Speciation and Bioavailability Measurements of Environmental Plutonium Using Diffusion in Thin Films

Abstract

The biological uptake of plutonium (Pu) in aquatic ecosystems is of particular concern since it is an alpha-particle emitter with long half-life which can potentially contribute to the exposure of biota and humans. The diffusive gradients in thin films technique is introduced here for insitu measurements of Pu bioavailability and speciation. A diffusion cell constructed for laboratory experiments with Pu and the newly developed protocol make it possible to simulate the environmental behavior of Pu in model solutions of various chemical compositions. Adjustment of the oxidation states to Pu(IV) and Pu(V) described in this protocol is essential in order to investigate the complex redox chemistry of plutonium in the environment. The calibration of this technique and the results obtained in the laboratory experiments enable to develop a specific DGT device for in-situ Pu measurements in freshwaters. Accelerator-based mass-spectrometry measurements of Pu accumulated by DGTs in a karst spring allowed determining the bioavailability of Pu in a mineral freshwater environment. Application of this protocol for Pu measurements using DGT devices has a large potential to improve our understanding of the speciation and the biological transfer of Pu in aquatic ecosystems.

Evidence of plutonium bioavailability in pristine freshwaters of a karst system of the Swiss Jura Mountains

“…This precipitate was centrifuged and washed with deionized water (<0.05 μS cm -1 ) and dissolved in 20 mL of 8 M HNO 3 for radiochemical separation of Pu. The radiochemical separation of Pu for AMS measurements was done by solidphase extraction using AG 1-X4 anion exchange resin (chloride form) from Bio-Rad Laboratories Inc. as described by (Cusnir et al, 2015).…”

“…The fabrication and deployment of large surface (105 cm 2 ) DGT devices for in-situ Pu bioavailability measurements were described and demonstrated by us earlier (Cusnir et al, 2015). To measure the bioavailable fraction of Pu in karstic freshwaters in-situ, we deployed large surface DGT devices of 0.39 mm and 0.78 mm gel layer thickness for 2 to 3 weeks in the two study sites.…”

“…After 24 h elution, the samples were centrifuged, decanted and washed twice with 5 mL of 8 M HNO 3 . The sample solutions were filtered through glass-fiber 0.45 μm Nalgene syringe filters when necessary and submitted to radiochemical separation of Pu for AMS measurements as described previously (Cusnir et al, 2015). The concentration of bioavailable (labile) Pu species in water C DGT (µBq mL -1 ) was calculated from the equation 1 (Cusnir et al, 2016;Warnken et al, 2007):…”

“…Previous work on the use of the DGT technique to determine the lability of the Pu-FA complexes paved the way for direct in-situ measurements of the labile environmental Pu (Cusnir et al, 2014;Cusnir et al, 2015). A DGT device for Pu bioavailability measurements contains a polyacrylamide (PAM) gel assembly with a Chelex resin-gel as binding phase, protected with a filter (Davison and Zhang, 1994).…”

Passive Sampling Tool for Actinides in Spent Nuclear Fuel Pools

“…Here, is the activity or mass of the analyte isotope in the resin-gel eluate; for sampler deployments includes an additional of 0.049 cm for each actinide, as reported for Pu by Cusnir et al 4 and Am by Chaplin et al; 1 t is the exposition time (s), and S is the surface area of the exposed filter membrane of DGT samplers.…”