PET dioxin toxicity equivalent (TEQ) testing quantifies trace-level polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like PCBs in polyethylene terephthalate resins, packaging, and recycled materials using isotope-dilution high-resolution gas chromatography and high-resolution mass spectrometry (HRGC/HRMS). Accurate TEQ determination is essential for food-contact compliance, recycled PET (rPET) process validation, and access to strictly regulated international markets.
Technical Overview
Dioxins and furans are a family of highly toxic, persistent organic pollutants (POPs) comprising 75 polychlorinated dibenzo-p-dioxin (PCDD) congeners and 135 polychlorinated dibenzofuran (PCDF) congeners. Of these 210 compounds, only the 17 congeners substituted at the 2, 3, 7, and 8 positions are toxicologically significant and are therefore regulated and monitored. These substances are extremely lipophilic, resist metabolic degradation, bioaccumulate through the food chain, and are listed under the Stockholm Convention on POPs. The reference congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), is classified as a Group 1 human carcinogen by the International Agency for Research on Cancer (IARC).
Because the toxic potency of individual congeners varies over five orders of magnitude, analytical results are expressed as Toxicity Equivalents (TEQ). Using the World Health Organization 2005 Toxicity Equivalency Factor (WHO-TEF) scheme, the TEQ is calculated as the sum of each congener concentration multiplied by its respective TEF. Results are typically reported in pg WHO-TEQ/g or ng WHO-TEQ/kg at parts-per-trillion levels, which demands the highest available analytical sensitivity and selectivity.
Virgin polyethylene terephthalate (PET) is a chlorine-free polyester, so dioxin formation during polymerization is inherently minimal. The analytical concern arises primarily from contamination: PVC and other chlorinated polymers entering recycled PET streams, chlorinated cleaning agents or process chemicals, environmental deposition, and thermal processing. When chlorinated contaminants are present, melt extrusion at 250 to 300 degrees Celsius can promote formation of chlorinated aromatic by-products. Consequently, dioxin TEQ testing is routinely requested for the authorization of recycled PET recycling processes in the European Union under Regulation (EC) No 282/2008, for general food-contact safety demonstration under Regulation (EC) No 1935/2004, and for export shipments to markets with strict packaging contaminant controls.
Testing Samples
PET Resins and Pellets
Virgin PET chips, granules, and amorphous and crystallized resins intended for bottle grade, sheet grade, or fiber grade applications. Resin testing establishes a baseline contaminant profile for incoming material qualification and supplier verification.
PET Bottles, Preforms, and Containers
Finished and semi-finished rigid packaging, including beverage bottles, wide-mouth containers, jars, and preforms. Testing supports food-contact compliance dossiers, customer specifications, and market surveillance responses.
PET Films, Sheets, and Thermoformed Trays
Biaxially oriented films, thermoforming sheets, and converted trays used for food and pharmaceutical packaging, including retort and dual-ovenable applications where thermal history is relevant.
Recycled PET (rPET) Flakes and Granules
Post-consumer and post-industrial recycled flakes, washed flake, and repelletized rPET. This is the most critical sample category because recycled streams carry an elevated risk of chlorinated polymer contamination, making TEQ data a core element of recycling process validation and EFSA dossier submissions.
PET Fibers, Strapping, and Other Products
Staple fiber, filament yarn, nonwoven materials, technical strapping, and engineering components where contaminant characterization is required for downstream applications, thermal recycling studies, or occupational and environmental assessments.
