Behavior and fate of ITER-like tungsten nanoparticles in freshwater ecosystems produced during operation and maintenance

Abstract

Within the ITER project (International Thermonuclear Experimental Reactor) an international project building a magnetic confinement device to achieve fusion as a sustainable energy source, tungsten (W) is planned to serve as a plasma-facing component (PFC) in the tokamak, a magnetic confinement device used to produce controlled thermonuclear fusion power. Post plasma-W interactions, submicron tungsten particles can be released. This study investigated the exposure of lentic freshwater ecosystems to ITER-like tungsten nanoparticles in indoor aquatic mesocosms. Monitoring included tungsten (bio)distribution, (bio)transformation, speciation, and impacts following a relevant exposure scenario (chronic, medium-term, low-dose contamination). Additionally, mechanistic studies using a combination of microfluidic cells and X-ray Absorption Spectroscopy (XAS) provided a time-resolved understanding of tungsten's oxidative dissolution in freshwater. Following contamination, tungsten persisted in the water column (over 90%), showing significant (~40%) and rapid (< 7 days) oxidation-dissolution and polymerization. This led to significant exposure of planktonic niches, strong affinity of polymeric tungsten species for aquatic vegetation, and potential transfer to higher trophic levels like aquatic snails. Over five weeks, the bio-physicochemical parameters of the mesocosms remained stable, and no acute impacts were observed on micro- and macro-organisms.

Environmental Implication

Tungsten nanoparticles (nanoW) are expected to be released into freshwater environments during the operation and maintenance of ITER (International Thermonuclear Experimental Reactor, a nuclear fusion research and engineering project aimed at creating energy through a fusion process similar to that of the sun). Although nanoW are a hazardous material of concern, there is a significant lack of knowledge regarding their behavior, fate, and toxicity in aquatic ecosystems. The present work investigates this topic by (i) mimicking a realistic exposure scenario in mesocosm, (ii) characterizing the (bio)distribution, fate, and (bio)transformation of tungsten nanoparticles in the environmental compartments, (iii) identifying its exposure pathways at ecological niches level and (iii) providing a time-resolved understanding of the nanoW speciation and oxidative dissolution mechanisms in freshwater environments.