Chemical information

NOTE. The name Dioxin has also been applied to dimethoxane.


The term ‘dioxins’ encompasses a large group of closely related chemicals known as polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). The most toxic is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Dioxins are byproducts in the manufacture of commercial chemical products such as chlorinated phenols and polychlorinated biphenyls (PCBs), and can also be produced in smaller quantities by combustion processes and industrial waste. They first came to public attention during the Vietnam war, when they were found to be present in the herbicide Agent Orange used as a defoliant. They are incriminated as causing chloracne (a severe and persistent acne caused by chlorinated compounds). They are potent teratogens and carcinogens in animals. An increased incidence of cancer at different organs due to dioxins has been claimed but this has not been substantiated by clinical and follow-up studies. An effect on cell-mediated immunity has been observed. Exposure should be limited to the lowest feasible concentration.

Adverse effects.

The impact of dioxins in food and the environment has been reviewed.1-4 An excess of soft tissue sarcomas was found in workers exposed to chlorophenoxy herbicides including those contaminated with TCDD,5 but cautious interpretation of these results was advised.6In Vietnam veterans the risk of non-Hodgkin’s lymphoma was about 50% higher than control subjects, but was not related to exposure to Agent Orange, nor was there evidence for an increase in other cancers.7 Exposure to TCDD was implicated in an increase in cancer mortality in chemical workers,8,9 but confounding factors such as smoking may have been present.9,10Other studies11,12 have not shown an association between dioxin exposure and an increase in the incidence of human cancer, and epidemiological studies after occupational or accidental exposures have found no clear persistent systemic effects, except for chloracne, and no clear association with carcinogenesis or reproductive disorders.1,2 Decreased plasma immunoglobulin G concentrations were measured in people after exposure to TCDD 20 years earlier as a result of accidental environmental contamination in Seveso, Italy.13 A statistically significant increase in the incidence of breast cancer related to serum levels of TCDD was observed in a cohort of 981 women who ranged in age from infancy to 40 years in 1976 at the time of the Seveso accident.14The authors pointed out that this cohort is relatively young and continued follow-up would clarify any possible pathogenic role of TCDD. In the USA, the National Academy of Sciences’ Institute of Medicine is reported to have carried out an evaluation of publications on herbicide exposure, largely in industrial and agricultural workers.15 They concluded that exposure to herbicides or dioxin was associated with soft-tissue sarcomas, Hodgkin’s disease, non-Hodgkin lymphoma, chloracne, and porphyria cutanea tarda, and that there was limited evidence of an association with respiratory and prostate cancers and multiple myeloma. An update to the report has also suggested a link between Agent Orange exposure and spina bifida in veterans’ offspring.16 There is some evidence that exposure of men to TCDD is associated with a decreased male to female sex ratio in their offspring.17 Results from studies18-20 suggest that prenatal exposure to PCBs has an effect on mental and motor development in early childhood, although this may be counteracted by an advantageous home environment. However, virtually no adverse effects in relation to postnatal exposure to PCBs present in breast milk were demonstrated.20
1. Food Standards Agency UK. Dioxins and PCBs in the UK diet: 1997 Total Diet Study (Number 04/00) (issued September 2000). Available at: http://www.food.gov.uk/science/ surveillance/fsis2000/4diox (accessed 24/07/08
2. DEFRA. Dioxins and dioxin-like PCBs in the UK environment (issued October 2002). Available at: http:// www.scotland.gov.uk/Resource/Doc/1052/0002248.pdf (accessed 24/07/08
3. WHO. Dioxins and their effects on human health (issued November 2007). Available at: http://www.who.int/mediacentre/ factsheets/fs225/en/print.html (accessed 24/07/08
4. FAO. Dioxins in the food chain: prevention and control of contamination (issued April 2008). Available at: http://www.fao.org/ag/agn/agns/files/Dioxin_fact%20sheet.pdf (accessed 24/07/08
5. Saracci R, et al. Cancer mortality in workers exposed to chlorophenoxy herbicides and chlorophenols. Lancet 1991; 338: 1027–32
6. Peto R. Occupational exposure to chlorophenoxy herbicides and chlorophenols. Lancet 1991; 338: 1392
7. Suskind R. The association of selected cancers with service in the US military in Vietnam. Arch Intern Med 1990; 150: 2449–50
8. Manz A, et al. Cancer mortality among workers in chemical plant contaminated with dioxin. Lancet 1991; 338: 959–64
9. Fingerhut MA, et al. Cancer mortality in workers exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin. N Engl J Med 1991; 324: 212–18
10. Triebig G. Is dioxin carcinogenic? Lancet 1991; 338: 1592
11. Coggon O, et al. Mortality and incidence of cancer at four factories making phenoxy herbicides. Br J Ind Med 1991; 48: 173–8
12. Green LM. A cohort mortality study of forestry workers exposed to phenoxy acid herbicides. Br J Ind Med 1991; 48: 234–8
13. Baccarelli A, et al. Immunologic effects of dioxin: new results from Seveso and comparison with other studies. Environ Health Perspect 2002; 110: 1169–73
14. Warner M, et al. Serum dioxin concentrations and breast cancer risk in the Seveso Women’s Health Study. Environ Health Perspect 2002; 110: 625–8
15. McCarthy M. Agent Orange. Lancet 1993; 342: 362
16. Stephenson J. New IOM report links Agent Orange Exposure to risk of birth defect in Vietnam vets’ children. JAMA 1996; 275: 1066–7
17. Mocarelli P, et al. Paternal concentrations of dioxin and sex ratio of offspring. Lancet 2000; 355: 1858–63
18. Walkowiak J, et al. Environmental exposure to polychlorinated biphenyls and quality of the home environment: effects on psychodevelopment in early childhood. Lancet 2001; 358: 1602–7
19. Vreugdenhil HJ, et al. Effects of prenatal PCB and dioxin background exposure on cognitive and motor abilities in Dutch children at school age. J Pediatr 2002; 140: 48–56
20. Jacobson JL, Jacobson SW. Association of prenatal exposure to an environmental contaminant with intellectual function in childhood. J Toxicol Clin Toxicol 2002; 40: 467–75.
Published May 08, 2019.