The purity and authenticity of essential oils is a vast and very vehemently debated topic both by users and producing companies as well as by many scientists trying to find the best testing methods to discover adulterated or contaminated oils. While contamination can be accidental, adulteration is most often intentional and aimed at economic benefits. Both can happen at any stage of production, from plant growth to bottling.

\"If we truly want to learn from nature, in our case from essential oils, resolving the issue of purity and authenticity is the critical element that determines whether or not we will be able to learn.\" (\"If we really intend to learn from nature, in our case from essential oils, resolving the issue of purity and authenticity is the pivot that determines whether or not we will indeed be able to learn.\") Kurt Schnaubelt, The healing intelligence of essential oils.

Over the years, numerous purity tests have been carried out on available essential oils. It is estimated that 80-90% of commercially available essential oils are contaminated or adulterated in some way. The percentage is all the more worrying as essential oils are increasingly used in various industries such as medicine, aromatherapy, agriculture, cosmetics, food, etc. An increase in demand automatically leads to an increase in production and, unfortunately, to the emergence of inappropriate practices and products.

In order to determine whether it is pure, we must first understand what an essential oil is. In aromatherapy, essential oils are simply those volatile substances obtained from different parts of plants (fruits, flowers, leaves, bark, bark, roots, rhizomes) by distillation or pressing.

Contamination of essential oils

Contamination of essential oils is the process by which the natural chemical composition of the oil is changed by the addition of substances, often toxic, that do not occur naturally in plants.

Contamination of essential oils can occur with:

• Pesticides, herbicides, fertilizers

• Solvents

• Metals

• Plastics

• Biological contamination (misidentified plants)

• Other plant parts

Contamination with pesticides, herbicides, fertilizers or metals usually occurs in the plant during growth or cultivation.

Metals can also find their way into the oil during distillation when the distillation tools are not suitable.

The essential oils most susceptible to contamination by pesticides, herbicides, fertilizers or plastics are, of course, citrus essential oils because of the extraction method. In an 8-year study in which 600 samples of essential oils were analyzed over a period of 8 years, 47% of them were found to contain at least 1 pesticide.

Contamination with plastics generally results from direct contact between citrus essential oils and plastic containers. Citrus oils are known to \"melt\" plastic. Therefore, the use of plastic containers in the industrial production of essential oils may lead to plastic contamination.

Several studies have investigated the presence of pesticides and plastics in essential oils. The results revealed the presence of various types of phthalates and pesticides in Bergamot oil produced in Calabria, Italy in 1999 and 2000.

Analyzing 120 essential oils from Italy and 70 from other countries, it was identified that the highest pesticide values were present in samples from Brazil and Spain. The results show a considerable decrease in pesticide levels compared to previous years and the absence of plastics (probably due to more efficient methods of storage and transportation of the oils).

Although pesticides should be absent in certified organic essential oils, studies indicate that they are present. However, organic essential oils have a lower contaminant content and much lower contaminant values. This contamination is generally considered to be an accident caused by older production practices.

Contamination with misidentified plants occurs, especially in the case of essential oils obtained from wild flora, when the harvester, knowingly or unknowingly, picks another plant. In this case, either no essential oil is obtained because that plant does not contain volatile compounds, or an oil with other therapeutic properties is obtained, or, in more serious cases, a toxic oil is obtained.

In a 2019 study led by renowned ecologist Anjanette DeCarlo, 5 certified organic Boswellia carteri essential oils were analyzed. Of these, 4 had a higher methoxydecane content than any other conventional oil. This chemical compound is specific to the species Boswellia oculta, morphologically very different from Boswellia carteri.

Contamination with other parts of the plant occurs during the distillation process. For example, Cinnamomum essential oil obtained from the bark of the Cinnamomum verum tree is sometimes contaminated with the cheaper version obtained from the leaves of the same tree.

While for food products we generally have clear acceptable limits for the presence of toxic substances (pesticides, fertilizers, metals, plastics, etc.), for essential oils there are still no very clear standards. In part, this is also due to the complexity and diversity of essential oils, which make the detection of contaminants a painstaking and elaborate process.

