2. Polystyrene for food Packaging aPPlications

ILSI Europe Report Series

REPORT

Commissioned by the ILSI Europe Packaging Materials Task Force

Packaging Materials:

About ILSI Europe

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The opinions expressed herein and the conclusions of this publication are those of the authors and do not necessarily represent the views of ILSI Europe nor those of its member companies.

PACKAGING MATERIALS2. POLYSTYRENE FOR FOOD PACKAGING APPLICATIONS

Updated Version

By Christian Block, Bart Brands and Thomas Gude

REPORTCOMMISSIONED BY THE PACKAGING MATERIALS TASK FORCE

December 2017

© 2017 ILSI Europe

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ISBN 9789078637448

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CONTENTS

1. INTRODUCTION 4

2. WHAT IS POLYSTYRENE? 4

3. BASIC CHEMISTRY OF POLYSTYRENE PLASTICS 5

3.1. Manufacture of Monomers 6

3.1.1. Styrene monomer 6

3.1.2. Butadiene monomer 7

3.2. Manufacture of Polymers 7

3.2.2 Manufacture of polystyrene homo-polymer (crystal polystyrene or GPPS) 7

3.2.3 Manufacture of high impact polystyrene (HIPS) 8

3.3 Additives used in polystyrene plastics for food contact use 8

3.4 Quality management and traceability during manufacturing of polystyrene 9

4 POLYSTYRENE AND FOOD PACKAGING APPLICATIONS 9

4.1 Migration of substances from polystyrene materials and articles

under conditions of use 10

5 FOOD CONTACT REGULATIONS 12

5.1 European Regulations that apply to polystyrene used for packaging of food 12

5.1.1 Regulation (EC) No 1935/2004, dated 27 October 2004 12

5.1.2 Regulation (EC) No 10/2011 dated 14 January 2011 13

5.1.3 Essential monomers 13

5.1.4 Essential additives 14

5.2 US Food and Drug Administration (FDA) Regulations 15

6 SAFETY AND TOXICOLOGY 16

6.1 Styrene monomer 16

6.2 Cancer risk 16

6.2.1 Recent studies on cancer risk 16

6.2.2 Other views on cancer risk 17

6.2.3 Discussion on the cancer risk 19

6.3 Reproduction and developmental toxicity 19

6.4 Possible estrogenicity of styrene oligomers 20

6.5 1,3-butadiene monomer 22

6.6 Polystyrene plastics – safety in use 22

7 ENVIRONMENTAL ASPECTS 24

7.1 European Commission Directives on packaging and packaging waste 24

7.2 Recyclability and reuse 25

7.3 Incineration through energy recovery 25

8 GENERAL CONCLUSIONS 26

GLOSSARY 28

REFERENCES 30

Authors: Dr Christian Block, Plastics Europe (BE), Dr Bart Brands, retired (CH), Dr Thomas Gude, Swiss Quality Testing Services (CH)Scientific Reviewers: Prof. Luciano Piergiovanni, University of Milan (IT) and Dr Frank Welle, Fraunhofer Institute (DE)Coordinators: Mr Jeroen Schuermans and Dr Lucie Geurts, ILSI Europe (BE)

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1. INTRODUCTION

P olystyrene (PS) and the styrene-butadiene co-polymer plastics have been used as commercial packaging materials since early 1950.

The clarity of the crystal polystyrene homo-polymer, the high impact resistance of the styrene-butadiene co-polymers and the low density combined with good strength and insulation properties of foamed polystyrenes, have made the plastics manufactured from these polymers especially suitable for formation into a variety of packaging materials and articles, particularly containers and trays, for use with a wide range of foods and beverages.

Polystyrene plastics packaging, specifically formulated to be brought in contact with food and beverages, comply with the safety requirements in the relevant European Commission Legislation on “Food Contact Plastics”, as well as national requirements in certain European countries. Besides being applied to the packaging of food, PS plastics are also used in household appliances such as kitchen machines, refrigerators and freezers as well as (disposable) cutlery in which contact with food is possible and the same legal requirements apply as for food packaging.

Polystyrene manufacturers also produce polystyrene products for applications such as TV housing, furniture, building insulation and automotive parts. These PS types may not be suitable for food contact applications, as they may contain additives or co-monomers not authorized for use in contact with food, or exceeding applicable restrictions.

2. WHAT IS POLYSTYRENE?

P olystyrene is the parent polymer of a family of styrene-based plastics, which are used for the manufacture of items ranging from furniture and electrical goods, appliances, insulation material, to toys, housewares and a wide variety of packaging. Enhanced physical properties such as impact strength suitable for food packaging can be achieved by polymerisation of

styrene in the presence of polybutadiene rubber. The resultant plastics are known as the High Impact Polystyrenes (HIPS).

Polystyrene homo-polymer, also known commercially as crystal polystyrene or general purpose polystyrene (GPPS), is an amorphous polymer and has the particular properties of high clarity, being colourless, hard, but rather brittle. The amorphous nature and other properties, which arise from the aromatic chemical structure and glass transition temperature (Tg) of around 100°C, differ markedly from those of the polyolefin plastics, such as polyethylene, which are based on aliphatic hydrocarbons.

The styrene-based plastics are considered to be some of the most versatile, easily fabricated and cost-effective plastics (Brady and March, 2009). The amorphous nature makes polystyrene an ideal plastic for several processing technologies such as injection moulding, extrusion of sheet and thermoforming.

Polystyrene is, however, susceptible to stress cracking by organic liquids and oils, which limits its use with foodstuffs containing high levels of fats and vegetable oils (Mark et al., 1985; Briston, 1992; Ashford, 2011). Certain types of HIPS are less sensitive to stress cracking.

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A major application of polystyrene plastics is in expanded / foamed sheet form. Expanded polystyrene plastics are extensively employed as general protective packaging, sometimes called cushioning packaging, but they also find wide use as packaging for food formed into trays and containers, and as disposable beverage cups (Robertson, 2008). Large fish boxes are another typical application for expanded PS. The excellent insulation properties save lots of energy during storage and transport. Other examples are trays for soft fruit and egg containers.

Polystyrene film can be bi-axially oriented, in this form maintains clarity, and overcomes some of the brittleness of un-stretched plastic. The stretching operation also improves the strength, even though crystallisation is not produced. It is manufactured in both thin gauges – less than 75 micrometers – and thick gauges, which can be used to make thermoformed containers (Briston, 1992; Ashford, 2011; Robertson, 2008; Brown, 1992).

