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Scientific Opinion on Mineral Oil Hydrocarbons in Food
Consumers are exposed to a range of mineral oil hydrocarbons (MOH) via food. Mineral oil saturated hydrocarbons (MOSH) consist of linear and branched alkanes, and alkyl-substituted cyclo-alkanes, whilst mineral oil aromatic hydrocarbons (MOAH) include mainly alkyl-substituted polyaromatic hydrocarbons. Products, commonly specified according to their physico-chemical properties, may differ in chemical composition depending on the oil source. Technical grade MOH contain 15 - 35 % MOAH, which is minimised in food grade MOSH (white oils). Major sources of MOH in food are food packaging and additives, processing aids, and lubricants. Estimated MOSH exposure ranged from 0.03 to 0.3 mg/kg b.w. per day, with higher exposure in children. Specific production practices of bread and grains may provide additional MOSH exposure. Except for white oils, exposure to MOAH is about 20 % of that of MOSH. Absorption of alkanes with carbon number above C35 is negligible. Branched and cyclic alkanes are less efficiently oxidised than n-alkanes. MOSH from C16 to C35 may accumulate and cause microgranulomas in several tissues including lymph nodes, spleen and liver. Hepatic microgranulomas associated with inflammation in Fischer 344 rats were considered the critical effect. The no-observed-adverse-effect level for induction of liver microgranulomas by the most potent MOSH, 19 mg/kg b.w. per day, was used as a Reference Point for calculating margins of exposure (MOEs) for background MOSH exposure. MOEs ranged from 59 to 680. Hence, background exposure to MOSH via food in Europe was considered of potential concern. Foodborne MOAH with three or more, non- or simple-alkylated, aromatic rings may be mutagenic and carcinogenic, and therefore of potential concern. Revision of the existing acceptable daily intake for some food grade MOSH is warranted on the basis of new toxicological information.
© European Food Safety Authority, 2012
Following a request from the European Commission, the EFSA Panel on Contaminants in the Food Chain (CONTAM Panel) was asked to deliver a scientific opinion on mineral oil hydrocarbons (MOH) in Food. Mineral oil hydrocarbons occur in food both as a result of contamination and from various intentional uses in food production. In order to assess the need for possible regulatory measures as regards MOH in food, EFSA was requested to assess the risks related to their occurrence in food. More specifically, the opinion should evaluate whether new toxicity data are available and whether the current acceptable daily intakes (ADIs) are still applicable, explore whether certain classes (or subclasses) of MOH are more relevant due to their toxicity or to differences in the way they are metabolised by the human body, and identify the different background sources, other than from adulteration or misuse, of MOH occurrence in food. In addition a dietary exposure assessment was requested for the general population and for specific subgroups of the population (e.g. infants, children and people following specific diets), by taking into account the background occurrence of MOH in food. Included in the request was also to advise on MOH and food classes to be included if monitoring were to be set up for their presence in food.
The scientific literature and other sources were searched for relevant information on the subject and, for the purpose of exposure assessment, EFSA issued a call for data on the occurrence of MOH in foods. The information gathered on MOH occurrence in food was assessed and then combined with data on food consumption in European countries, taken from EFSA’s comprehensive food consumption database.
Mineral oil hydrocarbons (MOH), or mineral oil products, considered in this opinion are hydrocarbons containing 10 to about 50 carbon atoms. Crude mineral oils are by far the predominant source of the MOH considered, but equivalent products can be synthesised from coal, natural gas or biomass. MOH consist of three major classes of compounds: paraffins (comprising linear and branched alkanes), naphthenes (comprising alkyl-substituted cyclo-alkanes), and aromatics (including polyaromatic hydrocarbons (PAHs), which are generally alkyl-substituted and only contain minor amounts of non-alkylated PAHs). MOH may also include minor amounts of nitrogen- and sulphur-containing compounds. Within these classes there are enormous numbers of individual components.
In this opinion, MOH have been divided into two main types, mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH). MOH are derived by physical separation (such as distillation or extraction) and chemical conversion processes (cracking, hydrogenation, alkylation, isomerisation, etc.) from crude oils and/or synthetic products derived from liquefaction of coal, natural gas or biomass. Of the many commercially available products, little is known about their composition, as specifications are generally expressed in terms of physico-chemical properties (such as viscosity), related to the applications of the products. Products with the same physico-chemical specification may vary considerably in their composition, depending on the source of the oil and its processing. Food grade MOH products are treated in such a way that the MOAH content is minimised. Technical grades of MOH typically contain 15-35 % MOAH.
