Wednesday, November 7, 2007 - 10:15 AM
326-4

Effects of a Common Gastric Bacterium on Soil Arsenic Bioaccessibility and Speciation in the Human Stomach.

Shahida Quazi, Konstantinos C. Makris, Dibyendu Sarkar, Rupali Datta, and Mandakini Patel. Earth and Environmental Science, University of Texas at San Antonio, San Antonio, TX 78249

Soil ingestion by children playing in residential yards and playgrounds is the number one pathway of human exposure to arsenic (As)-contaminated soils. Earlier studies have used soil and solution properties to explain soil As bioaccessibility dynamics in the human stomach, but most studies have overlooked the potential role of gastric microbiota. Despite the high acidity and low redox potential, the gastric solution harbors complex microbial communities comprised of a plethora of bacterial species. Microbially-driven soil-As redox transformations have been well documented in the environment, but not in the human stomach. Dissimilatory iron-reducing bacteria could mediate As release from soil particles, but this is yet to be documented under the anaerobic human stomach conditions. Lactobacillus acidophilus dominates the bacterial composition of the human stomach, and it is typically measured in large numbers (4-8 log CFU mL-1). We hypothesized that stomach bacteria mediate transformations of soil As particles in the gastric solution (such as, As(V) reduction to the As(III)), thereby affecting As fate (hence, toxicity) and stability. This study aimed at evaluating the effect of Lactobacillus species on As speciation and in-vitro bioaccessibility in simulated conditions of human stomach. Stomach conditions were simulated at 37° C and an atmosphere of 5 % CO2, 10 % H2, and 85 % N2 inside an anaerobic chamber. Test samples included crystalline and amorphous As mineral phases (arsenopyrite, scorodite, orpiment) as well as aged As-contaminated soils. Results were evaluated for changes in soil As bioaccessibility and oxidation state in the gastric phase.

Keywords: In-vitro, Bioaccessibility, Arsenic, Lactobacillus sp


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