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Environmental fate & pathways

Additional information on environmental fate and behaviour

Administrative data

Endpoint:
additional information on environmental fate and behaviour
Remarks:
Dispersion stability in simulated environmental media
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2020
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2020
Report Date:
2020

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
other: OECD 318
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: nanoform

Results and discussion

Any other information on results incl. tables

At any of the time points mentioned in the TG-318, the influence of Ca is critical. Regardless of pH, the pigment is categorized at the 24h-sampling time as “unstable” in 10 mM Ca, representing high water hardness.

After 6h, at pH 7 and 9 the samples showed high dispersion stability in 0 and 1 mM Ca. Stability at all other conditions was on the lower end of intermediate level

After 24 hours the stability for samples at pH 7 and 9 in 0 and 1 mM Ca became intermediate. For the samples at pH 4 and/or in 10 mM the stability was low.

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

16.9

1.0

6.0

0.4

4.0

0.3

pH 4

1

10.3

1.1

4.4

0.9

3.3

0.7

pH 4

10

10.7

1.6

4.2

0.5

3.2

1.0

.

 

 

 

 

 

 

pH 7

0

93.7

1.6

86.0

4.2

76.8

1.9

pH 7

1

98.7

0.5

93.1

1.9

83.7

5.3

pH 7

10

13.9

1.4

6.6

1.2

3.7

0.1

.

 

 

 

 

 

 

pH 9

0

99.2

0.5

92.7

2.1

86.6

3.4

pH 9

1

98.0

0.7

81.3

0.8

48.9

0.9

pH 9

10

11.2

0.4

5.6

0.8

4.4

0.7

 

 

Cross-check the apparent stability by a fractionating method that physically separates particles from dissolved matter, and centrifugation results

 

To rationalize the observed dispersion stability, we finally checked the particle size distribution directly in the environmental medium (exact same sample preparation as for the UV/VIS measurements). We applied the NanoDefine method of Analytical Ultracentrifugation (SOP AUC-RI).

 

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 c.a 0.014.This is a fraction of 0.7% of the initial absorption, but actually is close to the LOD of the built-in UV/Vis detector. Considering the LOD, between 0% and 0.7% of the sample may have been dissolved.

 

All evidence combined, the results after centrifugation confirm that at least 99.3% of the observed dispersion stability has to be attributed to the particles, not to dissolution.

Applicant's summary and conclusion

Executive summary:

The dispersion stability of Pigment Yellow 93 depends especially on pH and water hardness. At pH 7 and 9 in 0 and 1 mM Ca stability is intermediate, at all other conditions (pH 4 and/or 10 mM Ca) the stability is low.