.

(III) Interfacial Chemistry of Radionuclides in the Vadose Zone. Mobility of radionuclides (137Cs and 90Sr) in the vadose zone is controlled by sorptive interactions and co-precipitation with natural soil particles. This project addresses the problem of leaking waste storage tanks at the Hanford (WA) and Savannah River (GA) Department of Energy (DOE) facilities. Our results indicate that the intense geochemical conditions of DOE waste streams leads to weathering of silicates, intercalation of clay minerals with SRO hydroxy -aluminum and -aluminosilicate species, and formation of secondary precipitates such as zeolites and allophanes. These transformation reactions alter particle surface chemistry and retention of radionuclides. In this study, we are focusing on the sorption of radioactive Cs+ and Sr2+ onto altered clay surfaces and into secondary precipitates in the presence of high levels of competing cations Na+ and Ca2+ at alkaline pH. The conditions are intended to mimic those of the contaminated sites at Hanford and Savannah River. Detailed information on the molecular environment of sorbed Cs and Sr is being obtained using NMR and X-ray absorption spectroscopies.

(IV) Biogeochemical Gradient Studies. In collaboration with scientists at UC Santa Barbara and Stanford University, we are studying how soil chemical processes change along gradients in substrate age (300 to 4,100,000 years) and climate (0.1 to 4 m rainfall) in well constrained chrono- and climate sequences in Hawaii. The focus of my group is on surface chemistry and dissolution behavior of the soils. More recently, we have begun investigating redox biogeochemistry of the soils in well-controlled laboratory experiments.

Publications:

Journal Publications and Book Chapters are located in Chorover Environmental Chemistry Lab Website