Fatty Acid Methyl Esters are used indirectly in a wide range of food, pharmaceutical, cosmetic and industrial applications. Significant volumes of these materials are shipped regularly by sea and care needs to be taken to avoid contamination with noxious materials that could effect the safety of the final product and effect the processing of the oleochemical itself. For this reason oleochemical producers ensure that when shipping by sea the immediate previous cargo is on either of the Acceptable Immediate Previous Cargo lists set up by FOSFA and NIOP. The former is recognised in principle in Directive 96/3/EC. Methyl esters themselves are on both the FOSFA and the NIOP lists and provide useful safe previous cargoes for the shipment of oils and fats intended for use in food products following further processing.
The European Oleochemicals and Allied Products Group were surprised and concerned when an SCF AD Hoc Group proposed the removal of Fatty Acid Methyl Esters from the list of Acceptable Immediate Previous Cargoes appended to Directive 96/3/EC. This group of products have generally been considered safe and have already been given Regulatory Clearance for a wide range of direct and indirect food uses. Indeed the SCF's First Report on Chemically Defined Flavouring Substances (November 1995) lists methyl esters from the butyrate to the myristate in Category 1 (substances considered safe to use), the safest of the 5 categories used. It should be noted that Hedsets providing data on the safety of methyl esters (C6-12, CAS 67762-39-4); C10, CAS 110-42-9; C12, CAS 111-82-0; C12-18, CAS 68937-84-8; C16-18, CAS 85586-21-6) were deposit with the European Union Chemical Information Data Base, European Chemical Bureau of the European Commission, Ispra (Italy), under Council Regulations (EEC) 793/93 on the Control of Risks of Existing Chemical Substances, in 1995.
Removal of methyl esters from the Acceptable Previous Cargo list will reduce the availability of ships meeting the new EU criteria and will lead to difficulties in overseas trade and increased freight costs for both methyl esters and for oils and fats for food use.
The APAG Task Force set up to assess the safety of Methyl Esters
As a direct result of the Ad Hoc Group's proposal APAG set up a Task Force to assemble and evaluate the available data on the safety of methyl esters. Members of the task force were :
Dr W Aulmann : a Senior Toxicologist with Henkel KGaA and an expert in carcinogenicity and tumorigenicity.
Dr D Walker : Manager, Safety and Regulatory Matters with Procter & Gamble and having responsibility for the safety of it's oleochemicals world-wide.
Dr A Hinze : Manager, Safety and Regulatory Matters with Unichema International (part of the Unilever organisation) and having responsibility for the safety of it's oleochemicals world-wide.
Mr R Pearson : Secretary General of APAG
Ms Ch De Cooman : Sector Group Manager, CEFIC
The task force considered information in the following areas :
Each of these areas is discussed later in this position paper.
Conclusions from the Task Force
Review of the data
a) General Introduction to
Fatty Acid Methyl Esters
Fatty acid methyl esters are aliphatic organic esters primarily prepared by the reaction of a carboxylic acid derived from natural fats and oils and methanol. The fatty acids from which they are derived, such as oleic acid and stearic acid or their simple esters are not substances that one would expect to be carcinogenic, as was acknowledged by the authors of the articles cited by RTECS which we believe to be the source of the alleged classification of tumerogenic. Oleic and stearic acids as their glyceryl esters, are components of all natural oils and fats, including those in the human body. These same fatty acids, in the form of their esters with aliphatic alcohols, are components of natural waxes. And the alkali metal salts of stearic and oleic acid are very familiar to us as common soap. There is nothing in the structures of the common fatty acids or esters to suggest that they might be alkylating agents, or that they have other characteristics associated with carcinogenic potential.
