The Adulteration of Essential Oils
and the Consequences to Aromatherapy & Natural Perfumery Practice.
Copyright ©Tony Burfield 2003-2005. [Slightly updated from a Presentation to the IFA Annual AGM London Oct 11th 2003].

Part 1. Oil Adulteration.

Introduction.
As far as adulteration is concerned, producers and distributors of essential oils are frequently painted as “the bad guys”, but it should be pointed out that their oil customers frequently demand oils below the market price while still wanting to be told that they are authentic. In this climate, the honest oil trader may find it virtually impossible to survive on the margins he is allowed to make (many have already gone bust). For example, in the late 20th Century, lavender oil (Lavandula angustifolia) was being sold almost as a loss leader by many French producers as the market was unwilling to pay a realistic price; currently, the aroma industry is dominated by a handful of large and powerful international houses whose corporate buyers often attempt to drive raw material prices to impossibly low levels, not allowing workable profits to be made. This sets the scene for unethical practices.

Essential oils – a definition.
An essential oil (e.o.) is the volatile oil containing odiferous elements of the plant, produced by steam or hydro-distillation of aromatic vegetable plant matter. E.O. components arise via the secondary metabolism of plants and are stored within specialised structures; ideally they are isolated with minimum chemical changes from human intervention. Citrus oils, produced by the mechanical pressing of citrus peels, are also called essential oils, and, according to the International Standards Organisation (ISO), so are dry-distilled oils – such as cade oil (from the branches of Juniperus oxycedrus) and styrax pyrogenée (from Liquidamber spp).

Essential oils should be produced by purely physical means, and be 100% pure and wholly derived from the named botanical source – but how are these standards to be guaranteed? No quality standards for the authentication of essential oils exist in aromatherapy, in spite of the revelations of gross adulteration of aromatherapy oils for retail sale (Health Which 2000). Professional aromatherapy organisations have failed to issue standards, in spite of individual schemes being put forward (Jones 1998) but, in contrast, other essential oil-using industries are served by the following standards:

The Pharmaceutical Trade: British Pharmacopoeia (BP) 2004 is published on recommendation of the Medicines Commission UK. Oils specifications are also published in the European Pharmacopoeia 4th edn 2002 (Eur. Pharm 4th edn); United States Pharmacopoeia (USP); also the pharmacopoeia’s of individual nations such as China, India etc. Earlier editions of The British Pharmaceutical Codex (BPC), such as BPC 1949, contain many essential oil standards still in use today.
Essential Oil Trade: Monographs on individual essential oils (EOA Standards) were produced by the Scientific Committee of the Essential Oil Association Inc.
Flavourings Industry: Food Chemicals Codex IV (1996, US) produced at the request of the FDA (1992), is widely used for guidance by the food flavourings industry.
Aroma Companies: Many larger established Flavour & Fragrance Houses have their own internal purchasing standards.
Independent Certifying Bodies: International Standards Organisation (ISO Standards TC 54) & Association Française de Normalisation (AFNOR) both have detailed standards for e.o.’s.*

*An example is ISO 3515 for Oil of Lavender (2001) which includes minimum and maximum percentages of thirteen natural components, and their occurrence in French (spontaneous and clonal), Bulgarian, Russian, Australian and ‘other origin’, lavender oils. Limits for lavandulyl acetate, for example, are set at 2.0-5.0% in Bulgarian lavender oil by the standard.

Aromatherapy
Whilst it is apparent that the current European Pharmacopoeia, USP or ISO standards may serve the needs of particular industrial sectors, they do not entirely address the unique needs of the aromatherapy profession, since:

Holistic aromatherapists demand that “pure” and “complete” oils are used, rather than oils only distilled for economically short periods e.g. tea tree oil. It is now suggested that in some cases longer distillations may be disadvantageous e.g. for tea tree oil distillation again, increases, the proportion of sesquiterpenes rises and these are considered by some researchers as responsible for adverse skin reactions when applied topically. Secondly unnecessary energy ‘wastage’ associated with excessively long distillation times may not be seen currently as a particularly “deep green” strategy!

