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PAHs and waxes, mineral oils, and petroleum jelly July 19, 2008

Posted by fetzthechemist in Uncategorized.

I get Google Alerrts for the terms “PAHs” and “polycyclic”. About half of those refer to blogs about PAHs and consumer products – mineral oil, wax, petroleum jelly. A good chuck of others are on smoked or barbecued meats and PAHs.

Sheesh! The Internet spews so much false crap on this! It irritates me to no end because I worked on projects to get Food and Drug Administration approval for mineral oil and wax for human contact. The myths take the generic information for those products, like mineral oil used to lubricate machinery or wax for Presto logs, and assumes it applies. That is utter BS.

To be in contact with people in as lubricants for food-handling machinery, coating for wax, in cosmetic, or anything else ingest or touching the skin. the FDA requires that these products be cleaned up until the total of all of them is less than 1.0 parts-per-million. For individual targetted one, like benzo[a]pyrene or benz[a]anthracene, the limit is 10 parts-per-billion. This is a thousand times less than in the regular stuff!

The saturated hydrocarbons that form 99.9999 % are generally innocuous – they do dry the skin of moisture when they coat it or cause diarrhea if eaten in quantity, but these products are not the bad things bloggers are raving about. Some make cosmetics with plant extracts for medicinal use or fragrance. Ever look at the nasty compounds in most plant extracts? Those always have phenols, carboxylic acids, and other toxins.



1. psi*psi - July 20, 2008

This is kinda new to me–I’d always heard that PAHs were ubercarcinogenic. So which ones are more or less innocuous? Do you know of any studies out there on their eventual fate in the environment? (Since my research is so focused on aromatics, not knowing is a little unsettling.)

2. fetzthechemist - July 20, 2008

There is a whole field of research into the mechanisms of the carcinogenicity of PAHs. It is very structurally dependent. First, the PAH must be oxidized or metabolized. The PAH itself is not the carcinogen. Certain oxygen-containing derivatives are. These fit into the DNA structure, disrupt regular replication, and foster abnormal replication. That creates cancerous cells rather than normal ones.

This is a very specific key-in-the-lock mechanism. Some PAHs do not mebabolize into keys that fit DNA to cause bad replication – so both forming the ozxidized version and it fitting are important requirements.

Structures like benzo[a]pyrene and benz[a]anthracene do both. The toxicologists speak of their shape and location of oxidation as being a K-region (from some German origin, I think, that now escapes me). Isomers like benzo[e]pyrene and perylene for benzo[a]pyrene and naphthacene or triphenylene do not have similar shapes nor an appropriate oxidation site to fit.

The mechanism is so specific that a methyl group can totally deactivate a PAH or make it even more active, depending on the effects on oxidation likelihood and shape.

Some PAHs do both so well that they are super-hot carcinogens. Thinking used to be that bigger PAHs had to be less active. Until they synthesized and tried dibenzo[def,p]chysene (dibenzo[a,l]pyrene. It is more than a thousand times more active than benzo[a]pyrene. Doing work with it even scares the toxicologists.

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