Commercial fatty acid methyl esters are made from naturally occurring edible fats and oils by the esterification of the refined triglycerides with methanol in the presence of a base catalyst. These 'whole cut ' esters can be subsequently processed into various alkyl range cuts by fractional distillation. Fatty acid methyl esters are used extensively as intermediates in the manufacture of detergents, emulsifiers, wetting agents, stabilisers, textile treatments, and waxes among other applications. Lesser volumes of fatty acid methyl esters are used in a variety of direct and indirect food additive applications, including the dehydration of grapes to produce raisins, synthetic flavouring agents, and in metal lubricants for metallic articles intended for food contact use. Fatty acid methyl esters are also used as intermediates in the manufacture of a variety of food ingredients. [ Back to the top ]
Methyl esters in the range of C8 to C18 are practically non-toxic.
Gavage studies proved methyl laurate, methyl palmitate and methyl stearate to be non-toxic to rats with LD50s exceeding the limit dose of 2000 mg/Kg body weight (IUCLID data sheet for 68937-84)-8). The acute oral toxicity of methyl caprylate to rats was investigated and found not to be harmful up to a dose of 20.5g/Kg body weight (Clayton & Clayton, 1981-1982).
Methyl myristate was also found to be not harmful to white mice following a dose of 10ml/kg body weight by gavage.
Administration of an emulsion of methyl palmitate to mice by oral intubation or intraperitoneal injection produced no alteration in organ weight or phagocytic function of the reticuloendothelial system (Di-Luzio & Blickens, 1966)
C16-18 methyl esters of fatty acids were tested on Charles River SCD rats (200-300 gms) at 100% concentration and a dose level of 20.0 ml/Kg, resulting in a mortality rate of 0/10, giving an LD50 of > 17.4g/Kg. It appears that the single fixed dose test was done, rather than the typical dosage range due to the low toxicity of the methyl ester.[ Back to the top ]
Methyl oleate was fed to 4 groups of 5 male and 5 female rats for 12 weeks as 5% of their diet. Methyl oleate caused some loss of body weight in females. Food intake and food efficiency were not altered but symptoms of essential fatty acid deficiency as seen by "scaleness of the tail", were observed in the 7th week of the study (JAOCS 35, 156-8 (1958)). Male and female rats were fed either a fat-free diet or a fat-free diet supplemented with 100mg of methyl stearate/animal/day for 12 weeks. Males fed the supplemeted diet showed weight loss while no or little effect was observed in the females. Total hepatic lipid levels of male rats fed the supplemented diet were similar to those of males given the supplemented diet (J. Nutr. 87(2), 168-172 (1965)). [ Back to the top ]
Fatty acid methyl esters are metabolised as would other dietary fats. Higher molecular weight aliphatic esters are readily hydrolysed to the corresponding alcohol and acid and then generally oxidised to carbon dioxide and water via well known metabolism of breakdown into two-carbon fragments which are used by the body for energy and building blocks for synthesis. During digestion, they are hydrolysed to the free fatty acids for absorption from the intestine into the blood stream aided by lipase enzymes and bile salts as demonstrated in the rat by Mattison et al (J. Nutrition 102, 1171 (1972), J. Lipid Res 13, 325 (1972). Once formed the free fatty acid is metabolised by known oxidative processes or they are reconstituted into glyceride esters and stored in the fat depots in the body.[ Back to the top ]
Methyl laurate, methyl palmitate and methyl stearate were devoid of any mutagenic effect in the S. typhimurium reversion assay (IUCLID data sheet for 68937-84-8). Cis-methyl oleate and its parent compound, oleic acid, have given negative results in Salmonella/mammalian microsome assays conducted as part of NTP's chemical screening program for mutagenicity (Environ Mutagen 8, (Suppl 7): 1-119, 1986). A Salmonella preincubation assay, which is a modification of the standard plate incorporation assay was used in the short term mutagenicity test using Salmonella strains TA1535, TA1537, TA98 and TA100 with and without Aroclor 1254-induced rat and hamster metabolic activation systems. Fatty acid methyl esters containing 6 to 20 carbon atoms were tested for possible anticlastogenic effects on busulfan, a known alkylating agent, in Chinese hamster bone marrow cells using the chromosome aberration test. All of the fatty acid methyl esters, ranging from C12 to C19, with the exception of linolenic acid methyl ester, revealed a distinct antisclastogenic effect on busulfan-induced chromosome aberrations (Renner, 1986). In view of the close relations between mutagenesis and carcinogenesis, the inhibitory effect of various fatty acids/fatty acid methyl esters on busulfan-induced chromosome damage seen above is in contradiction to the reputed evidence regarding the promoting effect on carcinogenesis of dietary fats and their simple esters. [ Back to the top ]
Five investigations on the carcinogenicity of fatty acid methyl esters are reported in the literature, 3 of them are subcutaneous injection studies, one is a topical application study and one is a feeding study. They all suffer from major deficiencies. Most importantly, the only studies suggestive of a carcinogenic effect of methyl stearate by the s.c. route used a dosing vehicle now known to be carcinogenic itself. This confounds interpretation of the marginal effects observed. Other studies of fatty acid methyl esters had substantial design deficiencies, including lack of appropriate controls, and do not provide any credible evidence of carcinogenic effects. Methyl oleate may have a weak mouse skin tumour promoting activity, but many essential nutrients have also been shown to have tumour promoting activity in specific model systems at high doses. Generally, these effects are not relevant to the conditions of human exposure. Therefore they are not appropriate for risk assessment and legal application.
