Influence of tritium exposure route on vegetation types at the Savannah River Site.

Plant, soil, water, and other media from various locations at the Savannah River Site were measured for total tritium (T) content and T speciation to characterize T in these areas, as well as investigate its uptake behavior and the transport of T species in these media. This characterization included the isolation and measurement of T in tritiated water (HTO), and (when possible) exchangeable organic bound T (E-OBT) and non-exchangeable organic bound T (NE-OBT). Two areas of interest were investigated: (1) a holding pond with T-contaminated water and (2) open basins or streams with low to background levels of T. Water in the holding pond is used to irrigate forest plots in the local area as a T remediation approach. This study compares the analytical data for water, soil/sediment, plants, and lichens from these locations. The results indicate that the behavior of T in plants from these areas can be a function of one or more of the following: seasonal precipitation, the plant's primary route of access to the T-contamination (such as water uptake through the root vs. shoot), plant physical location (relative to T-contaminated water sources), plant rooting depth, pond water level, and plant height above the ground. Total T concentrations were lowest in the un-irrigated forest plants, followed by irrigated forest plants, shallow rooting plants near the pond, deep rooting plants further from the pond, and then water-saturated plants. The OBT:HTO and NE-OBT:E-OBT ratios were always greater for plants from irrigated forest plots compared to those from the holding pond.

Influence of irrigation approaches and spatial geolocation on tritium speciation, uptake and depuration.

Pine needles and tree cores from a tritium (T) contaminated phytoremediation forest at the Savannah River Site (SRS in Aiken, SC) Mixed Waste Management Facility (MWMF) were measured for total T and T speciation and compared to other locations at the SRS and the surrounding area. Tree core ages ranged from 9 to 14 years old, covering over half of the ∼20-year on-going remediation efforts, while pine needles represent more recent time periods of 1-to-2-year increments. Remedial irrigation efforts at the MWMF are found to directly influence the pine needle T concentrations. The T content in the MWMF samples is higher than non-irrigated needle samples from other locations around the SRS. Further, the different forms of organic bound T are preferentially stored in tree core tissue, compared to pine needles where tritiated water dominates.

Historical record of tritium from tree cores at the Savannah River Site.

Tree cores from various locations at the Savannah River Site (SRS) and local area were measured for total tritium (T) content and T speciation to include tritiated water (HTO), exchangeable organic bound T (E-OBT) and non-exchangeable organic bound T (NE-OBT) species. The tree cores dated back to the 1960's or prior which provided an opportunity to measure T over the last 60-70 years. The total T levels from pine and oak tree cores were consistent with the record of known T atmospheric releases from nuclear activities at the SRS between the mid-1950's and 1990's with a notable peak in T tree core levels during the late 1960's. The T speciation data for some tree core samples from SRS demonstrated elevated levels of OBT : HTO and NE-OBT : E-OBT identified primarily in the last ∼20 years due to T inputs from remedial irrigation with OBT-rich pond water. Elevated but lower levels of OBT : HTO and NE-OBT : E-OBT were observed due to inputs from SRS operations during the last 70 years and prior to irrigation with the T-rich pond water.

A new calibration technique for quantitative gas analyses of fluid inclusions using a quadrupole mass spectrometer.

RATIONALE: Quantitative gas analysis by quadrupole mass spectrometry is used widely in the study of fluid inclusion volatiles, but the currently available instrument calibration techniques have a number of limitations. We describe a new method to overcome these by employing custom-machined stainless-steel calibration volumes that fit into modified bellows valves and can be filled on the high-vacuum prep line of the instrument. This allows the calibration gas to be introduced in a pulse-like fashion, replicating a burst of sample gas from a ruptured fluid inclusion. METHODS: The modified bellows valves equipped with calibration volumes are loaded onto the high-vacuum inlet of a quadrupole mass spectrometer. Cobalt-based alloy stem tips are then used to seal calibration gases (dry air, in this case) at known pressures into the calibration volumes for analysis. RESULTS: Two volumes of different dimensions were used to produce a relationship between moles introduced and integrated beam area for m/z 14, 32, 40, and 44. A linear fit along with a 95% confidence band for the relationship of moles introduced and integrated beam area was determined for the purpose of quantitative gas analysis in fluid inclusions containing atmospheric air. The calibration curves for each m/z have R-squared (COD) values of 0.94 or better. For validation of this calibration technique, measurements were made using outside air as an unknown. CONCLUSIONS: A new calibration technique has been developed for measuring femto- to pico-mole quantities of atmospheric air that greatly reduces contamination and introduces calibration gas in a pulse similar to sample gas. This technique has reduced the error in quantifying these small aliquots of air to an uncertainty of ±1.5%.