To overcome the brittleness of non-orientated crystal polystyrene, butadiene synthetic rubbers (between 5% and 12%) are added with styrene during polymerisation to manufacture HIPS. The superior impact strength of HIPS, compared to that of crystal polystyrene plastics, is offset by inferior clarity, which makes them opaque. HIPS plastics also have reduced tensile strength and stiffness, but there is an improved resistance to stress cracking and to crazing caused by organic liquids, oils and fats. Depending on the final functional application requirements GPPS and HIPS are blended in specific blend ratio’s to obtain optimum performance. More recently, special polymerisation technology has been developed which results in clear high impact polystyrene (anionic polymerisation of styrene with butadiene).

GPPS and HIPS plastics have poor barrier properties to gases, such as oxygen and carbon dioxide, which may reduce shelf life time of the packed food, depending on wall thickness. This can be seen as an advantage for yogurt pot as some penetration of oxygen is necessary to assist the yogurt fermentation process, or, barrier properties can be adapted by using multilayer structures with other polymers (see also the section on Polystyrene and food packaging applications, ILSI Europe report on multilayer packaging 2011 (Dixon, 2011)).

Styrene can also be reacted with acrylonitrile to form styrene-acrylonitrile (SAN) co-polymers also including polybutadiene rubber (ABS) giving improved physical and chemical properties over crystal

PS. These plastics are however not part of this report.

3. BASIC CHEMISTRY OF POLYSTYRENE PLASTICS

S tyrene and butadiene monomers are the starting chemical substances from which polystyrene polymer and styrene-butadiene co-polymers are produced. During the manufacturing / polymerisation process, specific additives are added to obtain additional

functional properties for the end-use such as packaging of food (e.g. antioxidants). Certain additives can also be added during the conversion process from PS granules to finished articles (e.g. colorants).

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3.1. Manufacture of the monomers

3.1.1. Styrene monomer

Styrene, which is also commonly known as vinyl benzene or phenylethene, is a colourless liquid with a distinctive and penetrating odour (Ashford, 2011).

Styrene: C6H5-CH=CH2

Styrene is manufactured commercially from ethyl benzene (EB). Two different routes for the production of styrene are commercially used. The ethylbenzene styrene monomer (EBSM) process is based on the catalytic dehydrogenation of ethylbenzene and renders styrene as its main product and minor quantities of toluene as a co-product.

C6H5-CH2CH3 C6H5-CH=CH2 + H2 ethyl benzene styrene hydrogen

Styrene monomer is produced with high purity usually in the range of 99.7–99.9%. The main impurity in the styrene is residual ethyl benzene (see also the manufacture of polystyrene where EB is frequently used as solvent) (CEFIC, 2011).

The propylene oxide styrene monomer (POSM) process involves the co-production of propylene oxide and styrene: in this case, ethylbenzene is oxidized to form ethylbenzene hydroperoxide (EBHP). The formed product reacts next with propylene at 115°C under high pressure, in presence of silica, to form propylene oxide and α-phenyl-ethanol which is then dehydrated at 200°C in presence of alumina to form styrene.

Figure 1: Styrene formation process

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3.1.2. Butadiene monomer

1,3-Butadiene (butadiene) is a colourless gas with a mild aromatic or gasoline-like odour at room temperature and pressure.

1,3-butadiene: CH2=CH-CH=CH2

Butadiene is used primarily as a monomer for manufacturing synthetic rubber and plastics but also finds uses as a chemical intermediate for producing other chemicals. Butadiene is predominantly manufactured by extraction from C4 hydrocarbons as a by-product of the steam cracking process used to produce ethylene and other olefins. Butadiene is also produced to a lesser extent by dehydrogenation of n-butane using the Houdry catadiene process; from ethanol using either the single-step Lebedev process, or the two-step Ostromislensky process; and from butenes by catalytic dehydrogenation of normal butenes.

3.2. Manufacture of the polymers

3.2.1 Manufacture of Polybutadiene rubber

Polybutadiene rubber is polymerised from 1,3-butadiene monomer. The main commercial process for the production of polybutadiene rubber is solution polymerisation with Ziegler-Natta catalyst or with anionic polymerisation using butyl lithium. The stereochemistry of the rubber depends on the exact type of solvent and catalyst.

3.2.2 Manufacture of polystyrene homo-polymer (crystal polystyrene or GPPS)

There are two main commercial processes used for the manufacture of crystal polystyrene – the solution process and the suspension process.

Most general-purpose polystyrene (GPPS) is produced by solution polymerisation in a continuous bulk process consisting. The plant setup generally comprises a feed section, a polymerisation section, in one or more reactor vessels, a devolatilisation and solvent recovery section and a pelletizing section. The free radical polymerisation is initiated by either thermally or by means of organic peroxides. Solvents such as ethylbenzene or toluene can be added to control viscosity and reaction kinetics. Each reactor vessel has an internal agitating system and specific temperature features. The reacting and formed polymer, with increasing conversion and hence viscosity is continuously pumped from the first reactor vessel to the next process steps. Volatiles, including the solvent or diluent and un-reacted styrene, are removed by heat and vacuum stripping. The molten polymer is then cooled in a water bath, pelletised and transported to a storage silo or bagging system.

Figure 2: Diagram of the continuous solution process for polystyrene polymerisation

SolventStyrene Reactors

Devolatiliser

Polystyrenepellets

Extruder Cooler Cutter

Recovered styrene and solvent

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Applying adequate process control such as temperature, pumping speed, agitator speed and the devolatilisation conditions, the quality and specific properties of the PS grade are defined. Such physical-chemical properties are mainly defined by the molecular weight / distribution and for HIPS the amount of reacted polybutadiene. The conditions of the devolatilisation step are specifically important to minimise residual styrene, EB and oligomers to meet the high quality and safety requirements for use in food packaging applications.

In the suspension process, the styrene monomer is dispersed in water in the presence of a suspension agent and a peroxide polymerisation initiator. The mixture is heated in a closed vessel until polymerisation is substantially complete. The polymer is separated off, dried and un-reacted monomer together with other volatiles, removed by vacuum stripping before being pelletised (McGraw-Hill, 1997). Although the suspension process is still used to make expandable polystyrene, it has no commercial significance any longer for GPPS and HIPS products. Expandable polystyrene (EPS) is employed extensively in building insulation, protective packaging and to some extent in food packaging. The process is similar to that for suspension polystyrene with pentane expanding agent added during the polymerisation or post polymerisation. Expandable polystyrene is then expanded during specific moulding processes to produce expanded polystyrene articles.

