Uptake of Arsenic by Plants
Mentor: Marianna A. Kissell, graduate student: Dept. of Geosciences and CEMS, Stony Brook University
Some plants have the capacity to take up extraordinary amounts of a particular pollutant, toxin, or contaminant seemingly without any ill effect. The ability of plants to remove such substances from the environment in such vast amounts categorizes the plants as hyperaccumulators. As such, these plants are ideal candidates for use in environmentally friendly remediation strategies. However, a thorough understanding of the uptake mechanism of the plant for the substance, as well as its distribution and sequestration in the plant, is vital for understanding and predicting the possibility for success of these types of remediation efforts.
Arsenic is a known carcinogen with widespread geographic distribution and is found in soil, vegetation, water and air. The dominant forms of arsenic seen in the environment are arsenate, As (V), and arsenite, As (III).
Marianna uses X-ray Absorption Spectroscopy (XAS) to study arsenic cycling/sequestration and the kinetics of As redox reactions in an arsenic hyperaccumulating fern, Pteris cretica. Results suggest that arsenic, introduced into the roots as As (V), is reduced and sequestered in the leaves as an aqueous As (III) species, and is actively maintained in the reduced state in live plant tissue. When the leaves die, the As (III) is reoxidized back to an As (V) species.
Part of her ongoing research is to elucidate arsenic complexation in plants, in order to better understand the availability and mobility of arsenic in P. cretica. By virtue of its similar chemical and structural make up, As (V) is considered to be an analog for phosphate, an essential plant nutrient. Most workers agree that arsenate is taken up and transported by the phosphate uptake mechanism. Arsenite, however, does not appear to be associated thus far with any macro- or micro-nutrient in plants and so mechanisms of uptake and translocation are also undefined.
This CEMS Outreach Project will examine the cycling of several plant micro-nutrients (Fe, Ni, Zn, Cu) and attempt to identify the influence of arsenic on these nutrients. We anticipate that this project will put forward possible arsenite associations in plants, and therefore provide suggestions as to a likely arsenite analog and/or transport mechanism.
In order to accomplish our goal, some of the possible methods under consideration include the use of XAS to look at redox chemistry and the Direct Current Plasma (DCP) apparatus to examine total elemental concentrations.
Preparation of NH4 zeolites as starting materials for uranyl-exchange
Mentors: Dr. Ivor Bull, Postdoctoral Research Associate, and Aaron Celestian, graduate student: Dept. of Geosciences and CEMS, Stony Brook University
Due to their ability to ion-exchange zeolites are prime candidates for nuclear waste remediation. This application is highlighted by the proposed use of clinoptilolite as a radioactive waste repository at Yucca Mountain. Clinoptilolite is one of several zeolites reported to uptake uranium. Others include zeolite X, Y and L. Microcrystal X-ray diffraction will be utilized to structurally characterize uranium exchanged zeolites to confirm the presence of uranium within the zeolite channels and provide a greater understanding of influences on ion-exchange. In addition a more general study of the ion exchange of zeolites will be carried out using a combination of in-situ powder diffraction and ex-situ single crystal diffraction to observe structural responses towards a greater understanding of this phenomenon. Previous experiments have led to a refinement in the chemical conditions and zeolites which will be used to obtain a successful ion-exchange.
This CEMS Outreach Project will examine NH4-zeolites as the starting materials for uranyl-exchange. The ammonium should provide some self-buffering of pH during uranyl exchange which will prevent framework degradation and maintain a pH where ion-exchange is expected to occur.
NH4 exchange will be carried out on various natural zeolite samples such as calcium containing clinoptilolite. The zeolite is exchanged in a 1M solution of NH4Cl with stirring for 24 hours. This process may need to be repeated several times to get a full exchange. After each ion-exchange, an EDTA titration will provide information concerning the amount of calcium in solution and hence the degree of NH4 exchange which has occurred. This is essential in determining the starting chemical composition of the zeolite to ultimately allow an accurate analysis of uranyl-exchange.
Mercury Deposition around Coal-Fired Electric Power plants
Mentor: Biays Bowerman, Scientist, Environmental Research & Technology Division, Brookhaven National Laboratory
The deposition of mercury from coal-fired power plants proceeds under both dry and wet conditions, depending on weather. EPA models predict that wet deposition will occur within a limited range as rain wash-out, and that for the right meteorological condition, a "footprint" can be identified. From this footprint, health impacts can be predicted. This project consists of testing soil samples collected around a coal-fired power plant, and comparing measured concentrations with values calculated based on EPA models.
A Direct Mercury Analyzer (Milestone, DMA80) is capable of measuring mercury levels in soil to levels as low as 1 ppb. The DMA80 essentially automates an EPA procedure for determining total mercury in soil. The instrument drives mercury from the sample at high temperatures, traps it on a gold foil, then heats the foil to divert the mercury through an atomic absortion spectrometer. Additional experiments to measure As, Cd, and Pb are planned. These will be carried out with a PDV6000, which allows the investigator to conduct anodic stripping voltammetry for elemental identification. The soils will be leached with an acid solution, and then the solution is then tested.