Many essential oils used in aromatherapy are particular to that industry, and not necessarily extensively used elsewhere e.g. Ravensara aromatica, Rosemary oil verbenone chemotype, Helichrysum italicum ssp.­ serotinum etc.

As well as “pure and natural”, the words “wild-crafted”, “organic” and “clinical grade” are frequently over-hyped descriptor terms used by both aromatherapy and by “naturals” traders, which need more careful definition prior to professional endorsement.

Natural perfumery
Natural perfumers are other potential users of pure essential oils. Grimshaw (1989) discussed “purist” perfumers (who employ no chemically produced or chemically modified ingredients), but also discussed reasons why others may wish to use up to 50% synthetics in formulations. This was, in a way, a prediction today’s situation, whereby aromachology perfumes (worth £611 million for years 1999-2001 according to Mintel Database 2002) contain a proportion of synthetics stipulated by the perfume house, mixed in with the e.o.’s. The alleged psychopharmaceutical effects of these products still depend on the utilization of authentic essential oils in the formulation – as far as marketing claims/hype are concerned anyway. A realistic “in-practice” distinction between mass-marketed aromatherapy perfumes (as opposed to 100% e.o. blends) and aromachology perfumes, other than at a hypothetical level, has yet to be defined, since both commonly employ synthetics. The synthetics content can presumably have either symbiotic, neutral or opposing effects (mood changing etc.) to those claimed for the e.o.’s in the perfumes in question, hence the need for clinical testing of the finished formulations to support advertising claims.

Types of adulteration.
There are several distinct categories of adulteration:

1. Addition of single raw materials. This simple form of adulteration can be conveniently divided into two groups:

“Invisibles” – i.e. those materials undetectable by a gas chromatograph (GC) analysis operating under routine conditions to analyse essential
oils.
“Visibles – those materials normally detectable by GC.

“Invisibles”: an example of this type is the deliberate addition of vegetable or mineral oil to essential oils (Nour-el-Din et al. 1977) – rapeseed oil in the EU is a particularly cheap vegetable oil which has been used for this purpose. Theoretically the “total area” of the detectable components of the oil’s gas chromatogram should be reduced by this latter type of adulteration, creating suspicion for the analyst and the need for further investigation. These adulterant materials may be revealed by aqueous alcohol solubility tests, and their presence further verified by using a different GC column & operating conditions (to detect mineral oil), or by derivatisation (for example the use of a methylating agent for vegetable oils – whereby the volatile methyl esters of the fatty acid components of glyceryl esters are revealed by subsequent GC analysis).

“Visible” diluents in this context include a number of solvents and perfumery materials. For example the following have been found in commercial essential oils: in a few instances resulting in a warning or prosecution by regulatory authorities:

Abitol (a primary hydroabietyl alcohol) – often used for extending resinoids.
Benzyl alcohol (now classified as a sensitiser by SCCNFP opinion)
Benzyl benzoate (now classified as a sensitiser by SCCNFP opinion; formerly
widely used to extend resinoids)
Carbitol (diethylene glycol monoethyl ether or DEGME)
Diacetone alcohol
Dipropylene glycol (DPG)
Dipropylene glycol methyl ether (DPGME) and tripropylene glycol methyl ether
(TPGME) – both of these substances are in air freshener technology.
Herculyn DÔ (hydrogenated methyl ester of rosin)
Isoparä (odourless kerosene fractions often used as a candle perfume diluent)
Isopropyl myristate (IPM)
Phthalate esters such as di-n-butylphthalate (DNP), diethyl phthalate (DEP) and di-
iso-octyl phthalate (DIOP)
Polyethylene glycols
Triacetin (the anti-fungal compound glycerol triacetate – a popular food
flavourings vehicle).
3,3,5-Trimethyl-hexan-1-ol.

