United States Environmental Protection Agency Office of Research and Development National Exposure Research Laboratory Research Abstract GPRA Goal 8 - (Sound Science) Significant Research Findings: Perchlorate: Method for Analysis in Plant Tissue and Development of a Kinetic Model for Plant Uptake and Accumulation Perchlorate (C104") is an inorganic contaminant in soils, groundwater, surface waters, and irrigation waters used for growing vegetables. The perchlorate anion will remain in the water for many years. The majority of the winter vegetables consumed in the United States are irrigated with water from the lower Colorado River, which is polluted with perchlorate at 5-9 parts per billion (ppb). The possible presence of perchlorate in vegetables irrigated by the contaminated water and consumed by humans is under investigation. Environmental risks posed by perchlorate are currently being assessed by the United States Environmental Protection Agency, which has placed perchlorate on the Contaminant Candidate List and the Unregulated Contaminant Monitoring Rule. Perchlorate can disrupt thyroid function by interfering with the uptake of iodine. Possible health concerns with developing fetuses and the nervous systems of newborns have been reported. EPA has prepared a draft document, "Perchlorate Environmental Contamination: Toxicological Review and Risk Characterization" that incorporates results from extensive laboratory and field studies performed since 1999 to determine the risk posed to human health and the environment by perchlorate. The objective of this research was to develop a method for the analysis of perchlorate in vegetables and plant tissues and to develop a mathematical model to describe the uptake, translocation, and accumulation of perchlorate in a vascular plant. Since a standardized analytical method existed for the analysis of perchlorate in water by ion chromatography, the initial focus of the research was to develop a method for removal of other matrix ions without loss of perchlorate. A method for the analysis of perchlorate that utilized alumina to greatly reduce the ions in plant and food extracts without loss of perchlorate was developed and applied to the analysis of perchlorate in foodstuffs, and plant products. Since field-grown tobacco is often fertilized with Chilean nitrate fertilizers that are known to Scientific Problem and Policy Issues Research Approach ------- contain perchlorate, the method was applied to the analysis of perchlorate in commercial tobacco products. Confirmation of the presence of perchlorate in the majority of the tobaccos analyzed was followed by greenhouse studies designed to produce data needed for the development of a mathematical model for plant uptake of perchlorate. A few mathematical models have been developed to describe the uptake and translocation of organic chemicals in plants. However, models have not been developed for inorganic anions such as perchlorate. Unlike organic chemicals that have been previously modeled, perchlorate does not appear to degrade in plant tissues and is not expected to be lost to the atmosphere through transpiration. Data from three greenhouse hydroponics growth studies were used to develop a mathematical model that describes the distribution of perchlorate in the vascular tobacco plant. The research products (listed below) were subjected to extensive internal and peer review prior to publication. Results and Mass balance results showed that perchlorate was not degraded and all of Implications the perchlorate was transported from the roots and accumulated in the leaf tissue. The plants were exposed to a wide range of concentrations (10 parts per billion to 100 parts per million) from the hydroponics solution. The data were used to develop a mathematical model that describes the distribution of perchlorate in tobacco plants. The Plant Kinetic (PK) model defined a plant as a set of compartments, described by mass balance differential equations and plant-specific physiological parameters. Data obtained from a separate hydroponics growth study with multiple solution perchlorate concentrations were used to validate the predicted root, stem, and leaf concentrations. There was good agreement between model predictions and measured concentrations in the plant. The distribution of inorganic chemicals such as perchlorate has not been modeled previously. The model should be applicable to other vascular dicot plants including vegetables such as lettuce. The model, once adequately validated, can be applied to other terrestrial plants and inorganic chemicals and will be useful in performing ecological risk assessments. With this information, exposure and risk assessments can be much more certain. The method for analysis of perchlorate in foodstuffs has been adapted by the California Department of Health Services (CDHS) Food and Drug Laboratory and is being used for the analysis of perchlorate in lettuce. The CDHS placed an active link to the method on the CDHS web page. Research This research has been carried out in-house at the Ecosystems Collaboration and Research Division of NERL by Dr. Jackson Ellington, along with a Senior Publications Environmental Employee (SEE) and students. The software development ------- of the plant kinetic model involved colleagues at the University of Georgia. Examples of recent publications from this study include: Ellington, J.J. and Evans, J.J., 2000. Determination of Perchlorate at Parts- per-billion Levels in Plants by Ion Chromatography. J. Chromatogr. A, 898, 193-199. Ellington, J.J., Wolfe, N.L., Garrison, A.G., Evans, J.J., Avants, J.K., and Teng, Q., 2001. Accumulation of Perchlorate in Tobacco Plants and Tobacco Products. Environ. Sci.Technol. 35, 3213-3218. Sundberg, S.E., Ellington, J. J., Evans,J.J., Keys, D.A., and Fisher, J.W., 2003. Accumulation of perchlorate in tobacco plants: development of a plant kinetic model. J. Environ. Monitor. 5, 505-512. Also, Dr. Ellington has given, on invitation, 3 lectures on this topic at national conferences since 1999. In addition, he, or his coworkers, have presented 5 submitted posters during this time. Future Research No further research is planned in this area. Questions and inquiries can be directed to: J. Jackson Ellington, Ph.D. U.S. EPA, Office of Research and Development National Exposure Research Laboratory 960 College Station Rd. Athens, GA 30605 Phone: 706 355 8204 FAX: 706 355 8202 email: ellington.iackson@epa.gov Contacts for Additional Information Funding for this project was through the U.S. EPA's Office of Research and Development, National Exposure Research Laboratory, and the work was conducted by the Ecosystems Research Division. ------- |