XPS (extruded polystyrene) application is another form of extruded foamed polystyrene and is manufactured from polystyrene polymer into which an expanding agent – a volatile substance – has been incorporated. In the process used to produce foamed polystyrene for conversion into food packaging trays, containers and beverage cups, the expanding agent is directly injected into molten polymer in the extrusion process (Brady and March, 2009). The volatile expanding agents used are the hydrocarbons pentane or butane. Since 1995, industry has developed a new technology using carbon dioxide (CO2) as the foaming agent, which provides the benefit of reduced flammability. Carbon dioxide is also neutral with respect to volatile organic compounds (VOC) emissions and, in addition, the finished plastics benefit by having improved organoleptic properties opening new food packaging applications without affecting odour and taste of the food products.

3.2.3 Manufacture of high impact polystyrene (HIPS)

The commercial process most commonly used to produce high impact polystyrene is the continuous bulk polymerisation, which is similar to that used for the commercial manufacture of GPPS. At the start of the process polybutadiene rubber is dissolved in the styrene monomer. As the polymerisation process proceeds two phases are formed – a polybutadiene rich phase and a polystyrene rich phase with grafted polybutadiene. The grafting arises when some of the styrene free radicals react with the polybutadiene (McGraw-Hill, 2007).

The HIPS plastics used for food packaging are mostly a blend with GPPS. The ratio of GPPS and HIPS depends on the required functional performance of the final article.

3.3 Additives used in polystyrene plastics for food contact use

Polystyrene plastics and HIPS are manufactured with various additives, which include antioxidants, colorants, mould release agents and processing aids. Antioxidants, such as octadeyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate (Irganox 1076), are usually present at typical concentrations of up to 0.1% level. A common mould release agent is zinc stearate, added at a typical level of about 0.05-0.10%. White mineral oils are used as processing aids and flow promoters with levels of between 0.5 and 6 % by weight (several opinions by EC Scientific Committee for Food (SCF)

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since 1980 and the European Food Safety Authority (EFSA: 2009). The amount depends on typical process requirements; a higher percentage is applied for high melt flow rate for injection moulding or a low percentage mineral oil for extrusion or high heat applications. Except for nucleating agent, none or very low amounts of additives are used in foamed polystyrene (XPS) applications to optimise the cell nucleation behaviour. The section on Regulations provides a table with several additives used in PS products.

3.4 Quality management and traceability during manufacturing of polystyrene

Quality control is achieved by sampling pellets at well-defined intervals and comparison of chemical/physical characteristics against the values in the specification of the respective PS grade. Most important are purity, colour, Melt Flow Rate (MFR), Vicat softening temperature, impact strength and residual styrene monomer. Residual styrene and EB levels will adversely affect taste and odour on migration to food (Van Gemert and Nettenbrijer AH, 1977; Alexander HC et al., 1982). It is obvious that such levels should be as low as technically possible. Commercial PS products intended for contact with food have a residual styrene level below 500 ppm (500 mg/kg or 0.05 %) (see also section on migration).

Since the European Commission Regulation on “Good Manufacturing Practice” was implemented such quality management procedures have been further refined throughout the supply chain, which includes procedures on traceability (Regulation (EC) No 2023/2006, dated 22 December 2006).

4. POLYSTYRENE AND FOOD PACKAGING APPLICATIONS

C rystal polystyrene is used as a packaging material where its inherent transparency can be utilised to advantage. These are containers for a variety of foods and as disposable “plastic glasses” for beverages.

Foamed polystyrene plastics are thermoformed into a variety of trays for meat, poultry, fish, fruit and vegetables; “clam-shell” containers for eggs, and fast foods, and disposable cups for beverages. Some foamed polystyrene trays, cups and containers have surface layers of crystal polystyrene, which provide a “barrier” layer between the plastic and the foodstuff. The bulk density of foamed polystyrene plastics used for food packaging trays and containers is typically in the range 0.05 to 0.19 g/cm3. The thickness range is typically 0.3 to 6.5 mm.

Bi-axially oriented polystyrene films in thin gauges are used for food packaging carton windows. They have also been used as “breathable” films for over-wrapping fresh produce, such as lettuce. Thicker gauges are used to manufacture clear vending cups, and tubs for desserts and preserves, using the thermoforming process.

HIPS are used in the form of pots for dairy products, such as yoghurts, as vending cups for beverages such as coffee, tea, chocolate and soup, and in the form of “clam-shell” for eggs. In the dairy packaging segment HIPS has its particular strength in producing portion packs via the Form-Fill-Seal (FFS) process. As mentioned earlier, HIPS plastics are usually produced from blends

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of styrene-butadiene co-polymer and crystal polystyrene; the ratios being selected to achieve the required balance of physical properties for the different forms of packaging and the conversion process – injection moulding or extrusion followed by thermoforming. Pots for dairy products are manufactured either by the injection moulding process or the thermoforming process. Vending cups are usually manufactured by extrusion and thermoforming process, to obtain thin walls and light weight.

Some pots and containers have multilayer structures, which often consist of one or more layers of HIPS (different colours), and an attractive “glossy” external appearance by using crystal PS. Other multilayer composites contain layers with barrier resins such as ethylene vinyl alcohol (EVOH), PVC and polyesters (PET/PETG).

In recent years, polypropylene (PP) plastics have replaced HIPS plastics in some of the above mentioned uses, but for some types of food packaging, the reverse has occurred due to advantages of ease of processing and low shrinkage provided by polystyrene plastics. Market prices also influence the preference of PS or PP.

The physical properties and performance of polystyrene and HIPS plastics may set limitations on the use as food packaging. For example, crystal polystyrene and HIPS cannot physically withstand “high” temperatures and therefore consequently limitations occur for microwave as well as oven applications. As mentioned earlier, polystyrene plastics are normally not suitable for use with food with a high fat content (e.g. salad dressings, margarine). The high fat level in the food may cause stress cracking of the PS packaging and associated decreased barrier function. The full extent of the use limitations is described in product literature of the producers and well understood by the polystyrene plastics converters from the extensive knowledge accumulated over the years and potential users are always suitably advised.

