Calcium bis[2-[(2-hydroxynaphthyl)azo]naphthalenesulphonate]

Additional information on environmental fate and behaviour

Administrative data

Endpoint:

additional information on environmental fate and behaviour

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2022

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2022

Report date:

2022

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: OECD 318

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Calcium bis[2-[(2-hydroxynaphthyl)azo]naphthalenesulphonate]

EC Number:

214-161-1

EC Name:

Calcium bis[2-[(2-hydroxynaphthyl)azo]naphthalenesulphonate]

Cas Number:

1103-39-5

Molecular formula:

C20H14N2O4S.1/2Ca

IUPAC Name:

calcium bis{2-[(2-hydroxy-1-naphthyl)diazenyl]naphthalene-1-sulfonate}

additive 1

Reference substance name:

Resin acids and Rosin acids, calcium salts

EC Number:

232-694-8

EC Name:

Resin acids and Rosin acids, calcium salts

Cas Number:

9007-13-0

Molecular formula:

not applicable

IUPAC Name:

Resin acids and Rosin acids, calcium salts

additive 2

Reference substance name:

Reference substance 001

Cas Number:

73612-32-5

Molecular formula:

C40H26CaN4O8S2

Details on test material:

Batch CHILJ709

Results and discussion

Any other information on results incl. tables

At any of the time points mentioned in the TG-318, the influence of both pH and Ca is critical. However, regardless of pH, the pigment is least stable in 10 mM Ca, representing high water hardness. After 6h, the samples showed intermediate dispersion stability in all media with 10 mM Ca and in media with 1 mM Ca and pH = 4 and 7. The dispersion stability at other conditions was high. After 24 hours the stability remained intermediate in all media with 10 mM Ca and in media with 1 mM Ca and pH = 4 and 7. The stability remained high in all other media.

 

Table 1: full results of the dispersion stability in the presence of NOM

	Ca(NO3)2	Stability after 6h	Standard deviation	Stability after 15h	Standard deviation	Stability after 24h	Standard deviation
	[mM]	[%]	[%]	[%]	[%]	[%]	[%]
pH 4	0	100.2	0.1	100.2	0.1	100.2	0.1
pH 4	1	55.7	2.1	29.1	1.7	22.5	1.0
pH 4	10	36.6	1.6	21.2	1.0	17.2	0.5
.
pH 7	0	100.4	0.5	100.4	0.4	100.3	0.4
pH 7	1	61.6	1.0	28.2	0.5	19.1	0.4
pH 7	10	32.6	2.9	19.4	1.5	16.0	1.0
pH 9	0	99.9	0.4	99.8	0.4	99.8	0.5
pH 9	1	100.2	0.1	100.1	0.2	99.6	0.8
pH 9	10	36.9	3.8	23.9	1.7	21.3	1.2

 

To rationalize the observed dispersion stability, we finally checked the particle size distribution directly in the environmental medium. We applied the NanoDefine method of Analytical Ultracentrifugation (SOP AUC-RI, published by 3). The centrifugation parameters are given in the methods section.

As required by TG318, paragraph 31, the tested nanomaterial was pre-wetted in ultrapure water and left in the form of wet-paste for 24 h. The TG318 requires this step “to insure the proper interaction of nanomaterial surface with ultrapure water.” We visually observed incomplete wetting, and so any ensuing measurement would have been incorrect. In accord with the NanoGenoTox dispersion protocol, a drop of ethanol was added, successfully transferred the powder into a paste, which was then further diluted as specified in the TG318

The observed size distributions confirm the moderate agglomeration at 1 mM Ca, pH7, with NOM. If the particles would have been significantly dissolved, no size distribution would be observable at all by this method, which relies on the detection of the movement of particles during centrifugal separation.

Additionally, the centrifugation methods include a determination of the remaining absorption after centrifugation, fully consistent with the conventional determination of the dissolved fraction after centrifugation as recommended by the TG-318. The remaining absorption was measured at ca. 0.06. This is a fraction of approximately 4% of the initial absorption, but actually is close to the LOD of the built-in UV/Vis detector. Considering the LOD, between 0% and 4% of the sample may have been dissolved.

All evidence combined, the results after centrifugation confirm that at least 96% of the observed dispersion stability has to be attributed to the particles, not to dissolution.

Applicant's summary and conclusion

Conclusions:

At any of the time points mentioned in the TG-318, the influence of both pH and Ca is critical. However, regardless of pH, the pigment is least stable in 10 mM Ca, representing high water hardness. After 6h, the samples showed intermediate dispersion stability in all media with 10 mM Ca and in media with 1 mM Ca and pH = 4 and 7. The dispersion stability at other conditions was high. After 24 hours the stability remained intermediate in all media with 10 mM Ca and in media with 1 mM Ca and pH = 4 and 7. The stability remained high in all other media.
Taken together, the dispersion stability of Pigment Red 49:2 depends on both pH and water hardness. The stability is intermediate in all media with 10 mM Ca and in media with 1 mM Ca and pH = 4 and 7. The stability is high at all other conditions.