Adulteration of essential oils

Adulteration of essential oils is the process of changing the natural chemical composition of the oil by adding compounds that are naturally found in the composition of the oil but are of a different origin. Adulteration can be carried out with other, cheaper oils of the same species or extracted from another part of the plant, or with certain natural or synthetic compounds; all to obtain a standard composition and often to make higher profits.

Types of adulteration of essential oils:

• Addition of carrier oils

• Addition of non-volatile solvents (glycols, phthalate esters)

• Addition of other essential oils (from the same or similar plant)

• Addition of natural chemical compounds

• Addition of synthetic chemical compounds

• Blending with cheaper oils

• Reconstitution of oils by mixing natural or synthetic chemical compounds

The addition of carrier oils is only a problem when this is not specified on the bottle and the essential oil is diluted for the sole purpose of obtaining economic benefits by obtaining larger quantities of essential oils. However, this is perfectly normal practice if the dilution is stated on the packaging and the price is adjusted accordingly.

The most commonly adulterated essential oils are those of high economic importance, i.e. the very expensive ones (Rose, Melissa, Neroli...) and the very popular/used ones (Lavender, Tea Tree, Peppermint...)

The adulterants for most essential oils, both natural and synthetic, are largely known. But those who resort to such methods are becoming increasingly inventive, making the detection of adulterants a challenging task even for highly skilled researchers.

Rose lat. Rosa damascena can be partially reconstituted from certain constituents such as damascone, beta-ionone and citronellol, etc. but is often adulterated by adding its cheaper variants produced in Morocco or the Crimea. In the past it was often 'enriched' with essential oil of Palmarosa lat. Cymbopogon martinii, a practice less common today.

Melissa lat. Melissa officinalis can be partly reconstituted from the much cheaper Citronella lat. Cymbopogon winterianus, Lemon lat. Citrus limon and May chang lat. Litsea cubeba. Lemon eucalyptus lat. Eucalyptus Citriodora or Citronella lat. Cymbopogon winterianus, oils which are much cheaper and have a similar flavor, making this type of adulteration difficult to detect by the untrained eye.

Neroli lat. Citrus aurantium is one of the oils that because of the high price of production is often entirely reconstituted from synthetic compounds.

Lavender lat. Lavandula angustifolia is often interbred with the inferior hybrid, but which produces up to 10 times the amount of essential oil, Lvandin lat. Lavandula × intermedia, with Spike lavender lat. Lavandula latifolia, or oil fractions of Rosemary lat. Salvia Rosmarinus. The addition of constituents such as linalool, linaloyl acetate, lavandulol, lavandulyl acetate, terpinyl propionate, isobornyl acetate or terpineol is also practiced.

The optimal concentration of chemical constituents can also be obtained for Teatree lat. Melaleuca alternifolia by the addition of terpinen-4-ol, alpha-terpinene or gamma-terpinene, compounds naturally present in this oil, but which, due to certain environmental factors are not at standard values.

Peppermint lat. Mentha × piperita is often 'enriched' with synthetic menthol, with menthol obtained from Cornmint lat. Mentha arvensis.

There are certain compositional standards for essential oils, generally in the form of ranges, and this is because a variation in composition is not only a proof of authenticity but also of purity, as the chemical compounds in a plant vary depending on several factors (harvest time, soil, climate, altitude, geographical area, how it is grown and harvested, etc.).

For example, Lavender lat. Lavandula angustifolia grows equally well on mountain ridges or plains, but lavender grown at high altitudes is much more appreciated by aromatherapists. It is harvested by hand and is called Fine Lavender.

Peppermint lat. Mentha × piperita, has a higher amount of menthol and eucalyptol if the essential oil is extracted from dried plants than from fresh plants. The harvesting period also influences the composition; the amount of menthone decreases between harvests 1 and 5 (June-August), while the amount of menthol increases.