Testing Items
The core analytical scope covers all seventeen toxic 2,3,7,8-substituted PCDD/F congeners with their WHO 2005 Toxicity Equivalency Factors:
- 2,3,7,8-TCDD (TEF = 1)
- 1,2,3,7,8-PeCDD (TEF = 1)
- 1,2,3,4,7,8-HxCDD (TEF = 0.1)
- 1,2,3,6,7,8-HxCDD (TEF = 0.1)
- 1,2,3,7,8,9-HxCDD (TEF = 0.1)
- 1,2,3,4,6,7,8-HpCDD (TEF = 0.01)
- OCDD (TEF = 0.0003)
- 2,3,7,8-TCDF (TEF = 0.1)
- 1,2,3,7,8-PeCDF (TEF = 0.03)
- 2,3,4,7,8-PeCDF (TEF = 0.3)
- 1,2,3,4,7,8-HxCDF (TEF = 0.1)
- 1,2,3,6,7,8-HxCDF (TEF = 0.1)
- 1,2,3,7,8,9-HxCDF (TEF = 0.1)
- 2,3,4,6,7,8-HxCDF (TEF = 0.1)
- 1,2,3,4,6,7,8-HpCDF (TEF = 0.01)
- 1,2,3,4,7,8,9-HpCDF (TEF = 0.01)
- OCDF (TEF = 0.0003)
An extended scope covering the twelve dioxin-like polychlorinated biphenyls (dl-PCBs) is available on request, calculated as a separate PCB-TEQ and a combined total TEQ:
- Non-ortho PCBs: PCB 77, PCB 81, PCB 126 (TEF = 0.1), and PCB 169 (TEF = 0.03)
- Mono-ortho PCBs: PCB 105, 114, 118, 123, 156, 157, 167, and 189 (TEF = 0.00003 each)
Calculated and reported parameters include individual congener concentrations, the total PCDD/F WHO-TEQ, the optional PCB-TEQ, the combined sum TEQ, and both I-TEQ (NATO/CCMS) and WHO-TEQ (2005) values. Upper-bound, lower-bound, and medium-bound calculation conventions are applied and clearly stated on the report, with upper-bound WHO-TEQ being the convention most frequently required by European regulators.
Testing Methods
Sample Preparation and Extraction
Representative samples are homogenized, typically by cryogenic milling to ensure uniformity, and a test portion of 10 to 50 grams is spiked with a full suite of carbon-13 labeled internal standards covering all target congeners. Extraction is performed by Soxhlet extraction or accelerated solvent extraction (ASE) using toluene or toluene-acetone mixtures, ensuring quantitative recovery of tightly bound residues from the polymer matrix.
Clean-Up and Fractionation
Crude extracts undergo multi-stage column clean-up to remove the polymer matrix, pigments, additives, and interfering halogenated compounds. Typical sequences include multilayer acidic and basic silica gel, neutral alumina, and activated carbon or florisil columns. Carbon column fractionation separates the PCDD/F fraction from the mono-ortho and non-ortho PCB fractions, allowing independent determination of each analyte class from a single extraction.
HRGC/HRMS Analysis
Analysis is performed on a high-resolution gas chromatograph coupled to a double-focusing magnetic sector mass spectrometer operated at a resolving power of at least 10,000 (10 percent valley) in selected ion monitoring mode. At least two exact masses are monitored for each congener and its corresponding isotope-labeled standard, providing definitive identification through isotope ratio criteria. Quantification uses the isotope dilution method, in which the measured ratio of native to labeled analyte directly yields the concentration, automatically correcting for recovery losses. Confirmation columns of different polarity are used where required to resolve co-eluting congeners such as specific HxCDF isomers.
Reference Methods and Standards
- US EPA Method 1613B: Tetra- through octa-chlorinated dioxins and furans by isotope dilution HRGC/HRMS
- US EPA Method 8290A: Dioxins and furans by high-resolution gas chromatography and high-resolution mass spectrometry
- US EPA Method 1668C: Chlorinated biphenyl congeners in water, soil, sediment, biosolids, and tissue by HRGC/HRMS, applied to the dioxin-like PCB extension
- EN 1948 series: Determination of PCDD/PCDF mass concentration, referenced for associated emission and environmental matrices
- Laboratory procedures accredited to ISO/IEC 17025 with documented traceability of calibration standards
Quality Assurance and Control
Every analytical batch includes method blanks, ongoing precision and recovery (OPR) samples, calibration verification standards, and duplicate determinations. Labeled compound recoveries are validated against method acceptance windows, typically 40 to 140 percent, and reported alongside the data. Instrument detection limits reach 0.01 to 0.1 pg/g per congener, with a practical TEQ reporting limit generally below 0.5 pg WHO-TEQ/g of PET. Results below detection limits are handled according to the stated bounding convention, ensuring transparent and defensible reporting.