Because of their complexity it is not possible to resolve MOH mixtures into individual components for quantification. However, it is possible to quantify the concentration of total MOSH and MOAH fractions, as well as certain sub-classes, using methods based on gas chromatography (GC). Currently, the most efficient methods for analysis of MOSH and MOAH in food and feed comprise extraction followed by pre-separation by high performance liquid chromatography (HPLC) on-line coupled to GC with flame ionisation detection (FID). Detection limits depend on the mass distribution, the sample matrix and any prior enrichment, and can be as low as 0.1 mg/kg. Comprehensive GCxGC-FID enables a rough separation and quantification of paraffins and naphthenes in the MOSH fraction, but it is of limited practicality for routine analysis. Contamination with polyolefin oligomeric saturated hydrocarbons (POSH), e.g. from plastic bags, heat sealable layers or adhesives, may interfere with MOSH analysis. Analytical capacity to distinguish the different MOAH subclasses in food is limited. For this purpose, GCxGC appears to be the most effective method. Due to the complexity and the variable composition of MOH mixtures, it is not possible to define certified standards of general applicability.
The CONTAM Panel identified numerous sources for the occurrence of MOH in food. Among food contact materials, sources are food packaging materials made from recycled paper and board, printing inks applied to paper and board, MOH used as additives in the manufacture of plastics, e.g. internal lubricants in polystyrene, polyolefins, adhesives used in food packaging, wax paper and board, jute or sisal bags with mineral batching oil, lubricants for can manufacture and wax coating directly applied to food. Food additives, processing aids and other uses contribute to MOSH levels, together with release agents for bakery ware and sugar products, and oils for surface treatment of foods, such as rice and confectionery. MOH are used in feeds as binders for minor additives added as powder. Paraffinic waxes are authorised for use in e.g. chewing gum and coating of certain fruits, and in pesticide formulations. Further uses of MOH are as defoamers and as anti-dusting agents for cereal grains. Environmental contamination sources are lubricating oil from engines without a catalyst (mainly diesel), unburned fuel oil, debris from tyres and road bitumen. Further sources are machinery used for harvesting (diesel oil, lubricating oil) and food processing, e.g. lubricating oils in pumps, syringe type dosing and other industrial installations. In addition, solvents consisting of individual alkanes or complex MOH mixtures containing cyclic- and open chain alkanes defined by their chromatographic co-elution with n-alkanes of carbon numbers ranging from C10 to C14, used as cleaning agents, may contaminate food products.
Occurrence data on MOH were available only for a limited number of food groups and only from a few countries. These data partly originated from targeted sampling. Nearly all data refer to total MOSH and little information is available on specific sub-classes, such as cyclic, branched and linear alkanes. MOAH measurements were not available for the majority of the samples, but MOAH concentrations can be estimated based on the typical composition of the mineral oil product detected. For MOH found in food, the number of carbon atoms typically ranges from 12 to 40.
MOSH are present at different levels in nearly all foods. In the available dataset (except for the high values for ‘Bread and rolls’ and ‘Grains for human consumption’ (mainly represented by rice), which showed a bi-modal distribution of occurrence values) the highest mean occurrence values were found in ‘Confectionery (non-chocolate)’, ‘Vegetable oil’, ‘Fish products’ (canned fish), and ‘Oilseeds’ varying from 38-46 mg MOSH/kg), followed by ‘Animal fat’, ‘Fish meat’, ‘Tree nuts’ and ‘Ices and desserts’ varying from 14-24 mg MOSH/kg).
The food groups ‘Bread and rolls’ and ‘Grains for human consumption’ showed some high values that could be due to the use of MOSH as release agents or spraying agents, respectively. In these cases, the distribution of values was modelled using maximum likelihood log-normal fitting in order to identify a mean value for both the ‘background’ occurrence and the additional high levels of occurrence. The resulting mean background occurrence values for ‘Bread and rolls’ and ‘Grains for human consumption’ were 1.8 and 4.1 mg/kg, respectively. The resulting mean occurrence values for high levels of MOSH in the same food groups were 532 mg/kg and 977 mg/kg. In contrast to the background occurrence, which is of unknown composition and most likely contains MOAH, these high values arise from food grade white oils, which are virtually free of MOAH.
