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

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption: screening

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the physicochemical properties of the substance indicate that it can be expected to have a low potential for adsorption

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
see attached justification

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

data waiving: supporting information

Remarks:

dispersion stability

Reference

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.

Cross-reference 2

Reason / purpose for cross-reference:

data waiving: supporting information

Remarks:

dispersion stability

Reference

Studies on the Dispersion stability of nanomaterials are to be found in chapter 5.6 Additional information on environmental fate and behaviour.

Cross-reference 3

Reason / purpose for cross-reference:

data waiving: supporting information

Remarks:

dispersion stability

Reference

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(NO3)2 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 pH 9 with 0 or 1 mM Ca(NO3)2, the stability was high.

→ Details refer to the endpoint 5.6

The OECD TG 318 on Dispersion Stability of Nanomaterials in Simulated Environmental Media is the first nano-specific test guideline, published 2017. Here we applied it to an organic pigment in order to map the ranges of stability in different media of surface water.

→ The study record maintained at the endpoint 5.6

Cross-reference 4

Reason / purpose for cross-reference:

data waiving: supporting information

Remarks:

dispersion stability

Reference

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

Qualifier:

according to guideline

Guideline:

other: OECD 318

GLP compliance:

yes (incl. QA statement)

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.

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.

Cross-reference 5

Reason / purpose for cross-reference:

data waiving: supporting information

Remarks:

logKow

Reference

Estimated based on solubility ratio:

log Pow= -0.57

Log Kow (Log Pow):

-0.57

at the temperature of:

20 °C

The solubility was determined by flask method based on OECD Guideline 105 and the ETAD method. The solubility was quantified by UV/Vis absorption.

Cross-reference 6

Reason / purpose for cross-reference:

data waiving: supporting information

Remarks:

logKow

Reference

Endpoint:

partition coefficient

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Principles of method if other than guideline:

The partition coefficient was estimated based on the ratio of the solubilities in n-octanol and in water.
The individual solubilities were determined by the flask method based on OECD Guideline 105 and the ETAD method. The concentration was quantified by UV-Vis absorption.

GLP compliance:

no

Type of method:

estimation method (solubility ratio)

Partition coefficient type:

octanol-water

Analytical method:

photometric method

Key result

Type:

log Pow

Partition coefficient:

-0.57

Temp.:

23 °C

Remarks on result:

other: pH not available

Details on results:

The solubility in water is 91 µg/L
The solubility in n-octanol is 24 µg/L

Each solubility test was measured 2 times. The results of the solubility represented a mean value of 3 tests.

Estimation of log Pow value:

Pow= c(n-octanol) / c( water)= 24 µg/L / 91 µg/L= 0.27

Log Pow= -0.57

Conclusions:

The partition coefficient of test substance was estimated to be log Pow= -0.57 at 23°C.