Due to recent findings that suggest childhood leukemia may be linked to exposure to tungsten (W) in drinking water or atmosphere particles, a need has arisen to better understand biogeochemical reactions affecting W concentrations and speciation in groundwater flow systems. Previous data along two different groundwater flow paths show a correlation between increasing sulfide concentrations and elevated W concentrations. One hypothesis is that the complexation of W with sulfides creates thiotungstates which are more mobile in the environment. To determine thiotungstate stability constants, a sulfidic solution is first made under the fume hood by bubbling water with nitrogen to make it anoxic, then with hydrogen sulfide, to make it sulfidic. Because the sulfide can oxidize if exposed to our atmosphere, the solution must be kept anoxic while running the experiments. The glove box has an anoxic atmosphere composed solely of nitrogen. When tungstate is added to the sulfide solution, a chemical reaction takes place forming a variety of thiotungstate species. My research seeks to find the stability constants for the four thiotungstate species- WO3S, WO2S2, WOS3, and WS4 which will be used in conjunction with field data to create a biogeochemical model of W along groundwater flow paths.
My goal is to learn about geochemistry, especially as it pertains to water quality. Having joined Dr. Karen Johannesson’s lab Spring 2009, I have had the opportunity to travel to India, visit a local estuary, and learn a variety of laboratory methods. At the end of my first semester, I accompanied my advisor to India to collect water samples from high arsenic groundwater wells. While letting the water pass through our speciation columns- a process which separates As(III) from As(V), a local showed us some kind of water that turned black when fresh, crushed guava leaves were added. This phenomenon piqued my interest. After returning from India, I spent the rest of my first summer analyzing Indian well waters, and doing some side experiments with guava leaves. Alas, the ability to reproduce the dark water I observed in India eluded my laboratory skills, but valuable data was gathered pertaining to As in the Murshidabad region. The following spring led to a field trip to a local urban estuary where I collected surface water samples. I analyzed these water samples for both rare earth elements and metals, but the ultimate goal of determining how trace elements partition with different sizes of dissolved organic carbon (DOC) was hindered by a refrigerator malfunction which destroyed the bulk of the DOC samples. My current project will include collecting and analyzing field samples, but the bulk of the work involves laboratory experiments. I am grateful to have had this journey through water geochemistry research before arriving at my current project. It has given me a variety of skills, and given me a glimpse of the breadth of this field.
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