Occurrence data on dry foods which could be attributed to the use of recycled paperboard packaging, were available from two different surveys. Mean concentrations of MOH were up to 32 mg/kg for MOSH found in creme/pudding mix and 4.5 mg/kg MOAH found in noodles. Maximum occurrence values were 100 mg/kg in semolina and 17 mg/kg in noodles, for MOSH and MOAH, respectively.
Chronic exposure was estimated for different age classes of the population based on mean occurrence values in the different food groups. These values were considered to represent background occurrence, normally expected in the respective food groups. Dietary exposure to MOSH ranged in the general population across European dietary surveys between approximately 0.03 and 0.3 mg/kg body weight (b.w.) per day and was higher in younger consumers than in adults and the elderly. The highest exposure estimate per kg b.w. was for high consumers among children 3 to 10 years old.
The percentage contribution to background chronic exposure was calculated for the different age classes. Main food groups contributing to the exposure include ‘Animal fat’, ‘Bread and rolls’, ‘Confectionery (non chocolate)’, ‘Fine bakery wares’, ‘Fish meat’, ‘Fish products (canned fish)’, ‘Ices and desserts’, ‘Pasta’, ‘Sausages’, ‘Vegetable oil’.
Additional exposure on top of the background was calculated for specific consumers of ‘Bread and rolls’ or ‘Grains for human consumption’ with high levels of MOSH originating from release- or spraying agents. Although it would not be appropriate to include such discrete high values in the background occurrence, for calculation of chronic exposure, it cannot be excluded that some groups of consumers (buying always from the same source or having brand loyalty) are exposed on a regular basis to food with such levels. Excluding infants, the additional exposure across European dietary surveys and age classes is in the range 0.7-6.4 mg/kg b.w. per day for the ‘Bread and rolls’ scenario and in the range 0.02-3.8 mg/kg b.w. per day in the ‘Grains for human consumption’ scenario.
For the subgroup of exclusively breast-fed infants, an exposure of roughly 0.3-0.5 mg/kg b.w. per day was estimated.
Whereas the background exposure to MOAH via food can be estimated to be roughly 20 % of the exposure to MOSH, additional high exposure to white mineral oils used as release agents for treatment of bread or for spraying of grains would not imply any increase in MOAH exposure.
Exposure to MOSH and MOAH attributed to extensive migration from recycled paper and board packaging without an internal barrier was estimated based on limited occurrence data. This indicated that toddlers and other children were the age classes of consumers potentially more exposed to MOH. Exposure to MOSH, for toddlers and other children was up to 0.04 mg/kg b.w. per day from bakery wares, 0.07 mg/kg b.w. per day from breakfast cereals and 0.11 mg/kg b.w. per day from rice. These estimates indicate that the migration from recycled paper packaging could contribute significantly to the total exposure.
Absorption of alkanes may occur through the portal and/or the lymphatic system. For n- and cyclo-alkanes the absorption varies from 90 % for C14-C18 to 25 % for C26-C29. The absorption further decreases with increasing carbon number, until above C35 when it is negligible. Limited data suggest that cyclo-alkanes are absorbed at similar levels as n-alkanes of comparable molecular weight, whereas absorption of branched alkanes is slightly less. Alkanes are initially oxidised to the corresponding fatty alcohols by the cytochrome P450 system, subsequently biotransformed to fatty acids and in some cases subjected to the normal β-oxidation pathway. This reaction is more rapid for n-alkanes than for branched- and cyclo-alkanes. Due to low biotransformation rates, in particular for some branched- and cyclo-alkanes, MOSH having carbon number between 16 and 35 may accumulate in different tissues including adipose tissue, lymph nodes, spleen and liver. In rats, the terminal half-life of MOSH in blood (estimated from P15(H) white oils) was between 23 and 59 hours, depending on the strain. However, this reflects the elimination of the easily degraded MOSH. Although limited information exists on toxicokinetics of MOAH, the available data indicate that these compounds are well absorbed and are rapidly distributed to all organs. The data also indicate that MOAH are extensively metabolised and do not bioaccumulate. The concentration of MOSH in human tissues (mainly lymph nodes, liver, spleen and adipose tissue) demonstrates that accumulation of these compounds, mostly branched- and cyclo-alkanes, occurs in humans.
