If oil is supposedly inert, why are we talking about quality issues?
One thing is clear: if an oil’s hydrocarbons are not fully saturated, whether alkenes, cycloalkenes or PAHs, they are susceptible to oxidation that can produce toxic peroxides in culture. A useful analogy is olive oil – it is monounsaturated and becomes oxidized over time leading to rancidity. Olive oil has a shelf life – eventually, it becomes oxidized and rancid.
In contrast, if mineral oil is fully saturated and lacks any readily oxidizable carbons, it is inert and requires enormous amounts of energy to become oxidized. To illustrate the stable nature of oil that is fully saturated, I’ve used the same batch of oil as a control for all of my studies on quality control, that was purchased in 2008. I even exposed one bottle from this lot to UV light for a week, and it has yet to develop peroxides and is nontoxic.
There are two classes of oil toxins: contaminants and reactive molecules called peroxides. Over 10 years ago my lab at the Mayo Clinic was the first to identify a contaminant in a batch of research grade mineral oil³. This oil was from a chemical supply company that does not test oil as rigorously as ART suppliers. We found high levels of Triton x-100, a detergent that was likely a carryover from the manufacturing process of the oil or the bottles containing the oil.
Since oil is, well, oil, it is very hydrophobic and will readily take up other hydrophobic molecules. This could potentially be a concern and requires that manufacturers have tight control of their supply chain to assure the oil is not exposed to high airborne concentrations of toxic volatile organic compounds (VOCs), and then, of course, good quality control testing to check for toxicity. The expectation is that thorough quality control testing will detect toxicity prior to shipping. One other approach to improve quality of oil is via washing – we showed that washing oil can reduce the concentration of TX-100 as well as the toxicity of peroxide-containing oil³.
Peroxides are far and away the most common cause of oil toxicity.4,5,6 Before an oil goes to the ART manufacturer, the refining plant treats the oil with high-pressure hydrogenation to effectively turn all double bonds, or alkenes, into single bond carbon chains (alkanes). Because of the homogeneous nature of the different hydrocarbons in oil, it is virtually impossible to isolate alkenes from alkanes, and the test for the presence of unsaturated alkenes is crude at best. Advanced analytic methods, such as FTIR, NMR, and GC-FID, offer promise in this area.