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Environmental fate & pathways

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

Test material

Constituent 1
Chemical structure
Reference substance name:
2,2'-[(3,3'-dimethoxy[1,1'-biphenyl]-4,4'-diyl)bis(azo)]bis[3-oxo-N-phenylbutyramide]
EC Number:
229-388-1
EC Name:
2,2'-[(3,3'-dimethoxy[1,1'-biphenyl]-4,4'-diyl)bis(azo)]bis[3-oxo-N-phenylbutyramide]
Cas Number:
6505-28-8
Molecular formula:
C34H32N6O6
IUPAC Name:
2,2'-[(3,3'-dimethoxy[1,1'-biphenyl]-4,4'-diyl)bis(azo)]bis[3-oxo-N-phenylbutyramide]
Test material form:
solid: nanoform

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 unstable in 10 mM Ca, representing high water hardness. After 6h, the samples showed intermediate dispersion stability at all conditions studied. The stability in 0 and 1 mM Ca at pH7 was not evaluated due to the deposition of pigment on the cuvette walls. After 24 hours the stability in 0 mM Ca at pH 9 remained intermediate. For the samples at all other conditions the stability became low (stability in 0 and 1 mM Ca at pH7 was considered to be 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



64.4



8.5



29.5



9.2



14.8



3.2



pH 4



1



34.7



1.0



9.9



1.0



5.8



1.2



pH 4



10



42.8



7.5



14.3



3.0



8.9



1.8



.


 

 



 



 



 



 



 



pH 7



0



N/A



N/A



N/A



N/A



0



0



pH 7



1



N/A



N/A



N/A



N/A



0



0



pH 7



10



28.4



2.4



6.4



1.1



5.5



0.6



.


 

 



 



 



 



 



 



pH 9



0



89.0



1.0



63.4



2.3



54.9



2.7



pH 9



1



38.8



8.0



13.6



2.3



8.8



0.5



pH 9



10



11.9



0.4



5.2



0.3



3.9



0.2



To rationalize the observed dispersion stability, we finally checked the particle size distribution directly in the environmental medium. We applied the NanoDefine method of Analytical Ultracentrifugation. The centrifugation parameters are given in the methods section.


As required by TG318, paragraph 31, the tested nanomaterial was pre-wetted in ultrapure water and left in the form of wet-paste for 24 h. The TG318 requires this step “to insure the proper interaction of nanomaterial surface with ultrapure water.” We visually observed incomplete wetting, and so any ensuing measurement would have been incorrect. In accord with the NanoGenoTox dispersion protocol, a drop of ethanol was added, successfully transferred the powder into a paste, which was then further diluted as specified in the TG318


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. 0.04. 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.


 


 

Applicant's summary and conclusion

Executive summary:

At any of the time points mentioned in the TG-318, the influence of Ca is critical. Regardless of pH, the pigment is unstable in 10 mM Ca, representing high water hardness. After 6h, the samples showed intermediate dispersion stability at all conditions studied. The stability in 0 and 1 mM Ca at pH7 was not evaluated due to the deposition of pigment on the cuvette walls. After 24 hours the stability in 0 mM Ca at pH 9 remained intermediate. For the samples at all other conditions the stability became low (stability in 0 and 1 mM Ca at pH7 was considered to be low).

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