Strontium 4-[(4-chloro-5-methyl-2-sulphonatophenyl)azo]-3-hydroxy-2-naphthoate (1:1)

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption: screening

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

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

Reference

Endpoint:

additional information on environmental fate and behaviour

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.

The dispersion stability of Pigment 52:Sr was strongly depended on water hardness and pH. Dissolution was excluded as the main cause of the apparent stability. The stability in 0 mM Ca was high. The stability in 1 mM Ca at pH 4 was intermediate. For the samples at all other studied conditions the stability was 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	0.7	100	0.8	100	0.7
pH 4	1	95.5	0.3	80.4	2.2	67.7	3.0
pH 4	10	14.6	0.5	9.0	0.1	7.5	0.1
.
pH 7	0	99.9	0.1	98.8	0.1	97.7	0.2
pH 7	1	24.3	2.9	12.4	1.7	9.8	1.3
pH 7	10	14.0	1.4	8.1	0.2	6.9	0.0
.
pH 9	0	99.9	0.1	99.0	0.2	98.0	0.2
pH 9	1	25.6	3.4	13.2	0.6	10.6	0.5
pH 9	10	15.2	0.4	9.0	0.5	7.5	0.6

 

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. 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 ca. 0.08. This is a fraction of 5.4% of the initial absorption, but actually is close to the LOD of the built-in UV/Vis detector. Considering the LOD, between 0% and 5.4% of the sample may have been dissolved.

All evidence combined, the results after centrifugation confirm that at least 94.6% of the observed dispersion stability has to be attributed to the particles, not to dissolution.

Executive summary:

The dispersion stability of Pigment 52:Sr was strongly depended on water hardness and pH. Dissolution was excluded as the main cause of the apparent stability. The stability in 0 mM Ca was high. The stability in 1 mM Ca at pH 4 was intermediate. For the samples at all other studied conditions the stability 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:

2012

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar 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.

GLP compliance:

no

Type of method:

estimation method (solubility ratio)

Partition coefficient type:

octanol-water

Specific details on test material used for the study:

- Name of test material (as cited in study report): Pigment Rot 52:Sr
- Physical state: powder
- Lot/batch No.: JW111201

Analytical method:

high-performance liquid chromatography

Key result

Type:

log Pow

Partition coefficient:

1.22

Temp.:

23 °C

Remarks on result:

other: pH was not reported

The concentration of the pigment in water and in n-octanol was determined by HPLC-UV

Average concentration of 3 tests:

C_n-octanol= 197µg/L

C_water= <15µg/L

The n-octanol/water partition coefficient can be approximated with the following equation:

Pow= (C_n-octanol/ C_water)= 16.7

logPow= 1.22

Cross-reference 3

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2012

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Version / remarks:

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.

GLP compliance:

no

Type of method:

flask method

Specific details on test material used for the study:

- Name of test material (as cited in study report): Pigment Rot 52:Sr
- Physical state: powder
- Lot/batch No.: JW111201

Key result

Water solubility:

< 15 µg/L

Conc. based on:

test mat. (total fraction)

Incubation duration:

72 h

Temp.:

23 °C

Remarks on result:

other: mean value of 3 tests

Conclusions:

The water solubility of test substance was determined to be <15 µg/L at 23°C

Cross-reference 4

Reason / purpose for cross-reference:

data waiving: supporting information