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June 29, 2008

Pine Oil Tick and Mosquito Repellent

In one of those strange serendipitous moments that can happen with Google Alerts, I visited an article entitled "Tick and Mosquito Repellent Can Be Made Commercially from Pine Oil" which describes "a naturally-occurring compound prepared from pine oil" that deters mosquito biting and repels ticks.

After I read the press release, which contains the curious statement

Some segments of the public perceive efficient synthetic active ingredients as somehow more dangerous than botanical compounds, giving additional importance to the discovery of plant-based isolongifolenone.

my interest was piqued , so I read the patent which has been issued covering the preparation of the compound and "its use in repelling arthropods". Would this product meet the requirements of the NPA Natural Products standard? Would it meet the requirements of the NIRC definition of "Natural"? It's been over 40 years since I had my last chemistry course, but I think I can figure this out.

Reading through the patent, some interesting facts are revealed. Deet has long been considered the standard for mosquito repellency,

However, Deet is a plasticizer and clinical literature reports the association of Deet with neurotoxicity in humans (Robbins, P. J., and M. G. Cherniack. J. Toxicol. Environ. Health, 18: 503-525 (1986)). Thus, there is a great need for effective alternatives to Deet.

Essentially the process of producing takes isolongifolene, which is a naturally occurring component of Pinus longifolia, and converts it to isolongifolenone, which is also naturally occurring in smaller quantities. This is done via oxidation with tert-butyl hydroperoxide in the presence of a catalyst chromium hexacarbonyl. The process has a high yield but may not meet the natural standard because benzene is used to recover the catalyst (which itself is a considered toxic).

According to Wikipedia

In common with many of the other homoleptic metal carbonyls (e.g. nickel carbonyl and iron carbonyl), chromium hexacarbonyl is toxic and thought to be carcinogenic.

Tert-butyl hydroperoxide doesn't have its own entry in Wikipedia, but a search of the ToxSeek database reveals 143 entries.  Without detailed analysis, one can only conclude that it is a toxic hazard.

The NPA Natural Standard

To see what this means, let's look at the definition of natural in the NPA Standard:

Ingredients that come or are made from a renewable resource found in nature (Flora, Fauna, Mineral), with absolutely no petroleum compounds.

OK, that may work, except for the Tert-butyl hydroperoxide, benzene and the chromium hexacarbonyl.  A check of the NPA Standard's list of prohibited ingredients doesn't have any of those on it, except for the prohibition on petroleum.  We can only conclude from this standard that the isolongifolenone would only be natural if all the traces of either the catalyst or the chemical used to remove it are completely removed.

A look at the processes allowed or disallowed in the NPA Standard reveals that this process is not on either list.  Not surprising, considering that it wasn't known when the standard was written.

NIRC Definition of Natural

The NIRC definition of Natural requires a natural material to be "present in or produced by nature, produced using minimal physical processing, and directly extracted using simple methods, simple chemical reactions or resulting from naturally occurring biological processes."  Based on this part of the definition, our product would seem to pass.  However, the NIRC definition goes on to require that "Natural Ingredients are . . . not produced synthetically, free of all petrochemicals, not extracted or processed using petrochemicals, [and] not extracted or processed using anything other than natural ingredients as solvents."

So it looks like it won't meet this requirement either, even worse than the NPA definition, because of the petrochemical ban and the non-natural catalyst and solvent situation. Even if you could get all traces of the chemicals removed from the isolongifolenone, the processing is not natural.


Based on this analysis, the repellent isolongifolenone cannot be considered a "natural" product under the definitions of either the NPA or the NIRC.

Related Information

While researching this subject, I came across a 2005 Indian study on the effectiveness of Pine Oil as an insect repellent. The pine oils used in the study was analyzed, but didn't reveal the presence of either of the two compounds involved in the patent (they were probably included in the 13% unidentified ingredients. The paper states that pine oil is used traditionally as a repellent in India.

Posted by Rob on June 29, 2008 in Essential Oils/Plant Extractions, Research, Safety/Toxicity, Standards | Permalink


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