4.1 Migration of substances from polystyrene materials and articles under conditions of use

The conditions of use of the polystyrene family of food packaging plastics range from low temperatures (refrigeration) for periods of days or weeks, for example packaged dairy and meat products, to elevated temperatures approaching the boiling point of water for short periods of time, for example vending cups.

The substances which can migrate from polystyrene plastics to foods and beverages are: residual monomers, low molecular weight components (oligomers, principally dimers and trimers) and any applied additives. In general, it can be assumed that substances migrating to foodstuffs are of concern if they present a potential health hazard to the consumer, or cause unacceptable changes to the organoleptic properties of the food or beverage. This general safety requirement is enshrined in the Framework Regulation (EC) No 1935/2004 applicable to all materials and articles in contact with food. All substances migrating from the plastics to the packaged foods and beverages must however, be in full compliance with the legislative requirements. The intentionally used monomers and additives must be listed in Annex I of the Specific Regulation on Food Contact Plastics (EC) No 10/2011 on food and may have a Specific Migration Limit (SML) assigned. In addition, the total of all migrating substances shall not exceed the Overall Migration Limit (OML) of 10 mg/dm2 (see section on food contact regulations). Enforcement Bodies in the Member States also verify compliance with the legal restrictions under the foreseeable conditions of use.

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Numerous studies and investigations have been carried out to establish levels of migration of styrene monomer into foods and beverages from the various polystyrene plastics used for food packaging and for beverage containers under the many conditions of use. Especially the Ministry of Agriculture, Fisheries and Food (MAFF) in the UK (now called the Food Standards Agency (FSA)) has published several Food Surveillance Information Sheets in addition to studies by industry and final food packers.

These studies – best to be found at the FSA homepage – highlighted the fact that despite residue levels of styrene monomer in the various polystyrene plastics being found to be around 500 mg/kg food (ppm), with a few samples as high as 1000 ppm (1000 mg/kg), the quantities determined in the foods and beverages, which came into contact with the plastics as a result of migration during use, were relatively low. The mean styrene values found in various food types were in the region of 10 ppb (μg/kg), with maximum levels around 200 ppb (μg/kg) (MAFF, 1994, 1999). It was observed that migration levels varied, for instance, with the nature of the food (e.g. higher fat content resulted in higher styrene migration), the level of residual styrene in the container and the length and temperature of storage. The results from the studies were evaluated by the UK Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) and it was concluded that the levels of styrene monomer present in food did not present a toxicological risk to man. To better understand the migration behaviour of styrene it is important to recognise that the migration of additives and other residuals in food contact materials largely depends on the solubility of the substances in the food versus solubility in the food contact material (the so-called partitioning effect). In this regard, styrene has a very poor solubility in water and therefore expresses a low tendency to migrate into aqueous foods. Furthermore, EU food packaging materials regulations assumes that 1 kg of food is ingested per person per day and that all of this is packaged in polystyrene, which can obviously be considered a worst-case assumption. Consequently, the actual daily intake of trace amounts of styrene via food packaged in polystyrene is therefore considered only to be a small fraction of the estimated exposure when calculated using migration data (Duffy, 2007).Oligomers of styrene are important Non Intentionally Added Substances (NIAS) that may migrate from polystyrene, and dimers and trimers are by far quantitatively the most important part of oligomers. Dimers and trimers have been analyzed in polystyrene food containers (for example Kawamura et al., 1998a, b). Weel (2016) did not observe any higher oligomers apart from dimers and trimers up to the molecular weight range equivalent to styrene hexamers. The concentration of the sum of dimers and trimers in polystyrene ranged from about 200-600 mg/kg for EPS and were clearly higher for other packaging materials (mainly HIPS and GPPS) with a range between 4000 and 12000 mg/kg. In EPS the relative amounts of dimers in percent of the sum of dimers and trimers were generally around 20% and are clearly higher than those of dimers in other polystyrene materials (generally around or below 5%). Kawamura et al. (1998c, d) was the first to analyze dimers and trimers in polystyrene packed ready-to-use food items in Japan. Some further investigations on such food items in Japan were reported later. Dimers were in most cases not detectable (detection limit 0.001-0.005 mg/kg food) and the sum of trimers ranged from 0.004-0.03 mg/kg food (means determined by different investigators) up to a maximum of 0.06 mg/kg in a single food item. In 7 food items from the US packaged in polystyrene, trimers were not found and in only 3 samples 1.3-diphenylpropane could be analyzed at <5 µg/kg food (limit of quantification 2 µg/kg food) (Genualdi et al. 2014).

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5. FOOD CONTACT REGULATIONS

5.1 European Regulations that apply to polystyrene used for packaging of food

As part of the process of harmonising legislation of the Member States in the European Union (EU), the European Commission has developed legislation concerned with the safety of all materials and articles intended to come into contact with food over the last 40 years. These regulatory developments are ongoing, and step-by-step all food contact materials and articles, for which it is considered necessary, will have specific measures in place, replacing national legislation in certain countries. Over time, new regulations have been implemented, repealing older versions to reflect scientific developments and advances in risk assessment practices and policy. It is not the intention of this report to provide an in-depth evaluation of all current EU regulations in place applicable to food contact materials and articles. However, the most important legal requirements to ensure safety of the used materials will be addressed. More details and complete text of the respective regulations can be found on the European Commission website (Regulation (EC) No 1935/2004; Regulation (EC) No 10/2011).Polystyrene used in applications with food contact is subject to an in-depth safety assessment according to the Plastics Regulation (EC) No 10/2011. Residual monomeric styrene that will always be present in PS is considered as an Intentionally Added Substance (IAS) and is approved as a listed monomer since many years. Besides IAS, all polymers also contain Non Intentionally Added Substances (NIAS), the composition of which will depend on the basic material of the polymer, its production process, inclusion of additives (including their degradation products), etc. Oligomers, and in this context especially dimers and trimers, are an important part of NIAS that may contribute substantially to the total migrate. According to regulation (EC) No 10/2011 (Article 19) the potential risk to health of NIAS also has to be assessed which requires a safe level of exposure to be determined. A valuable guidance on how to deal with and assess NIAS was published by ILSI Europe (Koster et al., 2015). A general cut-off is given by the regulation (EC) No 10/2011 that migration of a substance should not be detectable at a Limit of Detection of 10 µg/kg food (or food simulant). This limit was not derived based on toxicological considerations, but was introduced based upon the current state of analytical technology. As shown above, the concentrations of dimers and trimers and the sum of both may sometimes exceed this limit, which might call for a more refined toxicological assessment.

