The Effects of Dioxin

1. The Effects of Dioxin Cassie Kuroda Biology 2B May 04, 2005

2. The Molecular Structure • Chlorinated organic chemicals with similar structures. • The chlorine atoms can be attached in 8 different places on the molecule. • The harmful effects of dioxin vary according to where the Cl atoms are located.

3. Chemical Properties • Dioxin is almost insoluble in water. • Instead, it has a high affinity for lipids. • Dioxin tends to stick to organic matter, such as ash, leaves, and soil. • Since dioxin binds strongly to soil, it does not easily contaminate the water supply. • When dioxin is in water, it sticks to organic matter or even plankton.

4. Where Does It Come From? • Non-human causes are forest fires and volcanic activity, but these produce a minimal amount. • There is no industrial use for dioxin. It is an unintentional byproduct caused by incomplete combustion: waste incineration, burning wood, coal, or oil, chlorine bleaching of paper, and cigarette smoke are a few examples.

5. How Does It Enter Animals? • Remember that dioxin sticks to plants. • Herbivores obtain dioxin by eating plants. • Dioxin also sticks to fats, so it will remain in the animal’s fat supply. • Larger animals eat the smaller animals with dioxin in their fat supply.

6. Spreading of Dioxin • Biomagnification: The concentration of dioxin increases as you go up the food chain. • Bioaccumulation: Dioxin accumulates in the animal’s body and milk supply. • Dioxin can then be spread to an animal’s offspring through their milk or even the placenta.

7. Human Exposure • Over 90% of human exposure comes from our food supply, mainly from the animals we eat. • Our daily intake is about 1-3 pg/kg body weight. The average is 2.2 pg/kg body weight. • The WHO (World Health Organization) states that 1-4 pg/kg body weight per day is tolerable. • The amount of dioxin in the human body increases during childhood, but reaches equilibrium around age 20.

8. How Does It Affect Humans? • Dioxin interacts with AhR (Aryl hydrocarbon receptors), which results in the formation of proteins in the nucleus that interfere with cellular growth and differentiation. • Since dioxin dissolves in fat, it must be transformed in the liver to become water soluble so it can be excreted. This is a slow process, so dioxin accumulates in our fat and liver.

9. What About Animal Testing? • Dioxin itself does not seem to cause cancer. Instead, it promotes the growth of already existing cancers. • In rats: Uterine disease, neurobehavioral effects, lower sperm count, female urogenital malformations, effects on the immune system. • At the lowest doses in rats: liver tumors and thyroid tumors in males.

10. Studies on Humans • Herbicide plant workers heavily exposed to dioxin have more cancers of all types than the general population. • Agent Orange and the US Air Force during Vietnam. • There seems to be a 40% increase in cancer risk when heavily exposed to dioxin.

11. Studies in Japan and Taiwan • There was a 22 year study done in Japan involving the high dioxin contamination of rice-oil. There was an increase in liver cancer. • A 12 year study in Taiwan involving a similar situation, but slightly lower levels of dioxin showed no significant cancer increases.

12. Effects on Children • Neurobehavioral effects. • They are more easily exposed through the placenta instead of through breast feeding. • The newborns in Japan and Taiwan after the rice oil incidents had skin defects, low birth weight, behavioral disorders, reduced height at puberty, and hearing loss.

13. Effects on Adults • Increase in diabetes • Cardiovascular diseases in men • Higher rate of heart disease in men • Liver diseases • Chloracne and hyperpigmentation

14. Seveso, Italy • In the summer of 1976, the extreme heat and pressure caused an explosion at a chemical factory. • The level of dioxin ranged as high as 56,000 pg/g lipid, but the average was 450 pg/g lipid in Zone A (the most heavily contaminated area) and 126 pg/g lipid in Zone B (just outside of Zone A).

15. Effects in Seveso, Italy • Chloracne in children who were exposed to the toxic clouds. • Spontaneous abortions, congenital malformations, impaired liver and lipid formation, immunologic and neurologic impairment. • Heavily exposed males fathered fewer boys and more girls.

16. Controversy About Seveso • Many believe that dioxin only caused chloracne while the other effects are due to something else. • Others believe that dioxin is the cause for all the effects in Seveso. • Some are remaining practical and are waiting for more long-term research to be completed in Seveso.

17. Why is the Seveso Incident So Important? • It is the only incident involving pure TCDD (the most toxic form of dioxin). • Those who were exposed were of all ages and both genders. • This allows for more vast research to be done.

18. The Follow Up on Seveso • An increase, but no deaths from liver cancer. • An increase in digestive cancers, rectal cancer, and lung cancer. • A few deaths from melanoma. • Increase in Hodgkin’s disease. • However, some believe these increases are not significant enough to draw conclusions about dioxin.

19. What Does the EPA Have To Say About It? • The EPA states that the risk of an American getting cancer from exposure to dioxin is1 in 10,000. • 1 cancer per million is considered the “acceptable risk value.” • Our cancer risk is 100-300 times higher than the “acceptable risk value.” • “ [Dioxins] do not pose a significant risk to human health or the environment.” - EPA

20. What’s Being Done About It? • The amount of dioxin exposure decreased during the 1990’s because of environmental regulations. • TCDD only accounts for 10-20% of total dioxin exposure. • The World Health Organization (WHO) ultimately wants to decrease human intake levels to below 1 pg/kg body weight per day.

21. Works Cited • http://www.sciencenews.org • http://www.greenfacts.org • http://www.planetark.com • http://www.mindfully.org