Dioxins and polychlorinated biphenyls (PCBs) are two distinct but related groups of highly toxic, persistent organic pollutants (POPs) that bioaccumulate in the food chain, primarily through dietary fat. Their extreme environmental persistence, lipophilicity (fat-solubility), and long biological half-lives in humans make them among the most serious food contaminants regulated worldwide.
Dioxins is a collective term for two chemically related compound families: polychlorinated dibenzo-p-dioxins (PCDDs), consisting of 7 toxicologically relevant congeners, and polychlorinated dibenzofurans (PCDFs), consisting of 10 toxicologically relevant congeners. They are not intentionally produced but form as industrial by-products — primarily from waste incineration, chemical manufacturing (especially chlorinated chemicals), metal smelting, and the bleaching of paper. Once released into the environment, dioxins persist in soil and sediment for decades.
PCBs (Polychlorinated Biphenyls) were widely manufactured and used as electrical insulating fluids, plasticizers, and flame retardants until banned in most countries in the 1970s–1980s. PCBs are classified into dioxin-like PCBs (dl-PCBs) — 12 congeners that bind to the aryl hydrocarbon receptor (AhR) and have dioxin-like toxicity — and non-dioxin-like PCBs (ndl-PCBs), represented by 6 indicator congeners (PCB-28, -52, -101, -138, -153, -180).
Toxicity is expressed as Toxic Equivalents (TEQ) using WHO-established Toxic Equivalency Factors (TEF), which normalize each congener’s toxicity relative to the most toxic dioxin (2,3,7,8-TCDD). Long-term exposure causes immunotoxicity, reproductive and developmental toxicity, endocrine disruption, and cancer (IARC classifies 2,3,7,8-TCDD as a Group 1 human carcinogen). The primary human exposure pathway is consumption of fatty foods: meat, fish, dairy products, and eggs. Ovalab’s contaminants testing service includes accredited dioxin and PCB analysis using high-resolution GC-HRMS.
Analytical Methods
- GC-HRMS (Gas Chromatography – High-Resolution Mass Spectrometry) — The ISO/EU reference method for dioxin and dl-PCB analysis (EN 1948-1/2/3 series, ISO 18073). Uses magnetic sector high-resolution instruments (HRMS) operating at ≥10,000 resolving power to achieve selective detection of individual PCDD/PCDF/PCB congeners at fg/g (femtogram) levels. Gold standard for regulatory compliance testing.
- GC-MS/MS (Gas Chromatography – Tandem Mass Spectrometry) — Triple quadrupole GC-MS/MS systems can achieve sensitivity approaching HRMS for selected congeners. Used as a confirmatory method and increasingly as an alternative to HRMS in accredited laboratories, offering faster throughput at lower instrument cost.
- DR CALUX Bioassay (Dioxin Receptor Chemical-Activated Luciferase Gene Expression) — Cell-based bioassay screening method that detects the combined AhR (dioxin receptor) activity of all PCDD/PCDF/dl-PCB congeners. Approved as an EU screening method under Commission Regulation (EU) 2017/644. Positive screening results must be confirmed by GC-HRMS or GC-MS/MS.
- Lipid Extraction + Multi-Step Column Chromatography Clean-up — Dioxin and PCB analysis requires extensive sample preparation: fat extraction from food matrices, followed by multi-layer silica and alumina column chromatography plus activated carbon column fractionation to separate PCDDs, PCDFs, and PCBs from co-extractive interferences. This is the most technically demanding sample preparation in food contaminant analysis.
EU Regulatory Framework
Maximum levels for dioxins and PCBs in food are set by Regulation (EU) 2023/915 (Annex I, Section 4), incorporating updates from Commission Regulation (EU) 2022/2002, which extended limits to additional food groups and lowered levels for certain foods based on EFSA’s updated 2018 scientific opinion. EFSA established a Tolerable Weekly Intake (TWI) of 2 pg TEQ/kg body weight for the sum of dioxins and dioxin-like PCBs.
