Chemistry
N-Phenyl-1-naphthylamine, (CAS No 90-30-2), also known as Phenyl-alpha-naphthylamine (PAN), is a lipophilic solid used as an antioxidant used in lubrication oils and as a protective agent in rubber products. In these products, the chemical acts as a radical scavenger in the auto-oxidation of polymers or lubricants. It is usually used in these products at a concentration of about 1%.
The commercial product has a typical purity of about 99%. Named impurities are: N-Phenyl-2-naphthylamine (CAS No 135-88-6, 500 to below 5000 ppm), 1-Naphthylamine (below 100-500 ppm) and 2-Naphthylamine (below 3 to 50 ppm), aniline (below 100 to 2500 ppm), 1-naphthol (below 5000 ppm), 1,1-dinaphthylamine (below 1000 ppm) (see Figure below).[i]
Figure 1: Possible Contaminants in
N-Phenyl-1-naphthylamine
2-Naphthylamine (CAS No 91-59-8) is also known as the established carcinogen b-Naphthylamine.[ii] Similarly 1-Naphthylamine is also known as a-Naphthylamine.
The formulation concentration of N-Phenyl-1-naphthalenamine in Mobil Jet Oil II is about 1%. As ingredients such as the naphthylamines have been deleted from product documentation such as the MSDB, the level of contamination of naphthylamines is presumed to be below the concentration cut off values for disclosure of Category 1 carcinogens specified in the Approved Criteria for Classifying a Hazardous Substance of 0.1% (1000 ppm).[iii]
Indeed, information from Mobil Australia notes that the level of contamination of some of the contaminants in this material is partially known (50 ppm for N-Phenyl-2-naphthylamine; 0.5 ppm for 2-Naphthylamine), and that they stopped listing such ingredients in about 1992 “solely to a reassessment of what was considered meaningful information from a hazard communication perspective”.[iv]
2-Naphthlyamine is not listed on the 1992 Australian inventory of Chemical Substances (AICS),[v] and dependent on the amount present in the formulated product (0.2%), could technically breach the requirements of the Commonwealth Industrial Chemicals (Notification and Assessment) Act 1989. However, the probable concentration of this contaminant in Mobil Jet Oil II is too low to exceed requirements of this legislation. Further, this chemical is listed as a prohibited substance under the Australian Hazardous Substances Regulation.
Toxicology
PAN is readily absorbed by mammalian systems and rapidly converted to metabolites.[vi] Both urine and faeces appear to be the main routes of excretion.[vii]
By single dosing, PAN does not seem particularly toxic, with LD50s above 1 g/kg. The chemical has a similar mechanism of toxicity of many aromatic amines, of methaemoglobin production. PAN is not irritating in primary skin and eye irritation studies. However, in a guinea pig maximisation test, PAN was shown to be a strong skin sensitiser.[viii] This result is supported by case studies in exposed workers.[ix],[x] At the concentration used (1%), Mobil Jet Oil II is classified as a hazardous substance in Australia for its sensitisation properties.iii
Most genotoxicity studies report negative results, suggested little genotoxicity potential.vii
Most repeated dose toxicological studies focus on its potential carcinogenicity. An experimental study, using both PAN and the related compound N-phenyl-2-naphthalenamine administered subcutaneously to mice found a heightened incidence of lung and kidney cancers.[xi] While the methodology used in this study makes evaluation of the results problematic (use of one gender, small sample sizes, limited number of dose groups, subcutaneous administration as an inappropriate route of exposure, and so on). A high incidence of various forms of cancer was also found among workers exposed to antirust oil containing 0.5% PAN.[xii] While these animal and human results offer only limited information, they are at least supportive of a mild carcinogenic effect.
This must be contrasted with the results of long term carcinogenicity bioassays in rats and mice conducted by the US National Toxicology Program with the structurally related N-phenyl-2-naphthylamine (studies were not carried out on PAN), which have not reported any carcinogenic potential for this chemical.[xiii]
Regulatory Classification
PAN is not listed on the NOHSC Designated List of Hazardous Substances.[xiv]
However, the NOHSC Approved Criteria for Classifying Hazardous Substances note that mixtures containing sensitisers should be classified as an “Irritant” hazardous substance if included in the product at a concentration at or greater than 1%. Further, a product containing a skin sensitiser at or above this value should carry risk statement R43 – May cause skin sensitisation by skin contact.iii
The data on carcinogenicity of PAN is too limited to make a determination sufficient to allow classification for regulatory purposes.
Nevertheless, based on established sensitisation properties and possible carcinogenic properties, exposure to materials containing N-phenyl-1-naphthylamine should be avoided.