Trace amounts of a new compound dioxin were present in. a defoliant sprayed on v

Question

Trace amounts of a new compound dioxin were present in. a defoliant sprayed on vegetation during the Vietnam War Animal tests suggest that dioxin can cause birth defects, cancer, liver and thymus damage, immune system suppression. sometimes leading to death. But the animal tests are equivocal: a hamster is nut affected by a dose that can kill guinea pig. dioxin acts somewhat like a steroid hormone, entering a cell and binding to a receptor protein that then attaches to the cell?s DNA. a. How might this mechanism help to explain the variety of dioxin?s effects on different body systems and in different animals? b. How might you determine whether a type of illness is related to dioxin exposure? c. How might you determine whether a particular individual became ill as a result of exposure to dioxin? d. Which of the above (b or c ) would be more difficult to demonstrate? Why?

Explanation / Answer

a)

Dioxins are polychlorinated dibenzene dioxins (PCDD). They are the organochemicals exhibiting various harmful affects on humans and animals. Of the various dioxins, 2,3,7,8 TCDD is most toxic dioxin. The dioxins are formed by the incomplete combustion of organic wates and eruption of valconoes, forest fires and burning fuels.

The dioxins cause cancerous as well as noncancerous effects based on dosage. at minimum dose they cause uterine disorders in fmale animals, neuronal defects affecting cognitive behavior, reducing the sperm counts, uterine malformations etc.. The cancerous effects include the promotion of proliferative growth in previously fromed cancer lesions in both sexes. even at lower dose they are found to cause thyroid cancer in rats. Mainly dioxins cause neuro toxicity in rhesus monkeys, reproductive toxicity in rats, immunotoxicity in rats, hormonal toxicity or endometriosis in rhesus monkey were well known. The LD50 of dioxin also varies wildly between species with the most notable disparity being between the ostensibly similar species of hamster and guinea pig. The oral LD50 for guinea pigs is as low as 0.5 to 2 ?g/Kg body weight, whereas the oral LD50 for hamsters can be as high as 1 to 5 mg/Kg body weight, a difference of as much as thousandfold or more, and even among rat strains there may be thousandfold differences.

b)

Exposure to dioxins can be occur through environmental facts by accidental or occupational contaminations. The bioaccumulation of dioxins in aquatic and terrestrial food chains cause the exposure of dioxins to humans. Dioxins build up primarily in fatty tissues. Exposure to high levels of dioxins in humans causes a severe form of persistent acne, known as chloracne. High levels of occupational exposure to dioxins lead to form epithelial cancerous tissues.

c)

In many instances dioxin contamination is introduced via contaminated animal feed, for example, incidences of increased dioxin levels in milk or animal feed were traced back to clay, fat or citrus pulp pellets used in the production of the animal feed. Due to the high prevalence of dioxins, all people have background exposure and a certain level of dioxins in the body, leading to the so-called body burden. Current normal background exposure is not expected to affect human health on average. However, due to the high toxic potential of dioxins, the disease resulted can be determined by the estimation of exceeding amounts of dioxins in tissue samples.

d)

Individula body burden limit of dioxins should be known inorder to determine the disease is resulted due to the exposure to dioxines. It can be difficult because of the varying toxicity doses in humans due to facts like accidental and occupational exposures. The occupational exposers are prone to toxicity caused by dioxins than the other individuals and hence, (b) is more difficult to determine rather to determine at the level of individual.

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