Comprehensive evaluations of the tumorigenic potential of fatty acid methyl esters have been carried out by Dr Robert Binder and Dr Daniel Marsman, P&G Corporate Toxicology Dept. and by Dr Walter Aulmann, Henkel Toxicology Dept.. A compendium of their joint findings has been prepared by Dr Walter Aulmann, and is appended to this position paper. It formed the basis for the above comments.
It is suggested that the original reference to methyl esters being classified as tumorigenic was misinterpreted. This was an extract from the Registry of Toxic Effects of Chemical Substances (RTECS) which is a compendium of toxicity data extracted from the scientific literature. All data listed in the Registry are referenced to the sources in which the data appeared. The Registry has not evaluated the data; inclusion in the Registry does not mean endorsement of the reference. Evaluation of the cited reference is the responsibility of the reader. Tumorigenic citations are classified according to the reported results of the study only to aid the reader in selecting appropriate references for in depth review and evaluation. The in depth review attached concludes that the referenced work reported in RTECS does not justify classification of methyl esters as tumorigenic. Also we know of no athoritive body that has classified these materials as tumorigenic which is noteworthy given the long course of time that has passed since the publication of the data reported in RTECS.[ Back to the top ]
Skin irritation: Methyl myristate, when applied undiluted in four-hour occlude patch tests, produced slight to moderate skin irritation in rabbits (Safety evaluation of the methyl esters of saturated fatty acids - Unichema International, July 1992). Methyl laurate, methyl palmitate and methyl stearate were shown to be irritating in a test according to OECD guideline No 404 (IUCLID data sheet for 68937-84-8). While the rabbit skin displayed extraordinary sensitivity to the irritation potential fatty acid methyl esters proved to be readily compatible to the human skin : in tests conducted by Procter & Gamble using human subjects, virtually no irritation was observed for C8-C10, C12-C14 and C16-C18 methyl esters applied to the skin. A 24 hours standard patch test of C16-18 methyl esters at 100% concentration resulted in an average irritation grade of 0.0. This compares to an average irritation grade of 0.1 for C12-14 methyl ester and 0.4 average irritation grade for a 4% aqueous bar soap solution tested under the same conditions (Procter & Gamble, review of the safety of methyl esters, November 1996). Thus, it can be concluded, that long chain methyl esters derived from natural fats and oils have been shown to be very mild to the human skin.
Eye irritation: In a OECD 405 test the individual substances methyl laurate, methyl palmitate and methyl stearate were only slightly irritating (IUCLID data sheet for 68937-84-8). Undiluted methyl myristate was not irritant to rabbit eyes when tested using a modified Federal Hazardous Substances Labelling Act method (Safety evaluation of the methyl esters of saturated fatty acids - Unichema International, July 1992). Standard eye irritation tests were conducted on rabbits according to the Draize method by instilling 0.1 mL of C8-C10, C12-C14 and C16-C18 methyl ester at 100% concentration, non rinsed and rinsed. Based on this work C16-18 methyl esters are judged to be very mild. Slightly, readily clearing conjunctivitis was the only sign of irritation produced (Procter and Gamble, review of the safety of methyl esters, November 1996). Based on this work C8-C18 methyl esters are judged to be very mild to the eye.
