Perspective Cite This: J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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Toxicological Assessment of Mineral Hydrocarbons in Foods: State of Present Discussions Koni Grob*
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Kantonales Labor (Official Food Control Authority of the Canton of Zurich), Fehrenstrasse 15, CH-8032 Zürich, Switzerland ABSTRACT: The evaluation of mineral oils by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) provided high acceptable daily intakes for classes largely falling into the mass range strongly accumulated by humans. Because they are roughly 2 orders of magnitude above the present exposure, they authorize strongly increased exposure. An approach based on accumulation seems more adequate. Increased organ weights might be more critical than granulomas. Aromatic hydrocarbons with 1−2 aromatic rings should be distinguished from those with at least 3 aromatic rings. If mineral oil saturated hydrocarbon limits were low, no limit might be needed for the 1−2 ring aromatics. It should be considered to phase out substantial use of mineral oils in food application. KEYWORDS: mineral oil saturated hydrocarbons (MOSH), mineral oil aromatic hydrocarbons (MOAH), granuloma formation, increased organ weight
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INTRODUCTION Many foods are contaminated with mineral oil hydrocarbons (MOH) from numerous sources. During the past decade, this was spotlighted and brought to attention that the MOH evaluation is unsettled. The public perception changed from “food grade” and “highly purified” mineral oil toward a “dangerous contamination”. Also, the toxicological evaluation changed, and maybe the “highly purified” mineral oils (essentially MOSH) are of potential concern by themselves. The author notes great reservation of the experts to draw conclusions, perhaps partly because this presupposes the reevaluation of the reference values from the past. However, at least some temporary assessments would be badly needed to guide the large running analytical work, such as the European monitoring.1 In some parts of Europe, the requested detection limits seem to constantly fall, whereas in other parts of the world, the attitude to the use of mineral oils in the food sector is quite relaxed. Taking the available facts together, the author believes that the range of uncertainty is narrower than often thought and some guidance should be possible. Following the current discussions, MOH are primarily separated into mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH), because their toxicological end points are different.
increase in occurrence of what they called follicular lipidosis, with incidences ranging from 10 to 50% of the spleens investigated in the 1950s and 1960s, depending upon age and area of residence. In 1970/1971, granulomas were detected in 24−76% of the spleens sampled in Canada. The occurrence was higher in North America and Australia than Europe. The medicinal use of mineral oil did not seem to represent a main cause. These findings should have alerted authorities. In 1989, the European Scientific Committee on Food (SCF) noted abnormalities in spleens, livers, and lymph nodes of Fischer 344 rats and concluded on temporary tolerable daily intake (TDI) of 0−0.005 mg/kg of body weight (bw) for oleum-treated MOH and of 0−0.05 mg/kg of bw for hydrogenated products.7 However, the limits that would normally have been derived (0.3−3 mg/kg of food) were not imposed. At that time, they were frequently exceeded 100−1000 times.8 SCF and Joint FAO/WHO Expert Committee on Food Additives (JECFA) Assessments in 1995. Further toxicological studies on a broader range of mineral oil products in Fisher 344 rats (refs 9 and 10 and unpublished industry reports) prompted the SCF to issue a less restrictive opinion for specified oils and waxes.11 The thorough evaluation was followed by a long list of observed effects, with the main histopathological findings being granulomas in the liver and collections of vacuolated macrophages (histiocytosis) in the lymph nodes. For certain waxes, inflammatory lesions at the base of the mitral valve in the heart were observed. Toxicity was correlated with accumulation and not with specific components or types of components. The severity of the effects of various mineral oil products was compared. The P100(H) oil tested showed minimal
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MOSH Early History. Before 1990, the public considered “purified” (“white”, i.e., largely MOAH-free) mineral oils almost as a food, not fundamentally different from vegetable oils. Apparently, some medical doctors even recommended their use for salad sauces to fight obesity. The food industry used mineral oils rather loosely. There was, however, little justification for this. On the contrary, frequent granuloma formation in human tissues was ascribed to mineral oil as from the late 1940s (e.g., refs 2−5). Cruickshank et al.6 pointed out the rapid and continuous © XXXX American Chemical Society
Received: April 27, 2018 Revised: June 10, 2018 Accepted: June 15, 2018
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DOI: 10.1021/acs.jafc.8b02225 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Perspective
Journal of Agricultural and Food Chemistry
