First of all, I should have addressed reply #16 to you, too.
Dioxin is more or less a generic term; those of us in the field (or who have recently left it, like I did) use the term TCDD to mean the 2,3,7,8-tetrachloro molecule that is the most potent of these molecules. Not all dioxins are toxic; mostly the toxic ones are the ones with chlorine substitutions around the benzene rings. Even these have varying levels of toxicity. Other substitutions are possible besides chlorine, and these are generally less toxic or non-toxic.
As for the stability of these compounds, it is more or less proportional to their toxicity. Some chlorinated dioxins are susceptible to lysis by various microorganisms, and thus have a reduced stability. Because of the placement of the chlorines, TCDD is resistant to biological destruction. It has a half-life in the human body of ~7 years. It is destroyed by UV light, but tends to stick to dust and dirt particles that shield it from sunlight, so that in the environment, it has a half-life of 10 to 12 years. There are situations where chlorinated dioxins have apparently been stable for millenia, for instance, in clays that have been submerged in salt water at some time in the geologic past.
Transformer explosions using ordinary mineral oils as insulating coolants caused so many fires that a deliberate re-design of the coolant oils led to compounding of PCBs; this cut down on the resultant fires to a level of incidental risk while the hue and cry from the toxicity and potential carcinogenity of the compound was only made to seem like an imminent threat based on laboratory studies of the type Bruce Ames rejected and regretted having introduced into the field of analysis to no avail and to his eventual shame and professional disapprobation and finally, virtual ostracism.
The simple fact remains that other than sloppy handling of the raw compounds or the unwise application prior to case study implication, these compounds present no clear and present danger to the public at large and, in my opinion, are undeserving of the reputation they have gained.
Unlike the iconic Nobel who redeemed his conscience at the expense of his fortune, not many modern scientists seem willing or able to make sufficient apology from the grave.