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Environmental fate & pathways

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No information on the bioconcentration or accumulation in aquatic organisms are found for tungsten oxide. However, data are available for sodium tungstate and tungstn metal which are used for read-across.

Aquatic Bioaccumulation:

Bioconcentration is the tendency of materials to concentrate directly from water in a living organism over time. There is no testing performed according to standard methodology in the published literature regarding bioconcentration of tungsten compounds in general or tungsten oxide specifically, in aquatic organisms. However, in a static renewal, toxicity test on Poecilia reticulate testing sodium tungstate, Strigul et al (2010) measured tungsten uptake in 5 fish-2 controls, 3 exposed to 7.5 g/L (nominal sodium tungstate concentration). The fish from the test group had died within the first 24 hours of exposure. BCF was calculated as the ratio of tungsten concentration in fish tissue (in mg W per kg wet or dry) to tungsten concentration in water (in mg/L). The BCF was calculated on both wet and dry weight of fish. Wet weight BCF for the test substance was calculated as 0.29 +/- 0.94 L/kg. Dry weight BCF for the test substance was calculated as 1.57 +/- 0.5 L/kg. These BCFs are low, indicating little to no immediate accumulation even at toxic exposure levels.

Terrestrial bioaccumulation

No data on the behavior of tungsten oxide in the environment are available. Bioconcentration data for tungsten metal and sodium tungstate are presented in this section. The soluble species released are expected to be similar for each of the compounds and are thus expected to behave similarly in the environment. However, the amount of soluble species resulting from tungsten metal and sodium tungstate is different, with sodium tungstate being much more soluble. Therefore, data for sodium tungstate and tungsten metal are expected to adequately capture the range of bioavailability of tungsten oxide in the environment. For more details, refer to the read-across category approach description in the Category section of this IUCLID submission or Annex 3 of the CSR.

Relatively low bioaccumulation of tungsten is observed in sunflower leaves at soil concentrations of 3900 mg W/kg soil, with calculated concentration factors plateauing at approximately 0.05 (Johnson et al, 2009). Tungsten concentrations factors calculated for ryegrass were higher and ranged from 56.1-0.202 (Strigul et al, 2005). However, it should be noted that, in this study, background levels of tungsten in the collected soils used for testing were not determined prior to testing. Tungsten concentrations measured in earthworm tissue ranged from 1.52-193.2 mg/kg wet weight in soils with tungsten concentrations of 10-10000 mg/kg soil, respectively (non-aged soil) (Strigul et al, 2005). Additionally, tungsten concentrations of 10 and 10000 mg/kg soil yielded earthworm tissue concentrations of 3.45 and 25.9 mg/kg wet weight, respectively (Strigul et al, 2005). Using these paired concentration data, the BCFs for earthworms in non-aged soils ranged 0.152 to 0.019 and BCFs for aged soils ranged from 0.345 to 0.00259. Tungsten concentrations measured in earthworm tissue in another study with soil spiked with sodium tungstate (Inouye et al, 2006) ranged from 2.9 to 41.3 mg/kg wet weight in soils with tungsten concentrations of <2 to 4643 mg/kg soil, respectively. These data would indicate concentration factors ranging from 1.45 to 0.008, respectively, with only the lowest tungsten concentration resulting in a BCF of > 1. Therefore, tungsten compounds such as tungsten oxide are not expected to bioaccumulate in terrestrial organisms.

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