Where is Dioxin? Part 2

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 dioxins.

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 less.

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 end up.

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 expert.

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 plant.

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.