Tungsten hexachloride

Endpoint summary

Description of key information

The acute aquatic toxicity of tungsten hexachloride to aquatic organisms is described by way of read-across from the structural analogues tungsten trioxide and sodium tungstate dihydrate. Studies are available for fish, invertebrates and algae. Results obtained in the studies with sodium tungstate dihydrate are considered most relevant due to the higher solubility of this compound which allows for the derivation of (no) effect values. For further details and justification of read-across please refer to the attached report in section 13 of IUCLID.

The effect concentration for fish (D. rerio) was recalculated fromsodium tungstate dihydrate, resulting in a 96-h LC₅₀ for soluble tungsten of > 106 mg/L. Analogously, re-calculation for freshwater algae and aquatic invertebrates leads to the following (no observed) effect concentrations of soluble tungsten:

- NOEC (D. magna) = 56.7 mg W/L

- EC₅₀ (D. magna) > 101.9 mg W/L

- 72-h ErC₁₀ (P. subcapitata) = 3.82 mg W/L

- 72-h ErC₅₀ (P. subcapitata) = 33.06 mg W/L

The toxicity of tungsten hexachloride towards microorganisms was assessed via read-across from tungsten trioxide. The available study was conducted similar to the OECD guideline 209 and showed 3.1 % respiration inhibition of activated sludge at the test substance concentration of 10,000 mg/L (corresponding to 7,900 mg W/L). The EC₅₀ was determined to be > 10,000 mg/L. Recalculation of this values to the corresponding concentrations of tungsten hexachloride results in a theoretical EC₅₀ of > 17,000 mg WCl₆/L.

When dissolved in water, tungsten hexachloride is quickly hydrolysed in a strong exothermic reaction leading to a marked pH shift (acidification) in the test solution. The hydrolysis study (Golz, 2017) reported in IUCLID section 5.1.2 shows a shift to pH 2-3 after addition of tungsten hexachloride to water. Soluble tungsten concentrations were in the range of 20.0-42.1 µg/L. After adjustment to pH 7, the tungsten concentration was 44.8 µg/L (mean of three measurements; please refer to IUCLID section 4.8). Please note that the concentration of soluble tungsten ions released from tungsten hexachloride in water is significantly lower than the effect values reported for sodium tungstate dehydrate.Therefore, no ecotoxicolgical effects are expected to occur following release of tungsten hexachloride to water.

Additional information

If aquatic toxicity tests were conducted directly with tungsten hexachloride, pH values would have to be adjusted in all tests by the addition of e.g. NaOH to make any ecotoxicity testing possible; compensating the strong pH shift to values of 2-3. pH values below 3-5 are considered as detrimental to aquatic organisms (please refer to OECD SIDS for Hydrogen chloride (CAS# 7647-01-0), 2002). Furthermore, the aquatic toxicity testing aims at investigating possible effects caused by the release of the respective metal ion, not the pH shift.

Therefore, sodium chloride (NaCl) concentrations that would originate from neutralization in (hypothetical) ecotoxictiy tests with tungsten hexachloride have to be considered. Testing at a concentration of 100 mg WCl₆/L (= 0.2521 mmol WCl₆/L) would require neutralization of test solutions with 1.5126 mmol NaOH/L, resulting in a NaCl concentration of 88.33 mg/L. Reported EC₅₀ values in daphnia and inhibitory concentrations in algae for NaCl vary but may be as low as EC₅₀ = 874 mg/L (ECHA registry for sodium chloride) and IC₅₀ = 870-2500 mg/L (IC = inhibition of fluorescence; Santos et al., 2007; Geis et al., 2000), respectively. The 96-h LC₅₀ for the freshwater fish Lepomis macrochirus is stated to be 5,840 mg/L (see Sigma Aldrich SDS for sodium chloride, available online¹).

In conclusion, no ecotoxicological effects would occur based on a (theoretic) sodium chloride concentration of 88.33 mg/L in hypothetical tests at 100 mg WCl₆/L.

¹ https://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=DE&language=de&productNumber=433209&brand=ALDRICH&PageToGoToURL=https%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fproduct%2Faldrich%2F433209%3Flang%3Dde; accessed on December 14, 2017.