Ask A Scientist© Chemistry Archive

 
name       Alvin
status     student
age        30s

Question - What toxix substance is produced that is harmful to our
health when a plastic material is burned?
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Hi Alvin!
Many plastics, particularly PVC when burned resuts in emissions
of the deadly poison named dioxin.
Dioxin is a toxic organic chemical that contains chlorine and is
produced when chlorine and hydrocarbons are heated at high temperatures.
To inhalate dioxin or to be exposed anyway to its fumes can cause
many deadly results.
Dr. Mabel R.
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There are lots of them. Any carbon-based material produces hazardous
products under most combustion conditions, mostly due to incomplete
combustion. For instance, burning gasoline can produce carbon monoxide
and hydrocarbons, burning charcoal can produce carbon monoxide, and
burning methanol can produce formaldehyde.
Some types of plastic contain elements besides the standard carbon,
hydrogen, and oxygen. Nylons contain nitrogen, and polyvinyl chloride
contains, of course, chlorine. These constituents also find their way into
the combustion products. Probably the particular component you have heard
about most is TCDD, which is an abbreviation for the chemical name
tetrachloro-dibenzo-dioxin. This compound contains four chlorine atoms, and
is inevatibly formed when polyvinyl chloride plastics are burned. (Complete
combustion of PVC would yield only water, carbon dioxide, and hydrogen
chloride; in practice, some incomplete combustion products such as TCDD are
always formed, if at low levels.) TCDD is also formed when wood burns,
because wood also contains small amounts of chlorine. Because of the much
higher proportion of chlorine in PVC, however, it is the material leading to
the highest levels of TCDD.
The toxicity of TCDD to animals is well-established. It is often considered
to be the man-made compound most toxic to animals. Its toxicity to humans,
however, is not as well-established. The only absolutely confirmed human
health effect from exposure to TCDD is a skin rash called chloracne.  Other
health effects are suspected. It is considered a carcinogen on the basis of
animal studies.
TCDD is also an unwanted by-product of the manufacture of the herbicides
2,4-D and 2,4,5-T. A manufacturing accident at a plant manufacturing these
chemicals occurred near Sevesto, Italy in 1976 released an estimated 1-10 lb
of TCDD into the surrounding countryside, killing many farm animals and
causing chloracne. Since 2,4-D and 2,4,5-T were components of the defoliant
"Agent Orange" used in Vietnam, many U.S. servicemen (and of course
Vietnamese) were exposed to elevated levels of TCDD. TCDD is thus suspected
as the cause of the symptoms attributed to "Agent Orange" exposure.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois 
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