Skin sensitization: Methyl esters of tallow acids did not display sensitizing effects in the guinea pig maximization assay (IUCLID data sheet for 68937-84-8). A repeated insult patch test of C16-C18 (palm methyl ester) on 68 human subjects did not induce skin sensitization (P&G unpublished data). Synopsizing these findings no indications exist for fatty acid methyl esters to have a sensitizing potential. [ Back to the top ]
Methyl esters of fatty acids have been fed to experimental animals without toxic effects. Toxicity, growth and feed efficiency were tested in chickens by Reiser, et al (Agricultural and Food Chemistry 4, 798 (1956) with a conclusion that methyl esters are not toxic to poultry when included at the level of 3-15% in their feed rations as determined but their rate and efficiency of gain. Methyl esters of fatty acids have been fed to turkeys by Atkinson, et al (Poultry Science 36, 767 (1957), rats by Alfin-Slater, et al (J. Nutrition 87, 168 (1965) and to rabbits by Kritchevsky, et al (American J. Physiology 185, 279 (1956) without toxic effects.
Methyl esters of higher fatty acid methyl esters, including methyl myristate, methyl palmitate, methyl palmitoleate, methyl stearate, methyl oleate, methyl linoleate, methyl docosahexanoate, methyl ecosapentanoate and lesser amounts of the associated acid esters are cleared by the FDA as a supplementary source of fat for animal feed under 21CFR573.640. Additionally methyl esters of fatty acids derived from animal and/or vegetable fats are approved feed ingredients by the American Feed Control Officials as a fat nutrient supplement. Higher fatty acid methyl esters derived from tallow, coconut oil, palm kernel oil and palm oil, among other fats and oils have been widely used as fat supplements in animal feed over many years in the U.S. and in Europe.[ Back to the top ]
The safety of the fatty acid methyl esters is recognised by the U.S. Food and Drug Administration (FDA) who have approved, as a direct food additive, methyl esters of fatty acids produced from edible fats and oils for use in aqueous emulsions in dehydrating grapes to produce raisins (21CFR 172.225). Residues on the raisins are approved up to 200ppm. Additionally the lower fatty acid methyl esters, including methyl myristate and methyl laurate are approved for use as synthetic flavouring substances and adjuvants by the FDA (21CFR172.515) and by the European SCF (First report on Chemically Defined Flavouring Substances - November 1995). Methyl linolate (48%) methyl linolenate (52%) mixture has been deemed to be Generally Recognised as Safe (GRAS) by the Flavour and Extract Manufacturers' Association (FEMA).
Indirect food additive clearances include use of methyl esters of coconut fatty acid (C8-18) and methyl esters of C16-18 fatty acid derived from animal and vegetable fats and oils in surface lubricants employed in the manufacture of metallic articles that contact food (21CFR178.3910); defoaming agents used in coatings (21CFR176.200); defoaming agents used in the manufacture of paper and paper board intended for use in holding or transporting food (21CFR176.210); as a constituent of cellophane intended for food packaging (21CFR177.1200) or water-insoluble hydroxyethyl cellulose film (21CFR177.1400) and as a constituent of adhesives (21CFR175.105). C10-18 fatty acid methyl esters are cleared for use in the production of resin bonded filters intended for use in production, manufacture, processing and preparation of food.
