Dioxin

"TCDD has been called the most toxic synthetic chemical known to man" (7)

The first thing to know about Dioxin is that the term "Dioxin" describes a group of chemicals that contain chlorinated-diphenyl compounds. Some types of chemicals that belong to this category are dioxins, furans, and polychlorobenzenes (PCB's) (10).

(Dioxin)

(Furan)

(PCB) (10)

The dioxin that contaminated 2,4,5-T in Agent Orange was TCDD (2,3,7,8-Tetrachlorodibenzo-p-dioxin). Because of its fame, this chemical is simply referred to as "Dioxin"

Some chemical info on TCDD is as follows:

C12H4Cl4O2

MW- 321.96g

LD50(monkey)- 114-280 mg/Kg (8)

(9)

SEVESO

There are very few recorded instances of people being exposed to TCDD. Because of this it is very difficult to study the effects of exposure to humans. There is, however, one well-known and well-documented incident where a city was exposed to high levels of Dioxin. This happened in Seveso, Italy. On July 10, 1976 a valve broke at a local chemical plant (ICMESA), and a cloud of toxin chemicals was released into the air that traveled toward the city. Among the chemicals released were 2,4,5-T and anywhere from 100g to 20kg of TCDD. The response time to this accident was quite long because it was a Saturday afternoon and there was no one at the plant. A few hours after the accident "burn-like lesions" started appearing on the children in Seveso. Another 5 days after the valve broke, when animals; such as rabbit, cats, dogs, etc, began to die the local authorities began and investigation. Two weeks after the accident people were finally evacuated from the areas of the town that had been exposed to high levels of Dioxin. Because of the high concentration of TCDD, ~4% of the local farm animal population had died. Once it was determined that the cause of death was Dioxin, the remainder was slaughtered to prevent contamination of the food supply. Roughly 80,000 farm animals died.

While the investigation was taking place in Seveso, Dr. Mocarelli was being put in charge of a special investigation of his own. He was asked to set up a laboratory to test people of the town for health problems. This eventually turned into an investigation to study the long-term effects of exposure to Dioxin. Some results that Dr. Mocarelli found are as follows:

1. Dioxin appears to shift the male/female birth ratio in the offspring of those exposed to it
    (28/46 as opposed to ~50/50 before accident).
2. Exposure to Dioxin can cause Chloracne.
3. There is probable some effect on the immune system.
4. There appears to be some correlation with neurological disorders.
5. Only minor increases in some cancers.

Today people have returned to Seveso, and all the cleanup work has been done to remove the dioxin, but it is still the only case where levels of Dioxin exposure can be measured, and results from these exposures can be documented as well as researched. (11)

How Does Agent Orange Still Affect Me Today?

After the accident in Seveso, Dioxin became very scrutinized. So much so that on July 20, 1978 the chairman of the Vietnam Veterans Agent Orange Victims, Inc. (Paul Reutershan) filed a class action law suit (MDL-381) against the companies involved in manufacturing Agent Orange, including Dow. Nearly a year later the EPA, "ordered the immediate halt to most uses of the herbicide 2, 4,5 T which contains Dioxin…" on March 11, 1979 (13)

Unfortunately, the lawsuit never made it to trial because a settlement of $180 million was reached on May 7, 1984 (13). I say unfortunately because the trial never reached the courtroom, so the effects of exposure to TCDD could not be formally connected to any health effects.

But how does Dioxin affect you and me?

This chart is from an EPA study released in 1994, on TCDD exposure in North America (9). Dioxin isn't water soluble, but it is very fat-soluble. As you can see from the chart, TCDD tends to build up in dairy products. The EPA has something called a reference dose. This is the highest amount you can consume without regularly incurring a disease (not including cancer). The reference dose for TCDD is 1pg/Kg/day. Considering that the average male weighs 70kg and average females weigh 55kg, that comes out to 70pg/day for an average male and 55pg/day for an average female (7).

Given all of the information from Seveso and the findings of the EPA, the IARC (International Agency for Research on Cancer) declared TCDD a class 1 carcinogen on Feb. 14, 1997(9). Although Dioxin doesn't destroy DNA or alter it, it does penetrate the cell membrane, and it can bind to DNA. One such illustration of the mode of action for TCDD is this:

(12)

So knowing all of this you would think that there are many documented medical issues. This, however, is not the case. Most of the health effects that people believe are associated with exposure to Dioxin have not been "proven" to be results from this exposure. Here is a table of some of the health effects believed to be associated with Dioxin:

Agent Orange in the Environment