Also, in 2003, data on MOH in human milk were reported.17 The mean concentration related to fat was 95 mg/kg, and the maximum (after application of breast salves) was 1300 mg/kg. Molecular masses ranged from C15 to C45, with maxima commonly at C23−C25. According to the JECFA classification and considering human milk as a food for babies, this composition corresponded to class III oils with an ADI of 0.01 mg/kg of bw (which was exceeded roughly 1000 times). Because more than half of MOH accumulated by the mothers fell into the range of the class I oils, exposure to class I oils was likely to be responsible for a large part of the high concentrations. European Food Safety Authority (EFSA) Opinion from 2012. Between 2010 and 2012, EFSA thoroughly evaluated the data available about MOSH and MOAH.18 Human MOSH exposure was estimated at 0.03−0.3 mg kg−1 of bw day−1. It was stated that MOSH from C16 to C35 are accumulated and cause microgranulomas in several tissues, including lymph nodes, spleen, and liver. Hepatic microgranulomas associated with inflammation in Fischer 344 rats were considered as a critical effect. None of the existing ADIs were considered adequate for the risk characterization. A margin-of-exposure (MOE) approach was used on the basis of the no observed adverse effect level (NOAEL) of 19 mg kg−1 of bw day−1 for the most potent products forming microgranulomas in the liver of Fischer 344 rats, i.e., the low and intermediate melting point waxes. From MOEs in the range of 59−680, the current exposure to MOSH via food was considered of “potential concern”. The high ADIs of JECFA were not commented, even though their exploitation would result in far higher exposure. It is remarkable that the conclusion was based on a wax, even though in the same opinion the classification of products used by SCF and JECFA was criticized and n-alkanes (of which waxes largely consist) were considered easily degradable. There is, furthermore, no comment on the discrepancy between the low concern for class I oils stipulated previously and the high accumulation of MOH in the same molecular mass range observed in human tissue. A revision of the existing ADIs was considered warranted but not possible as a result of insufficient data. This might explain why just a year later, in 2013, the Panel on Food Additives and Nutrient Sources Added to Food (ANS) of the EFSA returned to the high ADI specified by JECFA for food additives,19 considering a potential dietary intake of 10.1 mg kg−1 of bw day−1 by toddlers acceptable, even though it exceeds the estimated present exposure, considered of “potential concern” just a year before, 34−340 times. Data in Human Tissues. In 2007, MOH were analyzed in human adipose tissue collected from 144 volunteers living in Austria during Caesarean sections as well as in milk from days 4 and 20 after giving birth.20 The MOH largely consisted of an unresolved mixture of iso- and cycloalkanes ranging from n-C17 to n-C32 and centered at n-C23/C24. Concentrations in the adipose tissue varied between 15 and 360 mg/kg of fat, with an average of 60.7 mg/kg and a median of 52.5 mg/kg. It was estimated that the total MOH content of the human body would normally be around 1 g and reach 10 g. Considering that only a small fraction of MOH resists degradation and elimination, it was estimated to take decades to accumulate such amounts. The fat in the milk from day 4 after delivery contained virtually the same MOH mixture as the tissue at 10−355 mg/
accumulation and toxicity within the 90 day study, and the P70(H) oil showed slightly greater accumulation in the liver, lymph node, and kidney but not as much as other oils. The SCF took note of the uncertainties from the variability in the composition of mineral oil products and the potential longterm accumulation in humans. It allocated an acceptable daily intake (ADI) of 0−20 mg/kg of bw to waxes characterized by a minimum viscosity, a minimum carbon number of 25 at the 5% boiling point (i.e., at most, 5% of the dose of 20 mg/kg of bw may consist of compounds < C25), and an average molecular weight of ≥500 Da. A temporary ADI of 0−4 mg/kg of bw was set for white paraffin oils specified by a minimum viscosity, a minimum carbon number of 25 at the 5% boiling point, and an average molecular weight of no less than 480 Da (C34 paraffins have a molecular weight of 478 Da). Using the same toxicity data, JECFA12 classified mineral oils, mainly distinguishing low- and high-melting-point waxes as well as high-viscosity and medium-/low-viscosity paraffin oils. The latter group was further divided into three classes (I, II, and III). The viscosity, average relative molecular mass, and carbon number at the 5% distillation point were used in the specifications. Interestingly, the frequent occurrence of MOH-related granulomas in human tissues was not commented. Further, it should have been noted that the observed granulomas in humans occurred at far lower (external) exposure than in animal experiments. In fact, accumulation of MOH in the human spleen has been reported as early as 1966.13 JECFA Assessment from 2002. For the 2002 JECFA assessment,14 new studies were included, such as 2 year studies with P70(H) and P100(H) oils, in JECFA terms representing the class I medium- and low-viscosity mineral oils and the high-viscosity oil, respectively (later published by Trimmer et al.15). Findings essentially confirmed the previous