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Basis for evaluating mineral oils in foodstuffs and packaging materials

For ecological reasons, cardboard packaging cartons are manufactured using a high proportion of recycled paper. Tests have shown that recycled cardboard can contain high proportions of mineral oils.

Mineralöle aus Druckfarben und Recyclingkarton können in hohen Mengen in verpackte Lebensmittel übergehen.
n-Alkan-Testmischung
Additivfreies Dieselöl
Additives Schmieröl
Paraffinöl (Weißöl)
Reis - unbelastet
Reis - kontaminiert mit Mineralöl aus Recyclingkarton
Reis - MOSH
Reis - MOAH

Background

Mineral oil hydrocarbons (MOH) are distillation products from mineral oil or coal tar. They contain straight and branched aliphatic, cycloaliphatic and aromatic hydrocarbons. Polycyclin aromatic compounds and heterocycles can also be present. The range of MOHs spans volatile and easily degradable hydrocarbons right up to poorly soluble, low-volatility and persistent high molecular compounds of grease and oils.

The origin of mineral oils in packaging material is printing ink, of the sort that is usually used with newsprint. Mineral oils in printing inks and recycled cardboard can pass into packaged foodstuffs at high rates. These are shorter-chained mineral oil fractions with hydrocarbon values of <25 and a high proportion of aromatic compounds (10–25%). Measured values are the sum of mineral oil saturated hydrocarbons (MOSH) that consist of open-chain paraffins and cyclical alkalines, as well as mineral oil aromatic hydrocarbons (MOAH), of 1-5 aromatic rings. That being said, mineral oils of various structures can also enter foodstuffs in many other ways:

  • Contamination with batching oil from jute bags (hazelnuts, rice)
  • Mineral mould oil from baked goods
  • Paraffin oil from fining rice
  • Hydraulic oils: Dosing systems
  • Mineral oil in cooking oils (Ukrainian sunflower oil)
  • Production disaster (lubricating oil, engine oil, hydraulic oil)
  • Effects of environmental polution (soot)
  • Paraffin oil as a dust binder

Critical foodstuffs

The BfR assumes that, especially with foodstuffs with a large surface, such as flour, semolina, rice, breakfast cereals, cocoa powder or breadcrumbs, transfer of mineral oil out of the carton packaging is to be expected.

Toxicological classification

As the available data for a toxicological analysis of the mineral oil mixtures is not currently sufficient, the BfR has not yet carried out a risk evaluation. As a result, we do not know for certain the extent that foodstuffs can be contaminated by mineral oil transferring from cardboard packaging, and what proportion can be resorbed by the body. Furthermore, there lacks a sufficient classification of the composition of the mineral oil mixtures.

There are also no existing toxicological studies for the special mixtures MOSH and MOAH that have already been proven to be present in cardboard packaging.

In principle however, in accordance with article 2, paragraph 2 of the EEC Directive 315/93 of the Council of Europe, 8 February 1993 on the determination of joint procedures for controlling contaminants in foodstuffs, such contaminations should be limited to as low an amount as reasonably achievable (ALARA principle).

This should be the level that is achievable in good practice for all substances named in article 1 of the directive.  However, if a toxicological assessment of the mineral oil demonstrates that the substances transferred to the foodstuffs or the quantities of mineral oil transferred are enough to be able to endanger human health, then it is no longer permitted to place this foodstuff on the market (article 2, section 1 of Directive (EEC) 315/93) or to use this packaging material (section 31 of the Code on Use of Food, Commodities and Animal Feed (LFGB)) in conjunction with article 3 of Directive 1935/2004 of the European Parliament and Council from 27 October 2004 on materials and objects that are intended to come into contact with foodstuffs).

Prevention strategies

  • Packing with functional barriers (inner bag made from suitable material)
  • Avoidance of cardboard packaging
  • Switching to fresh fibres
  • Use of mineral oil-free printing inks

According to the BfR, it should be assumed that ingested mixtures are only slowly excreted out of the human body and that they can therefore accumulate in the body.
Furthermore, mineral oils in printing inks contain a relatively high proportion of aromas (approx 20%), which has a very complex composition. It cannot be ruled out that the complex mixture of subsituted PAH presents a carcinogenic risk, on the basis of structural homologies.

The ADI value for Class II/III mineral oils (mineral oils with low to medium viscosity, a hydrocarbon content <25 and an average molecular weight <480 g/mol; EFSA 2009 is 0.01 mg/kg of body weight. This means that a daily intake of 0.6 mg for an adult weighing 60 kg is seen as acceptable.

When estimating the consumer’s exposure to mineral oils in foods, it should however be kept in mind that, depending on the method of preparation (soaking rice or cooking it in water methods), the mineral oil content can be reduced. Accordingly, a definitive legal assessment is not currently possible.

Analysis

Measuring mineral oil content in foodstuffs is a demanding process, because it deals with a complex mixture that must be quantified as the sum of all its components. This is only possible with a flame ionisation detector, which is neither selective nor especially sensitive, which therefore means that efficient purification is required. Due to the enormous amount of compounds, single component analysis is not possible. Added to this, MOSH and MOAH must be differentiated from the foodstuff’s own hydrocarbons, and often also separated. This requires special techniques, such as the separation of long-chained plant-based alkanes and olefins (eg isomerised squalene).

Principle

The mineral oil hydrocarbons are extracted from the sample using an organic solvent, and after purification are determined on a solid-phase cartridge using GC-FID. Quantification is according to standards, with an internal standard on the methodology of the external standard. A certified standard mineral oil mixture (additive-free lubricating oil) is used for calibration. Special separation material (activated silica gel with added silver nitrate) is used for the separated determination of the MOSH and MOAH.

Interpretation

When interpreting the analytic results, the most important thing is clarifying the type of mineral oil (evidence of source) and the suspected composition of the contamination. (Toxicological residues – mineral paraffins with a high molecular weight are less toxic than paraffins of shorter chains. Especially critical: C20–C26.)

Example: Rice with mineral oil from recycled cardboard

The documented mineral oil mixture in rice comprises a multitude of moderately volatile hydrocarbons with a chain length in the range C14 to C25 (shorter-chained mineral oil fraction; distribution is centred around C18). It was determined that each kg of rice contains 8.0 mg mineral oil saturated hydrocarbons (MOSH) and 2.0 mg mineral oil aromatic hydrocarbons (MOAH). On the ‘mineral oil mountain range’, regularly occuring peaks are visible, which represent the n-alkanes. On the basis of the characteristic molecular mass distribution, it can be assumed that a considerable proportion of the measured transfer was the result of mineral oils outgassing from the packaging carton (printing inks). (From C24, barely in the gas phase any more.)

Literature:

[1]Questions and answers on mineral oil transfers from packaging materials to foodstuffs (BfR FAQ from 10/03/2010)

[2]Mineral oil migrations from packaging material to foodstuffs (BfR Statement no 008/2010 of 09/12/2009)

[3] Mineral oil analysis in the food sector. Workshop of the German Federal Institute for Risk Assessment (BfR), Berlin and the Cantonal Laboratory Zurich, June 2010

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