Tungsten hexachloride

Endpoint summary

Description of key information

No data on bioaccumulation or levels of tungsten hexachloride in aquatic and/or terrestrial organisms are available.

There is no testing performed according to standard methodology in the published literature regarding bioconcentration of tungsten compounds in general or tungsten hexachloride specifically, in aquatic organisms. However, in tests with sodium tungstate according to OECD guidelines 203 and 204, which were conducted to determine the acute and prolonged toxicity of the test substance to Poecilia reticulata, the uptake of tungsten was determined in 5 fish used in these experiments (2 fish from the control group and 3 fish from the test chemical group). These fish all died during the first 24 h after they were exposed to respectively 1.5 g sodium metatungstate/L and 7.5 g sodium tungstate/L (nominal concentrations).

BCF was calculated as the ratio of tungsten concentration in fish tissue (in mg W per kg wet or dry weight) to tungsten concentration in water (in mg/L). BCF was calculated on both wet and dry weight of fish. BCF values for sodium tungstate were calculated as 0.29 ± 0.94 L/kg and 1.57 ± 0.5 L/kg wet and dry weight, respectively.

Relatively low bioaccumulation of tungsten is observed in sunflower leaves at soil concentrations of 3,900 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 10-10,000 mg/kg soil, respectively (non-aged soil) (Strigul et al., 2005). Additionally, tungsten concentrations of 10 and 10,000 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 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 – 4,643 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 are not expected to bioaccumulate in aquatic and terrestrial organisms.

Additional information

The most prevalent bioavailable form of tungsten is the soluble tungstate ion. However, because tungsten has a significant affinity for adsorption onto soils and stream or river sediments, levels in proximal natural waters are relatively much lower than the surrounding sediment and soil. The extent to which tungsten compounds would release bioavailable tungstate ions into the aquatic environment is furthermore dependent on many factors including dissolved organic carbon (DOC), pH, and water hardness (Bednar et al., 2008).

A test performed using tungsten hexachloride in a combined OECD 105/111 study showed very low release of soluble tungsten ions in the range of 20.0 - 42.1 µg/L.

Another important concern for the bioaccumulation/bioconcentration of metals is methylation. Methylation of metals (i.e., mercury) can allow metals to passively cross membranes and accumulate without homeostatic regulation. There is currently no evidence of methylated species of tungsten in the natural environment.