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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
Guideline:
other: OECD 318
GLP compliance:
yes (incl. QA statement)

Test material

Constituent 1
Chemical structure
Reference substance name:
N,N'-(2-chloro-1,4-phenylene)bis[4-[(2,5-dichlorophenyl)azo]-3-hydroxynaphthalene-2-carboxamide]
EC Number:
226-106-9
EC Name:
N,N'-(2-chloro-1,4-phenylene)bis[4-[(2,5-dichlorophenyl)azo]-3-hydroxynaphthalene-2-carboxamide]
Cas Number:
5280-78-4
Molecular formula:
C40H23Cl5N6O4
IUPAC Name:
N,N'-(2-chloro-1,4-phenylene)bis{4-[(2,5-dichlorophenyl)diazenyl]-3-hydroxy-2-naphthamide}
Test material form:
solid

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 with 0 or 1 mM Ca induce stability on the level of 85-93%, and only one medium (1 mM Ca, pH 4induces a stability of 25%. Stability in 10 mM at regardless pH value is low

At 24h, all media at pH 7 and pH 9 in 0 mM Ca and 1 mM Ca induce an intermediate stability. The difference between pH 7 and pH 9 is low, but pH 4 systematically induces a lower 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

85.4

2.5

75.8

5.0

68.4

6.7

pH 4

1

25.3

0.5

11.1

0.9

7.7

0.3

pH 4

10

13.3

1.1

6.8

0.7

5.0

0.5

pH 7

0

92.7

0.1

90.2

0.2

87.7

0.1

pH 7

1

91.4

0.8

89.7

1.4

87.4

1.7

pH 7

10

10.6

1.0

5.1

0.5

3.8

0.3

pH 9

0

93.3

1.1

92.4

0.5

90.3

0.6

pH 9

1

85.9

1.2

81.8

0.5

78.8

0.9

pH 9

10

12.3

0.1

6.0

0.5

4.6

0.4

  

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 moderate agglomeration at 1 mM Ca, pH7, with NOM (Figure 4). 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 0.03. 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:

The dispersion stability of the pigment was dependent especially on pH and water hardness. Dissolution was excluded as the main cause of the apparent stability. In very hard water with 10 mM Ca and at pH 4 with 1 mM Ca, the dispersion stability was low. At all other conditions, the stability was at least intermediate.