Migration Analysis of Polycyclic Aromatic Hydrocarbons (PAHs) in Polypropylene (PP) Products

Migration analysis of polycyclic aromatic hydrocarbons (PAHs) in polypropylene (PP) products is essential for verifying the safety of food contact materials, toys, childcare articles, and consumer goods. This technical article explains the sources and hazards of PAHs in PP, the applicable regulatory limits, standard migration and total-content testing protocols, and the instrumental methods used for detection and quantification.

Technical Overview

Polypropylene (PP) is one of the most widely used thermoplastics in food packaging, kitchenware, toys, household appliances, and automotive components. Although PP resin itself is not a direct source of polycyclic aromatic hydrocarbons (PAHs), PAHs can be introduced during compounding and conversion through carbon black pigments and masterbatches, extender and process oils, recycled feedstock contaminated with petroleum residues, degraded additives, and inadequate purging of processing equipment exposed to mineral-oil-based lubricants.

PAHs are a large family of fused-ring aromatic hydrocarbons, many of which are classified as carcinogenic, mutagenic, or reproducible-toxic (CMR) substances. Benzo[a]pyrene is the best-known marker compound, but regulatory frameworks now assess groups of PAHs because toxicological evidence indicates that other members contribute significantly to overall risk. Because PAHs are not chemically bound to the polymer matrix, they can migrate from PP articles into food, saliva, sweat, and skin-contact media under realistic use conditions.

Migration analysis therefore serves two complementary purposes: it demonstrates compliance with regulatory restrictions on PAH content in consumer products, and it quantifies the actual consumer exposure arising from foreseeable use. The key regulatory drivers include REACH Annex XVII Entry 50 (eight restricted PAHs in plastic and rubber articles with skin or oral contact), the German AfPS GS PAK evaluation scheme for the GS Mark, Regulation (EC) No 1935/2004 and Regulation (EU) No 10/2011 for plastic food contact materials, and EFSA guidance recognizing PAH4 and PAH8 as indicator groups for dietary exposure assessment.

Testing Samples

Food Contact Materials and Articles

PP food packaging and repeat-use articles represent the highest-volume sample category because migration into food is directly relevant to dietary exposure. Typical submissions include microwave containers, drinking cups and straws, food trays and lids, bottle closures and caps, cutlery, storage boxes, and flexible PP films for wrapping confectionery or snacks.

Toys, Childcare Articles and Skin-Contact Products

Articles intended for children are subject to the strictest PAH limits due to mouthing behavior and prolonged skin contact. Common samples include PP toys and toy components, teethers and rattles, bath toys, baby bottles and accessories, pacifier shields, tool handles, wristwatch straps with plastic elements, sports equipment grips, and jewelry with plastic parts.

Industrial and Technical PP Components

Automotive interior parts, cable sheathing and insulation, appliance housings, electrical accessories, and industrial containers are tested when workers or end users handle them regularly, when they are recycled into consumer-grade material, or when a supply-chain specification requires PAH screening of resins, colorants, and masterbatches prior to production.

Testing Items

Target PAH Compounds

Depending on the applicable regulation and client specification, analytical scopes typically cover one of the following compound lists:

• The eight REACH Annex XVII Entry 50 PAHs: benzo[a]pyrene, benzo[e]pyrene, benzo[a]anthracene, dibenz[a,h]anthracene, benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, and chrysene.
• The AfPS GS PAK list, expanded from eight to fifteen and subsequently eighteen PAHs in successive revisions, including naphthalene, acenaphthene, acenaphthylene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[g,h,i]perylene, and indeno[1,2,3-cd]pyrene in addition to the REACH eight.
• The sixteen US EPA priority PAHs, frequently requested for environmental and export-market screening.
• The PAH4 and PAH8 indicator groups used in food exposure assessment following EFSA opinions.

Content Versus Migration Parameters

Two distinct measurements are reported. Total content analysis determines the concentration of each PAH in the PP matrix, expressed in mg/kg, and is compared directly against content-based limits such as the REACH thresholds of 0.5 mg/kg benzo[a]pyrene and 5 mg/kg sum of eight PAHs for toys and childcare articles, and 1.0 mg/kg and 10 mg/kg respectively for other skin-contact articles. Migration analysis determines the mass of each PAH transferred into a defined contact medium under specified time and temperature conditions, expressed in µg/kg of food simulant, in µg/dm² of contact surface, or in mg/kg of article for saliva and sweat testing per DIN 53160 and related procedures.

Testing Methods

Sample Preparation

Samples are documented photographically, conditioned at laboratory temperature, and any non-PP laminates, labels, or adhesives are separated so that only the PP layer in actual consumer contact is analyzed. For content testing the specimen is cryo-milled or cut into pieces smaller than 3 mm to ensure homogeneous extraction. For migration testing the article is tested in its finished, as-supplied form whenever possible so that the real surface-to-volume ratio governs the transfer; when the intended filling volume is unknown, the conventional ratio of 6 dm² of contact surface per kilogram of food simulant is applied.

Total Content Extraction

PP is dissolved under reflux in toluene or xylene at approximately 120 to 140 °C, or extracted by accelerated solvent extraction and ultrasonic extraction with toluene, hexane-acetone mixtures, or cyclohexane. The polymer is then reprecipitated with cold methanol or acetone, the extract is filtered, concentrated, and cleaned up through silica gel or florisil solid-phase extraction to remove oligomers and additives. Isotopically labeled internal standards, typically deuterated benzo[a]pyrene, benzo[a]anthracene, chrysene, and phenanthrene, are added before extraction to correct for losses throughout the workflow.

