[No public or meaningful name is available]

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Remarks:

Dissolution study performed on nanoform

Type of information:

experimental study

Adequacy of study:

key study

Study period:

February 2022

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

No defined standards available for nanomaterials

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Version / remarks:

OECD 105/OECD 318

Deviations:

yes

Remarks:

ICP-OES used to probe saturation concentration of the substance

Principles of method if other than guideline:

- Principle of test: The solubility and dissolution rate of the test item was measured over 6 hours using ICP-OES analysis of silicon present in the sample. Using the mass ratio between Si and carbon, a solubility value for the whole substance was estimated.

- Short description of test conditions: 60 mg of sample was dissolved in 150 ml solution under a quick sonication (less than 30 seconds), then aliquoted for triplicate samples in three separate 300 ml plastic jars. Each of three jar was diluted to 200 ml with ultrapure water, before they were put in incubator with a shaking speed of 200 rpm at 18 oC. The 15 ml sample was collected at different time points (0, 30 minutes, 1h, 2h, 3h, 4h, 5h and 6h) by pouring the solution into 15 ml centrifugal filter with a cut-off size of 3k Da, and the supernatant was obtained by centrifugation at 4300 g for 10 minutes at 18 oC (Eppendorf 5400). To avoid the potential Si contamination from glassware, the dissolution study was carried out inside plastic bottles with cover. Triplicate samples with an initial concentration of 100 mg/L were placed on an incubator with a speed of 200 rpm at 18oC, 15 ml samples were collected at time points (t= 0, 30 min, 1 h, 2 h, 3 h, 4 h, 5 hand 6 h), for purification by a centrifugal filter with a cut-off-size of 3 K Da at 4300 RCF for 10 minutes. The level of Si, Ca, Zn and S in the supernatant were measured by ICP-OES, to investigate the dissolution of recovered carbon sample.

- Parameters analysed / observed: Solubility/dissolution rate based on detected elemental concentration of Si within the test media

GLP compliance:

no

Type of method:

other: ICP-OES

Key result

Water solubility:

1.9 other: ppm

Conc. based on:

element

Remarks:

The level of Si measured by ICP-OES were used as a surrogate for solubility of the substance as a whole. A saturation concentration of 120 ppb was measured. Using the mass ratio between Si and carbon, this equates to 1.9 ppm for the substance.

Temp.:

18 °C

pH:

7

Remarks on result:

other: The test was performed in ultrapure water with NOM added to mimic natural organic matter. The pH was not directly measured but is assumed to be around neutral.

Conclusions:

ICP-OES measurements of silicon over a 6 hour period indicated that saturation is achieved after 30 minutes. A saturation concentration of 120 ppb for Si was converted into a solubility value for the substance using the mass ratio between silicon and carbon. The solubility was determined to be 1.9 ppm, although this may well be an overestimate.

Executive summary:

Humic acid was used to mimic NOM. To avoid the potential Si contamination from glassware, the dissolution study was carried out inside plastic bottles with cover. Triplicate samples with an initial concentration of 100 mg/L were placed on an incubator with a speed of 200 rpm at 18oC, 15 ml samples were collected at time points (t= 0, 30 min, 1 h,  2 h, 3 h, 4 h, 5 hand 6 h), for purification by a centrifugal filter with a cut-off-size of 3 K Da at 4300 RCF for 10 minutes.  The level of Si, Ca, Zn and S in the supernatant were measured by ICP-OES, to investigate the dissolution of recovered carbon sample.  All of four elements showed a similar tendency over a period of 6 hours, quickly reaching a plateau within 30 minutes. Despite a much lower abundance of calcium carbonate and zinc sulphide than amorphous silica,  the level of Ca and S appeared to be much higher than Si in supernatant. There is a lack of  the structure and element distribution information for this sample. However, we can plausibly contribute it to their location in the composite and/or physiochemical properties. The amorphous silica are possibly less exposed than Calcium carbonate. For this reason, together with the high abundance of SiO₂ (up to 11%), Si was selected as the labelling element to analysis the dissolution behaviour and dispersion stability for this sample.

Si reached its saturated concentration of 120 ppb within 30 mins. A mass ratio of C to Si can be calculated roughly as 17 from XRF and XRD results, so the solubility of this recovered carbon sample was calculated as 1.9 ppm. It is worth to note that this value could be overestimated, due to the fact that amorphous silica could be released from carbon particles into solution phase. 

Description of key information

As the substance is a nanomaterial, dissolution and dispersions properties were measured to assess the behaviour of the substance in water.  Humic acid was used to mimic NOM. Triplicate samples with an initial concentration of 100 mg/L were placed on an incubator with a speed of 200 rpm at 18oC, 15 ml samples were collected at time points (t= 0, 30 min, 1 h,  2 h, 3 h, 4 h, 5 hand 6 h), for purification by a centrifugal filter with a cut-off-size of 3 K Da at 4300 RCF for 10 minutes.  The level of Si, Ca, Zn and S in the supernatant were measured by ICP-OES, to investigate the dissolution of recovered carbon sample.  All of four elements showed a similar tendency over a period of 6 hours, quickly reaching a plateau within 30 minutes. Despite a much lower abundance of calcium carbonate and zinc sulphide than amorphous silica,  the level of Ca and S appeared to be much higher than Si in supernatant. There is a lack of structure and element distribution information for this sample. However, we can plausibly attribute it to their location in the composite and/or physiochemical properties. The amorphous silica are possibly less exposed than Calcium carbonate. For this reason, together with the high abundance of SiO₂ (up to 11%), Si was selected as the labelling element to analysis the dissolution behaviour and dispersion stability for this sample.

Si reached its saturated concentration of 120 ppb within 30 mins. A mass ratio of C to Si can be calculated roughly as 17 from XRF and XRD results, so the solubility of this recovered carbon sample was calculated as 1.9 ppm. It is worth to note that this value could be overestimated, due to the fact that amorphous silica could be released from carbon particles into solution phase. 

Key value for chemical safety assessment

Water solubility:

1.9 mg/L