WORK PACKAGE 1: EXPOSURE, FATE AND LIFE CYCLE ASSESSMENTS

Results so far: Cobalt rapidly dissolves from tungsten cobalt nanoparticles and there is no interaction between molecules of natural organic matter and tungsten-containing nanoparticles. As a direct result, the majority of particles sediment and agglomerate. The acute toxicity of these nanoparticles is very low when seen from the response of a benthic isopod, zooplankton and fish. Tungsten carbide nanoparticles do not show acute toxic effects on the tested aquatic wild life.

Anna Furberg, PhD Student, under the supervision of Professor Sverker Molander and Assistant Professor Rickard Arvidsson, Department of Energy and Environment, Chalmers University of Technology, is investigating the flows of tungsten hard materials through society and the emissions that arise from the use of these materials from a systems perspective. The environmental assessment methods that she applies are substance flow analysis and life cycle assessment.

Swedish WC-Co emissions comparable to other nanomaterials

Most tungsten is used in hard material applications. About 60% of the tungsten that is used worldwide dissipates (i.e., is not recycled or reused) according to Zimmermann and Gößling-Reisemann (Sci Tot Environ . 461-462: 774-780, 2013). This constitutes a hindrance for circular material flows of tungsten. Recommendations on steps towards making tungsten a future circular material have been formulated and include having a higher resolution in characterizing societal flows. Anna Furberg’s analysis shows annual Swedish tungsten cobalt emissions in the same order of magnitude as a number of other, more well- investigated nanomaterials, including silver, titanium dioxide, cerium oxide, fullerenes and carbon nanotubes.

 

Advanced methods to characterize nanomaterials

New methods are being developed to detect and characterize nanomaterials in real-world systems within the research group of Martin Hassellöv at the Department of Marine Sciences, University of Gothenburg. Advanced imaging and spectrometry techniques are applied to road dust and road runoff waters in order to quantify the presence of tungsten carbide nanomaterials from tire studs in waters that eventually enter large water bodies, such as seas and lakes. Their earlier work on particles produced as a result of friction between tires and road materials revealed that tungsten rich particles are omnipresent in road environments. Along with ecotoxocity studies indicating that there is potential hazard from WC particles mixed with Co, this finding provided the incentive to create this case study for WC particles.

“Measurements of nanomaterials in real-world systems are scarce, but very much needed in order to complete risk profiles of these materials” says Martin Hassellöv.

Tungsten carbide in road dust from Gothenburg’s Tingstads Tunnel

Road dust samples from Tingstads Tunnel were analyzed with electron microscopy, where tungsten-rich particles were detected in a variety of sizes, from nano- to microparticles. Tunnels are isolated from non-traffic inputs of dust and are thus ideal for detecting particles emitted from cars and the road. The particles emitted in roads are likely to be washed off by rain water or melting snow and transported into larger water bodies, through stormwater drainage systems. Further sampling in these waters and sediment will reveal to what extent tungsten containing particles enter these waters and how widely they are spread.

Low environmental risks of dispersion of tungsten carbide

Within the MISTRA Environmental Nanosafety program, Professor Inger Odnevall Wallinder’s research team at the Division of Surface and Corrosion Science, KTH Royal Institute of Technology, focuses on metallic nanoparticles. More accurate, their environmental transformation, dissolution, interaction, fate and release of ionic species in contact with aquatic settings of different chemistry and redox conditions. Their research contributes with knowledge on the fate of metal nanoparticles in the environment and whether they are in a toxic form or not. Knowledge on effects of biomolecule adsorption to metallic nanoparticles and chemical speciation knowledge enables the prediction of particle reactivity and hazards towards aquatic organisms.

Sparse interaction with biomolecules

In order to investigate the potential hazard from WC particles mixed with Co, the KTH team, with researcher Dr Jonas Hedberg, has analyzed tungsten (WC) and tungsten cobalt (WC-Co) nanoparticles in the laboratory under realistic conditions observed in the environment adjacent to traffic areas. They have found that interaction between the tungsten particles and biomolecules of natural organic matter is very sparse, and this results in rapid agglomeration and sedimentation of the particles, and hence limited transport and mobility in aquatic systems. However, the smallest fraction of tungsten nanoparticles was more stable in solution and sedimented at a slower rate compared with the larger fraction.

Cobalt quickly released

These nanoparticles are therefore more prone to be mobile and transported into different aquatic settings of the environment and should be considered in future studies. Parallel studies with tungsten cobalt nanoparticles show that almost all cobalt was released from the nanoparticles within 24 hours. These aspects need to be considered from an environmental perspective, as soluble species of cobalt may, under some circumstances, be toxic.

“An improved understanding of the environmental fate of dispersed metal nanoparticles is essential for risk assessment and risk management of their use in different applications”, says Inger Odnevall Wallinder. “ We want to contribute with knowledge to prevent and mitigate risks of nanoparticles dispersions at an early stage of usage to minimize potential negative environmental effects”.

Tungsten carbide nanoparticles do not have acute negative effect on the tested aquatic wildlife

At Lund University’s Dept of Biochemistry and Structural biology and the Aquatic Ecology unit, tests are made of the toxicity of nanoparticles and other biological effects, such as behavior and reproduction, on aquatic organisms. The researchers also study how nanoparticles travel through an ecosystem, up the trophic levels. Mikael Ekvall, Post doc researcher, has tested the effect of tungsten carbide nanoparticles on three aquatic organisms: zooplankton (Daphnia magna), fish (Carassius carassius) and a benthic isopod (Asellus aquaticus). These three organisms represent different levels in a food chain and inhabit different locations in a lake ecosystem.

No acute toxicity

Daphnia magna is exposed to nanoparticles either directly or after incubation of nanoparticles with algae that is fed to the Daphnia. Asellus is exposed to sedimenting nanoparticles with or without mixing with algae. Although nanoparticles are taken up by Daphnia, they see no acute (24 hour of exposure) toxicity even in high concentrations of nanoparticles. Prolonged studies of reproduction, and for Asellus also food processing, do not indicate negative effects of the nanoparticles. The fish were exposed to the tungsten-containing nanoparticles after the particles were first taken up by Daphnia that were then fed to the fish every second day. After 4 weeks of treatment, no acute toxicity was observed in the fish. Their results indicate that tungsten carbide nanoparticles do not have acute negative effects on the tested aquatic wildlife.

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