Plasticizers do not cling to plastic films

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Ezine

  • Published: Sep 1, 2008
  • Author: Steve Down
  • Channels: Gas Chromatography
thumbnail image: Plasticizers do not cling to plastic films

Plastic cling film and freezer bags intended for use with foods are generally manufactured from poly(vinyl chloride), poly(vinylidene chloride) or polyethylene. Their flexibility and extensibility are assured by adding a set of compounds known as plasticizers, which are generally esters of adipic acid, citric acid or phthalic acid, at concentrations of 5-30 % by weight. However, these additives tend to migrate from the plastic into foods, presenting very real health problems.

Certain adipates, citrates, and, particularly phthalates, have adverse effects on the endocrine and reproductive systems of rodents and can also be the cause of respiratory malfunctions. So, the EC banned the use of phthalates in plastic food wrapping in 1999 and laid down rules listing the approved plasticizers and their maximum allowed migration amounts. Now all that remained was an analytical method to measure the levels of plasticizers in plastics and in foods packaged in plastic.

The most accurate procedure would be to measure the amounts of plasticizers in the food itself but massive variations in the types of food make that an unworkable premise. So, it has been tacitly agreed that the more realistic approach is to measure the levels in the plastic material and determine the migration rates of the individual plasticizers from plastic to foods. In practice, simulated foods are used, consisting of solvents that replicate the lipophilicity of foods.

Many of the methods that have been devised rely on GC with various detectors, such as mass spectrometry or flame ionisation detection. They have been recognised by a team of Italian scientists as "very precise and sensitive in determining these analytes" but are deemed to be not entirely suitable for the rapid measurement of multiple, sometimes undeclared, components in large numbers of samples. So, this team decided to adapt an existing GC-FID method that was designed to determine phthalates in soft plastics intended for use in toys.

Stefano Girotti and co-researchers from the University of Bologna and the Regional Agency for Environmental Protection (APRA) in Bologna optimised their procedure using a mixture of 16 standard plasticizers, including phthalates, terephthalates, sebacates, maleates, adipates and citrates ranging in molecular mass from 194 to 246. The mixture was separated within 25 minutes by GC following splitless injection using a 5% diphenyl dimethylsilicone column, giving well resolved peaks.

The repeatability CV averaged 5.8% and the detection limits fell in the range 0.07-0.7 % by weight. The calibration curve correlation coefficients were 0.74-0.99%.

The modified procedure was then applied to 12 food packaging films and 6 food freezer bags purchased from a local market in different years. Pieces of each sample were Soxhlet extracted in a single step with ethyl acetate over 220 minutes, using methyl margarate as a tracer internal standard. These extracts were analysed directly, as they gave recoveries of 95% ± 10% after one extraction cycle.

Both the freezer bags made from polyethylene and the cling films declared to be PVC-free contained none of the plasticizers at detectable levels. The most common types that were found were adipates, generally in association with citrates, the main compounds being bis(2-ethylhexyl) adipate and tributyl O-acetylcitrate. Phthalates were notable by their absence in plastics produced since 1999, their prohibition date.

The total levels were 3-10% by weight, far lower than values reported in the literature which approach 30%. The researchers interpreted this as an indication of improved production processes that require lower amounts of additives.

Migration of the plasticizers from the plastics into 96% ethanol as a simulated food was carried out at 5 °C for up to 60 days, or in isooctane at 20 °C for 1-3 days. The extracted and migrated amounts of individual plasticizers showed good agreement.

The important finding was that migration reached equilibrium after 10 days, so that longer contact times did not increase the levels of plasticizers transferred to the food simulant. So, from a public health point of view, longer contact did not increase the risks. Nevertheless, the actual amounts that did migrate were still regarded as too high in some cases, being above the specific migration limits cited in the EC Directive.

The initial GC method for specific plasticizers in plastic toys was successfully extended to 16 plasticizers in plastic food packaging, with a simple extraction and good detection limits. The researchers declared that, given the relatively high migration levels into foods, the products should be clearly labelled, listing both the recommended and inadvisable uses of the plastics. Alternatively, a move to polymeric plasticisers that do not migrate to foods would solve the problem.


The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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