5.1.1 Regulation (EC) No 1935/2004, dated 27 October 2004

Regulation (EC) No 1935/2004, dated 27 October 2004, is the current legal framework applicable to all food contact materials and articles. It is setting the basis for a very high safety standard for such materials and final articles (Article 3), at the same time ensuring the effective functioning of the internal market (Article 1). Most essential elements of this Regulation are:

- Migrating substances shall not endanger human health;

- Migrating substances shall not lead to unacceptable change in the composition of the food;

- Migrating substances shall not lead to deterioration in the organoleptic characteristics of the food.

Other requirements:

- Good Manufacturing Practices (GMP) requirements (See also Regulation (EC) No 2023/2006 with more specific provisions);

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- Special requirements for active and intelligent materials and articles (See also Regulation (EC) No 450/2009 with specific provisions);

- Procedure for the authorisation of new substances involving risk assessment by EFSA;

- Requirements on the labelling and information to the user of the materials and articles plus the specific Symbol that the article is suitable for contact with food;

- Requirements on the Declaration of Compliance with all applicable provisions;

- Requirements on traceability.

Annex I of Regulation (EC) No 1935/2004 mentions 17 groups of materials for which specific legislation (measures) have been implemented or may be implemented in the coming years. For plastic materials and articles intended to come into contact with food, the European Commission has published on the 25th of August 2016 its 6th amendment to the Plastics Regulation (EC) No 10/2011 – Commission Regulation (EU) 2016/1416.

5.1.2 Regulation (EC) No 10/2011 dated 14 January 2011

Regulation (EC) No 10/2011, dated 14 January 2011, and its amendments apply to plastic materials and articles intended to be brought in contact with food. The basic requirements of this regulation have been taken from Directive 2002/72/EC with its 7 Amendments. At the same time, next to an extension of the scope to multimaterial multilayers, this Regulation, also known as Plastic Implementing Measure (PIM) includes the respective Directives and Regulations on the compliance testing (migration) of finished materials and articles with several significant updates, such as e.g. the list of simulants and the test conditions for specific migration.

The most important requirements and principles of this EU Regulation are:

- A list of authorised monomers and additives with restrictions on migration, max concentration levels in the finished article and/or specifications on use or composition, excluding other substances;

- Specific provisions on migration testing in relation to the final use of the plastic article;

- Detailed provisions for the content of the Declaration of Compliance;

- Exemptions for including in the list of authorised substances for certain substances in plastics.

This Regulation on plastics in contact with food contains all monomers and additives applied in PS intended for contact with food / food packaging (See for more information: Table 1). The laws of some European Member States will contain additional legislative specifications and/or restrictions for food contact plastics materials and articles, particularly on components not yet covered by Regulations, such as colorants, solvents, polymer production aids (e.g. surfactants) and aids to polymerisation (e.g. peroxides, catalysts). Some countries that are not European Union Member States, for example Switzerland, have adopted provisions of the European Directives / Regulations by incorporating them into their national laws.

5.1.3 Essential monomers

Styrene is listed without a restriction. In practice, the tainting properties of styrene monomer in foodstuffs and the pungent odour act as a restriction on the level at which styrene is tolerated by the consumer in most foodstuffs. As mentioned before these taste and odour effects from styrene will limit its use for certain foods, and can be observed at migration levels well below 100 µg/kg food.

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Butadiene is listed with a restriction in the form of a maximum concentration in the finished article of 1 mg/kg PS and a migration limit of Non Detectable (ND) with a Limit of Detection of 10 µg/kg food (analytical tolerance excluded). In practice, the residual level of butadiene in PS is extremely low due to its high volatility. Nearly all residual butadiene is removed during the manufacturing process.

The provisions of the harmonised EU legislation are brought into use by European Member States implementing them into their individual national laws and legislative systems.

5.1.4 Essential additives

Additives which are used in PS intended for contact with food are all included in Annex I of the new Regulation (EC) No 10/2011. The most frequently used additives are mentioned in Table 1. Frequently, additives and also colorants are being incorporated into polystyrene plastics using master batches based on polystyrene as a carrier. To ensure that the final food contact material or article is in compliance with Regulation (EU) 10/2011, and where applicable national legislation, the carrier as well as the additives must meet the requirements of this legislation.

Table 1: Frequently used monomers and additives used in the manufacturing of polystyrene

Substance Ref Nr. (FCM Nr.) in Regulation 10/2011

Restriction

Styrene 24610 (193) None (*)

1,3-Butadiene 13630 (223) SML: Non Detectable (ND)- LOD 10 µg/kg Quantity in Material (QM): < 1 mg/kg in finished article

Pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxphenyl)propionate] antioxidant, (e.g. Irganox 1010)

71680 (496) None (*)

Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate antioxidant, (e.g. Irganox 1076)

68320 (433) SML = 6 mg/kg

Zinc stearate Covered by stearic acid

A limit for Zinc is set in Annex II of the PIM (SML = 25 mg/kg food or food simulant)

Poly(ethylene propylene)glycol 79920 (551) None (*)

Stearic acid 89040 (106) None (*)

White mineral oils, paraffinic, derived from petroleum based hydrocarbon feedstocks

95883 (95) - Average molecular weight not less than 480 Da;

- Viscosity at 100 °C not less than 8.5 cSt;- Content of mineral hydrocarbons with

Carbon Number less than 25: not more than 5 %

(*) When no Specific Migration Limit (SML) applies, the Generic Specific Migration Limit of 60 mg/kg food applies.

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Colorants used in food contact plastics are currently not covered by specific European Commission Regulations, apart from the general safety requirements of article 3 in Regulation (EC) No 1935/2004. They are however covered by national law. Moreover, there is a Council of Europe Resolution AP (89) 1 on the use of colorants in plastics coming into contact with food. It requires that colorants do not pose a risk to health, or affect food quality, and are sufficiently integrated within the finished material so that there is no visible migration under normal conditions of use. There are also purity criteria and specifications covering polychlorinated biphenyls (PCBs) contaminants, if present.

5.2 US Food and Drug Administration (FDA) Regulations

The US Food and Drug Administration regulations are mandatory in the US. The US Code of Federal Regulations (CFR) set a high standard within regards to the safety of food contact materials and articles. However, in comparison with the EU, FDA applies other approaches with regard to risk assessment. For instance, exposure is more refined than in the EU applied risk assessment. The FDA U.S. CFR are frequently used by other countries, not yet having specific legislation on food contact materials and articles as an external regulatory reference. Both the EU Regulations as well as the US CFR are used as a starting point by other countries to draft their own legislation.

