N,N'-di-sec-butyl-p-phenylenediamine

Long-term toxicity to fish

Description of key information

The chronic toxicity of N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD) to fish was tested with Oryzias latipes in a Early-Life Stage Toxicity Test according to OECD Guideline 210. The 30d NOEC is 0.0037 mg 6PPD/L. ( National Institute of Technology and Evaluation, Japan, 2003). Based on structural analogy it is considered that these results can also be used for 44PD. This corresponds to a 30d NOEC of 0.0030 mg 44PD/L after correction for molecular weight. 

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

0.003 mg/L

Additional information

Since no testing data were available for 44PD, read across was done with 6PPD. The chronic toxicity of N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD) to fish was tested with Oryzias latipes in a Early-Life Stage Toxicity Test according to OECD Guideline 210. The 30d NOEC is 0.0037 mg 6PPD/L. Based on structural analogy it is considered that these results can also be used for 44PD. After correction for molecular weight this corresponds to a 30d NOEC of 0.030 mg/L

RATIONALE FOR READ ACROSS

Justification Document for the Read-Across Approach from 6PPD to 44PD

 

Summary

The justification for the read-across is outlined considering the physico-chemical similarity, degradation potential and ecotoxicity

 

6PPD:

CAS                           793 -24-8

EC                             212-344-0

Empirical formula        C18H24N2

EC name                     N-1,3-dimethylbutyl-N’-phenyl-p-phenylenediamine

 

 

1. Justification of read-across based on physico-chemical data

 

Table 1. Relevant physico-chemical parameters

Parameter	6PPD	44PD
Melting point	49.2°C	17°C
Boiling point	163-165°C	310°C
Vapour pressure	6.57E-06 hPa calculated	40 - 207 E-06 hPa calculated
Partition coefficient	4.68 calculated	3.7 at pH 8 calculated
Water solubility	1.1 mg/L	< 10 mg/L measured
Dissociation constant (pKa)	6.73 calculated ACD labs	7.5 measured

 

Vapour pressure: Both 6PPD and 44PD have low vapour pressures and thus they are considered as non-volatile.

Partition coefficient: Both substances have relatively high log Kow values. The lower log Kow for 44PD can be explained by its shorter alkyl chain.

Water solubility: Although the determination of the water solubility is questionable due to the rapid hydrolysis, all existing values are in the same range. 6PPD and 44PD can be considered not very soluble, 44PD having a somewhat higher solubility than 6PPD.

 

 

Dissociation constant: Values for 6PPD and 44PD are in the same range. The values demonstrate that both the neutral and the mono-protonated form both substances will be present at the environmentally relevant pH of 7.

 

Conclusion: The main physico-chemical parameters log Kow, vapour pressure, water solubility and dissociation constant of the PPDs are in the same range. Read across based on physico-chemical data therefore is justified.

 

 

2. Justification of read-across due to degradation

 

It has been shown that the percentage biodegradation of 6PPD is ca. 2%. Nevertheless, in HPLC measurements it was found that during the biodegardation test the parent compound had nearly completely degraded due to hydrolysis. The half-life of 6PPD was established to be ca. 8 hrs at pH7.The main hydrolsys products are 4-hydroxydiphenylamine, p-benzoquinone and p-hydroquinone.

 

Although no experimental results are available for 44PD, QSAR models indicate that -although the substance is expected to display a certain degree of biodegradation - it does not biodegrade rapidly. Similar to 6PPD, 44PD hydrolyses rapidly and has a half-life of 5.3 hrs at pH 7. The main hydrolysis products are p-benzoquinone, p-hydroquinone and 1-methyl propylamine.

 

Conclusion: according to available information on degradation, 6PPD and 44PD are not readily biodegradable. However, 44PD displays a somewhat higher tendency to biodegrade than 6PPD. Both substances hydrolyse rapidly, with half-lives that are very similar. Common hydrolysis products are p-benzoquinone and p-hydroquinone.

 

3. Justification of read-across due to effects in ecotoxicity

 

An overview of the relevant ecotoxicological key data for the 6PPD and 44PD Table 2.

 

Table 2. Results of all available ecotoxicity tests, except those with reliability 3 (references are explained in the IUCLID dossier and in the CSR)

 

	6PPD	44PD
Short-term toxicity to fish	96h-LC50 0.028 mg/L (MITI, 1999)   96h-LC50 0.29 mg/L (MITI, 2001)   96h-LC0 5 mg/L (Bayer, 1984)	96h-LC50 0.4 mg/L (MITI, 2010)   96h-LC50 0.18 mg/L (Monsanto, 1983)   96h-LC50 0.13 mg/L (Monsanto, 1983)
Long-term toxicity to fish	NOEC 0.0037 mg/L (MITI, 2002)	n/a
Short-term toxicity to aquatic invertebrates	48h-EC50 0.23 mg/L, (MITI, 1999)   48h-EC50 0.51 mg/L (Monsanto, 1984)   48h-EC50 0.79 mg/L (Monsanto, 1984)   48h-EC50 0.82 mg/L (Monsanto, 1978)	48h-LC50 1.4 mg/L (Monsanto, 1983)   48h-EC50 0.54 mg/L (MITI, 2008)
Long-term toxicity to aquatic invertebrates	n/a	n/a
Toxicity to aquatic algae and cyanobacteria	72h-ErC50 4.46 mg/L NOEC 0.5 mg/L (Flexsys, 1998)	72h-EC50 0.939 mg/L 72h-NOEC 0.0958 mg/L (MITI, 2010)

 

 

All ecotoxicity values for 6PPD and 44PD are in good agreement. For fish and invertebrates the most sensitive value is found with 6PPD. For both substances, algae are the least sensitive trophic level.

 

 

Conclusion

Based on the structural similarity of 6PPD and 44PD, their fast hydrolysis and the ecotoxic values, it is concluded that it is warranted to read across from 6PPD to 44PD.