Use of materials like isotridecyl acetate (ITDA, Fixateur 404Ô), Herculyn D and Abitol, can be moderately difficult to spot, because the materials may show a myriad of late-eluting small peaks on a GC trace representing their different constituent isomers, which could be overlooked by an inexperienced analyst especially at low levels.

In all the above instances of “visible” and “non-visible” adulterants, the added material is merely a diluent, and makes no odour contribution of its own. Addition of 10-14% of such a material may pass un-noticed if the material is evaluated against a retained standard solely on an odour basis – even by an expert nose – but it will in all probability be revealed by subsequent physio-chemical testing e.g. added vegetable oil in patchouli oil can often be revealed by a solubility test in 90% alcohol at 20°C.

2. The addition of cheaper essential oils and adjuncts.
Blending in cheaper oils to meet a customers’ target purchasing price, or to make additional profit for the producer, is commonplace in the oil trade. Some practices mentioned by Arctander (1960) – for example, the practice of extending of Amyris oil (Amyris balsamifera) with Cedarwood oil Virginia (Juniperus virginiana) and Copaiba Balsam (Copaifera spp.) – are unlikely to fool too many potential customers in these present & more educated times, but other more common adulteration practices still remain, which include:

Bergamot oil (Citrus bergamia): addition of lemon oil, rectified ho oil (Cinnamomum
spp.) and acetylated ho oil.
Bitter orange oil (Citrus aurantium subsp. aurantium): addition of sweet orange
oil (Citrus sinensis) & orange terpenes, plus trace amounts of character
compounds.
Cedarwood oil Virginia (Juniperus virginiana): addition of cedarwood oil
Chinese (Cupressus funebris).
Cinnamon bark oil (Cinnamomum zeylanicum): addition of cinnamon leaf oil.
Cinnamon leaf oil (Cinnamomum zeylanicum): addition of clove fractions,
eugenol, cinnamic aldehyde etc.
Clove Bud oil (Syzygium ­aromaticum): addition of clove stem oil & isolates
(eugenol) & eugenyl acetate.
Fir Needle oils (Abies spp.): addition of turpentine fractions, camphene, (-)-
bornyl acetate etc.
Geranium oil Chinese (Pelargonium hybrids): addition of adulterated Indian
geranium oil (which itself has been known to contain diphenyl oxide!)
Grapefruit oil (Citrus paradisi): addition of orange terpenes or sweet orange oil
distilled + minor amounts of (+)-nootkatone & others.
Lavender oil (Lavandula angustifolia): addition of cheaper lavandin (Lavandula
x intermedia) oil varieties; the addition of spike lavender oil (Lavandula
latifolia); the addition of ho oil rectified (Cinnamomum spp) and acetylated
ho or acetylated lavandin oils etc.
Lemon oil (Citrus limon): addition of orange terpenes, lemon terpenes & by-
products (e.g. steam-stripped lemon oil). For lemon oil BP, expressed lime or
grapefruit oil is added to poor grades to raise the UV absorbance level
sufficiently to pass the BP specifications.
Nutmeg oil (Myristica fragrans): the addition of nutmeg terpenes, a- pinene,
limonene, turpentine fractions etc.
Patchouli oil (Pogostemon cablin): addition of gurjun balsam (Dipterocarpus
spp.); vegetable oils, Hercolyn D; patchouli and vetiver distillation residues.
The superior Indonesian patchouli oil is often blended with the cheaper
Chinese oil.
Petitgrain oils (Citrus spp): addition of other citrus leaf oils & fractions, fatty
aldehydes, linalyl acetate, orange terpenes etc.
Peppermint oil (Mentha X piperita): addition of cornmint oil (Mentha arvensis).
Sandalwood oil EI (Santalum album): addition of sandalwood terpenes,
sandalwood fragrance chemicals etc.
Rosemary oil (Rosmarinus officinalis) addition of eucalyptus oil Eucalyptus
globulus) & camphor oil white (Cinnamomum camphora).
Verbena oil (Lippia citriodora): L. citriodora herb distilled over lemon oil.
Violet Leaf absolute (Viola odorata): addition of spinach absolute (Spinacia
oleracea).
Ylang Ylang oil qualities (Cananga odorata subsp. genuina): addition of
cananga oil (Cananga odorata), ylang ylang oil tails etc., ylang ylang oil
reconstitutions.

