Determination of dioxin migration from PET (polyethylene terephthalate) is a critical ultra-trace analysis that verifies the safety of PET packaging and recycled PET materials intended for food contact. Using isotope-dilution high-resolution gas chromatography coupled with high-resolution mass spectrometry (HRGC-HRMS) or validated GC-MS/MS, laboratories quantify 17 toxic PCDD/F congeners and 12 dioxin-like PCBs migrating into food simulants, expressed as toxic equivalents (WHO-TEQ). This article explains the sample types, tested parameters, migration protocols, cleanup procedures, regulatory framework, and typical applications of PET dioxin migration determination.
Technical Overview
PET (polyethylene terephthalate) is one of the most widely used food-contact polymers, found in beverage bottles, preforms, thermoformed trays, films, and an expanding range of recycled PET (rPET) applications. Although virgin PET is a chlorine-free polyester, dioxin contamination can enter the PET value chain through recycled feedstock (for example, PVC carryover in baled post-consumer flakes, mis-sorted containers, or incinerator-adjacent environmental deposition), contaminated wash water, certain processing aids, or thermal abuse during reprocessing. Because dioxins are highly lipophilic, persistent, and bioaccumulative, and because 2,3,7,8-TCDD is classified by IARC as a Group 1 human carcinogen, regulatory authorities and brand owners require demonstrable control of dioxin transfer from packaging into food.
Dioxins comprise 75 polychlorinated dibenzo-p-dioxin (PCDD) congeners and 135 polychlorinated dibenzofuran (PCDF) congeners, of which only the 17 congeners substituted in the 2,3,7,8 positions are toxicologically significant. Together with the 12 dioxin-like polychlorinated biphenyls (dl-PCBs), they are evaluated as a toxic equivalent (TEQ) sum using the World Health Organization toxic equivalency factors (WHO-TEF, 2005, with 2022 updates). Migration determination exposes PET articles to food simulants under standardized time-temperature regimes, then measures the transferred dioxins at sub-picogram levels using isotope-dilution HRGC-HRMS or equivalently validated triple-quadrupole GC-MS/MS. The testing framework draws on Regulation (EU) No 10/2011 (migration test conditions), Regulation (EU) 2022/1616 and EFSA guidance for recycled plastics, US FDA 21 CFR 177.1630, and reference analytical methods such as US EPA Method 1613B and Method 8290A.
Testing Samples
PET Bottles and Preforms
Stretch-blown beverage bottles, wide-mouth jars, and their corresponding preforms are the most frequently tested articles, particularly for mineral water, carbonated soft drinks, juices, and edible oil applications. Single-sided (filling) migration testing is typically performed to reflect real-use exposure of the internal surface.
PET Trays, Clamshells, and Thermoformed Containers
Thermoformed trays and clamshells produced from virgin or recycled PET sheet are tested for ready-meal, bakery, produce, and delicatessen applications, including articles intended for hot-fill, microwave, or conventional oven reheating.
PET Films and Multilayer Laminates
Biaxially oriented PET films, metallized PET layers, and PET-containing multilayer laminates used in flexible packaging and lidding films can be assessed by total immersion or film-pouch exposure depending on the finished-article configuration.
Recycled PET (rPET) Pellets, Flakes, and Finished Articles
Post-consumer recycled flakes, decontaminated rPET pellets, and finished rPET bottles or trays represent the highest-risk matrix and the most common trigger for dioxin migration testing. Testing supports recycling process validation, batch release, and conformity with EU 2022/1616 or FDA thresholds of concern.
Other PET-Based Food Contact Materials
Additional matrices include PET closures and liner components, PET strapping and carriers used in food handling, PET-based tea and coffee packaging components, and PET liners or components used in food-processing equipment.
