Detecting traces of methyl eugenol in essential oils: tea tree oil, a case study

Methyl eugenol is a naturally occurring flavour and fragrance found in a variety of different food sources, including spices, herbs and fruit and also as a component of natural essential oils. Commonly used oils with more than 0.1% of methyl eugenol include calamus, rosewood, elemi, ylang ylang, cymbopogon, star anise, lovage, verbena, nutmeg, basil, pimento, bay leaf, rose and clove. In addition there are other potential sources of exposure to methyl eugenol, including agriculture, wine consumption and ambient background in air and water. Because high doses of some allyl alkoxybenzenes have induced tumours in rats and mice, use is recommended as either restricted or, in the case of safrole, prohibited. Many reviewers and researchers present clear evidence that these restrictions are excessive, especially those who accept that carcinogenesis is a threshold phenomenon. This paper describes suitable gas chromatographic methods for the determination of trace amounts of methyl eugenol in the essential oil of tea tree, Melaleuca alternifolia, terpinen-4-ol type. Published 'trace' amounts were interpreted as being as high as 0.3-0.9% by one regulator. Peak assignment by GC-MS and co-elution with a standard facilitated the GC-FID determination of 128 commercial samples. Inter-laboratory confirmation was achieved using GC-MS with selected ion monitoring. These determinations indicated that the methyl eugenol content of tea tree oil ranged from less than 0.01% to 0.06% ( mean 0.02%), i.e. 20-fold lower than the regulator's interpretation and one million times lower than the logarithmic scale levels known to cause carcinomas in rats. Copyright (C) 2011 John Wiley & Sons, Ltd.