Diisopropyl 3,3'-[(2,5-dichloro-1,4-phenylene)bis[iminocarbonyl(2-hydroxy-3,1-naphthylene)azo]]bis[4-methylbenzoate]

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

Test material information

Constituent 1

Reference substance name:

Diisopropyl 3,3'-[(2,5-dichloro-1,4-phenylene)bis[iminocarbonyl(2-hydroxy-3,1-naphthylene)azo]]bis[4-methylbenzoate]

EC Number:

275-639-3

EC Name:

Diisopropyl 3,3'-[(2,5-dichloro-1,4-phenylene)bis[iminocarbonyl(2-hydroxy-3,1-naphthylene)azo]]bis[4-methylbenzoate]

Cas Number:

71566-54-6

Molecular formula:

C50 H42 Cl2 N6 O8

IUPAC Name:

diisopropyl 3,3'-[(2,5-dichloro-1,4-phenylene)bis[iminocarbonyl(2-hydroxy-3,1-naphthylene)azo]]bis[4-methylbenzoate]

Test material form:

solid: nanoform, no surface treatment

Details on test material:

- State of aggregation:
- Particle size distribution:
- Mass median aerodynamic diameter (MMAD):
- Geometric standard deviation (GSD):
- Shape of particles:
- Surface area of particles: BET = 29.5 +/- 0.3 m2/g
- Coating: none

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 and pH is critical. Regardless of pH, the pigment is categorized at the 24h-sampling time as “unstable” in 10 mM Ca, representing high water hardness. The same “instable” categorization can be applied for any media at pH 4. After 6h at pH 9 and 0 or 1 mM Ca induces high dispersion stability. The samples at pH 4 and 7 and 0 and 1 mM Ca are rated as intermediate-high stability. At high Ca concentrations of 10 mM the stability was generally intermediate regardless of the pH value.

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. Regarding the environmental relevance the substance is treated as intermediate stable.

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	30.1	0.2	14.1	0.2	9.0	0.4
pH 4	1	25.1	0.5	12.7	0.4	7.6	0.5
pH 4	10	21.0	0.5	9.8	0.3	7.6	0.5
pH 7	0	88.6	0.6	84.1	1.1	81.6	1.2
pH 7	1	88.5	0.1	80.1	0.2	73.5	0.5
pH 7	10	19.6	1.3	10.1	0.5	7.8	0.1
pH 9	0	94.1	0.8	89.7	1.3	86.7	1.3
pH 9	1	90.3	1.1	83.1	1.2	78.8	1.3
pH 9	10	17.1	0.6	9.2	0.4	7.2	0.5

 

  

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 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 on the scale of 0.06. This is a fraction of 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

Executive summary:

The dispersion stability of Pigment Red 221 was strongly depended on water hardness. Dissolution was excluded as the main cause of the apparent stability. In very hard water with 10 mM Ca and/or pH 4, the dispersion stability of the tested substance was low. At all other conditions, the dispersion stability was at least intermediate. At pH9 with 0 or 1 mM Ca, the stability was high.