Polycyclic (or Polynuclear) Aromatic Hydrocarbons (PAH) is a large group of related substances with more fused benzene rings. PAH occur for instance as mixtures in petroleum products and coals. In addition, PAH mixtures are formed at incomplete combustion and pyrolysis of organic matters e.g. in wood stoves and smokeries, and they have become important air pollutants, especially in large cities.
Other more general name for this type of chemicals for including other chemicals than hydrocarbons are: “PolyNuclear Aromatics (PNA)” or “Polycyclic Aromatic Compounds (PAC)”.
Many PAH are toxic and carcinogenic. The most well-known carcinogenic member of this group is benzo[a]pyrene (BaP), which often is used as a marker for PAH, and the presence of other PAH can be expressed as BaP-equivalents:
Extender oils are commonly used in the rubber industry for the production of tyres. Like many other petroleum products extender oils may contain PAH as impurity. EU Directive 2005/69/EC sets restrictions on the content of polycyclic aromatic hydrocarbons (PAH) in extender oils, and these oils may not be placed on the market and used for the production of tyres or parts of tyres, if they contain:
- more than 1 mg BaP/kg , or
- more than 10 mg/kg of the sum of all listed PAH.
The eight listed PAH with corrected names were:
- Benzo[a]pyrene (BaP)
- Benzo[e]pyrene (BeP)
- Benz[a]anthracene (BaA)
- Chrysene (CHR)
- Benzo[b]fluoranthene (BbFA)
- Benzo[j]fluoranthene (BjFA)
- Benzo[k]fluoranthene (BkFA)
- Dibenz[a,h]anthracene (DBAhA)
In the actual substance list in the Directive there are several mistakes in the chemical nomenclature. The parentheses inside the substance names were normal but have to be square brackets, and the letters inside the brackets, which describe a fused ring position, should have been in italics. If the part of the name after the bracket begins with a vocal, then “Benzo” before the bracket has to be “Benz” only. That were not done for substances 3 and 8. Substance 2 and 4 were lacking an “e” at the end of the name.
This indifference in spelling names of chemical substances correctly seems to be rather common in the EU bureauchracy. As I also mentioned in a previous news post concerning phthalates. A quick screening I made recently indicated that more than 20% of the names in ECHA’s various lists in some way were spelled wrongly. Hopefully it is better with the juridical expressions.
The EU Directive was passed without adoption of a harmonized analytical test method for the determination of PAH in the extender oils and the tyres. The Directive couldn’t wait for that development but methods were expected to be developed by international standards organisations.
In February 2013 the European Committee for Standardization (CEN) finally published the standard: “EN 16143 Petroleum products – Determination of content of Benzo(a)pyrene (BaP) and selected polycyclic aromatic hydrocarbons (PAH) in extender oils – Procedure using double LC cleaning and GC/MS analysis”.
In this standard, which is not freely available but can be purchased for 70 €, most of the mistakes in the naming of the 8 PAH were repeated.
In the Commission Regulation (EU) 2015/326 of 2 March 2015 it was specified that the EN 16143 standard has to be used for control of the content af the 8 PAH in extender oils and tyres.
It is probably the right methods for the purpose. However, regards analysis of PAH in air pollution normally 16 PAH congeners are analysed. Six of these are part the eigth in the Directive and the EN standard discussed above. PAH nr. 2 and 6 among the eight are not part of the air pollution standard method. The additional 10 PAH in air pollution measurements are: Naphthalene, acenaphthene, acenapthylene, anthracene, benzo[ghi]perylene, fluoranthene, fluorene, indeno[1,2,3-cd]pyrene, phenanthrene, and pyrene.
Every two years the scientists working with PAH and other polyaromatic compounds gather at an international symposium. The 25th gathering will be at ISPAC2015 to be held in Bordeaux, France, from 13-17 September 2015.