Zinc bis(hydroxymethanesulphinate)

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

yes

Remarks:

Two vessels were set up in a parallel design at 20.0 ± 1.0 °C, each vessel was sampled several times instead of sampling one single vessel at each point in time. This modification helps to avoid weighing errors.

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

GLP compliance:

yes (incl. QA statement)

Type of method:

flask method

Water solubility:

283.81 g/L

Conc. based on:

test mat.

Loading of aqueous phase:

750 g/L

Incubation duration:

<= 72 h

Temp.:

20 °C

pH:

>= 2.7 - <= 3.3

Water solubility:

71.36 g/L

Conc. based on:

element

Remarks:

Zn

Incubation duration:

<= 72 h

Temp.:

20 °C

pH:

>= 2.7 - <= 3.3

According to the MSDS a water solubility of 500 g test item/L is expected. Based on these results and according to the guideline (5 times the amount needed for solubilility equilibrium) at first a loading of 375 g/ 150 mL = 2500 g /L (374.9988 and 375.0022 g / 150 mL in vessel 1 and 2, respectively) was applied in 500 mL Erlenmeyer flasks. Within two hours, it had been observed that one test vessel had been broken.

Therefore, two 500 mL test vessels have been loaded again with these amounts (375.0010 and 375.0025 g/ 150 mL). The next day it has been observed that both test vessels had been broken again.

The undissolved test item swells and expands in water, which leads to breaking of the glass vessels.

It was agreed with the monitor that a lower loading of 750 g/L is applied, which still is above the solubility as mentioned in the MSDS.

Therefore, a pretest to investigate the stability of the vessels was performed: A loading of 112.5379 g/ 150 mL was applied. The vessel (500 mL Erlenmeyer flask as used for water solubility) did not break within 24 h.

Therefore, two vessels (500 mL Erlenmeyer flask) with loadings of 112.551 g/ 150 mL and 112.563 g/ 150 mL (corresponding to 750.34 g/ L and 750.42 g/ L) were set up for the main test.

The applied loading did not correspond to at least five times of the quantity of test substance necessary to saturate the desired volume of water as mentioned in the MSDS. However, undissolved white material (probably the test item) was observed in the test vessels throughout the test (section 6.1).

The test was performed in duplicate. Samples from each vessel at each sampling point were analyzed in duplicate. Dissolved zinc concentrations were measured by ICP-OES.

Samples were taken after 1 d (24 h), 2 d (48 h), and 3 d (72 h) days. After a few days and prior to ICP-OES measurement a white precipitate had been formed in the acidified test item loaded samples. Directly after sampling and acidification these samples were visually clear. The precipitate might be due to formation of paraformaldehyde or (polymer) organic molecules.

In general zinc is dissolved under the acidic conditions but to be on the safe side more nitric acid had been added. As expected for the probable organic precipitate, this did not dissolve. If not dissolved slight Zn residues might be enclosed in this organic precipitate, this will not affect

the value for the water solubility (283.81 ± 24.46 g test item/L) of the test item. Therefore, the samples were filtered and the filtrate was measured by ICP-OES. The pH value of solutions containing the test item started at 3.1–3.3 at day 1 and decreased to 2.7–2.8 at day 3 (Table 5) whereas the pH value in method blanks was in the range of 5.7 -5.9.

Zinc concentrations remain constant from day 1 to day 3. Dissolved Zn concentrations of samples from two consecutive days did not differ by more than 15 %, and an increasing trend in concentrations from day 1 to day 3 was not observed (Figure 1). Thus, the validity criteria as foreseen in OECD 105 [4] and Regulation 440/2008/EC A.6 [5] was met.

The following mean dissolved Zn concentrations were measured:
Mean dissolved zinc concentration day 1–day 3 (± standard deviation):

Vessel 1:

62.53 ± 3.66 g Zn/L

Vessel 2:

80.20 ± 8.70 g Zn/L

mean of vessel 1 & 2:

71.36 ± 6.15 g Zn/L

Based on a purity of 98.3 % w/w of the test item and the measured Zn concentrations the dissolved amount of test item was calculated.

However, according to the CoA in the impurities of 1.7 % zinc is also present. The Zn content of the identified impurities (regarding their percentage in test item) accounts to 0.61 % compared to 25.15 % for the pure substance and therefore, the impurities do not significantly affect the results.

The following mean dissolved Zinc Formaldehyde Sulphoxylate (based on 98.3 % w/w purity) concentrations were calculated:

Mean calculated test item dissolved day 1–day 3 (± standard deviation):

Vessel 1:

248.66 ± 14.54 g test item/L

Vessel 2:

318.96 ± 34.59 g test item/L

mean of vessel 1 & 2:

283.81 ± 24.46 g test item/L

The difference of the dissolved amount of test item in vessel 1 and 2 might be due to the observation that in vessel 1 a white slurry was observed, whereas in vessel 2 a crystalline precipitate appeared. The latter might be due to crystal nuclei at the glass walls of the used vessel.

Conclusions:

Under the conditions of this test (flask method; loadings 750 g test item/L), a solubility equilibrium was observed during testing from day 1 – day 3. The mean dissolved zinc concentration at 20.0 ± 1.0°C as measured on day 1, 2 and 3 amounts to 71.36 ± 6.15 µg Zn/L (separated by filtration from undissolved test item). This corresponds to a calculated mean (based on a purity of 98.3 % according to CoA) of 283.81 ± 24.46 g Zinc Formaldehyde Sulphoxylate /L. The pH value of solutions containing the test item started at 3.1 – 3.3 at day 1 and decreased to 2.7 – 2.8 at day 3 (Table 5) whereas the pH value in method blanks was in the range of 5.7 -5.9.

Key value for chemical safety assessment

Water solubility:

283.81 g/L

at the temperature of:

20 °C