Disodium peroxodisulphate

Endpoint summary

Additional information

Appearance/physical state/colour

Diammonium, dipotassium and disodium persulfate, the three members of the persulfate category, are white, crystalline and odourless salts which are solid at 20 °C and 1013 hPa.

Melting point/freezing point

The melting point for the persulfate category was determined according to EU method A.1 applying the capillary method. Diammonium, dipotassium and disodium persulfate were found to decompose at about 120 °C (393 K), 100 °C (373K) and 180 °C (453 K), respectively, at atmospheric pressures of about 1000 hPa before the melting point was reached. Thus, for all three substances, no value for melting temperature was determined.

Boiling point

The boiling point for the persulfate category was determined according to EU method A.2 applying photocell detection. Diammonium, dipotassium and disodium persulfate were found to decompose at about 120 °C (393 K), 100 °C (373K) and 180 °C (453 K), respectively, at atmospheric pressures of about 1000 hPa before the boiling point was reached. Thus, for all three substances, no value for boiling temperature was determined (see also IUCLID, Section 4.1: Melting point).

Density

The relative density (D4/20) for the persulfate category was determined according to EU method A.3 applying the pycnometer method. The determined values for Diammonium, dipotassium and disodium persulfate were 1.26, 1.39 and 1.68, respectively, at 20 °C.

Particle size distribution (Granulometry)

Based on the results of company specific experimental analyses for all three persulfates, the overall ranges which cover 98 % or more of the particle size of the respective test substance were as follows:

a) diammonium persulfate: >= 50 - >= 2000 µm

b) dipotassium persulfate: >= 5 - >= 400 µm

c) disodium persulfate: >= 10 - >= 1000 µm

The overall mass median diameters (D50) were as follows:

a) diammonium persulfate: 250 - 900 µm

b) dipotassium persulfate: 30 - 150 µm

c) disodium persulfate: 86 - 350 µm

Fractions (%) <= 5 and/or >= 10 µm particle size (aerodynamic diameter):

a) diammonium persulfate: <= 5 µm: max. 0.3 % ; <= 10 µm: max. 1.3 %

b) dipotassium persulfate: <= 5 µm: max. 5 % ; <= 10 µm: max. 13 %

c) disodium persulfate: <= 5 µm: max. 0.5% ; <= 10 µm: max. 5 %

According to the Technical Guidance document on Risk Assessment particles with aerodynamic diameters <100 µm have the potential to be inhaled. Particles with aerodynamic diameters of above 1 - 5 µm have the greatest probability of settling in the nasopharyngeal region whereas particles with aerodynamic diameters below 1 - 5 µm are most likely to settle in the tracheobronchial or pulmonary regions. All samples revealed fractions <100 µm, <10 µm and <5 µm (aerodynamic diameter). With a total fraction of max 18 % of particles <10 µm (aerodynamic diameter), dipotassium persulfate revealed the highest fraction of small particles.

All applied testing methods were in accordance with OECD guideline No. 110, Method A: Particle size distribution, 12 May 1981.

Notably, all three substances are classified and labelled asRespiratory sensitizing category 1 (H 334: May cause allergy or asthma symptoms or breathing difficulties if inhaled) and specific target organ toxicity – single Category 3 (H335: May cause respiratory irritation) according to Regulation (EC) No 1272/2008.

Vapour pressure

As the available experimental methods allow a determination of vapour pressure down to 1E-05 Pa only, no meaningful experimental determination of the vapour pressure for the persulfate category was possible. Therefore, in accordance with the respective EU method A.4 no experimental determination of the vapour pressure was carried out. Instead, the vapour pressure for the three persulfates was estimated applying the Modified Grain method, US EPA EPIWIN (v4.0).

Following results were obtained:

a) diammonium persulfate: 1.47E-23 mm Hg (= 1.96E-21 Pa) at 25 °C

b) dipotassium persulfate: 6.07E-30 mm Hg (= 8.09E-28 Pa) at 25 °C

c) disodium persulfate: 6.07E-30 mm Hg (= 8.09E-28 Pa) at 25 °C

Notably, inorganic chemicals are outside of the domain of EPIWIN (v4.0). The vapour pressure used in risk assessment was: 1E-06 Pa (EUSES default)

Partition coefficient

In accordance with column 2 of REACH Annex VII, the determination of the partition coefficient in n-octanol/water (required in section 7.8) does not need to be conducted for inorganic substances. Therefore, an experimental determination was not performed for the persulfate category. For risk assessment a default value of log Pow = -1 (EUSES default) was used.

