Where is Dioxin? Part 2
Part 1 discussed the presence of dioxins due to the use of
2,4,5-T herbicide and from combustion. This issue continues with a discussion of the
presence of dioxins in pentachlorophenol and petroleum.
Pentachlorophenol (sometimes called simply penta, but not PCP which is something else)
is made from an exhaustive chlorination of chlorophenol tars. The product is purified
by dissolving the penta in water (by the addition of caustic to make the water-soluble
salt) and the subsequent phase separation of non water soluble materials (tars). The
water solution is then made acidic and the precipitated penta filtered and dried.
Pentachlorphenol has a wide range of dioxins in it (virtually every possible isomer)
with the higher chlorinated analogs predominating. The level of total dioxins in
pentachlorophenol is in the mid to high part per million range, and in the separated
tars in the percent range. It should be noted that the major portion of dioxin in
both is octachlorodibenzo-p-dioxin which is about as toxic as table salt
The major use of pentachlorophenol is as a wood preservative. It is used commercially
in the preservation of telephone poles, fence posts, and board lumber used in contact
with the ground. It is also available for household use as a formulated product which
is painted on wood to preserve it.
The treating of telephone poles with pentachlorophenol is done in large vessels under
pressure to aid the penetration of the wood. It is common for workers to come in
contact with the treating solution and wood, causing visible evidence of toxification
(chloracne). This may be the most common vector for human industrial exposure to
It is now forbidden to use pentachlorophenol treated wood as the construction material
for animal feed storage bins. This has, in the past, been a source for the exposure
of cattle to dioxins by transfer of dioxins in treated wood to the feed and hence
humans through the consumption of meat and milk from those exposed animals.
Pentachlorophenol has also been used as a bactericide in many products. These have
included paint, cosmetics, ink, fabric dyes, and other substances used in the home.
This may be (may have been?) the most common route for exposure of the general
population to above background levels of dioxins.
Cow hides have been preserved using penta in South America. Contaminated gelatin
extracted from those hides was imported to the US and used to make capsules to hold
medication. This caused a recall of that medication and restrictions on the sources
of gelatin for capsules.
It should be noted that a Canadian study found that penta was one of the most
significant sources of dioxins in that country.
Since dioxins are formed as a natural product of combustion, fires during the period
when the plant life source of petroleum was alive would have produced traces of
dioxins just as they do today. Those dioxins which fell on the plant life would have
been incorporated in the crude oil. In the absence of studies to determine it, I
would estimate that the total level of dioxins in crude oil from such a source to be
less than 1 part per trillion and probably in the part per quadrillion range or
Crude oil undergoes extensive processing to make the final products such as gasoline,
heating oil, and kerosene. Where do the dioxins, if any, end up in this complex
process? The possibilities are that they are unaffected by the process, are destroyed
in the process, are formed in the process, or are changed in the process. Since
dioxins are not very volatile, if any remain I would expect them to end up in a
"heavies" of some type. It is also possible that they are concentrated wherever they
No studies have been done, as far as I know, to determine any of this. Based on a
knowledge of chemistry and the properties of dioxins, an educated guess could be made
as to the most likely scenario(s), not by me, however, I am no petroleum chemistry
When petroleum products are burned, the level of dioxins formed would depend on the
availability of chlorine and the temperature. Even very low levels of dioxin
emissions from automobiles, home heating, and power generation would be a significant
portion of the total dioxins produced throughout the world due to the large quantities
of petroleum involved.
I do not know of any definitive studies which have been carried out on these
combustion products to determine the dioxin levels produced. Reassuringly, no
detectable dioxins were found in a study of emissions from a coal-fired power
It is fair to state that the "jury is still out" on the question dioxins in petroleum
products and process streams and of petroleum combustion as a source of dioxins until
definitive studies are done.
(To be continued....)
This article is Copyright 1994 by Lewis A. Shadoff. It may be freely
redistributed in its entirety provided that this copyright notice is not removed. It
may not be sold for profit or incorporated in commercial documents without the written
permission of the copyright holder. While all information in this article is believed
to be correct at the time of writing, this article is for educational purposes only
and does not purport to provide legal advice.