Proficiency testing of 78 international laboratories measuring tritium in environmental waters by decay counting and mass spectrometry for age dating and water resources assessment

Abstract

Tritium ( 3 H) is an important hydrological tracer commonly used for over 60 years to evaluate water residence times and water dynamics in shallow/recent groundwaters, streams, lakes and the ocean. We tested the analytical performance of 78 international laboratories engaged in low-level 3 H assays for water age dating and monitoring of environmental waters. METHODS:Seven test waters were distributed by the IAEA to 78 international tritium laboratories. Set 1 included a tritium-free groundwater plus three ultra-low 3 H samples (0.5-7 TU) for meeting groundwater dating specifications. Set 2 contained three higher 3 H-content samples (40-500 TU) suitable for testing of environmental monitoring laboratories. RESULTS:Seventy of the laboratories used liquid scintillation counting with or without electrolytic enrichment, seven utilized 3 He accumulation and mass-spectrometry, and one used gas-proportional counting. Only ~50 % of laboratories demonstrated the ability to generate accurate 3 H data that was precise enough for water age dating purposes.CONCLUSIONS: TRIC2018 helped identify recurrent weaknesses and potential solutions.Strategies for performance improvement of 3 H laboratories include: a) improved quantification of 3 H detection limits and analytical uncertainty, b) stricter quality control practices in routine operations along with care and recalibration of 3 H standards traceable to primary NIST standards, c) annual assessment of enrichment factors and instrumental performance, and d) for water age dating purposes the use of electrolytic enrichment systems having the highest possible 3 H enrichment factors (e.g. > 50x).

Progress and challenges in dual‐ and triple‐isotope (δ18O, δ2H, Δ17O) analyses of environmental waters: An international assessment of laboratory performance

“…Our data evaluation and assessment for WICO2020 followed the methods described in previous IAEA proficiency tests 1,3,20,21 proficiency tests, we applied a two-fold "coverage factor" to σ p for acceptable laboratory evaluation as reflected in the z-score criteria.…”

Reconstruction of the record of tritium in precipitation in the temperate zone of South America

“…Several examples of tritium applications in South‐America can be mentioned, such of those in hydrological (Martinez et al, 2017), hydrogeological (da Silva et al, 2020; Martinez et al, 2016), or the use of South‐American information for atmospheric applications (Aggarwal et al, 2016). Contemporary natural concentrations (0.5–30 TU) observed in South‐America (Martinez et al, 2017; Silva & Cota, 2021), are often below the detection limit of modern Liquid Scintillation Counters, which is the reason why pre‐concentration via electrolytic enrichment is typically applied (Copia et al, 2020; GNIP, 2021; Östlund & Werner, 1962; Taylor, 1976).…”

High spatial resolution prediction of tritium (3H) in contemporary global precipitation

“…In our analysis we found that 3 H records with at least three years of continuous monthly sampling, whether during the rising or falling limb of the solar cycle, corresponded within the 3 H measurement uncertainty to the stations’ mean value for the period 2008–2018. For our mapping purposes we applied a lower 3 H detection limit cutoff as < 0.5 TU which is in accordance with the lower limit of international laboratory performance 29 but also corresponds to the lowest values of recent GNIP samples analyzed (from Galapagos and Ascension Islands).…”

“…2–4 TU. For some regions, like Central America, the Amazon basin, and the large archipelagos in Southeast Asia and the western Pacific, our model predicted 3 H contents < 1 TU in precipitation which is at or below the analytical detection limits of most tritium laboratories 29 , thereby posing significant challenges for practical applications of 3 H as a natural radiotracer for hydrology in these areas. Marine coastal fringes for all continents exhibited lower 3 H in precipitation compared to inland and is clearly influenced by low- 3 H oceanic moisture impacts; yet the continental gradients are not impacted as much as higher latitudes.…”