Limits are expressed in picograms (pg) of Toxic Equivalent (WHO-TEQ) per gram of fat, or per gram of wet weight for fish/fishery products and baby foods. Three parameters are regulated: the sum of dioxins (PCDDs+PCDFs), the sum of dioxins and dioxin-like PCBs, and the sum of 6 indicator ndl-PCBs (PCB-28, -52, -101, -138, -153, -180). Selected maximum levels:
| Food product | Dioxins (PCDDs+PCDFs) max. | Dioxins + dl-PCBs max. | Indicator ndl-PCBs max. |
|---|---|---|---|
| Poultry meat/products | 1.75 pg TEQ/g fat | 3.0 pg TEQ/g fat | 40 ng/g fat |
| Pork meat/products | 1.0 pg TEQ/g fat | 1.25 pg TEQ/g fat | 40 ng/g fat |
| Beef, lamb, goat meat/products | 2.5 pg TEQ/g fat | 4.0 pg TEQ/g fat | 40 ng/g fat |
| Most fish and fishery products | 3.5 pg TEQ/g wet wt | 6.5 pg TEQ/g wet wt | 75 ng/g wet wt |
| Raw milk and dairy products | 2.0 pg TEQ/g fat | 4.0 pg TEQ/g fat | 40 ng/g fat |
| Eggs and egg products | 2.5 pg TEQ/g fat | 5.0 pg TEQ/g fat | 40 ng/g fat |
| Vegetable oils and fats | 0.75 pg TEQ/g fat | 1.25 pg TEQ/g fat | 40 ng/g fat |
| Baby food and infant formula | 0.1 pg TEQ/g wet wt | 0.2 pg TEQ/g wet wt | 1.0 ng/g wet wt |
Analytical methods for official control are specified in Commission Regulation (EU) 2017/644 (sampling and analytical methods). All laboratories performing official control dioxin/PCB analysis must be ISO/IEC 17025 accredited and participate in proficiency testing schemes.
Frequently Asked Questions
What is the difference between dioxins and PCBs in food regulation?
Although both are persistent organic pollutants regulated together, they differ in origin and structure. Dioxins (PCDDs and PCDFs) are unintentional industrial by-products formed during combustion and chemical manufacturing. PCBs were intentionally manufactured industrial chemicals, now globally banned. In EU food regulation, three separate parameters are measured: (1) the sum of dioxins (PCDDs+PCDFs), (2) the sum of dioxins plus dioxin-like PCBs (expressing combined AhR-mediated toxicity in TEQ), and (3) the sum of 6 indicator non-dioxin-like PCBs as a general contamination marker.
Why are dioxin and PCB levels expressed in Toxic Equivalents (TEQ)?
Dioxins and dioxin-like PCBs consist of dozens of individual congeners with widely varying toxicities. The Toxic Equivalency Factor (TEF) system, established by the World Health Organization (WHO), assigns each congener a factor relative to the most toxic dioxin (2,3,7,8-TCDD, TEF = 1). Multiplying each congener’s measured concentration by its TEF and summing the results gives the Toxic Equivalent (TEQ) — the concentration of pure 2,3,7,8-TCDD that would produce the same toxic effect. This allows a single regulatory limit to cover the combined toxicity of multiple congeners.
Which foods are most contaminated with dioxins and PCBs?
Because dioxins and PCBs are highly lipophilic (fat-soluble) and bioaccumulate up the food chain, fatty foods of animal origin pose the highest exposure risk: fish and fishery products (especially fatty fish like salmon, eel, mackerel, and herring from contaminated waters), meat and offal, dairy products, and eggs. Wild-caught freshwater fish can have significantly higher dioxin/PCB levels than marine fish due to local sediment contamination. Vegetable foods contribute minimal exposure. Infants fed formula are protected by the strictest EU limits (0.1 pg TEQ/g wet weight for dioxins).
How is dioxin and PCB testing performed in a laboratory?
Dioxin and PCB analysis is one of the most technically demanding analyses in food safety testing. It requires: (1) lipid extraction from the food matrix; (2) extensive multi-step column chromatography clean-up using silica/alumina columns and activated carbon separation; (3) GC-HRMS (gas chromatography with high-resolution mass spectrometry, ≥10,000 resolving power) for individual congener quantification. The DR CALUX bioassay is used for initial screening. Isotope-labelled internal standards (⁹C-labelled PCDD/PCDF/PCB congeners) are used for quantification. Analysis typically takes several days and requires highly specialized expertise.
What is the EFSA Tolerable Weekly Intake for dioxins?
In 2018, EFSA re-evaluated the risk of dioxins and dioxin-like PCBs and established a Tolerable Weekly Intake (TWI) of 2 picograms (pg) of WHO-TEQ per kilogram of body weight (2 pg TEQ/kg bw/week) for the combined sum of dioxins and dioxin-like PCBs. This is substantially lower than the previous TDI and reflects improved understanding of effects on thyroid function and reproductive development. EFSA estimated that average EU consumer dietary exposure may exceed this TWI, particularly in high consumers of contaminated fish and animal products, underpinning continued strict regulation.