Arsenic Contamination in Groundwater
Arsenic contaminated groundwater, used for both drinking and irrigation purposes, is a growing global concern. World wide, ingestion of arsenic negatively impacts the health of millions of people.
In Bangladesh, arsenic contaminated groundwater has been referred to as the largest poisoning of a population in history1. Past work done by Dr. Neumann and her colleagues suggests that current patterns of arsenic concentration in the aquifer are related to groundwater flow and recharge chemistry. Constructed ponds and groundwater irrigated rice fields serve as the primary aquifer recharge sources, with pond recharge evolving into high-arsenic groundwater and rice field recharge evolving into low-arsenic groundwater. Recharge is largely controlled by the practice of groundwater irrigation, which removes water from the aquifer, creating a downward gradient that drives surface water into the subsurface. These dynamics suggest that rice field water management schemes that reduce irrigation water demand will necessarily change arsenic concentration patterns in the aquifer by reducing the total amount of surface recharge pulled into the aquifer and by altering the proportions of rice field and pond recharge. Our project in Bangladesh is field testing the water savings potential of specific field management schemes, modeling the subsequent effects of this scheme on groundwater arsenic concentrations, and experimentally probing the chemical changes that occur when different proportions or recharge enter the aquifer.
Groundwater contamination is a known threat to drinking and irrigation water throughout the world, but few investigations have considered future contamination of currently clean sources. The goal of our project in Cambodia is to determine the vulnerability of arsenic-free groundwater to future arsenic contamination. Research is focused at a field site situated in a transition zone with high “upstream” arsenic concentrations and zero or low concentrations “downstream.” Arsenic contamination may be geogenic (created at the point of measurement), allogenic (transported to the point), or a combination of the two. Investigation of the site is important given Cambodia’s continued economic development, which may change domestic and agricultural groundwater demands and alter recharge rates and chemistry. In our work, we will identify the processes that may stimulate future arsenic contamination and the time scales on which these processes may occur. Our findings will advance basic understanding of groundwater arsenic contamination, and will provide concrete, useful information about the sustainability of currently ‘safe’ wells – information that policy makers, development organizations, and individuals can use both locally to aid in decisions about specific water use options, and broadly to inform larger policy initiatives.
1Smith, A., Lingas, E., & Rahman, M. (2000). Contamination of drinking-water by arsenic in Bangladesh: a public health emergency. Bulletin Of The World Health Organization, 78(9), 1093–1103.
Nutritional Quality of Rice Grain
A major lab-based project in the Neumann lab focuses on visualizing the oxygenation zone of growing rice roots and understanding the sensitivity of this zone to external variables. Diffusion of oxygen from the root tissues of plants in otherwise anoxic soil plays an important role in the chemistry of the soil around rice roots, particularly the oxidation of iron(II), which in turn can impact availability and root uptake of toxins (e.g., arsenic) and micronutrients (e.g., zinc). We are probing rhizosphere oxygen dynamics using planar optical oxygen sensors ("optodes," Larsen et al, 2011), which allow for real-time two-dimensional visualization of concentrations. We use optode oxygen profiles to direct sampling of porewater and soil from mm-scale oxic and anoxic soil zones for key solutes and parameters that help us assess the impact that oxygenation dynamics have on the availability of toxins and micronutrients in the soil zone around rice roots.