Applications
- Recycled PET process authorization: analytical support for EFSA-evaluated recycling process dossiers under Regulation (EC) No 282/2008 and Regulation (EU) 2022/1616
- Food-contact material compliance: demonstration of general safety requirements under Regulation (EC) No 1935/2004 and supporting documentation for Regulation (EU) No 10/2011 conformity assessments
- Export market access: conformity documentation for shipments to the European Union, the United States, Japan, and other jurisdictions with stringent packaging contaminant controls
- Supplier and incoming material qualification: baseline contaminant profiling of virgin and recycled feedstocks for resin buyers and converters
- Recycling process development: verification of sorting, washing, and decontamination efficiency and evaluation of PVC carry-over risks
- Research and environmental programs: thermal treatment studies, chemical recycling development, incineration emission assessments, and academic investigation of POPs in polymer streams
- Litigation, market surveillance, and due diligence: defensible third-party data for regulatory responses, customer disputes, and supply chain audits
FAQ
Why is dioxin TEQ testing required for PET when the polymer contains no chlorine?
Virgin PET polymerization does not generate dioxins because no chlorine source is present. The risk is introduced through contamination: PVC and other chlorinated plastics entering recycled streams, chlorinated process aids, environmental deposition, and thermal processing of contaminated feedstock. Regulatory frameworks for recycled plastics, retailer specifications, and national authorities therefore request TEQ data to demonstrate that the finished material remains safe for its intended use.
What detection limits can be achieved?
Using isotope-dilution HRGC/HRMS, per-congener detection limits of approximately 0.01 to 0.1 pg/g are routinely achieved, corresponding to a TEQ reporting limit generally below 0.5 pg WHO-TEQ/g. This parts-per-trillion capability is sufficient to meet the most demanding regulatory and customer thresholds.
How much sample is required and how should it be submitted?
A minimum of 20 to 100 grams of representative material is recommended, submitted in pre-cleaned amber glass containers with PTFE-lined closures. Samples should never be packaged in PVC or contact chlorine-containing materials prior to submission, and a completed chain-of-custody form should accompany every shipment.
What is the typical turnaround time?
Standard turnaround is 7 to 15 working days from receipt of sample, reflecting the extensive extraction, multi-column clean-up, and mass spectrometric analysis required. Expedited services can be arranged for urgent regulatory deadlines, and pre-project consultation is available to confirm scope and reporting conventions.
What is the difference between I-TEQ and WHO-TEQ?
I-TEQ is based on the 1988 NATO/CCMS toxic equivalency factors, while WHO-TEQ applies the World Health Organization 2005 scheme, which was reaffirmed by WHO and UNEP in 2017. The schemes differ for several congeners, most notably 1,2,3,7,8-PeCDD and the hepta- and octa-chlorinated congeners. Most current regulations and customers specify WHO-TEQ (2005), and reports can present both values to satisfy legacy specifications.
How are non-detected congeners treated in the TEQ calculation?
Three conventions exist. The upper-bound approach assumes every non-detected congener is present at its limit of detection, the lower-bound assumes zero, and the medium-bound assumes half the detection limit. European regulatory practice generally requires upper-bound WHO-TEQ, and all three values can be provided on the certificate of analysis upon request.
Can dioxin-like PCBs be tested together with PCDD/Fs?
Yes. The twelve dioxin-like PCBs can be determined from the same extract through the carbon column fractionation step, providing a PCB-TEQ and a combined total TEQ in a single project. This combined scope is recommended for full POPs characterization and is increasingly requested by European buyers of recycled materials.