evaluations: high ADIs for MOSH with 95% of the hydrocarbons at or above C25 and a 1000 times lower temporary ADI for oils with more than 5% components below C25 (a puzzling large difference for little difference in MOSH mixtures). The ADI for medium- and low-viscosity mineral oils of class I (average relative molecular mass of 480 and a carbon number of at least 25 at the 5% distillation point) was increased to 0−10 mg/kg of bw, whereas a temporary ADI of 0−0.01 mg/kg of bw was allocated to oils of lower mass (average mass of 400−480 and 5% distillation point at ≥C22) based on the increased incidence of histiocytosis in the lymph nodes. An ADI of 0−20 mg/kg of bw was specified for microcrystalline wax (average relative molecular mass of ≥500 and a carbon number of at least 25 at the 5% distillation point) but none for lower melting point waxes. First Doubts. This evaluation based on data from whole mineral oil products was soon questioned. Scotter et al.16 fed the same white oils and waxes to Fischer 344 rats but analyzed MOH in tissue extracts in terms of concentration, molecular mass distribution, and n- versus isoalkanes. The accumulation ranged from C16 to C35, mainly starting from C20, which largely falls into the mass range considered of little concern by SCF and JECFA. The link between histopathological effects and MOH accumulation was confirmed, although noting that the same concentration does not necessarily mean the same severity of the effect. These authors concluded that the current specifications were not prescriptively adequate in controlling the amount of accumulated MOSH. Even though well supported, this message remained largely unheard. B
DOI: 10.1021/acs.jafc.8b02225 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Perspective
Journal of Agricultural and Food Chemistry
Various MOSH mixtures were applied for up to 120 days. The highest concentration in rat liver, obtained with MOSH largely below C25 dosed at 4000 mg/kg of feed, was 14 600 mg/kg,22,25 which is roughly 15 times above the highest concentration measured in human liver (900 mg/kg). The maximum in the rat spleen, however, was 555 mg/kg, clearly below the highest value in human spleen (1400 mg/kg). The maximum in the adipose tissue of the rats (339 mg/kg) was also below that in human adipose tissue (493 mg/kg). According to EFSA,18 the human exposure was 1.8−18 mg of MOSH/kg of food if daily 1 kg of food contaminated at this level was consumed by a 60 kg person. This is in the order of 1000 times less than the highest dose applied in the animal tests, still neglecting that rats consume more per body weight than humans. Hence, extrapolation from animal tests grossly underestimates accumulation in human tissues. Far longer lasting exposure is one reason, and the higher absorption at a low dose is another.26 The (external) exposure should not be compared but concentrations in the tissues. It was concluded that the animal tests did not allow for an appropriate risk assessment, because there was effectively no safety margin: the highest concentration in human spleen has not even been reached, and this compared to Fischer 344 rats, which are known to accumulate more MOSH than, e.g., Sprague Dawley rats.27 In Fischer 344 rats, n-alkanes (and probably other wax constituents) are strongly accumulated between C25 and C35. This was correlated with granuloma formation: a 1:1 mixture of oil and wax dosed at 400 mg/kg of feed produced a large number of granulomas, whereas a 4000 mg/kg dose of the same (well-deparaffinated) oil alone (resulting in 3805 mg of MOSH/kg of liver) did not produce any significant number.25 It was hypothesized that crystallization hindered degradation and formed the nuclei for granulomas:22 pure n-C25, the accumulated n-alkane of the lowest mass, has a melting point of 54 °C. Granuloma Formation. In the past, granuloma formation was the pivotal end point for risk assessment, used by EFSA in 2012,18 but also criticized, e.g., by ref 28 in 2001. As early as 196229 and later confirmed by several authors, e.g., ref 27, it was shown that waxes do not trigger granuloma formation in Sprague Dawley rats, which raised the question whether the Fischer 344 or Sprague Dawley rats would be the more adequate model for humans. Doubt have been raised repeatedly, e.g., ref 30. Human livers and spleens contain little n-alkanes.21,31 It may be argued that this is due to low exposure. However, the exposure to natural n-alkanes, e.g., from the skin of apples or edible oils,21 is higher than that to MOH, indicating that humans efficiently metabolize them. In MLNs and adipose tissue, n-alkanes are present, from which it could be concluded that primarily MLNs are in danger for granuloma formation. There remains, however, an open question: what triggered the granulomas frequently observed in human tissues in the past? If it was not the waxes, the hypothesis proposed in ref 22, it must have been the oil. In livers of Fischer 344 rats containing 3805 mg/kg of well-deparaffinated oil L-C25, no granulomas were detected.25 This concentration is about 4 times higher than the highest concentration recently measured in human liver. Is it that in the past the human exposure to mineral oils was that far higher, or are the humans more sensitive to granuloma formation than Fischer 344 rats?
kg (average, 44.6 mg/kg; median, 30 mg/kg). That from day 20 contained