MOSH and MOAH have low acute oral toxicity and acute toxicity is not relevant in the context of the pattern of MOH exposure via food. Low molecular weight alkanes can cause α2u-microglobulin related nephrotoxicity in male rats. This effect is known to be of no biological relevance to humans. MOSH mixtures with carbon number in the range C10-C13 caused moderate liver cell hypertrophy, but in the absence of pathological effects the CONTAM Panel did not consider this to be an adverse effect.
In rats, bioaccumulation of MOSH can lead to formation of microgranulomas in liver and mesenteric lymph nodes (MLN). Microgranulomas in MLN are considered of low toxicological concern because they are not associated with an inflammatory response or necrosis, do not progress to adverse lesions and available studies did not show any effect on immune functions. In rat liver, microgranulomas were associated with inflammatory reactions.
In humans exposed to MOSH, microgranulomas have been observed in liver, spleen, lymph nodes and other organs, but these changes have not been associated with inflammatory reactions or other adverse consequences. There is no information on exposure levels at which these effects occur in humans.
In arthritis-prone rodent models, intradermal and intraperitoneal injections of high doses of certain MOSH can alter immune function or induce autoimmune responses. Weaker effects were observed following short term exposure through abraded skin. Whether long term oral exposure would have similar consequences is unknown although one short term study suggests this might not be the case.
All MOH are mutagenic unless they are treated specifically to remove MOAH. The mutagenicity of MOH is caused mainly by 3-7 ring MOAH, including non-alkylated PAHs. These PAHs are mainly formed by the heating of the oil, and are a minor fraction of MOAH. Some of these are covered by monitoring programmes in food. Many MOAH with three or more aromatic rings and little or no alkylation, and heterocyclic-containing analogues, can be activated by P450 enzymes into chemically reactive genotoxic carcinogens. These also form DNA adducts. MOSH are not carcinogenic, though long chain MOSH can act as tumour promoters at high doses. Some highly alkylated MOAH can also act as tumour promoters, but they are not carcinogens themselves. Some simple MOAH, such as naphthalene, are carcinogenic by a non-genotoxic mode of action, involving cytotoxicity and proliferative regeneration.
In view of the complexity and the lack of information on the composition of MOH mixtures and inability to resolve these into single compounds, it is not meaningful to establish health-based guidance values on the basis of studies on individual components. Hence, if possible, whole-mixture studies should be used for this purpose.
For MOAH mixtures there are no dose-response data on the carcinogenity and hence it is not possible to establish a Reference Point (RP) upon which to base a margin of exposure (MOE) calculation, which would normally be the approach for the risk characterisation of MOAH mixtures.
The CONTAM Panel considered the formation of liver microgranulomas produced in Fischer 344 rats to be the critical effect of MOSH with carbon number between C16 and C35. From the available information on the different white oils and waxes tested in toxicological studies it is not possible to differentiate between subclasses (e.g. n-, branched- or cyclo-alkanes) of MOSH. Studies used to identify the respective no-observed-adverse-effect levels (NOAELs) were 90-day studies. The published data did not allow modelling of the dose-response data of the different studies. The CONTAM panel concluded that these NOAELs could potentially be used to select RPs for establishing health based guidance values.
The existing ADIs have been established for specific products intended for food use. The current classifications of food grade-MOH were set by SCF (1995), JECFA (FAO/WHO, 2002) and EFSA (2009), and are all based on toxicological studies with poorly characterised products with regard to chemical composition. Ideally, MOSH mixtures should be assessed by considering the molecular mass range and subclass composition (e.g. n-, branched- or cyclo-alkanes), rather than on physico-chemical properties such as viscosity. Based on new information about the lack of toxicological relevance for humans of the effects in MLN observed in the (sub)chronic studies in Fischer 344 rats and on newly available toxicokinetics studies, the CONTAM Panel concluded that a revision of the existing ADIs, particularly the temporary group ADI established by JECFA for medium- and low-viscosity mineral oils class II and III is warranted. With respect to microcrystalline waxes, high-viscosity mineral oils and medium- and low-viscosity class I mineral oils, the existing ADIs are of low priority for revision, although they are based on products with a poor chemical characterisation.