Methyl esters of the higher fatty acids are exempted from the tolerance requirements under 21CFR182.99 for use as adjuvants for pesticide chemicals applied to growing crops or raw agricultural commodities after harvest. Additionally, the U.S. EPA has classified pesticide inert ingredients according to their toxicity to encourage the use of the least toxic inert ingredients available. Several fatty esters, including methyl myristate and methyl esters of cottonseed oil (composed of 2% methyl stearate, 17% methyl oleate, 24% methyl palmitate, and 55%methyl linoleate) are classified by the EPA in List 4B, inert ingredients for which the EPA has sufficient information to conclude that their current use patterns in pesticide products will not adversely affect public health and the environment (60FR 35396, July 7, 1995), based on the following:
1) These substances were reviewed by the Structure Activity Team of EPA's Office of Pollution Prevention and Toxics and were judged to be of low concern for potential human health and/or environmental effects.
2) These substances are approved by the U.S. FDA as a direct food additive under 21CFR Part 172.
3) These inert ingredient substances were evaluated by the Office of Pesticide Program's Inert Review Group and determined to be of minimal risk.
The 4B list, which includes the methyl esters listed above, were provided to EPA's Office of Water and to FDA's Centre for Food Safety and Applied Nutrition for comment. No adverse comments were received. [ Back to the top ]
Fatty acid methyl esters are readily cleanable from ship's deep tanks. Although not water soluble, fatty acid methyl esters are amenable to standard water blasting or detergent cleaning and do not adhere to metal surfaces any more than other fats and oils substances. Indeed fatty methyl esters have lower viscosity than the corresponding fats and oils from which they are derived and are liquids at ambient temperature. These physiochemical characteristics of fatty acid methyl esters facilitate their removal. The following comment was received from Stolt Nielsen a major international shipping company :
"With reference to your request on our procedures for the cleaning of cargo tanks after the carriage of methyl esters, and any comments on the ease of cleaning or otherwise, please note the following. Parcel Tanker operators would generally regard this product as a clean product, relatively easy to clean and remove prior to the following cargoes. It presents no problems with regard to softening or absorption into coatings or with odour. We would use a recirculation method of washing using a vegoil remover. (Details of the procedure are appended to this position paper). After washing and rinsing thoroughly the tanks are drained and hand dried and followed by an inspection of the tank, sump, manifolds and draincocks to ensure they are dry and free of all traces of washings"[ Back to the top ]
Fatty acid methyl esters are readily removed from edible fats and oils in the refining processes normally employed. The methyl esters are more volatile than the free fatty acids of the same carbon number and therefore can be readily removed by either physical refining or deodorisation processes. As an example, stearic acid has a boiling point of 209°C at 4mm Hg, whereas methyl stearate has a boiling point of 181°C at 4mm Hg, 28 degrees lower which indicates considerably higher volatility for the methyl ester. The lower vapour pressures are consistent for the homologous series of methyl esters versus the corresponding fatty acids (JAOCS - 56, 770A, 1979).
In the physical refining process, methyl esters can be removed in the refining/deodorising step, being removed along with the free fatty acid. In the caustic refining process, methyl esters are for the most part unaffected by the caustic at the conditions employed, but are removed in the deodorisation step along with traces of free fatty acid and odorous components.
The following comment was received from Ad Rozendaal of Unilever Research on the subject of ease of removal:
"I am somewhat surprised by the SCF proposal to remove FAME from the list of acceptable previous cargoes. Fatty Acid Methyl Esters (FAME) are relatively easy to remove during the deodorisation or stripping stage and there is no reason to suspect that undesirable reaction products will be formed during the various refining stages. Approximate removal percentages during deodorisation/stripping are 90% at 210oC and 99% at 230°C (standard steam volumes)". He also infered that methyl esters are produced at low levels during normal edible oil processing: "During interesterification with sodium methylate catalyst (standard dose), about 0.3% FAME is formed; after full refining under the above conditions this will be reduced to far below 0.1% which I believe is the current limit accepted by Unilever".
In consideration of the above physicochemical and toxicological properties of the fatty acid methyl esters and the appended review regarding the alleged tumorigenic properties we consider methyl esters, including the C12 to C18 range to generally be regarded as safe as an acceptable immediate previous cargo for transport by sea of edible oils and fats intended for food use following further processing. [ Back to the top ]