Regulations for polystyrene and rubber-modified polystyrene are contained in Title 21 CFR Part 177.1640. In this regulation, the amount of total residual styrene monomer in polystyrene basic polymers is limited to 1 % (w/w), except when used in contact with fatty foods of specific types, in which case not more than 0.5 % (w/w) of total residual styrene monomer is allowed. For rubber-modified polystyrene basic polymers, the amount of total residual styrene monomer shall not exceed 0.5 % (w/w). It can be noted that 21 Part CFR 177.1640 mentions a maximum residual styrene level of 0.5 % (5000 ppm) though, current commercial PS products (intended for contact with food) in the USA have similar styrene residual levels as in Europe (0.05 %).

Regulations for additives used in the production of polystyrene and rubber-modified polystyrene can be found in 21 CFR Part 178. Colorants are specifically regulated in 21 CFR Part 178.3297. Additional clearances for polymers, additives or colorants may be found in the list of cleared Food Contact Notifications (FCNs) maintained on the FDA’s website. Full details of these regulations applicable to polystyrene, the copolymers and the additives that can be used with these plastics are available on the FDA websites (see References).

In cases of new compositional substances, FDA authorises the safe use of substances in contact with food through the Food Additive Petition (FAP) process in Title 21 of the U.S. Code of Federal Regulations part 174 through 179 (21 CFR Parts 174-179), through the Food Contact Notification (FCN) Process in 21 CFR Part 170, started in October 1999. In the words of the FDA: “This notification process is intended to replace the petition process as the primary means for authorizing new uses of food additives that are food-contact substances. However, discretion is given to the FDA for deciding when the petition process is more appropriate for evaluating data to provide an adequate assurance of safety”.It is also possible in certain cases to assess the safety of a food contact substance, by taking advantage of the threshold of Regulation Exemptions under CFR Part 170.39.

Though the U.S. FDA Regulations are updated annually, Food Contact Notifications are now the primary route for authorisations of food contact substances (FCS) and authorisations through this programme do not result in modifications of regulations. As such, FDA voluntarily maintains a listing of authorised FCS’s on their website. Other links to FDA can be found in the section on References.

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6. SAFETY AND TOXICOLOGY

6.1 Styrene monomer

As a volatile substance used widely in industry for more than 50 years, a considerable body of toxicological and epidemiological data has been developed for styrene. As inhalation is the major route of exposure for the majority of workers manufacturing and handling styrene, many toxicological studies have studied potential adverse effects of this monomer via this route of exposure. When considering the hazard of styrene upon ingestion, as a result of i.e. migration from food packaging applications, it should be noted that the results of the inhalation studies should be evaluated with care.

Styrene has low acute toxicity after inhalation or ingestion, although in the EU it is classified as harmful by inhalation and irritating to skin and eyes. Very high exposures can induce dizziness, drowsiness, headache and potentially unconsciousness. Studies in experimental rodents have demonstrated that high inhalation exposures to styrene can produce adverse effects on hearing by destroying sensitive hair cells in the inner ear. Based on the likelihood of anatomical and physiological similarities between the inner ear of rodents and humans it is not possible to exclude the possibility of hearing deficits occurring in humans following high exposures to styrene. This is supported by some studies with styrene-exposed workers reporting hearing deficits. These findings led to a STOT R1 classification in the EU (causes damage to hearing organs through prolonged or repeated exposure). Risk assessment evaluations do indicate however that maintaining occupational exposure levels at or below 20 ppm does protect against potential hearing toxicity.

For the oral route of exposure, the US Agency for Toxic Substances and Disease Registry (ATSDR, 2010), has derived an Acute-Duration Oral MRL (Minimal Risk Level) of 0.1 mg/kg bw/d for acute duration oral exposure (14 days or less) to styrene, based on neurological effects (impaired learning) as critical effect in a study in rats. Intermediate- or Chronic-Duration Oral MRLs were not derived due to a calculated (Intermediate-Duration Oral) MRL exceeding the Acute-Duration MRL or the absence of a long-term oral study examining neurological endpoints. The MRL is defined as likely to be without an appreciable risk of adverse effects (non-carcinogenic) over the specified duration of exposure. Besides the above cited values other similar values are available from Santé Canada, EPA, REACH, CSR etc. In addition it may be noted that at present there is no specific migration limit in the EU; this would allow for migration of 60 ppm, corresponding to about 1 mg/kg bw/d.

Styrene is metabolised to mandelic and phenylglyoxylic acids (detoxication products that are safely excreted in urine) via a transient metabolite, styrene oxide. In addition, experimental work has shown that styrene oxide is unstable in foods (Philo et al., 1997).

6.2 Cancer risk

6.2.1 Recent studies on cancer risk

Extensive epidemiological investigations of workers have shown no consistent associations between styrene exposure and any specific cancer type either within or among studies with no indication of an increased risk with increased exposure. While there are some reports of statistically significant associations between styrene exposure and specific cancer types these are outnumbered by studies showing no associations for each cancer type.

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Over the years, styrene has been investigated in a variety of studies in experimental rodents to determine if life time exposures of rats or mice to styrene via oral or inhalation routes of exposures will induce an excess of cancers. However, the majority of these studies are not ideal in design, and while they had shown no convincing evidence of cancer induction there was an agreed need for more robust investigations. Additional lifetime-inhalation exposure studies in both the rat and mouse were carried out, using contemporary toxicological protocols to determine if high life time exposures to styrene could produce an excess of tumours in experimental rodents. Supporting the findings of earlier investigations, styrene inhalation exposures in the rat failed to produce any evidence of treatment related induction of cancer (Cruzan et al., 1998). An excess of lung cancer was however found in the mouse study (Cruzan et al., 2001). Subsequent investigations (Cruzan et al., 2009, 2012) to study the mode of action responsible for the tumours in the mouse and assess the relevance for human health have demonstrated that the mouse lung tumours are caused by mouse specific lung metabolism mediated by a particular mouse enzyme. Rats have a different variant of the enzyme and thus are not susceptible to tumour development. Humans also have a different variant of the mouse enzyme and have little to no capacity to metabolise styrene to lung toxic metabolites corresponding to those in mice showing that, like the rat, humans are not susceptible to styrene induced lung toxicity and resulting cancer. Recent studies (Cruzan et al., 2009, 2012) in genetically modified mice lacking the mouse specific lung enzyme system responsible for producing the toxic metabolites of styrene were, like the rat and humans, resistant to the toxic effects of styrene. From the studies in rodents it can be concluded that tumour induction, relevant for humans and related to styrene exposure, is not demonstrated (Cruzan et al., 2009, 2012). In addition, exposure of these genetically modified mice to styrene oxide did not lead to alterations in the lung typical for wild-type mice after exposure to styrene, concluding that styrene oxide is not driving lung tumour development in mice after styrene exposure. Ring-oxidized metabolites of styrene that are formed by the specific CYP2F2 of mouse lungs are the proximate toxic metabolites (Cruzan et al., 2012).

