I found this discussion in Bill McGurn’s latest column useful:
Chemical risks are real, says Josh Bloom, but in this case likely exaggerated. Mr. Bloom, who holds a doctorate in chemistry from the University of Virginia and is director of chemical and pharmaceutical science for the American Council on Science and Health, says there are two broad concerns from the main chemical involved, vinyl chloride. There’s the danger from exposure to vinyl chloride itself, and the more severe dangers from the chemical reactions that occurred while it was being burned.
“Vinyl chloride, despite everything you see in the press, is actually not especially toxic,” Mr. Bloom says. “It is comparable to alcohol and chloroform, both of which are also carcinogens. And when tested in lab rats it is far less toxic than everyday drugs like aspirin, caffeine and Tylenol.”
“The cancer scare,” he says, “has also been exaggerated. Vinyl chloride is an occupational carcinogen — dangerous to people who work with it and are exposed for years. The chances of anyone developing liver cancer from a single exposure or two are very low.”
Nor is it likely to be a persistent environmental hazard. An EPA report estimates that because of its volatility, most residual vinyl chloride will evaporate from standing water or soil within about a day.