Arsenic speciation analysis in environmental and food samples and investigation of sulfide in groundwater

This work consists of three parts: (1) analytical methods development for arsenic speciation in natural water samples, (2) speciation analysis and investigation of bioaccessibility of arsenic in food, specifically in rice samples, and (3) determination of trace level sulfide, a crucial compound participating in metal mobility in the environment, and investigating its interaction with Fe(II) in natural water systems.; Two arsenic speciation methods based on cathodic stripping voltammetry (CSV) were developed for arsenic speciation in water samples. These methods are simple, fast, sensitive, inexpensive and applicable both in the laboratory and in the field. The first method employs a hanging mercury drop electrode (HMDE), on which As(III) is deposited in the presence of Cu and Se in HCl medium. As(III) is determined by direct measurement. Determination of total As was performed by reducing As(V) to As(III) using sodium meta-bisulfite/sodium thiosulfate reagent stabilized with ascorbic acid. As(V) is quantified by difference. The second method further improved the reducing efficiency by using L-Cysteine as reducing reagent and had the capability to differentiate organic arsenic and inorganic arsenic through Na2S2O 8-assisted UV photooxidation. Concentration of organic arsenic is the difference between total inorganic and total arsenic concentration.; The risk of exposure to arsenic from ingestion of cooked rice was evaluated. Total arsenic of a dozen commercial rice samples was determined by high resolution inductively coupled plasma-mass spectrometry (HR-ICP/MS). The bioaccessibility of arsenic was evaluated by in vitro gastric and small intestinal fluid sequential incubation. The effect of arsenic in cooking water was also investigated. Speciation of As using ion chromatography (IC) coupled with ICP/MS showed inorganic arsenic to be the major arsenic species in rice.; A simple approach for determining trace level sulfide was developed using differential pulse CSV (DPCSV). The method was applied on-site to analyze Fe-rich reducing ground water samples collected at landfill sites in Winthrop, Maine, and Vineland, New Jersey. Additionally, based on this method, interactions between Fe(II) and sulfide were studied in both environmental and laboratory solutions and three situations were established according to different Fe(II) concentrations.