The effects of dioxin
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The Effects of Dioxin. Cassie Kuroda Biology 2B May 04, 2005. The Molecular Structure. Chlorinated organic chemicals with similar structures. The chlorine atoms can be attached in 8 different places on the molecule.

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The Effects of Dioxin

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The Effects of Dioxin

Cassie Kuroda

Biology 2B

May 04, 2005

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Effects on Adults

  • Increase in diabetes

  • Cardiovascular diseases in men

  • Higher rate of heart disease in men

  • Liver diseases

  • Chloracne and hyperpigmentation

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).

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.

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.

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.

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.

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

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.

Works Cited





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