Testing for PAHs in rubbers and plastics

Polycyclic aromatic hydrocarbons are restricted in rubbers and plastics under the EU REACH and UK REACH legislation.

by Martin Heels

Polycyclic aromatic hydrocarbons (PAHs) are organic substances that occur naturally in coal, crude oil and petrol, and can also be formed through the incomplete combustion of these fossil fuels. This can result in the unintentional presence of PAHs in various materials, with black-coloured rubbers and plastics being especially affected.

Although PAHs contain only carbon and hydrogen atoms and are composed of multiple aromatic rings, it is possible for these atoms to have many structural arrangements. Therefore, this results in the existence of hundreds of PAH compounds. Some of these have been restricted through both national and international legislation, as studies showed both short- and long-term health effects are possible from contact with these compounds.

PAHs present in rubbers and plastics

As they are not intentionally added to materials, the question is often asked why PAHs might be present in footwear materials. Because PAHs are formed by incomplete combustion of fossil fuels, it is more likely that they will be present in black plastics and rubbers, because the pigment typically added to give a black appearance is carbon black. This is manufactured through the partial combustion of natural gas and oil. Although the use of carbon black increases the likelihood that PAHs can be found in black-coloured plastics and rubbers, they may be present in all colours, as softening or extender oils used in the rubber and plastic manufacturing processes could introduce PAHs as contaminants.

Health effects of PAHs

These substances can pose a risk through many different exposure routes, including ingestion, skin absorption and inhalation. Studies into their effects have shown that some PAHs can have hormonal, mutagenic, carcinogenic and fertility-impairing actions. As a result of these health effects, eight PAHs have been restricted in international legislation, such as UK and EU REACH Annex XVII entries 50 and 72 (see table 1). Entry 72 was explained in detail in the article ‘Update to REACH entry 72’, and this restricts the same eight PAHs in textiles that will be in close proximity to the skin for a prolonged period of time.

Table 1: The eight PAHs restricted under REACH Annex XVII entries 50 and 72
PAH	CAS number
Benzo[a]anthracene	56-55-3
Chrysene	218-01-9
Benzo[b]fluoranthene	205-99-2
Benzo[k]fluoranthene	207-08-9
Benzo[j]fluoranthene	205-82-3
Benzo[e]pyrene	192-97-2
Benzo[a]pyrene	50-32-8
Dibenzo[a,h]anthracene	53-70-3

Testing for restricted PAHs is also mandatory for some PPE products – for instance, mandatory testing is required as part of the general requirements for protective gloves (EN ISO 21420:2020). Nine PAHs are included in the REACH Candidate List as substances of very high concern (SVHCs). Table 2 lists these nine, four of which are also restricted in Annex XVII. Californian Proposition 65 also includes PAHs in the list of chemicals which are known to be carcinogenic, toxic to reproduction or cause birth defects. The legal obligations regarding Proposition 65 substances were discussed in the article 'An introduction to California Proposition 65'.

Table 2: The nine PAHs included on the Candidate List (those in bold are not in table 1)
PAH	CAS number
Benzo[k]fluoranthene	207-08-9
Benzo[a]pyrene	50-32-8
Chrysene	218-01-9
Benzo[a]anthracene	56-55-3
Benzo[ghi]perylene	198-55-0
Anthracene	120-12-7
Fluoranthene	206-44-0
Phenanthrene	85-01-8
Pyrene	129-00-0

In REACH Annex XVII entry 50, the eight restricted PAHs have a maximum concentration limit of 1 mg/kg in rubber and plastic components in prolonged contact or short-term repetitive contact with the skin or the oral cavity. While the PAHs included on the Candidate List are not restricted in articles, the European Chemicals Agency (ECHA) is gathering information about the use of these substances via the SVHC legal obligations. Therefore, future restrictions may be extended to more than the current eight.

If any of the nine PAHs that are SVHCs are present in quantities above 0.1 per cent based on the weight of the article, obligations such as creating a ‘Substances of Concern in articles or complex articles (Products)’ (SCIP) notification for EU-based companies and information sharing down the supply chain (for companies based in the EU and the UK) apply. The legal obligations for SVHCs apply to all materials, not only to rubbers and plastics in contact with the skin and oral cavity. Due to these restrictions and legal obligations, regular laboratory testing is recommended to confirm their absence in articles. This activity will ensure that these obligations are satisfied.

Testing for PAHs

When PAHs were initially restricted, SATRA tested rubbers and plastics to the international standard PD CEN ISO TS 16190:2013 to quantify PAH concentrations. This analytical procedure specifies an extraction of the test specimens with hexane in an ultrasonic bath at 60°C and defines Gas Chromatography Mass Spectrometry (GC-MS) or High-Performance Liquid Chromatography (HPLC) as the techniques to be used for detection.

A revised version of this method was published in December 2021, which supersedes the 2013 version of this method. There are a few notable changes in the current version, with the most significant being that the extraction solvent has changed to toluene. Previously, SATRA carried out development work using different extraction methods and both hexane and toluene extraction solvents have advantages and disadvantages.

Another change to the method is that GC-MS and GC-MS/MS (Gas Chromatography-Tandem Mass Spectrometry) are listed as detection techniques. HPLC is no longer an option and the inclusion of GC-MS/MS minimises one of the main disadvantages of using toluene as an extraction solvent. As toluene is a reasonably aggressive solvent, more substances are extracted than with a less aggressive solvent such as hexane. This results in more substances than just the PAHs being present in the extracted toluene. Hence, specimen clean-up is needed to remove substances that might interfere with the detection of PAHs. The GC-MS/MS is more selective than GC-MS, so confirming the presence of PAHs is more conclusive than when GC-MS is used.

Advantages of GC-MS/MS

SATRA has previously utilised gas chromatography with single quadrupole mass spectroscopy (GC-MS) to detect and quantify PAHs present in specimens after a hexane extraction. SATRA has invested in a GC-MS/MS as a result of its inclusion in the 2021 version of EN ISO 16190, to be able to offer testing to the updated method. The GC-MS/MS is a more sensitive and precise instrument which can select which mass fragment ions reach the detector and which ions are rejected. This is effectively a similar process to that conducted at a specimen clean-up stage.

The ions of interest can be selected instead of other ions that are interferences, as the instrument can be programmed to only detect the ions that are generated by the PAHs of interest. As a result, when compared to GC-MS, GC-MS/MS provides a lower limit of detection and provides a more conclusive result when using more aggressive solvents that can extract a considerable number of substances from the specimens being tested.

In summary

Eight PAHs are restricted in EU and UK REACH, and there are nine PAHs included as SVHCs which have legal obligations if they are present in articles including footwear. PAHs are also included in the Californian Proposition 65 list of substances that are known to be carcinogenic. As PAHs are not intentionally added but are impurities from carbon black or extender oils, regular testing is recommended in order to evaluate materials against the required restrictions and obligations.

Publishing Data

This article was originally published on page 30 of the December 2022 issue of SATRA Bulletin.

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