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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:
2019
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2019
Report Date:
2019

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
other: OECD 318
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: nanoform, no surface treatment

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 “instable” in 10 mM Ca, representing high water hardness. At 6h, most media induce “intermediate stability”, and only one medium (0 mM Ca, pH 9) induces a stability above 90%. At 24h, all media at 0 mM Ca and 1 mM Ca induce an intermediate stability between 60% and 87%. The stabilities systematically decrease over time, decrease slightly between 0 mM Ca and 1 mM Ca. The difference between pH 4 and pH 7 is low, but pH 9 systematically induces a slightly higher stability.

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

84.2

0.7

75.3

1.2

64.5

1.1

pH 4

1

81.9

0.4

70.3

0.7

60.3

0.6

pH 4

10

9.0

0.8

3.3

0.6

2.3

0.5

pH 7

0

80.3

0.6

70.6

0.3

63.4

0.6

pH 7

1

81.3

0.7

69.9

0.0

62.0

0.5

pH 7

10

9.7

0.9

4.1

0.2

3.2

0.2

pH 9

0

93.8

0.6

90.0

1.3

86.7

1.6

pH 9

1

86.9

0.5

75.2

1.8

69.3

1.3

pH 9

10

10.6

0.2

5.9

0.3

4.5

0.4

 

 

The results showed that under NOM-free conditions, the pigment was minimally less stable.The differences are not statistically significant.

 

Table 2: Comparison of the results of the dispersion stability with and without the presence of NOM

sedimentation time

6h

24h

1mM Ca, pH7, with NOM

99.45±0.39

99.22 ± 0.05

1mM Ca, pH7, without NOM

99.67 ± 0.02

98.81 ± 0.29

 

To rationalize the observed dispersion stability, the particle size distribution directly in the environmental medium (exact same sample preparation as for the UV/VIS measurements) was checked.

The NanoDefine method of Analytical Ultracentrifugation (SOP AUC-RI, published by 3) was applied. The centrifugation parameters are given above.

The observed size distributions confirm the low agglomeration at 0 mM and 1 mM Ca, against the high agglomeration at 10 mM Ca.

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. Even for the case of highest stability (pH 9, 0 mM Ca, with NOM), the remaining absorption was measured at 0.0504 ± 0.0024. This is a fraction of 2% of the initial absorption, but actually is close to the LOD of the built-in UV/Vis detector. Considering the LOD, between 0% and 2% of the sample may have been dissolved.

All evidence combined, the results after centrifugation confirm that at least 98% of the observed dispersion stability has to be attributed to the particles, not to dissolution.

Applicant's summary and conclusion

Executive summary:

We found that the organic pigment is rather insensitive to pH changes, with little differences in dispersion stability between pH 4 and pH 9.

This is a significant difference against the metal oxide (TiO2) that was proposed as benchmark material of “intermediate stability” by the TG318.

Dissolution was excluded as the main cause of the apparent stability. The dispersion stability of Pigment Red 53:1 is of “intermediate stability” and depends especially on water hardness.

Only in very hard water with 10mM Ca, the stability of “low”. In all other conditions, the stability is at least “intermediate”, such that the aquatic compartment is relevant to risk assessment.