With respect to background exposure to MOSH mixtures via food the distribution of carbon numbers range from C12 to C40 with centres ranging from C18 to C34 in different foods. None of the existing ADIs was considered adequate for the risk characterisation of the range of MOH present in the background exposure of humans. In the absence of toxicological studies on MOSH mixtures typical of those humans are exposed to, the CONTAM Panel considered it inappropriate to establish a health based guidance value for MOSH. Given the deficiencies in the toxicity data base, the CONTAM Panel decided to use an MOE approach and for the background exposure selected as an RP the NOAEL of 19 mg/kg b.w. per day for the most potent MOSH grades for formation of microgranulomas in the liver, the low and intermediate melting point waxes. The range of MOSH grades involved in the high exposure scenarios (MOSH used as release agents for bread and rolls and for spraying of grains) is more restricted than that for the background exposure and therefore the CONTAM Panel used the highest NOAEL below the lowest LOAEL (lowest-observed-adverse-effect level) for these grades of MOSH, 45 mg/kg b.w. per day, as an RP.
In the risk characterisation, the background exposure to MOAH and MOSH, and two high exposure scenarios for MOSH were considered. The MOAH content of MOH present in food are mostly around 20 %, but may in vegetable oil and oil seeds be up to 30- 35 % of the MOH levels. The MOAH fraction may be both mutagenic and carcinogenic, but no MOE for MOAH exposure via food could be derived. Because of its potential carcinogenic risk, the CONTAM Panel considers the exposure to MOAH through food to be of potential concern.
For MOSH background exposure from all sources, the MOEs for average consumption (based on maximum UB and minimum LB exposure across European dietary surveys, respectively) for toddlers and children and for adolescents and adults were from 100 to 290 and from 200 to 680, respectively. For high consumers of the same groups MOEs varied from 59 to 140 and from 95 to 330, respectively.
In the high exposure scenarios with regular consumption of bread and rolls with high contents of MOSH, the MOEs (based on maximum and minimum exposure across European dietary surveys, respectively) were from 16 to 55 for average consumption, and in some cases were below 10 for high level consumption of bread and rolls. For the regular mean consumers of grains, the MOEs varied greatly between different age classes and were between 35 (toddlers, maximum exposure across European dietary surveys) and 1 900 (other children, minimum exposure across European dietary surveys), and between 12 (toddlers) and 200 (elderly) for high consumers.
The CONTAM Panel took into account that the RPs were based on 90-day studies and that some of these compounds might have very long elimination half lives in humans when interpreting the obtained MOEs. In view of this, the CONTAM Panel considers that there is potential concern associated with the current background exposure to MOSH in Europe and in particular in the situation of use of white oils as release agents for bread and rolls and to some extent for spraying of grains.
The CONTAM Panel has identified MOH classes to be included if monitoring were to be set up for the presence of MOH in food. Total MOSH and MOAH should be separately determined. Among MOSH, sub-classes should be distinguished based on molecular mass ranges and structure. Two sub‑classes were identified based on molecular mass: MOSH up to n-C16 and MOSH from n-C16 to n-C35. Based on the MOSH structure, distinction should be made among n-alkanes, branched alkanes and cyclic alkanes. Additionally, hydrocarbons with structures similar to MOSH, such as poly alpha olefins and oligomeric polyolefins (POSH), should be distinguished from the MOSH. The total MOAH should be separately quantified. However, routine monitoring of subclasses of MOAH is presently not feasible. Improvement of the analytical methods to allow separation of MOAH in subclasses is recommended. The CONTAM Panel recommended the identification of the sources of contamination at various stages of food production, to design an effective monitoring programme. With respect to the food classes to be included in monitoring, those food groups making a relevant contribution to the background exposure, including the particular cases related to use of white oils, should be taken into account. It is recommended to investigate whether other food groups not included in the present evaluation also make a relevant contribution to total chronic exposure.
A significant source of dietary exposure to MOH may be contamination of food by the use of recycled paperboard as packaging material. It can be effectively prevented by the inclusion of functional barriers into the packaging assembly. Other measures may include segregation of recovery fibre sources intended for recycling and the increasing of the recyclability of food packages by avoiding the use of materials and substances with MOH in the production of food packages.
Mineral oil hydrocarbons (MOH), alkanes, aromatic hydrocarbons, analysis, sources of MOH, human dietary exposure, toxicokinetics, toxicity, risk assessment, margin of exposure (MOE), acceptable daily intake (ADI), food contact materials