Registration Dossier

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:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent

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 “high stability”, and only few media (1 mM Ca at pH 4 and all in 10 mM Ca) induces low stability.

At 24h, stability map is similar. pH 7 is generally induces a slightly higher stability than pH9 and much higher than pH 4. Stability at pH 4 is the most sensitive to the water hardness. In general, two effects can be observed. A pH-dependent effect with low stability at low pH values and high stability at higher pH values and a Ca-dependent effects showing lower stability at higher Ca levels.


 

 

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

0.1

95.5

2.1

87.3

4.6

pH 4

1

13.9

1.1

7.4

0.7

5.7

0.5

pH 4

10

8.3

0.9

4.3

0.3

3.1

0.3

.

 

 

 

 

 

 

 

pH 7

0

99.1

0.1

97.5

0.4

94.9

0.9

pH 7

1

99.4

0.6

97.6

0.9

95.7

1.6

pH 7

10

8.8

0.2

5.3

0.8

4.4

0.5

.

 

 

 

 

 

 

 

pH 9

0

98.9

1.2

94.1

0.5

89.6

2

pH 9

1

96.2

0.4

90.1

1.8

77

0.8

pH 9

10

9.1

0.6

5.8

0.2

5.1

0.3

 

 

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, published by 3). The centrifugation parameters are given in the methods section.

The observed size distributions confirm the low agglomeration at 1 mM Ca, pH7, with). 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. 0.06. This is a fraction of 5% of the initial absorption, but actually is close to the LOD of the built-in UV/Vis detector. Considering the LOD, between 0% and 5% of the sample may have been dissolved.

All evidence combined, the results after centrifugation confirm that at least 95% of the observed dispersion stability has to be attributed to the particles, not to dissolution.

Applicant's summary and conclusion

Executive summary:

Elevated apparent dispersion stability may originate from dissolution. This was excluded by determination of the particle size distribution, which indicated low agglomeration -consistent with the dispersion stability- , but no dissolution. The remaining absorption after centrifugal separation of particles was determined to be not more than 5% of the total signal. Thus, dissolution is not the main cause of the observed stability. Taken together, the dispersion stability of Pigment Red 178 depends especially on water hardness and pH. Only in very hard water with 10 mM Ca and under acidic conditions with 10 mM Ca, the dispersion stability is low. At all other conditions stability was intermediate or high.