Polychlorinated dibezno-p-dioxins and dibenzofurans. Documentation of proposed values of occupational exposure limits (OELs)
Authors: Szymańska Jadwiga , Frydrych Barbara , Struciński Paweł , Szymczak Wiesław , Hernik Agnieszka , Bruchajzer Elżbieta 
Published: January 2020

Polychlorinated dibezno-p-dioxins (PCDD) and dibenzofurans (PCDF) are compounds with similar structure, physicochemical and toxicological properties. They are not used commercially, they are formed as by-products during certain industrial processes, combustion, failures, etc.
LD50 values (0.002-300 mg / kg) depend on the species of animal tested and the chemical structure of the compound. On chronic toxicity, the information available mainly relates to 2,3,7,8-TCDD and 2,3,4,7,8-PeCDF.
Potential routes of human exposure are: the digestive system, lungs and skin. These compounds are accumulated mainly in the liver and adipose tissue. Their polar metabolites may undergo conjugation with glucuronic acid and glutathione. The main routes of excretion are bile and feces. In mammals, PCDD / F are also eliminated in breast milk.
The results of mutagenicity and genotoxicity tests of PCDD (mainly 2,3,7,8-TCDD) and PCDF and their effects on fertility and reproduction are inconsistent. Among PCDD and PCDF, the compound that most strongly affects fertility, reproduction and fetal development is 2,3,7,8-TCDD.
Epidemiological studies are the basis for assessing the carcinogenic potential of dioxins (including 2,3,7,8-TCDD) and furans in humans. Cohorts include those professionally exposed to chlorophenols, phenoxyacetic herbicides and a mixture of polychlorinated dibenzodioxins and furans.
PCDD / F have a common mechanism of toxic action associated with the Ah receptor. PCDD / F are considered to be inducers of several enzymes (e.g. CYP1A) and modulators of hormones and growth factors. CYP1A1 activity is one of the most sensitive indicators of exposure to 2,3,7,8-TCDD.
Adenocarcinomas and hepatocellular carcinomas as well as bile ducts have been found in rats and mice after 2,3,7,8-TCDD. Tumor changes have also been observed in other organs. NTP studies also showed carcinogenic effects 2,3,4,7,8-PeCDF. According to IARC, sufficient evidence of a carcinogenic effect on humans exists only for 2,3,7,8-TCDD (CAS: 1746-01-6) and 2,3,4,7,8 PeCDF (CAS: 57117-31-4). Other PCDD / F cannot be classified as carcinogenic to humans.
The basis for determining the MAC value for the mixture of PCDD and PCDF was the results of the assessment of the risk of developing additional liver cancer in people exposed in the work environment for 2,3,7,8-TCDD in 2017. This risk was estimated at 1 · 10-4 for 40 years of exposure to the compound at a concentration of 18 pg / m3.
In the case of combined exposure, the content of polychlorinated dibenzo-p-dioxins and furans in the tested samples, as well as their maximum acceptable levels are expressed in the form of the so-called toxicity equivalent (TEQ).
For the PCDD and PCDF mixture, we propose the value of 18 pg WHO2006-TEQ / m3. The result expressed as pg WHO-TEQ / m3 is not a de facto concentration, but a determination of the toxicity of the mixture of dioxin and furan congeners contained in the sample in relation to TCDD.
This article discusses the problems of occupational safety and health, which are covered by health sciences and environmental engineering.