Dioxins

The text on this page is taken from an equivalent page of the IEHIAS-project.

• A theoretical maximum of 75 polychlorinated dibenzo-p-dioxins and 135 polychlorinated dibenzofurans.
• Dioxins are generally present as a mixture of compounds, and therefore toxicity and effects are expressed in toxic equivalency factors (TEFs).
• The most toxic dioxin, 2,3,7,8-TCDD has a TEF value of 1 and the toxicity of all other dioxins and furans is expressed relative to this value (range: 1-0.0003).

Dioxins as a biomarker

Sample collection and storage

Matrix:

• Adipose tissue but mainly blood and breast milk have frequently been used as matrices for dioxins
• Expressed on a lipid basis, correlations between different tissues are generally good.

Kinetics:

• For the general population, more than 90% of the total daily intake is derived through food
• For different European countries, total daily intake is around 0,8-2 pg TEQ/kg body weight/day.
• Dioxins are generally very resistant to metabolization and excretion, with half-lives of several years.

Sampling conditions:

Standard sampling methods for blood, adipose tissue or breast milk should be followed. Samples are stored at -20°C.

Sample measurement

Analytical aspects:

• Mostly combinations of high resolution gas chromatography and mass spectroscopy (HRGC/HRMS).
• Bio-analytical methods (in vitro and ligand binding assays) have been developed as a rapid, relatively cheap and sensitive alternatives, though they cannot replace chemical-analytical methods.
• For milk and serum, levels of detection for individual congeners are around 0,05 pg/g lipid.

Performance characteristics:

• For almost 20 years, WHO/EURO has been coordinating inter-laboratory quality assessment studies for dioxins in breast milk ald blood.
• Generally good inter-laboratory comparability (relative standard deviations of 13%), though variability for individual congeners can be considerably higher.

Validation:

Analytical methods have been validated by several international agencies (e.g. USEPA, EC).

Confounding factors:

Age, food patterns, body mass index and gender can have profound effects on dioxin levels in human tissues.

Data interpretation

Concentrations reported in literature:

• Median dioxin levels in breast milk ranged from 3,34–22,3 pg/g fat
• Concentrations in blood are reported to be around 20-60 pg TEQ/g fat.
• Daily intake concentrations are estimated to be around 0,8-2 pg TEQ/kg bw/day.
• Critical total daily intake values are around 1-4 pg TEQ/kg bw/day

Dose-response/effect relationships:

• Several dioxins are presumed to be human carcinogens, both for acute short term, and chronic long term exposure.
• Dioxin TEQ exposures within roughly 3-fold of current background levels may be carcinogenic.
• There are indications that in utero exposure to dioxins may result in (neuro)developmental delays, chloracne, alteration of thyroid hormone status and decreased long function.

Time trend, geographical variation, susceptibel groups:

• Dioxin levels in breast milk are decreasing, in some countries up to 50%.
• Global dioxin levels are highest in Western Europe highest.
• Babies, small children, and humans exposed through diet, are the most susceptible groups.