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Genotypic Variability and the Factors Controlling the Uptake and Metabolism of Perchlorate at Low Part-Per-Billion Levels Using IC-ESI-MS

EPA Grant Number: F5B20239
Title: Genotypic Variability and the Factors Controlling the Uptake and Metabolism of Perchlorate at Low Part-Per-Billion Levels Using IC-ESI-MS
Investigators: Seyfferth, Angelia L.
Institution: University of California - Riverside
EPA Project Officer: Thompson, Delores
Project Period: September 1, 2005 through June 1, 2008
Project Amount: $97,244
RFA: STAR Graduate Fellowships (2005)
Research Category: Academic Fellowships

Description:

Objective:

Objective: The primary goal of this research is to assess the extent of perchlorate uptake by different genotypes of winter lettuce that are grown in California’s Imperial Valley and are irrigated exclusively with water from the Colorado River. The Colorado River contains between 4 and 10 μg/L perchlorate and is the main source of irrigation water for vast acreages in southeastern California. The role of transpiration rate, salinity, and metabolism of perchlorate within plant tissues on the extent of plant uptake will also be evaluated.

Approach:

Uptake experiments will be conducted using Conviron controlled-environment chambers within which factors such as light intensity, temperature, and relative humidity can be closely monitored and controlled. Plants will be grown hydroponically in 3-Liter HDPE buckets of complete, aerated nutrient solutions into which prescribed levels of perchlorate will be added. Nutrient solutions will be changed every 3 – 7 days during the course of each 60-day experiment.

After harvesting, perchlorate will be extracted from edible tissues and prepared for analysis using IC-ESI-MS.

In the first set of experiments, several varieties of lettuce will be grown including Romaine, Butterleaf, Greenleaf, Iceberg, and Redleaf, in order to determine genotypic variability of plant uptake. These first experiments will aim to identify those genotypes that accumulate perchlorate to greater tissue concentrations, and these will be used in subsequent experiments involving the competitive role of salinity as well as in the perchlorate reduction experiments. These experiments will also assess the role of transpiration rate on perchlorate uptake.

In order to assess the extent of perchlorate metabolism in plant tissues, the use of radiolabeled perchlorate is necessary. Because the nutrient solution that will be used contains chloride, it will be impossible to distinguish between such chloride and the chloride present due to reduction/metabolism of perchlorate. By radiolabeling perchlorate in this study, any chloride due to reduction will be isotopically different from the chloride naturally present within the plant. This labeled chloride will be counted by liquid scintillation and will be used as a mass-balancing tool for perchlorate in the experiments.

Expected Results:

My research will improve the scientific understanding of the factors and mechanisms controlling perchlorate uptake by vegetable crops. From my work, regulators will have a better understanding of the risk associated with perchlorate consumption from food. It is my hope that this work will fuel more research on low-level perchlorate uptake by other food crops such as spinach, broccoli, cauliflower, tomato and melon. This research will also serve to assess the extent of perchlorate reduction within plant tissues in order to determine the potential food exposure to all oxyanions of chloride.

Supplemental Keywords:

Perchlorate; oxyhalides; plant uptake; lettuce; ESI-MS; agriculture; human health, , HUMAN HEALTH, Scientific Discipline, Health, Risk Assessments, Health Risk Assessment, Environmental Chemistry, Exposure, Environmental Monitoring, bioavailability, mass spectrometry, analysis of chemical exposure, human health risk, dietary exposure, chemical exposure, genotypic variability in lettuce, perchlorates

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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