Diarsenic trioxide

Water solubility

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

April 2010 through August 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP and guideline study.

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

signed by Ministerium für Umwelt und Naturschutz, Landwirtschaft und Verbraucherschutz des Landes Nordrhein-Westfalen (2007-03-21)

Type of method:

flask method

Water solubility:

17.8 g/L

Temp.:

20 °C

pH:

>= 2.6 - <= 2.9

Details on results:

OBSERVATIONS:
During the study, a whitish precipitate of possibly undissolved diarsenic trioxide was observed. Filtrated solutions were visually clear, and the absence of undissolved particles in the filtrates was also shown by turbidity measurements (see below).
The temperature of the water bath was held at 20.0 ± 1.0°C.

pH VALUES:
The pH of test solutions and blanks were measured after 24, 48, and 72h. The method control blanks had relatively constant pH levels ranging from 6.0 to 6.3. The pHs of aqueous solutions of diarsenic trioxide were in the range of pH 2.6 – 2.9.

TURBIDITY MEASUREMENTS:
The turbidity was measured after filtering to verify that only dissolved arsenic concentrations were measured. The turbidity of all samples was always far below 1 NTU, indicating that all material left after the filtration was dissolved.

ICP-OES MEASUREMENT:
Arsenic levels of all method control blanks from the test were below the respective LODs of 4.6 -8.6 µg/L, except sample 3 from flask B after 72h (BW 72h AsV) was below the LOQ (< 28 µg/L). All samples were analyzed within eight days.

TEST EVALUATION:
Only minor variations in measured total arsenic concentrations were observed in samples taken after 24, 48 and 72h (far below the limit of 15 % as required by the test guideline). In consequence, the applied equilibration times are considered to be sufficient and meet the requirements of the test guideline. Therefore, the water solubility of diarsenic trioxide was determined using mean dissolved As concentrations (Flask A and B) as follows:
As(III) and As(V) were separated by solid phase extraction tubes followed by arsenic analysis. Total arsenic concentration was also determined by this analytical method.
Mean total As concentration (n = 3) = 13.5 ± 0.3 g/L
Water solubility of diarsenic trioxide on the solved concentration of As:
13.5 ± 0.3 g/L (mean As conc.) * 197.84 g/mol (As2O3) / (2*74.92 g/mol (As)) = ± 17.8 ± 0.4 g/L.
The concentrations of As(III) in solution were always considerably higher than As(V). After 24h, 48h and 72h the ratio As(III)/As(V) was 160, 191 and 192,respectively. Correspondingly, only ca. 0.5 – 0.6 % of dissolved Arsenic were present as As(V).

FINAL RESULTS:
Under the conditions of this test (flask method; loading of 123.7 g/L and 118.0 g/L , flask A and B), the water solubility of diarsenic trioxide at 20.0 ± 1.0°C was determined as 17.8 ± 0.4 g/L (based on dissolved total As measured by ICP-OES, separated by filtration (0.2 µm) from undissolved test material). The resulting solution pH was measured to be in the range of 2.6 – 2.9. The concentrations of As(V) in solution were 0.07 – 0.08 g/L and the concentrations of As(III) in solution ranged from 12.8 – 13.6 g/L during the test. Almost all (99.4-99.5%) dissolved arsenic was present in the form of As(III).

Conclusions:

Interpretation of results (migrated information): very soluble (> 10000 mg/L)
Under the conditions of this test, the water solubility of diarsenic trioxide at 20.0 ± 1.0°C was determined as 17.8 ± 0.4 g/L (based on dissolved total As measured by ICP-OES, separated by filtration (0.2 µm) from undissolved test material). The resulting solution pH was measured to be in the range of 2.6 – 2.9. The concentrations of As(V) in solution were 0.07 – 0.08 g/L and the concentrations of As(III) in solution ranged from 12.8 – 13.6 g/L during the test. Almost all (99.4-99.5%) dissolved arsenic was present in the form of As(III).

Reference 2

Endpoint:

water solubility

Type of information:

other: Handbook data

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Information taken from peer-reviewed handbook

Qualifier:

no guideline followed

Principles of method if other than guideline:

Not applicable: Handbook data

Type of method:

other: no data

Water solubility:

17 g/L

Temp.:

16 °C

Conclusions:

Interpretation of results (migrated information): very soluble (> 10000 mg/L)
Arsenic trioxide is very solouble with 17g/L.

Description of key information

Diarsenic trioxide is very soluble in water. The water solubility of diarsenic trioxide has been determined experimentally (OECD 105, shake flask method, GLP) to be 17.8 g/L at 20°C. This result confirms previously available data from secondary literature.

Key value for chemical safety assessment

Water solubility:

17.8 g/L

at the temperature of:

20 °C