Ukrainian presidential candidate Viktor Yushchenko was poisoned with pure TCDD, one of the most toxic chemicals, the scientist analyzing his blood said.
The tests, confirmed by three separate labs in the Netherlands and Germany, also confirmed that Yushchenko's blood contained 100,000 units of the poison, the second highest concentration ever recorded.
Doctors had announced last weekend that Yushchenko was poisoned with a dioxin chemical, but lead investigator Abraham Brouwer told reporters on Friday that his team has now zoned in on TCDD, the most hazardous of all the dioxins.
There are hundreds of dioxins and they are usually produced inadvertently during manufacturing processes that use chlorine, such as those for herbicides, paper and pulp bleaching. Waste incinerators also produce dioxins.
TCDD was an element in Agent Orange, a herbicide sprayed by US troops during the Vietnam War to clear dense vegetation and expose their enemy. The herbicide became infamous after being linked to myriad health problems in US veterans and local villagers.
The poison, chemically known as tetrachlorodibenzoparadioxin, usually occurs mixed with other dioxins produced by the same processes.
However, the investigation led by Brouwer at BioDetection Systems in Amsterdam found Yushchenko was poisoned with pure TCDD, not a mixture.
"That excludes a huge number of sources," said dioxin expert Dr. Arnold Schecter, a professor of environmental Sciences at the University of Texas School of Public Health in Dallas who was not involved with the investigation.
"If it's pure TCDD that means it could only be labs that buy or sell TCDD [for research purposes], government biological or chemical weapons units or a clever chemist," Schecter said..
Brouwer said he agreed that the search for the source of the poison can now be focused on those three possibilities.
Most people living in Europe and North America have some level of several dioxins or dioxin-like poisons in their bodies, experts say. The pattern and concentration of those gives clues to the source, whether chiefly from an incinerator, factory or other location.
Brouwer, also a professor of environmental toxicology at the Free University in Amsterdam, said all of the other dioxins found in Yushchenko's blood were at levels normally found in people from his region.
None were elevated, except for TCDD, which means that even if the poison originally came from a factory or incinerator it must have been purified in a lab afterward.
TCDD is synthesized by labs in Europe, Russia and the United States for use as a benchmark sample in lab tests measuring dioxin levels.
Several labs around the world may also purify TCDD for research purposes. It is not used in any commercial products.