Tungsten hexachloride

Endpoint summary

Description of key information

Hydrolysis of tungsten hexachloride was assessed in a combined study on water solubility and hydrolysis (Golz, 2017). In summary tungsten hexachloride shows a rapid hydrolysis in contact with aqueous solutions. This exothermic reaction results in a temperature rise of the test solutions. Tungsten hexachloride was almost completely dissolved in the three buffer solutions at pH 4, 7 and 9. The determined concentrations of tungsten in the sample solution after preparation of the test item in citrate buffer (pH 4) ranged from 41.7 µg/L to 66.5 µg/L, corresponding to a mean recovery of 96.9 ± 8.1 %. The determined concentrations of tungsten in the sample solution after preparation of the test item in phosphate buffer (pH 7) varied between 43.3 to 59.4 µg/L, corresponding to a mean recovery of 88.9 ± 6.1 %. The determined concentrations of tungsten in the sample solution after preparation of the test item in borate buffer (pH 9) ranged between 48.9 to 58.7 µg/L, corresponding to a mean recovery of 94.3 ± 1.1 %.

The endpoint biodegradation is not applicable to tungsten hexachloride as inorganic substance.

Bioaccumulation/bioconcentration of tungsten metal and inorganic tungsten compounds is not expected to occur in aquatic or soil/sediment species. Calculated BCF values for sodium tungstate in the fish species Poecilia reticulata are 0.29 ± 0.94 L/kg and 1.57 ± 0.5 L/kg wet and dry weight, respectively. The BCF values for sodium metatungstate in Poecilia reticulata were 0.51 ± 0.24 L/kg and 2.74 ± 1.32 L/kg wet weight and dry weight (Strigul et al., 2010).

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.

Data from Strigul et al. (2005) and Inouye et al. (2006) indicate concentration factors for earthworms 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.

The adsorption in soil and sediment was evaluated in two studies with tungsten metal and two studies sodium tungstate dihydrate. Based on reported Kd values for tungsten compounds in soil and sediment, their mobility in respective compartments is expected to be low.

The following partitioning coefficients were statistically derived based on studies using appropriate methodology:

        Kd soils (Griggs et al., 2009 and Bednar et al., 2008):      

• 10th percentile: 44 L/kg       
• Median: 174 L/kg       
• 90th percentile: 692 L/kg

 Kd sediment (Salminen (ed.) et al., 2005):      

• 10th percentile: 28,395 L/kg       
• Median: 140,000 L/kg       
• 90th percentile: 700,000 L/kg

Information from inorganic tungsten compounds other than tungsten hexachloride is used in a read-across approach in the assessment of the target substance tungsten hexachloride. For details and justification of read-across please refer to the attached report in section 13 of IUCLID.