Genetic toxicology studies, to investigate the potential of styrene to damage genetic material in cells, have produced mixed results. The EU Risk Assessment Report on Styrene (EU, 2008) gives a comprehensive assessment of genotoxicity. Various in vitro studies have produced evidence of potential genetic damage whereas others have not. The results of studies carried out in experimental animals show no convincing evidence of genotoxicity. No appreciable level of interaction with DNA has been shown in studies of DNA adduct formation.

An overall conclusion derived from a comprehensive assessment of the total database on styrene genotoxicity is that the available information does not indicate a genetic, and therefore presumably carcinogenic, risk for styrene-exposed populations (EU, 2008). Moreover, the most recent carcinogenicity studies in rodents (Cruzan et al., 1998, 2001), being the most comprehensive studies, do not indicate carcinogenic effects due to styrene exposure relevant for humans (Cruzan et al., 2009, 2012).

6.2.2 Other views on cancer risk

The International Agency for Research on Cancer (IARC) classified styrene as a Group 2B carcinogen (possible human carcinogen) in 1994 (IARC, 2002) based on limited evidence in humans and experimental animals. In the USA the EPA and the US National Toxicology Program Centre for Evaluation of Risks to Human Reproduction (NTP-CERHR 2011) are proposing classification of styrene as “reasonably anticipated to be a human carcinogen”. The conclusions reported by the most recent evaluation of the NTP were based on limited evidence for the carcinogenicity of styrene in humans, by positive exposure-response relationships found in studies with reinforced-

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plastic workers, styrene-butadiene workers and subgroups of workers with higher levels of styrene exposure or longer times since first exposure, showing an increased incidence of cancer of the lymphohematopoietic system, increased levels of DNA adducts and genetic damage in lymphocytes from exposed workers. Furthermore, it was concluded that although styrene disposition differs quantitatively among species, no qualitative differences between humans and experimental animals have been demonstrated that contradict the relevance of cancer studies in rodents for evaluation of human hazard. Detection of styrene-7,8-oxide-DNA adducts at base-pairing sites and chromosomal aberrations in lymphocytes of styrene-exposed workers supports the potential human cancer hazard from styrene through a genotoxic mode of action (NTP-CERHR, 2011). However, in an evaluation of the US Agency for Toxic Substances and Disease Registry (ATSDR, 2010), it was concluded that the occupational studies are inconclusive due to exposure to multiple chemicals (including benzene) and the small size of the cohorts or, in case of the styrene-butadiene workers, may be due to 1,3-butadiene rather styrene exposure.

In the Draft EU Risk Assessment Report on Styrene, prepared by the UK rapporteur on behalf of the European Union (EU, 2008), the conclusion on the genotoxicity endpoint is that there is no convincing evidence that styrene possesses significant mutagenic/clastogenic potential in vivo from the available data in experimental animals. Furthermore, the UK rapporteur stated that pointing to a possible carcinogenic potential of styrene in other organs is highly speculative as:

a) Several large cohort and case-control studies of workers exposed to styrene have shown no evidence for a causative association between styrene exposure and cancer in humans at any site;

b) No consistent evidence for styrene-induced toxicity in any organ has emerged from studies of exposed workers;

c) The level of DNA damage found in workers exposed to styrene is very low (10-fold lower than that produced by endogenously-generated genotoxic substances such as ethylene oxide) and thus cannot be considered to be of any relevance for subsequent tumour formation. Mechanistic studies have shown that styrene-oxide (SO) and its genotoxicity are not the driving force for lung tumour formation in mice, the only experimental tumour site observed so far. Furthermore, DNA adducts in animals after styrene exposure do not show any specific species or target organ relationship. For example, there is no excess of SO-adduct formation in tissues where SO is formed (e.g. in the liver) at high levels;

d) Chromosomal damage caused by styrene exposure in humans is far away from being conclusive. Although 5 studies appear to present evidence that styrene may be weakly clastogenic in humans, there are 11 robust negative studies also. Together with a lack of evidence of a dose-response relationship and the negative response for induction of micronuclei when studied concurrently in two of the positive chromosome aberration studies, no clear conclusion on in vivo clastogenicity of styrene in humans can be made. Furthermore, at much higher exposures such effects were not observed in experimental animals.

In conclusion, no classification for carcinogenicity or mutagenicity was proposed by the experts of the EU Competent Authorities. This non-classification has not been challenged by the Risk Assessment Committee of ECHA (European Chemicals Agency) in 2012 when evaluating styrene.However, the discussion is still ongoing in the EU where EFSA Panel on Food Contact Materials, Enzymes, Flavourings and Processing Aids, working group on genotoxicity, in March 2012 agreed “that additional in vivo investigations by oral route should be performed to clarify styrene genotoxicity by oral route”. This request for additional studies prompted a physiological toxicokinetic modelling

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of blood burdens of styrene oxide after oral exposure to styrene (Filser, 2016). Based on cytogenetic studies with styrene in rats, it was concluded that no genotoxic effect by styrene oxide is to be expected in humans up to a daily amount of 100 mg styrene/kg bw/d, i.e. 100 times higher than the potential exposure to the Overall Migration Limit in the EU. Therefore, no potential genotoxic concern was predicted for styrene uptake from food contact polystyrene.

