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.