Testing Items
The analytical scope covers the full toxicologically relevant dioxin and dioxin-like PCB profile, reported both as individual congeners and as summed toxic equivalents. Typical reported parameters include:
- The 17 toxic 2,3,7,8-substituted PCDD/F congeners, including 2,3,7,8-TCDD, 1,2,3,7,8-PeCDD, OCDD, 2,3,7,8-TCDF, and the remaining tetra- through octa-chlorinated congeners.
- The 12 dioxin-like PCBs, comprising the non-ortho congeners (PCB 77, PCB 81, PCB 126, PCB 169) and the mono-ortho congeners (PCB 105, 114, 118, 123, 156, 157, 167, 189).
- Sum of PCDD/F TEQ, sum of dl-PCB TEQ, and the total TEQ (PCDD/F plus dl-PCB) calculated with WHO-TEF values and reported on both an upper-bound and lower-bound basis.
- Migration values expressed as pg WHO-TEQ per kg of food simulant, or normalized per dm2 of contact surface or per gram of PET where required by the client or specification.
- Optional screening of the six indicator PCBs (PCB 28, 52, 101, 138, 153, 180) and of the 13C-labeled surrogate recoveries as data-quality indicators.
Testing Methods
Sample Preparation and Migration Exposure
Finished articles are cleaned of external contamination, filled with (or immersed in) food simulants selected according to the intended food type, following Regulation (EU) No 10/2011 Annex V or an equivalent protocol: simulant A (10% ethanol) for aqueous foods, simulant B (3% acetic acid) for acidic foods, simulants C and D1 (20% and 50% ethanol) for alcoholic and dairy-type foods, simulant D2 (iso-octane) or E (95% ethanol / vegetable oil) for fatty foods. Time-temperature conditions reflect worst foreseeable use, for example OM3 (10 days at 60 degrees C) for long-term ambient storage, or shorter elevated-temperature exposures such as 2 hours at 100 degrees C for hot-filled products. The conventional surface-to-mass ratio is 6 dm2 per kg of food, with adjustments for small and large containers. After exposure, the simulants are transferred to amber glassware and protected from light.
Extraction of Food Simulants
A complete suite of 13C-labeled internal standards covering the target PCDD/F and dl-PCB congeners is spiked into each simulant before extraction to correct for losses throughout the procedure. Aqueous simulants are subjected to liquid-liquid extraction with n-hexane or dichloromethane, ethanol-based simulants are diluted with water and extracted in the same manner, and iso-octane or oil simulants are dissolved in a suitable solvent and handled by direct cleanup or gel permeation chromatography to remove lipids. Sample volumes are concentrated under nitrogen to a small volume for column cleanup.
Cleanup and Fractionation
The concentrated extract is purified on a multilayer silica gel column (acidic, basic, and neutral silica) to remove polar interferences, followed by acidic alumina or Florisil chromatography for hydrocarbon and pigment removal. An activated carbon column (for example, AX-21 dispersed on Celite) or carbon-dispersed HPLC fractionation separates the planar PCDD/Fs from the dioxin-like PCBs, which are collected in separate fractions. A 13C-labeled cleanup recovery standard added prior to extraction allows correction for matrix-dependent losses.
Instrumental Determination
Determination is performed by isotope-dilution HRGC-HRMS using a non-polar capillary column (DB-5MS or equivalent) with a confirmatory polar column (DB-225, Rtx-2330 or equivalent) where required for 2,3,7,8-substituted congener isomer specificity. The high-resolution mass spectrometer is operated in electron ionization SIM mode at a resolving power of at least 10,000 (10% valley), monitoring the molecular and M+2 chlorine isotope cluster ions for each homolog group with isotopic ratio criteria typically within plus or minus 15%. Alternatively, triple-quadrupole GC-MS/MS operated in MRM mode, validated to comparable sensitivity and selectivity in line with performance criteria established for dioxin analysis in EU method regulations, is accepted by many programs.
