Module 3: Toxicology - Section 19: Dioxin

TOX 19.2: Dioxin Toxicity - Case Histories

CASE HISTORIES OF EXPOSURE:

Monsanto

In Nitro, West Virginia, 1949, over 200 workers were exposed. 122 developed chloracne within few weeks. The othershad immediate but transient effects such as headache, dizziness, nausea, weakness.

The 1980 epidemiological study of the 122 chloracne victims (31 years later). Fewer died of cancer than expected in control. Only 32 died from all causes. 46 were expected to die.

Dow

In 1964, 61 employees were exposed to dioxin levels potentially reaching 10,000 ppm (10 µg/kg). 49 developed chloracne. However as of 1980, no excess total deaths were recorded.

Seveso, Italy

In 1976 an explosion occurred while making trichlorophenol, which emitted about 2 kg of dioxin. 37,000 people were potentially exposed (several hundred had symptoms of acute poisoning ( nausea, nervous symptoms, chloracne) - effects from other chemicals not known). There were no deaths.

In Seveso, an extensive surveillance system was put into effect to record long-term effects, involving medical and laboratory tests. Pregnant women were monitored in order to record miscarriages and birth defects, and a cancer registry was created.

Results for all three cases to date:

• Chloracne and minor reversible nerve damage.
• No evidence of chromosome abnormalities due to dioxin.
• Some impaired liver function (long-term effects unknown).
• No other organs or body functions affected.
• No adverse reproductive effects.
• No cases of cancer to date, but longer term studies continue.

Does Dioxin Cause Cancer in Humans?

• To date this has not be seen, but it has been seen in lab animals.
• Other exposures in industry failed to show chromosome abnormalities.
• Some suspicion it causes rare soft tissue sarcoma (STS) (tumors in muscles, tendons, connective tissue, fat tissues, blood vessels, nerves). In Sweden 19 cases of STS where 19 cases were expected following exposure. Experts believe that if dioxin was acting as an STS carcinogen it would cause an increase of one type of STS. The Swedish study has no confirmatory evidence to support it.

Dioxin/Birth Defects:

• Dioxin causes birth defects in female test animals.
• No solid evidence linking dioxin with human birth defects.
• Alsea, Oregon - reported increase in miscarriages from spraying 2,4,5-T herbicide. 18 reviews of this study uncovered numerous flaws.
• Children of Australian Vietnam vets there was no elevated birth defects and no unusual miscarriage rate.
• Same results in New Zealand for offspring of male applicators.
• Same results of children born to men exposed in industrial accident in Spolana, Czechoslovakia.
• Two major epidemiological studies of Vietnam veterans exposed to dioxin from 1963-1971.
1. "Ranch Hand Study": 15 to 20 year health history of 1045 herbicide applicators. There was no adverse health effects except some borderline incidence of increased infant deaths and minor birth defects which will be followed up. "Current evidence is insufficient to support a causal relationship between herbicide exposure and adverse health."
2. Center for Disease Control (CDC) - family health histories of 7000 children born with birth defects in Atlanta area. The control group had 10% of the parents with Vietnam experience. No significant correlation of birth defects or changes in fertility was found to be associated with Vietnam experience.
• No excess birth defects in Midland, Michigan, where Dow has a plant.
• In Hungary, no increase in national frequency of birth defects from 1966 to 1977, during which there was a 30-fold increase in use of 2,4,5-T.
• Seveso - reproductive patterns closely monitored in years following the 1976 explosion - no increase in frequency of miscarriage.

Summary:

Epidemiological evidence to date does not implicate dioxin as a cause of birth defects, miscarriages or reproduction in humans. Community exposures (Love Canal, Times Beach, Newark) are substantially lower than in various industrial accidents.

Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za. Last updated Jan 2007.
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