And also addition of these synthetics to “convert” one oil to another:

Basil oil exotic: add linalol to convert to Basil oil Sweet (Arctander 1960).
Eucalyptus globulus: add a-terpineol & others to convert to Eucalyptus radiata.
Geranium oil Chinese to Geranium oil Bourbon: addition of balancing
materials (monoterpene alcohols and esters, especially formates), copper
chlorophyll (for colour) and frequently a trace of dimethyl and/or dibutyl
sulphides.
Tangerine oil (Citrus reticula var. tangerine): addition of g-terpinene, dimethyl
anthranilate, a-sinesal & perilla aldehyde to convert to Mandarin oil (Citrus
reticulata var. mandarin).

3. The addition of cheap (nature identical) synthetics to oils that naturally contain these materials. Little detailed guidance has been previously published in this area. The older work of Arctander (1960) mentions a number of adulteration practices, but the sophistication of customer quality control procedures probably means that of the noted practices are now too obvious for today’s market. Looking at other published material on adulteration, Singhal et al. (2001) remarks on the adulteration of spice oils by simple additions of single raw materials e.g. the addition of synthetic citral to Litsea cubeba oil. My own guide to questionable practices include the following:

Anise oil (Pimpinella spp.): addition of technical grade anethol.
Basil oil exotic (Ocimum spp.): addition of methyl chavicol & linalol.
Benzoin resinoid (Styrax spp.): addition of small amounts of vanillin, benzyl
benzoate, ethyl & benzyl cinnamates, benzoic acid etc. to enhance odour (or
to pass off cheaper “Sumatra” grades as “Siam”).
Bergamot oil (Citrus bergamia): addition of linalol and linalyl acetate.
Bitter almond oil (Prunus amygdalus var. dulcis ): addition of, or passing off
benzaldehyde, as the oil.
Buchu leaf oil (Barosma betulina & B. crenulata): addition to cutters of
monoterpene sulphide fractions synthesised from the hydrogen sulphide
treatment of pulegone, including p-menthan-8- thiol-3-one.
Cassia oil (Cinnamomum aromaticum): the addition of synthetic cinnamic
aldehyde, methyl cinnamic aldehyde & coumarin.
Chamomile oil Roman (Anthemis nobilis): addition of isobutyl angelate and
bisabolols.
Cinnamon bark oil (Cinnamomum zeylanicum): the addition of synthetic
benzaldehde, eugenol and cinnamic aldehyde.
Citrus oils: the addition of fatty aldehydes and monoterpene alcohols and
esters to terpeneless and folded citrus oils.
Caraway seed oil (Carum carvii): the addition of limonene and (+)-carvone
Cardamom oil (Elletaria cardamomum): addition of linalyl acetate, 1,8-cineole and
a-terpinyl acetate.
Celery seed oil (Petroselenium crispum): the addition of limonene + touches of
alkyl phthalides.
Cognac oil: addition of ethyl esters of aliphatic acids e.g. ethyl oenanthate.
Coriander seed oil (Coriandrum sativum): addition of linalol and trace amounts
of certain pyrazines. NB price fluctuates – not always economic!
Cypress oil (Cupressus sempervirens): addition of a-pinene, d-3-carene &
myrcene.
Cumin seed oil (Cuminum cyminum): addition of cuminaldehyde and others.
Dill seed oil (Anethum graveolens): addition of a-phellandrene & limonene.
Elemi oil (Canarium luzonicum): addition of a-phellandrene & limonene.
Galbanum resinoid (Ferula galbaniflua): addition of b-pinene, undecatrienes and
others.
Garlic oil (Allium sativa): addition of aliphatic sulphide mixtures containing
2-propenyl disulphide, 1-propenyl disulphide etc.
Jasmine absolute (Jasmimum spp): reconstructions frequently added.
Juniper oil (Juniperus communis var. erecta): addition of terpene