Quantification, TEQ Calculation, and Reporting
Individual congeners are quantified by isotope dilution against a multi-point calibration curve, with detection limits on the order of 0.005 to 0.05 pg per congener per sample. TEQ values are calculated as the sum of each congener concentration multiplied by its WHO-TEF, reported separately for PCDD/Fs, dl-PCBs, and the combined total, together with upper-bound and lower-bound sums. Results are reported in pg WHO-TEQ per kg simulant with full congener-by-congener detail, labeled-standard recovery data, and comparison against the applicable specification.
Quality Assurance and Method Validation
Each analytical batch includes a procedural blank, duplicate analyses, ongoing precision and recovery checks, and continuing calibration verification. Identity confirmation relies on correct retention time relative to standards, both monitored isotopes exceeding defined signal-to-noise thresholds, and chlorine isotope-ratio compliance. Laboratories operating to ISO/IEC 17025 accreditation maintain method validation records demonstrating trueness, precision, and limits of quantification fit for sub-picogram TEQ decision-making, and participate in interlaboratory proficiency testing for dioxins and PCBs.
Applications
PET dioxin migration determination supports safety assessment and regulatory compliance across the packaging and recycling industries:
- Compliance verification of recycled PET bottles and trays destined for food contact in the EU under Regulation (EU) 2022/1616, and in the United States under FDA food-contact notification and threshold-of-exposure approaches.
- Suitability and decontamination-efficiency studies for recycling technologies, including challenge-test campaigns and quality-assurance monitoring of super-clean decontamination processes.
- Batch release and periodic surveillance testing of rPET pellets and finished articles against brand specifications and non-detect requirements.
- Root-cause investigation of contamination events, such as PVC carryover in flake input, thermal degradation during extrusion, or environmental deposition on stored material.
- Support for import and export conformity files, third-party certifications, and due-diligence documentation required by retailers and converters.
- Research and development, including studies on thermo-oxidative degradation of polyester streams, evaluation of alternative feedstocks, and validation of screening approaches prior to confirmatory HRGC-HRMS testing.
FAQ
Why is dioxin testing required for PET if PET contains no chlorine?
Virgin PET is chlorine-free and does not generate dioxins under normal processing. The concern arises from external contamination, principally PVC carryover in post-consumer recycled feedstock, contact with chlorinated chemicals during collection and washing, and environmental exposure. Migration testing verifies that any adventitious dioxin burden does not transfer to food at measurable levels.
What detection capability is achievable?
With isotope-dilution HRGC-HRMS, limits of quantification of approximately 0.005 to 0.05 pg per congener per sample are routinely achieved, allowing migration values to be reported at or below approximately 0.01 to 0.05 pg WHO-TEQ per kg simulant, which satisfies essentially all non-detect specifications.
Which simulants and conditions apply to beverage bottles?
For aqueous non-acidic beverages, simulant A (10% ethanol) is typically used with a 10-day exposure at 60 degrees C (OM3), which represents long-term ambient storage in a worst foreseeable sense. Carbonated and acidic beverages are additionally tested with simulant B where relevant.
Can GC-MS/MS replace HRGC-HRMS?
Triple-quadrupole GC-MS/MS has demonstrated sensitivity and selectivity comparable to HRGC-HRMS for dioxin analysis and is accepted under several regulatory performance frameworks. HRGC-HRMS remains the reference technique, and GC-MS/MS results for borderline or non-compliant findings are often confirmed by HRGC-HRMS.
How are results assessed against limits?
The EU has not established a specific harmonized migration limit for dioxins from plastics; instead, recycled-PET approvals, EFSA evaluations, and food contaminant maximum levels in Regulations such as (EU) 2023/915, together with brand-owner specifications, typically require non-detectable migration, defined by an agreed reporting limit, when evaluated on a TEQ basis.
What sample quantity and turnaround time are typical?
Approximately 30 to 50 finished articles or 100 to 200 g of flakes or pellets are generally sufficient for a full PCDD/F and dl-PCB migration study covering multiple simulants. The complete workflow, including migration exposure, extraction, dual-column confirmation, and reporting, usually requires 10 to 15 working days.
