PNNL

Abstract

Due to its long half-life (15.7 million years) and relatively unencumbered migration in subsurface environments, 129I has been recognized as a contaminant of concern at numerous federal, private, and international facilities. In order to understand the long-term risk associated with 129I at these locations, quantitative analysis of groundwater samples must be performed. However, the ability to quantitatively assess the 129I content in groundwater samples requires specialized extraction and sophisticated analytical techniques, which are complicated and not always available to the general scientific community. This paper highlights an analytical method capable of directly quantifying 129I in groundwater samples at concentrations below the MCL without the need for sample pre-concentration. Samples were analyzed on a Perkin Elmer ELAN DRC II ICP-MS after minimal dilution using O2 as the reaction gas. Analysis of continuing calibration verification standards indicated that the DRC mode could be used for quantitative analysis of 129I in samples below the drinking water standard (0.0057 ng/ml or 1 pCi/L). The low analytical detection limit of 129I analysis in the DRC mode coupled with minimal sample dilution (1.02x) resulted in a final sample limit of quantification of 0.0051 ng/ml. Subsequent analysis of three groundwater samples containing 129I resulted in fully quantitative results in the DRC mode, and spike recovery analyses performed on all three samples confirmed that the groundwater matrix did not adversely impact the analysis of 129I in the DRC mode. This analytical approach has been proven to be a cost-effective, high-throughput technique for the direct, quantitative analysis of 129I in groundwater samples at concentrations below the current MCL.