N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine

Endpoint summary

Additional information

6PPD is a member of the PPD “family”, which further includes 7PPD (N-(1,4-dimethylpentyl)-N'-phenylbenzene-1,4-diamine), 77PD (N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine), and 44PD (N,N'-di-sec-butyl-p-phenylenediamine), The justification for the read-across approach between these four substances is provided in a separate document (Allmendinger 2016). Additional read-across was performed with

1,4-Benzenediamine, N-(1-methylheptyl)-N'-phenyl- ("8PPD").

Conclusion on degradation:

According to available information on degradation, all PPDs in question are not readily biodegradable and no significant biodegradation is observed but full abiotic degradation takes place.

The pathway of hydrolysis occurs in the same manner for all PPDs: Half-lives for the primary degradation are in the range of 3.4 to 8 hours. Primary degradation products are 4 -hydroxydiphenylamine, N-phenyl-p-benzoquinone-monoimine and the alkylamine

1,3 -dimethylbutylamine in case of 6PPD).

There are indications that secondary degradation is faster in case of 77PD/44PD than in case of 6PPD/7PPD. Common secondary hydrolysis products of all PPDs are p-benzoquinone and p-hydroquinone and an amine. In case of 6PPD the amine is aniline. The question arises why the PPDs are not readily biodegradable, some of their hydrolysis products (p-benzoquinone, p-hydroquinone, aniline and 1,3 -dimethylbutylamine) are known to biodegrade quite rapidly. Thus, at least some biodegradation could have been expected. A possible explanation for this contradiction is the fact that p-hydroquinone is highly toxic against bacteria. Based on an EC50 of 71 mg/L and a NOEC of 1 mg/L the resulting PNEC(STP) is 0.71 mg/L. Biodegradation tests according to the OECD 301 series are typically performed with initial concentrations of 30 to 100 mg/L. Thus, even low concentrations of p-hydroquinone formed by hydrolysis may have a significant effect and kill bacteria or at least inhibit bacterial growth in the biodegradation tests on 6PPD.In the atmosphere rapid photodegradation takes place by reaction with photochemically produced OH radicals. The half-life of 6PPD is calculated to be 1.7 hours in that test system. (Currenta, 2009).

In order to evaluate the behaviour of PPDs in the environment,mechanistic studies have been performed: The reaction of paraphenylenediamines with oxygen and ozone radicals was studied (Klemchuk 1985 Polymer Stabilization and Degradation (ACS Symosium Series 280), Ignatz-Hoover 2012 Rubber & Plastics News (March 19, 2012):

• • Reaction with oxygen: Formation of quinone-diimines followed by oxidation of the nitrogene forming N-oxides.
  • Quninone-diimines may also react to mono-quinoneimines which might further react to p-benzoquinone
  • Reaction with ozone: Addition of ozone to nitrogen with cleavage of the C-N structure forming N-oxides. Quinone-imines and N-oxides are reactive species which might further react forming higher and more complex molecules

In an aerobic soil simulation test performed with the analogous substance 7PPD (N-(1,4-dimethylpentyl)-N'-phenylbenzene-1,4-diamine, CAS No. 3081-01-4)according to OECD 307 with 4 different soil types with a pH range of 3.86 to 7.19, 7PPD showed a rapid degradation loss in all soil types by strong and irreversible adsorption or binding. The half-lives were in the range of 0.03 to 1.9 days at 12°C. No metabolites were formed. At day 56 (end of study) only 4.5 to 9.1% of AR could be extracted using repeated Soxhlet-extractions with different solvents. NERs at day 56 were in the range of 76.4 to 84.8%. Several attempts have been made in order to characterise the non-extractable residues (NERs). Acidic reflux extractions at 100 °C, following ambient extractions, released 10.8 to 12.8% AR on day 56. The acidic reflux conditions were found to be residue altering. The residue released by reflux extraction was considered as part of the NER type 1, defined as non extractable residue that is sorbed or entrapped within the soil organic matter. The residue remaining in the soil after refluxing was considered as bound residue, consisting of NER-type 2 (covalently bound) and NER-type 3 (biogenic NER).

The anaerobic soil simulation test according to OECD 307 yielded a rapid degradation loss of the parent substance mainly during the aerobic phase with a half-life of 1.5 days. One metabolite was identified (1-N-(5-methyl-hexan-2-yl)-4-N-phenylcyclohexa-2,5-dione-4,4-diimine) which degraded with a half-life of 66.9 days at 12°C.

Conclusion on bioaccumulation:

A valid QSAR for the BCF of 6PPD was used yielding a BCF of 568.7. In a weight-of-evidence approach using an experimental study for a higher homologue of the parephenylenediamines ("8PPD") which resulted in a BCF of 1700 and supporting information from a QSAR for 8PPD the result of BCF 568.7 for 6PPD was validated.

Environmental data, monitoring data:

6PPD has been used as an indicator for other members of the PPD-family as it is commonly used in tyre production.

Currenta (2010): Waste water from 25 representative rubber manufacturing sites in Europe (France, Germany, Italy, Poland, Spain, UK), including tyre and general rubber goods manufacturing, were sampled and analysed for 6PPD and the hydrolysis product 4-hydroxydiphenylamine (4-HDPA). Additional information was collected from individual sites, mainly on tonnages, waste water flow and relevant production conditions.

The emission of the test substance to waste water at individual sites was measured reaching a value of 5.61 kg/year (90th percentile). Inserting this figure into the estimation program EUSES, the following result was determined:

Safe use can be demonstrated for a site with a waste water load of 6PPD of up to 3.5 kg/year, emitting to a standard sewage treatment plant (STP; 10.000 inhabitants, 2000 m³/day) and to a standard river (18.000 m³/day).

Statistical evaluation showed that with regard to local concentrations in receiving rivers and the concentration in agricultural soils, safe use is established using the 90^thpercentile of the rubber manufacturing sites.

Swedish Environmental Research Institute (2011): Monitoring data from surface water, WWTP effluents and from storm water in Sweden gave the following resulte:

Surface water (11 samples): median 0.071 µg/L

WWTP effluent (5 samples): median 0.018 µg/L

Storm water (4 samples): median 0.11 µg/L.

Sediment (6 samples): all values <0.0006 mg/kg

Soil (6 samples): all values <0.0006 mg/kg