N,N'-phenylene-1,4-bis[4-[(2,5-dichlorophenyl)azo]-3-hydroxynaphthalene-2-carboxamide]

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:

N,N'-phenylene-1,4-bis[4-[(2,5-dichlorophenyl)azo]-3-hydroxynaphthalene-2-carboxamide]

EC Number:

223-460-6

EC Name:

N,N'-phenylene-1,4-bis[4-[(2,5-dichlorophenyl)azo]-3-hydroxynaphthalene-2-carboxamide]

Cas Number:

3905-19-9

Molecular formula:

C40H24Cl4N6O4

IUPAC Name:

N,N'-phenylene-1,4-bis[4-[(2,5-dichlorophenyl)azo]-3-hydroxynaphthalene-2-carboxamide]

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 85-95%, and only at pH 4 induces a stability of 48-60%. Stability in 10 mM at regardless pH value is on the level of 12-18%

At 24h, all media in 0 mM Ca and 1 mM Ca induce an intermediate stability although stability at pH 7 is higher than at pH 9 and especially pH 4.

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	60.5	0.7	33.5	1.0	22.8	0.4
pH 4	1	48.0	1.2	21.8	1.4	14.3	0.6
pH 4	10	17.5	1.4	9.0	0.9	6.2	0.5
pH 7	0	94.9	0.3	91.4	1.0	90.7	1.4
pH 7	1	94.3	0.2	90.8	0.3	88.1	0.6
pH 7	10	19.1	1.1	8.4	0.5	5.4	0.2
pH 9	0	90.1	0.9	81.9	0.7	75.4	0.1
pH 9	1	85.1	0.4	74.1	0.2	66.7	0.3
pH 9	10	11.9	0.1	5.4	0.1	4.3	0.1

  

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 test substance was dependent especially on pH and water hardness. Dissolution was excluded as the main cause of the apparent stability. Regardless pH, in very hard water with 10 mM Ca, the dispersion stability was low. At all other conditions, the stability was at least intermediate although stability at pH 7 was higher than at pH 9 and especially pH 4.