Water solubility

Based on published data, the following results were obtained for water solubility of the persulfate category:

a) diammoniumpersulfate: 850 g/L (25 °C) (OECD-SIDS Report, 2005)

b) dipotassiumpersulfate: 60 g/L (25 °C) (OECD-SIDS Report, 2005)

c) disodiumpersulfate: 730 g/L (25 °C) (OECD-SIDS Report, 2005)

As dipotassium persulfate was revealed as an outlier – compared to the other substances of the Persulfate Category, for which the values for water solubility were in the same range – an additional experimental determination was performed for dipotassium persulfate:

The test was performed according to EU method A.6 applying the shake-flask method. The water solubility of dipotassium persulfate was determined at ca. 52.77 g/L at 20 °C. All three persulfates were considered very soluble.

As the experimental result and the value obtained from published data (60 g/L) are comparable, the hypothesis of dipotassium persulfate being an outlier concerning was verified. Thus, the mean values of diammonium and disodium persulfate were used for risk assessment.

Surface tension

In accordance with column 2 of REACH Annex VII, the determination of surface tension (required in section 7.6) only needs to be conducted if surface activity is expected or can be predicted. Based on the molecular structures, surface activity is not expected for the persulfate category. Therefore, an experimental determination was not performed.

Flash point

The determination of the flash-point according to EU method A.9 is not applicable as this method refers to liquid substances only, but the members of the persulfate category are all crystalline solids at room temperature (20 °C). Instead, a determination on flammability upon contact with air according to EU method A.10 was performed (see IUCLID Section 4.13: Flammability).

Auto flammability

For diammonium persulfate a test on auto flammability was performed according to DIN 51 794. While heating up to 600 °C, no self-ignition of the test substance could be determined. The other two members of the persulfate category were not tested for auto flammability. Instead, a read across approach was applied from the experimental data obtained for diammonium persulfate as similar physicochemical properties are expected for the category members. Thus, dipotassium- and disodium persulfate were considered not auto flammable. This statement was supported by the results obtained from the studies on melting point and boiling point, where all category members decomposed at 100 – 180 °C (see IUCLID, sections 4.2 and 4.3).

Flammability

For diammonium persulfate a test on auto flammability was performed according to EU method A.10. With a burning rate of 1, the test substance was determined not flammable. The other two members of the persulfate category were not tested for flammability. Instead, a read across approach was applied from the experimental data obtained for diammonium persulfate as similar physicochemical properties are expected for the category members. Thus, dipotassium- and disodium persulfate are considered not flammable. Additionally, based on experience in handling and use, neither flammability in contact with water nor pyrophoric properties were expected for the persulfate category and therefore, no experimental determination of these properties was performed.

Explosiveness

For diammonium persulfate a test on auto flammability was performed equivalent to EU method A.14 applying the BAM steel core method on thermal sensitivity and the BAM Fallhammer method on mechanical sensitivity. As the test substance showed neither thermal nor mechanical sensitivity, it was considered not explosive. For dipotassium and disodium persulfate, no study was available. However, company data on dust explosiveness revealed no such properties for the three persulfates (see: IUCLID, section 4.14, support). These data, as well as experience in handling and use, were used to support a read across approach which was applied from the experimental data obtained for diammonium persulfate as similar physicochemical properties were expected for the category members. Thus, dipotassium- and disodium persulfate were considered not explosive as well.

Oxidising properties

Experimental testing of oxidising properties was not performed for the persulfate category. Based on the results obtained from a weight of evidence approach from published data, all category members were considered oxidising. This statement was supported by experience in handling and use.

Stability in organic solvents

In accordance with column 2 of REACH Annex IX, the test on stability in organic solvents and identity of relevant degradation products (required in section 7.15) is not required for inorganic substances. Therefore, an experimental determination was not performed for the persulfate category.

Dissociation constant

As the members of the persulfate category are inorganic salts, they were expected to dissociate completely when dissolved in water. A dissociation constant could not be derived. Thus, an experimental determination was not performed as it was considered scientifically unjustified.

Viscosity

In accordance with column 2 of REACH Annex IX, the test on viscosity (required in section 7.17) does not need to be conducted for the persulfate category, as all members are solid at room temperature. Therefore, an experimental determination was not performed for the persulfate category.