hydrocarbon mixtures containing a-pinene & d-3-carene, also Juniper branch
oil and second grade oils from spoiled Juniper berries.
Labdanum resinoid (Cistus landiferus): formerly, the addition of DEP (now
discontinued) or Abitol, with small amounts of ambroxan and p-methyl
acetophenone to enhance odour.
Lavender oil, spike (Lavandula latifolia): addition of eucalyptus & white
camphor oil fractions, spanish sage oil etc.
Lemongrass oil (Cympogon spp.): addition of citral.
Mentha citrata oil: addition of linalol + linalyl acetate.
Mustard oil (Brassica nigra & B. juncea): allyl isothiocyanate passed off as the
oil (which is used in flavourings, but is banned in perfumery &
aromatherapy).
Neroli oil (Citrus aurantium subsp. aurantium): reconstructions frequently
added to, or passed off as the authentic oil.
Origanum oil (Origanum spp.): addition of para-cymene and carvacrol.
Onion oil (Allium cepa): addition of aliphatic sulphide mixtures.
Palmarosa oil (Cymbopogon martinii var. motia): the addition of geraniol.
Petitgrain oil Paraguay (Citrus aurantia subsp. aurantium ): addition of
admixture of linalol, linalyl acetate, a-terpineol, geranyl & neryl acetates &
trace amounts of pyrazines etc.
Pine needle oils (Pinus spp.): addition of (-)-bornyl acetate, isobornyl acetate, (-)-
limonene, a-pinene, camphene etc.
Rose oil: reconstructions using damascones, b-ionone plus (-)-citronellol
and other rose alcohols, plus rose steroptenes. Occasionally adulterated with b-
phenylethyl alcohol, rhodinol fractions and cheaper rose oils (Morocco, Crimea
etc.).
Rosemary oil (Rosmarinus officialis): addition of camphor, isobornyl acetate (+
Eucalyptus & turpentine oil fractions).
Rosewood oil (Aniba spp): addition of linalol, plus trace amounts of methyl
heptenone, methyl heptenol, 3-octanol, para-methyl acetophenone etc.
Spearmint oil (Mentha spicata): addition of (-)-carvone.
Thyme oil (Thymus spp.): addition of para-cymene & thymol. “Red thyme oil” is
often wholly synthetic.
Vetiver oil acetylated (Vetivera spp): the addition of cedrenyl acetate.
Wintergreen oil (Gaultheria procumbens): the adding of, or passing off methyl
salicylate, as the oil.
Ylang ylang oil (Cananga odorata var. genuina): addition of benzyl acetate,
methyl benzoate, para-cresyl methyl ether, geranyl acetate, benzyl benzoate,
benzyl cinnamate, cedarwood oil and others or complete
reconstitutions/bases.

Boelens (1997) described four types of odourants in essential oils: character compounds, essential compounds, balance compounds and artifacts. Adulterants such as monoterpene hydrocarbons, being balance compounds in Boelens scheme above, do little for the characteristic odour of the cut oils, since the added materials have little odour value in themselves. In practice, the addition of certain adulterants “flattens” the odour profile of the authentic oil, or otherwise dilutes or represses some true character, sparkle and richness. To compensate for this, a practiced oil counterfeiter will add small amounts of character compounds. Taking the example of Cypress oil Cupressus sempervirens var. stricta, the oil is often adulterated by the addition of the monoterpene hydrocarbons a-pinene and d-3-carene, which creates a crude terpinic aspect. The addition of a small amount of deca-2-(E),4-(Z)-dienyl isovalerate to the somewhat insipid cutting agent, will give a better impression of the oil’s normal character, a lead which follows on from the work of Garnero et al. (1978) who identified the compound above in cypress shoots, and found it strongly reminiscent of the typical odour of cypress oil.

