1,4-bis[(2-ethyl-6-methylphenyl)amino]anthraquinone

Endpoint summary

Description of key information

Bioaccumulation:

The concentration of Reinblau RLW in fish ranged from 0.37 to 1.08 µg/g (w/w) and the bioconcentration (BCF) was 2 to 5 (Mitsubishi, 2011). On the basis of the BCF obtained, it is concluded that the bioaccumulation potential of the test substance in fish is low under the test condition. Result of this experimental study are supported by QSAR value from the registered substance itself.

Additional information

Category approach:

LANXESS Deutschland GmbH has registered five mono-constituent anthraquinone dyes of similar chemical structure using a category approach: Solvent Violet 36 (CAS No 82-16-6), Solvent Green 28 (CAS No 4851-50-7), Reinblau RLW (CAS No 41611-76-1), Reinblau BLW (CAS No 32724-62-2) and Solvent Green 3 (CAS No 128-80-3). Additional data were taken from another registered anthraquinone dye, Solvent Blue 104 (CAS 116 -75 -6), leading to a category consisting of six members (see attached justification in IUCLID chapter 13). The category consists of substances all having the diamino-anthraquinone structure as a common moiety which is linked to phenyl groups via the amino groups. Differences within the category are described by various alkyl groups bound to the phenyl groups.

 

To further add weight of evidence for the category members not being bioaccumulative the following is true:

All substances included in the category approach are poorly water soluble (< 20 µg/L), which reduces the bioavailability of the substances. Moreover, the substances also have a high partition coefficient (log Kow > 8). For substances where their accumulation is driven by lipid solubility the peak of the Gaussian-Type relationship for the log Kow and bioaccumulation occurs at around a log Kow of 6, either side of this log Kow the (bio)accumulation potential begins to diminish. As such a cut-off of a log Kow of 10 has been suggested as part of a weight-evidence to highlight chemicals that are not bioaccumulative (ECHA R.11, 2017). The high log Kow of the group is suggestive of a lower potential for bioaccumulation, this is supported by the results for Reinblau RLW (BCF ≤ 5, log Kow ~8). Reinblau RLW has one of the lower log Kow values of the category indicating it may be one of the worst-case molecules to study for bioaccumulation, but is still not bioaccumulative. Solvent Green 28 and Solvent Blue 104 both have log Kow > 10, which would suggest they would be less bioaccumulative than Reinblau RLW or at least demonstrate comparably low bioaccumulation. This has been experimentally confirmed for  Solvent Blue 104  (BCF 5-27 L/kg) . The other members are similar as it concerns log Kow, thus bioaccumulation is expected to be similar – but again low. Further, the molecules are relatively large in 3-dimensional space. A cut-off for Dmax (molecular diameter maximum average) of 1.7 nm has been suggested to indicate low potential for bioaccumulation (ECHA R.11, 2017). From the current analysis, Reinblau RLW is below this cut-off but still does not bioaccumulate. Solvent Green 3 has a Dmax of 1.72 nm and Solvent Violet 36 has a Dmax of 1.7 nm. Based on this property it further supports that these latter chemicals are likely less bioaccumulative than Reinblau RLW and that read-across to this target is a worst-case. However, considering the whole profile of both these substances, further study on Solvent Green 3 is suggested to represent the extremes of either side of the boundary.  Note, all of the category members have a Dmax between ~1.6 to ≥ 1.7 nm.  

 

None of the category members meet all weight-of-evidence criteria as stated in ECHA R.11 (2017) to conclude them to be non-bioaccumulative. However, all meet at least one criteria, Solvent Green 3 and Solvent Violet 36 have a Dmax ≥ 1.7 nm, Solvent Green 28 and Solvent Blue 104 both have log Kow values greater than 10.  The only 2 for the group which do not meet any criteria are Reinblau RLW and Reinblau BLW.  Both are common in structure with ethyl and methyl substituents on the phenyl groups and have highly similar physical-chemical properties. The further ethyl group on Reinblau BLW is not expected to significantly change the results of any bioaccumulation assessment and log Kow and Dmax are not significantly different. As no criteria for excluding bioaccumulation were met for these 2 substances, these can be considered as a worst-case for potential bioaccumulation in the group, though the results are expected to be similar enough to negate the need for extrapolation of the value to other members of the group (direct read-across). Reinblau RLW, despite being the most likely to bioaccumulate to a significant degree, if at all, only had a BCF of 2 to 5. Therefore, the category members are also expected to have very low BCFs i.e. in single-digit or double-digit range in the worst-case.

To confirm the low potential of bioaccumulation of the category members, a testing proposal for a bioaccumulation study will be performed on Solvent Green 3.

This study is considered to be required as the the current experimental BCFs only represent one extreme of the boundary of the category.  The log Kow for Solvent Blue 104 is > than 10.2 and the log Kow is higher for Reinblau RLW, moreover, both have more than one substituent on the phenyl groups.  Therefore, Solvent Green 3 represents, the other extreme, with the lowest log Kow (8.2) and only one substituent.

Currently, experimental studies/read-across and the comparison with QSAR estimations show that the six category members have a low bioaccumulation potential far below the trigger values, i.e. 2,000 and 5,000 respectively, for B or vB (cf. ECHA Guidance Document R.11, V.2.0, p. 14). BCF values (experimental and predicted values) combined with meeting one criteria that indicates low potential for bioaccumulation for all category members act as a weight-of-evidence to indicate that the category members are not bioaccumulative. Therefore, this category and its members should not be classed bioaccumulative or very bioaccumulative.