Dioxins

Dioxins 

• A type of persistent organic pollutants (POPs)
• Dioxin is a substance that occurs naturally due to incomplete combustion such as volcanic activity or forest fires, or is created as an impurity during the synthesis of chlorine and aromatic hydrocarbons, and is frequently exposed in combustion processes such as waste incineration.
• The International Agency for Research on Cancer (IARC) classifies 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and 2,3,4,7,8-pentachlorodibenzofuran (2,3,4,7,8-PeCDF) among dioxins as human carcinogen Group 1.
• Dioxin is easily dissolved in fat and absorbed into the body, but is not easily excreted through urine and accumulates in fatty tissue, so dioxin can be detected in breast milk and milk.
• A general term for a mixture (210 types) of polychlorinated dibenzodioxins (75 types) and polychlorinated dibenzofurans (135 types) homologs, of which 17 congeners, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), are known to be highly toxic.

■   Environmental exposures in the general population

Dioxin is practically insoluble in water and chemically stable, meaning it doesn't break down easily once it's formed in nature. It's produced during the incomplete combustion of organic compounds containing chlorine or halogens, like during waste incineration and metal processing. These dioxins are released into the atmosphere and are found in small amounts in soil and water. However, dioxins dissolve readily in fat, leading to bioaccumulation through the food chain. They can be especially concentrated in high-fat foods, so the majority of exposure occurs through consuming contaminated food (97-98%).

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■    Occupational exposure

Dioxins are chemicals that aren't intentionally produced or used commercially but are by-products of various industrial processes involving chlorinated organic compounds, like manufacturing or burning. They stem from multiple sources such as incineration, metal production, power generation, transportation, and chemical manufacturing. Emissions also come from processes like pulp and paper bleaching, pesticide manufacturing, coal-fired power plants, automobiles, and diesel combustion. Since the rise of organochlorine herbicides in the 1940s, occupational exposure to high doses of polychlorinated dibenzo-p-dioxin (PCDD) has occurred, with incidents at industrial facilities contributing to higher concentrations. Awareness of dioxin's harmful effects has led to significant reductions in environmental concentrations over the past three decades as countries have worked to minimize dioxin generation and release. However, dioxins are stable and persistent, decomposing slowly, so most exposure stems from emissions dating back many years.

 

■    Exposure due to accidentsžincidents

Agent Orange was a herbicide used by the U.S. military during the Vietnam War (1962-1971) to kill trees for military purposes. It contained a mixture of acetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), with small amounts of the toxic by-product 2,3,7,8-tetrachlorodibenzodioxin (TCDD). Its use has since been banned due to its toxicity.

 In 1976, a chemical plant accident in Seveso, Italy, resulted in the release of chlorine gas and dioxin into the atmosphere. This led to the death of livestock and skin poisoning in local residents, causing symptoms such as chloracne, resembling severe acne. Pregnant women in the area feared miscarriages or birth defects, leading to abortions. The released dioxins severely polluted the surrounding, leading to the categorization of affected areas into zones A (above 50 μg/m2), B (5~50 μg/m2), and R (less than 5 μg/m2), based on TCDD concentration and toxicity risk. Residents in Zone A showed higher blood TCDD levels and chloracne symptoms compared to other zones.

Twenty years after the Seveso incident, a study found elevated TCDD concentrations in the blood of residents: 71.5 ng/kg in area A, 12.5 ng/kg in area B, and 5.5 ng/kg in a comparison group. Women in all zones had higher TCDD levels than men.

 In 1999, dioxins were detected in chicken and pork in Belgium due to contaminated feed containing polychlorinated biphenyls (PCBs). This led to over 2,500 farms receiving contaminated feed, resulting in slaughtered livestock being distributed to various countries.

 

■    References

The content is primarily based on Polychlorinated dibenzo-para-dioxins and polychlorinated dibenzofurans (IARC Monographs on the Evaluation of Carcinogenic Risks to Humans), Toxicological profile for chlorinated dibenzo-p-dioxins (ATSDR). Exposure and human health reassessment of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds (USEPA).