Commercial oils, adulterated by such synthetics, can often fool the less sophisticated nose, or satisfy those oil customers buying to a price, where authenticity is sometimes not a primary consideration. Depending on exact market conditions, some oils have a selling price which is so cheap that it is generally unrewarding for a trader to reconstitute, or even add, nature identicals to the product, except for some solvent-like diluents. This category includes the following oils:

Sweet orange oil (Citrus sinensis)
Clove leaf oil & stem oils (Syzygium aromaticum)
Citronella oil (Cymbopogon spp.): (but the oil has been known to have been
crudely adulterated with dipentine and citronella terpenes)
Camphor oil white (Cinnamomum camphora fractions)
Cornmint oil (Mentha arvensis subspp).
Eucalyptus globulus oil
Tea tree oil (Melaleuca altenaria) (NB a collapse in market price means potential
adulterants such as terpinen-4-ol and a- & g-terpinenes can now be as expensive
as the oil).

Other oils are difficult to reconstitute with anything other than diluents because the major components are not commercially available; this class of oils includes patchouli oil, vetiver oil and to some extent ginger oil.

4. The addition of isolates or natural components to essential oils e.g. the addition of pure natural eucalyptol ex E. globulus oil (Eucalyptus globulus) to rosemary oil (Rosemarimus officinalis) or rectified ho oil (very high in
(-)-linalol) to lavender and bergamot.

5. The addition of bases or reconstituted essential oils to genuine oils & absolutes. It is particularly economically attractive to extend high value floral absolutes such as rose (Rosa spp.), jasmin (Jasminum grandiflora other spp.) and osmanthus (Osmanthus fragrans var. auranticus), and the more valuable oils such as neroli oil and rose otto, and this practice occurs extensively within the trade.

6. The addition of individual unnatural components to oils and aromatic raw materials.
Absolutes have been traditionally produced for the consumption of the perfumery industry, but are being increasingly employed in aromatherapy (in spite of using un-natural solvents in their manufacture). Revelations that materials such as Linden Blossom absolute (Tilia spp.) contain hydroxycitronellal, or that Gardenia absolute (Gardenia spp.) has added styrallyl acetate, or that added Schiff’s bases have been found in floral absolutes, should not therefore come as a complete surprise. It has been suggested that if the synthetic fragrance compound is added in to the aromatic plant material during manufacture, the added material will “blend in” better. In other instances, absolutes may well contain perfume bases or reconstitutions, rather than a single key character compound.

Glossary.

Adulteration: the purposeful addition of cheaper alternative oils, oil fractions, by-products, isolates, natural or non-natural synthetics etc., to reduce the cost price of the oil.

Extending: a term for adulteration almost implying a degree of legitimacy.

Isolate: a specific fraction of an essential oil. May be composed of a single chemical e.g. eugenol from Clove oil.

Organic oil: a more expensive essential oil, which has been derived from vegetable matter which has been grown in a pesticide free environment, but which still liable to have a pesticide content reflecting background contamination/incorporation.

Reconstituted oil: An oil made from nature identical synthetics, to look like analytically as far as possible -, and to give an accurate odour impression of -, the named essential oil.
REFERENCES

Arctander S. (1960) Perfume and Flavour Materials of Natural Origin publ. Elizabeth NJ.
Boelens M. (1997) “Differences in chemical and sensory properties of orange flower and rose oils from hydrodistillation and from supercritical CO2 extraction” Perf & Flav. 22, May/June 1997 p31.
Garnero J. et al. (1978) Riv. It. Epos. 60, 99.
Health Which February 2001 pp 18-20.

Jones, L. (1998) “Establishing standards for essential oils and analytical standards” Proceedings of NAHA The World of Aromatherapy II International Conference and Trade Show St. Louis, Missouri, Sept 25-28, 1998, p146-163.

Nour-el-Din H., Osman A. E., Higazy S. et al. 1977. Egyptian Journal of Food Science 5(1/2): 67-77.

Singhal RS, Kulkarni PR, Rege DV 2001. “Quality indices for spice essential oils”. In Handbook of Herbs and Spices. ed. KV Peter, CRC Press, Woodhead Publishing 2001.

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