Strontium 3-hydroxy-4-[(4-methyl-2-sulphonatophenyl)azo]-2-naphthoate

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

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

data waiving: supporting information

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:

no

At any of the time points mentioned in the TG-318, the influence of Ca is critical. Regardless of pH, the pigment is least stable in 10 mM Ca, representing high water hardness. After 6h, the samples showed high dispersion stability in 0 mM Ca and 1 mM Ca at pH 4 and 9. The stability at all other conditions was intermediate. After 24 hours the stability in 0 mM Ca and 1 mM Ca at pH 4 and 9 remained high. The stability in 1 mM Ca at pH 7 and in 10 mM Ca at pH 4 remained intermediate. For the samples at all other conditions the stability became low.

 

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	99.2	0.2	98.2	0.4
pH 4	1	99.8	0.2	99.0	0.5	98.6	0.5
pH 4	10	34.0	0.7	27.2	0.7	25.3	0.5
.
pH 7	0	100	0.2	98.5	0.1	97.5	0.5
pH 7	1	76.5	2.6	33.9	1.2	22.5	2.2
pH 7	10	14.1	1.3	8.3	0.3	7.1	0.2
.
pH 9	0	99.7	0.3	97.9	0.8	96.2	0.9
pH 9	1	99.6	0.0	98.5	0.3	97.2	0.4
pH 9	10	14.4	0.3	8.9	0.8	7.6	0.8

 

 

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 by³). 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 at c.a 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:

Elevated apparent dispersion stability may originate from dissolution. The dissolution in environmental media has not yet been assessed, but the particle size distribution was measured in all media. The remaining absorption after centrifugal separation of particles was determined to be not more than 3% of the total signal. Thus, dissolution is not the main cause of the observed stability.

 

Taken together, the dispersion stability of Pigment Red 52_Sr depends especially on pH and water hardness. The stability for samples in 0 mM Ca and 1 mM Ca at pH 4 in 9 was high. Thestability in 1 MM Ca at pH7 and in 10 mM Ca at pH4  is intermediate. Stability at all other conditions was low.

Cross-reference 2

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Endpoint:

partition coefficient

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2008

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 105 and ETAD method

Principles of method if other than guideline:

To measure the partition coefficient of pigments utilising the standard OECD Guideline 107 is extremely difficult because of the problems associated with the inherent very low solubilities. The following procedure is used for determining the LogPow of low solubility substances and in particular that of pigments.
The partition coefficient was estimated based on the ratio of the solubilities in n-octanol and in water. The individual solubilities were determined by flask method based on OECD Guideline 105 and the ETAD method.

A defined amount of the pigment (see table 1) was transferred to a 100 ml flask with glass stopper and 60 ml of water (deionised, 18.2 MOcm). This was stirred at 70°C for 2 hours, and then 72 hours in an air conditioned laboratory (T = 23°C). The suspension was then centrifuged (10 000 rpm, 10 min) and filtered once through a standard paper filter, twice through a 0.2 μm membrane filter (Millipore) and twice through a 0.025μm membrane filter (Millipore). If particles were detected in the solution (turbidity), the final filtration step was repeated until a perfectly clear solution was acheived.
The above procedure was conducted in parallel for a total of 2 water (deionised, 18.2 MOcm) samples and of 2 n-octanol (Sigma-Aldrich, spectrophotometric grade) samples.

GLP compliance:

no

Type of method:

estimation method (solubility ratio)

Partition coefficient type:

octanol-water

Analytical method:

high-performance liquid chromatography

photometric method

Key result

Type:

log Pow

Partition coefficient:

-0.61

Temp.:

23 °C

Remarks on result:

other: The pH was not reported.

Details on results:

Solubility in n-octanol: 9.2-9.4 mg/L (HPLC-DAD)
Solubility in water: 37-39 mg/L mg/L (UV/Vis)
Weight in n-octanol/water: 53.2-58.6 mg/100 mL

Conclusions:

The partition coefficient of test substance was estimated to be log Pow= -0.61 at 23°C.