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Environmental fate & pathways

Endpoint summary

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Aquatic bioaccumulation

No data on bioaccumulation or levels of tungsten trioxide in aquatic organisms are available. However, bioaccumulation/bioconcentration of tungsten metal and inorganic tungsten compounds such as tungsten trioxide is not expected to occur in aquatic or sediment species, as the bioavailability of tungstate (the bioavailable form) from tungsten compounds is expected to be low in the water column due to stream and river sediment adsorption and low potential for leaching from soils. Furthermore, any uptake mediated by transport proteins would be expected to be internally regulated. The absence of methylated tungsten species also supports the claim that bioaccumulation is not expected to be of concern for tungsten and inorganic tungsten compounds.

Terrestrial bioaccumulation

No data on the behavior of tungsten trioxide 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 trioxide in the environment. For more details, refer to the attached read-across document (see Annex 1).

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 0.152-0.019 and BCFs for aged soils ranged from 0.345 - 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 - 41.3 mg/kg wet weight in soils with tungsten concentrations of <2 – 4643 mg/kg soil, respectively. These data would indicate concentration factors ranging from 1.45 – 0.008, respectively, with only the lowest tungsten concentration resulting in a BCF of > 1. Therefore, tungsten compounds such as tungsten trioxide are not expected to bioaccumulate in terrestrial organisms.

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