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PBT assessment

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PBT assessment: overall result

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Name:
N,N'di-sec-butyl-p-phenylenediamine
Type of composition:
legal entity composition of the substance
State / form:
liquid
Reference substance:
Composition 1
Name:
N,N'-di-sec-butyl-p-phenylenediamine - SIP
Type of composition:
boundary composition of the substance
State / form:
liquid
Reference substance:
Composition 1
PBT status:
the substance is not PBT / vPvB
Justification:

The substance 44PD (CAS 101 -96 -2) is considered not to be PBT/vPvB based on the following arguments:

1. Persistence

A hydrolysis test performed on 44PD revealed that the half-life of the substance at pH 7 and pH 9 - from an environmental perspective the most relevant pHs - are 5.3 and 1.5 hrs, respectively. Hydrolysis products are p-benzoquinone, p-hydroquinone and 1-methyl-propylamine. Hydroquinone has been shown to be readily biodegradable, while the amine biodegrades. Read across data from 77PD was used, yielding an estimated half-life in water of 2 hrs and 4 hrs in the light and dark, respectively, following phototransformation.

2. Bioaccumulation

No direct bioconcentration data are available for 44PD. However, other data on certain properties of the substance provide sufficient information in order to conclude that 44PD does not bioaccumulate: the partition coefficient of 44PD was determined experimentally, resulting in log Kow values of 2.7 and 3.7 at pH values of 5 and 8, respectively. In addition, the partition coefficient was calculated with a QSAR approach, which is well documented, gives excellent results in the training and validation datasets and consists of a well defined algorithm. 44-PD (CAS nr 101-96-2) falls well within the applicability range of the model and has a log Kow of 3.50. The log Kow is below the criterion of 4.5.

Besides measurement of the log Kow, a BCF value was estimated using a QSAR approach. 44PD has a log BCF of 2.1, corresponding to a BCF of 126. From this, it was concluded that 44PD does not bioaccumulate. Furthermore, QSAR estimation of the bioaccumulative potential of hydroquinone, one of the main hydrolysis products of 44PD, indicated that hydroquinone does not have the potential to bioaccumulate (BCF = 3.16 L/kg).

3. Toxicity

A repeated dose toxicity test with 44PD in rats indicated that the liver is the main target organ for adverse effects upon oral administration of the test substance. Marked histopathological alterations were found in rats dosed with 50 and 100 mg/kg bw of test substance, including periportal degeneration and necrosis. Furthermore, the death of 2 animals in the highest dose groups that died on days 4 and 5 was most likely caused by liver failure. At dose levels below 50 mg/kg bw, the histopathological effects were less severe and fewer in number. As a consequence, 50 mg/kg bw was selected as the lowest dose that induces significant toxic effects in a 28 day oral exposure test in rats. Based on the guidance values, a classification as STOT RE Category 2 is warranted for this level of toxicity. For ecotoxicity, a number of short term tests on 44PD are available for fish, Daphnia and algae. Fish is the most sensitive species, the lowest LC50 being found for Pimephales promelas and equaling 0.13 mg/L. Long term test results are available for hydroquinone (one of the hydrolysis products of 44PD) for invertebrates and for 6PPD in fish, a strucural analog of 44PD. The long term NOEC for 6PPD in fish was reported to be 0.0037 mg/L. Based on the available ecotox studies, it was concluded that 44PD should be classified for both acute and chronic aquatic toxicity Cat. 1. Taking into account both human and ecotoxicity results and the ECHA Guidance R.11 on PBT assessment, 44PD is considered to be Toxic.

Overall conclusion

Based on the information above, it can be concluded that while 44PD fulfills the T criterion, neither the P, nor the B criterion is fulfilled. The overall conclusion therefore is that 44PD is not PBT or vPvB.