If a company always has the same composition of oils this should give us pause for thought, because the plants from which they are obtained are living organisms that are always changing their volatile compounds according to current needs, and this is normal.

The most important aspect of adulteration is, of course, the therapeutic efficacy but also the possible adverse effects of modified oils. The answer is not very clear and often depends on both the substances used for adulteration and the person using them. Most aromatherapists believe that an adulterated essential oil cannot have the same therapeutic effects as a natural one. And while adulterated oils may work therapeutically for basic ailments, for more complex conditions where the oils act in more than one way (psoriasis, degenerative diseases, nervous system or emotional problems, etc.), the natural balance found only in nature is needed. In addition, the addition of other oils or constituents can have major safety implications for people with certain risks or diseases (babies, children, pregnant or breastfeeding women, the elderly, etc.)

Resources

Saitta, M., Di Bella, G., Salvo, F., Lo Curto, S., & Dugo, G. (2000). Organochlorine pesticide residues in Italian citrus essential oils, 1991-1996. Journal of agricultural and food chemistry, 48(3), 797-801. https://doi.org/10.1021/jf990331z https://doi.org/10.1021/jf990331z

DeCarlo, A., Johnson, S., Ouédraogo, A., Dosoky, N. S., & Setzer, W. N. (2019). Chemical Composition of the Oleogum Resin Essential Oils of Boswellia dalzielii from Burkina Faso. Plants (Basel, Switzerland), 8(7), 223. https://doi.org/10.3390/plants8070223

Barrek, S., Paisse, O., & Grenier-Loustalot, M. F. (2003). Analysis of pesticide residues in essential oils of citrus fruit by GC-MS and HPLC-MS after solid-phase extraction. Analytical and bioanalytical chemistry, 376(2), 157-161. https://doi.org/10.1007/s00216-003-1899-9

Di Bella, G., Saitta, M., Lo Curto, S., Salvo, F., Licandro, G., & Dugo, G. (2001). Production process contamination of citrus essential oils by plastic materials. Journal of agricultural and food chemistry, 49(8), 3705-3708. https://doi.org/10.1021/jf0100043

Di Bella G, Saitta M, La Pera L, Alfa M, Dugo G. Pesticide and plasticizer residues in bergamot essential oils from Calabria (Italy). Chemosphere. 2004 Aug;56(8):777-82. doi: 10.1016/j.chemosphere.2004.04.024.024. PMID: 15251292.

Di Bella G, Lo Turco V, Rando R, Arena G, Pollicino D, Luppino RR, Dugo G. Pesticide and plasticizer residues in citrus essential oils from different countries. Nat Prod Commun. 2010 Aug;5(8):1325-8. PMID: 20839646.

Saitta, Marcello & Bella, Giuseppa & Dugo, Giacomo. (2012). Pesticides and plasticizers in Citrus essential oils: An ordinary history of research. Journal of Essential Oil Research - J ESSENT OIL RES. 24. 171-180. 10.1080/10412905.2012.659522.

Saitta, Marcello & Bella, Giuseppa & Bonaccorsi, Ivana & Dugo, Giacomo & Dellacassa, Eduardo. (1997) Contamination of Citrus Essential Oils: The Presence of Phosphorated Plasticizers. Journal of Essential Oil Research - J ESSENT OIL RES. 9. 613-618. 10.1080/10412905.1997.9700798.

Fillatre, Yoann. (2015). Practical Guide for Pesticides Analysis in Essential Oils ( Guide Pratique Pour Le Dosage des Pesticides Dans Les Huiles Essentielles).

Fillatre, Yoann & Gray, François & Roy, Celine. (2017). Pesticides in essential oils: Occurrence and concentration in organic and conventional orange essential oils from eleven geographical origins. Analytica Chimica Acta. 992. 10.1016/j.aca.2017.08.039.

