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

Additional information on environmental fate and behaviour

Administrative data

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

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:

no

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.

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.

Applicant's summary and conclusion

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.