Migration Testing Conditions

Migration is carried out in food simulants or body-fluid simulants selected to represent the intended use of the article. Commonly applied regimens include:

• Aqueous simulants, namely 10% ethanol (simulant A), 3% acetic acid (simulant B), and 50% ethanol (simulant C), contacted for 10 days at 40 °C to represent long-term ambient storage, with shorter and hotter regimes such as 2 hours at 70 °C for hot-fill applications.
• Fat simulants or substitutes for fatty food contact, using iso-octane for 2 days at 20 °C or 95% aqueous ethanol for 2 days at 40 °C, which are validated alternatives to 10-day olive oil testing for polyolefins.
• Artificial saliva per DIN 53160-1 for mouth-contact toys and childcare articles, typically contacted for a defined period at 37 °C with gentle agitation.
• Acidic artificial perspiration per ISO 105-E04 for prolonged skin-contact consumer products, contacted at 37 °C under standardized agitation.

After contact, the simulant is liquid-liquid extracted or passed through a solid-phase extraction cartridge, the eluate is concentrated under nitrogen at low temperature to prevent naphthalene losses, and the residue is reconstituted in acetonitrile or iso-octane for instrumental analysis.

Instrumental Determination

Gas chromatography coupled with mass spectrometry (GC-MS) is the primary technique. Separation is performed on a low-bleed 5%-phenyl methylpolysiloxane capillary column of 30 m length, 0.25 mm internal diameter, and 0.25 µm film thickness, with a programmed temperature ramp from 60 °C to 300 °C or above, sufficient to elute the six-ring dibenz[a,h]anthracene and benzo[g,h,i]perylene. Detection uses selected ion monitoring with at least two characteristic ions per analyte for confirmation on the basis of retention time and ion-ratio criteria. High-performance liquid chromatography with fluorescence detection and programmable wavelength switching is used as a confirmatory or complementary technique for parent PAHs, while GC-MS/MS in multiple reaction monitoring mode is employed when required detection limits fall below 1 µg/kg in migration simulants.

Quantification and Quality Control

Calibration is performed with multi-level curves bracketing the regulatory limits, typically 0.5 to 500 µg/L, and analyte identity is confirmed by qualifier-to-quantifier ion ratios within ±30% of calibration standards. Method performance is validated through procedural blanks, matrix spike recoveries of 70 to 120%, duplicate determinations with relative deviations below 15%, and continuing calibration verification. Typical limits of quantification are 0.01 to 0.05 mg/kg for total content and 0.5 to 2 µg/kg for migration into aqueous simulants. Results are reported compound by compound, together with the sum of the regulated PAH group, the test conditions applied, and a clear pass or fail conclusion against the specified limit.

Applications

PP PAH migration analysis supports a broad range of compliance and quality objectives across the plastics value chain, including:

• Verification of GS Mark and REACH compliance for tools, consumer goods, toys, and childcare articles placed on the European market.
• Safety demonstration of PP food contact materials under Regulation (EU) No 10/2011 through migration testing into validated food simulants.
• Incoming quality control of PP resins, carbon black pigments, black masterbatches, and recycled pellets before mass production.
• Root-cause investigation when PAHs are detected in finished goods, distinguishing pigment, oil, recycled-content, or cross-contamination origins.
• Technical documentation for customer specifications, export certifications, supplier declarations, and regulatory enforcement responses.

FAQ

Why do PP products contain PAHs if the resin itself is clean?

The dominant sources are the compounding ingredients rather than the polypropylene polymer. Carbon black pigments produced by the furnace-black process can carry trace PAHs, mineral-oil-based extender oils and processing aids may contain PAH residues, and post-industrial or post-consumer recycled PP can introduce contamination from mixed waste streams.

What is the difference between total content testing and migration testing?

Total content testing measures how much PAH is present in the plastic itself and is compared with mg/kg limits such as those in REACH Entry 50. Migration testing measures how much of that PAH actually transfers into food, saliva, or sweat simulants under defined time and temperature conditions, which provides a more realistic estimate of consumer exposure, particularly for food contact articles.

How much sample is required and how long does testing take?

For total content analysis, approximately 10 to 20 g of homogeneous material is sufficient. Migration testing generally requires complete articles or at least 1 dm² of representative contact surface per condition. Standard turnaround is five to ten working days, extended when multiple simulant conditions, confirmatory GC-MS/MS, or repeat extractions are required.

Which simulant and condition should be selected for a specific PP product?

The selection follows the intended use: aqueous food simulants with the 10-day 40 °C regime for long-term ambient storage, iso-octane or 95% ethanol substitutes for contact with fatty foods, artificial saliva for mouth-contact articles, and acidic perspiration for prolonged skin-contact products. The laboratory can advise on the worst foreseeable use scenario when a product serves multiple functions.

What should be done if a result exceeds a limit?

Non-conforming results should first be verified with a repeat determination. If confirmed, corrective actions include switching to certified low-PAH carbon black grades, phasing out suspect extender oils, quarantining recycled feedstock, improving purging protocols, and requalifying the formulation with supplier documentation before resubmission of samples for verification testing.