Frey C (1988) Detection of synthetic flavorant addition to some essential oils by selected ion monitoring GC/MS. In: Lawrence BM, Mookherjee BD, Willis BJ (eds) Flavors and fragrance: a world perspective. Elsevier BV, Amsterdam, pp 517-524

Satyal P., Setzer W.N. (2019) Adulteration Analysis in Essential Oils. In: Malik S. (eds) Essential Oil Research. Springer, Cham. https://doi.org/10.1007/978-3-030-16546-8_9. https://doi.org/10.1007/978-3-030-16546-8_9.

Schmidt E, Wanner J. Essential Oil Adulteration. In: Baser KHC, Buchbauer G. Handbook of Essential Oils, 2nd ed. New York, NY: Taylor & Francis; 2016.

Cebi, N., Taylan, O., Abusurrah, M., & Sagdic, O. (2020). Detection of Orange Essential Oil, Isopropyl Myristate, and Benzyl Alcohol in Lemon Essential Oil by FTIR Spectroscopy Combined with Chemometrics. Foods (Basel, Switzerland), 10(1), 27. https://doi.org/10.3390/foods10010027 https://doi.org/10.3390/foods10010027

Nhu-Trang, T. T., Casabianca, H., & Grenier-Loustalot, M. F. (2006). Authenticity control of essential oils containing citronellal and citral by chiral and stable-isotope gas-chromatographic analysis. Analytical and bioanalytical chemistry, 386(7-8), 2141-2152. https://doi.org/10.1007/s00216-006-0842-2

Bonaccorsi, I., Sciarrone, D., Schipilliti, L., Trozzi, A., Fakhry, H. A., & Dugo, G. (2011). Composition of Egyptian neroli oil. Natural product communications, 6(7), 1009-1014.

Beale, D. J., Morrison, P. D., Karpe, A. V., & Dunn, M. S. (2017). Chemometric Analysis of Lavender Essential Oils Using Targeted and Untargeted GC-MS Acquired Data for the Rapid Identification and Characterization of Oil Quality. Molecules (Basel, Switzerland), 22(8), 1339. https://doi.org/10.3390/molecules22081339 https://doi.org/10.3390/molecules22081339

Raymond, C. A., Davies, N. W., & Larkman, T. (2017). GC-MS method validation and levels of methyl eugenol in a diverse range of tea tree (Melaleuca alternifolia) oils. Analytical and bioanalytical chemistry, 409(7), 1779-1787. https://doi.org/10.1007/s00216-016-0134-4

Davies, N. W., Larkman, T., Marriott, P. J., & Khan, I. A. (2016). Determination of Enantiomeric Distribution of Terpenes for Quality Assessment of Australian Tea Tree Oil. Journal of agricultural and food chemistry, 64(23), 4817-4819. https://doi.org/10.1021/acs.jafc.6b01803

Wong, Y. F., West, R. N., Chin, S. T., & Marriott, P. J. (2015). Evaluation of fast enantioselective multidimensional multidimensional gas chromatography methods for monoterpenic compounds: Authenticity control of Australian tea tree oil. Journal of chromatography. A, 1406, 307-315. https://doi.org/10.1016/j.chroma.2015.06.036

Cerceau, C. I., Barbosa, L., Alvarenga, E. S., Maltha, C., & Ismail, F. (2020). 1 H-NMR and GC for detection of adulteration in commercial essential oils of Cymbopogon ssp. Phytochemical analysis: PCA, 31(1), 88-97. https://doi.org/10.1002/pca.2869

Kuriakose, S., Thankappan, X., Joe, H., & Venkataraman, V. (2010). Detection and quantification of adulteration in sandalwood oil through near infrared spectroscopy. The Analyst, 135(10), 2676-2681. https://doi.org/10.1039/c0an00261e

Beale, D. J., Morrison, P. D., Karpe, A. V., & Dunn, M. S. (2017). Chemometric Analysis of Lavender Essential Oils Using Targeted and Untargeted GC-MS Acquired Data for the Rapid Identification and Characterization of Oil Quality. Molecules (Basel, Switzerland), 22(8), 1339. https://doi.org/10.3390/molecules22081339 https://doi.org/10.3390/molecules22081339

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