6.2.3 Discussion on the cancer risk

Discussions are ongoing concerning the potential genotoxicity and carcinogenicity of styrene in humans, which is also reflected by contradictory governmental evaluations as indicated above. For example, the evidence for styrene-induced carcinogenesis in experimental animals is limited to an increase in the incidences of mostly benign tumors observed in certain strains of only one species (mice) and at one tissue site (lung). The mode of action data shows the lung tumours in the mouse occur as a result of cytotoxicity and subsequent cell proliferation and is highly species-specific due to a cytochrome CYP2F2-related metabolism of styrene in the mouse, which is not of relevance for humans. In addition, the human lung morphology differs markedly from the mouse lung, which make humans much less sensitive than mice to toxicity due to reactive metabolites (Cruzan, 2009). Cruzan et al., (2012) demonstrated that the mouse lung toxicity of styrene and/or styrene oxide is critically dependent on metabolism by CYP2F2 in a 5 day comparison study with C57BL/6 (WT) and CYP2F2 (-/-) knockout mice. Moreover, Cruzan et al. (2012) concluded that the human isoform of CYP2F, CYP2F1, is expressed at much lower levels and likely does not catalyze significant styrene metabolism, supporting the hypothesis that styrene-induced mouse lung tumors may not quantitatively, or possibly qualitatively, predict lung tumor potential in humans. As such, based on the mode of action, tumor formation in mice is not applicable to humans and does not support the classification of styrene as a human carcinogen. Effects as observed in the epidemiological studies with styrene workers should be considered in relation to styrene metabolism to styrene-7,8-oxide taken into account saturation of styrene-7,8-oxide detoxification routes at high exposure levels. In addition, the overall genetic toxicity data on styrene is somewhat ambiguous and inconsistent but cannot be interpreted as suggesting styrene is a genotoxic carcinogen.

6.3 Reproduction and developmental toxicity

In Europe, while there are no current proposals to classify styrene as being carcinogenic or mutagenic, the Danish Authorities previously proposed that styrene should be classified as Reproductive Toxicant Cat. 2 under the old Dangerous Substances Directive (DSD) classification system. Denmark subsequently resubmitted this proposal for classification as category 1B under the Classification, Labelling and Packaging (CLP) regulation for reproductive toxicity. This proposal was reviewed by the ECHA Risk Assessment Committee and rejected. The Risk Assessment Committee (RAC) gave the opinion that styrene should be classified as category 2 for reproductive toxicity accompanied by the hazard statement H361d, “suspected of damaging the unborn child”. The proposed Classification has entered into regulatory force for classification and labelling in the EU. It is, in the main, based on several observations reported in a well-conducted OECD- and GLP-compliant two-generation study including developmental neurotoxicity assessment in F2 offspring (Cruzan et al., 2005a, b). The specific reasons for classification cited by Denmark include developmental delays both before and after weaning (decreased body weights, delays in attaining some pre-weaning developmental landmarks). Also for this endpoint, the discussions are ongoing as the few parameters that showed a statistical difference between the styrene exposed animals and control animals, these changes were not confirmed by other, inter-correlated measurements.

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In addition, the differences might be indicated as of limited biological relevance, as the study authors concluded that the slight developmental delays in some measured parameters were secondary to reduced body weights with no indication that styrene was causing direct adverse effects on reproduction and the developing foetus. This conclusion has been supported in two major evaluations of the toxicological effects of styrene, i.e. Draft EU Risk Assessment Report on Styrene (EU, 2008) and the Report on the Reproductive Toxicity of Styrene prepared by the US National Toxicology Program Centre for Evaluation of Risks to Human Reproduction (NTP-CERHR, 2006) (U.S. Department of Health and Human Services). A more complete overview on toxicology is given in the IARC monograph 82, Styrene (IARC, 2002).

In addition, studies in exposed workers do not show any significant risk of reproductive toxicity or birth defects from styrene exposure while no effects on fertility were observed in the rat in a-three-generation fertility study with dosing via the drinking water. In conclusion, while debates on classification and labelling of styrene still continue in some countries, the large toxicological database for styrene provides an adequate basis for assurance of the safety of polystyrene, given the low exposures of styrene monomer that the public are exposed to, as a consequence of consumer exposure by the use of styrene-based polymers in food contact plastics.

6.4 Possible estrogenicity of styrene oligomers

Recent research results suggest that some chemical substances can act similarly to the female sex hormone, oestrogen, which are sometimes referred to as xenoestrogens. When particularly male subjects take such chemicals into the human body, there is the possibility of adverse health effects. For example, it has been postulated that xenoestrogen chemicals may be responsible for the well-publicised reductions in sperm counts, which have been claimed to occur in some male populations in a number of countries.

During the manufacture of polymers, it is possible that not all of the monomer will be converted into long-chain/high molecular weight polymer. With a small proportion of the monomer, reaction may stop after only a few molecules have become linked together, resulting in very low molecular weight polymer units, known as oligomers. Where only two monomer units are linked together, the oligomer is called a dimer. A three-monomer oligomer is called a trimer. Concentrations of such dimers and trimers in PS packaging materials and food items in Japan and the US are given above.

As an oligostyrene-like chemical has been reported to have oestrogen-like activity, the Styrene Steering Committee of the European Chemical Industry Council (CEFIC) sponsored a series of comprehensive and closely controlled animal studies to evaluate oligomer migrates from 23 representative polystyrenes (9 general purpose polystyrenes, 8 high impact polystyrenes, and 6 foamed polystyrenes) for any oestrogenicity in the utero trophic assay. An independent organisation was appointed responsible for management, protocol development, monitoring, auditing and review of results, and interpretation of the study. Two concentrations of migrates of each of the 23 polystyrene samples were selected for testing to simulate human consumption of foods dosed with high and low levels. The report on the studies concluded that both low and high doses of the 23 polystyrene oligomer migrates tested did not induce an oestrogenic response (Christian et al., 1998; Bachmann et al., 1998). The oligomer migrates for the studies were prepared using an aggressive food simulant (50% aqueous ethanol) with exaggerated exposure conditions. The highest levels of both dimers and trimers were from HIPS samples, but these were very low with a maximum dimer level of 0.65 mg/l (ppm) and a maximum trimer level of 1.55 mg/l (ppm) (Klärner et al., 1998).

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Since 1998, experiments focused on human exposure to styrene dimer and trimer that were eluted especially from polystyrene containers. In addition, chemically synthesized styrene dimers, trimers, and extracts from polystyrene have been studied in a variety of in vitro and in vivo screening tests for estrogenic or anti-androgenic activity. Notwithstanding of some positive results in studies with deficits in conduct or reporting, the vast majority did not indicate to estrogenic or other endocrine effects:

• No effect on dams and offspring was noted in a comprehensive oral administration test conducted from day 6 of gestation to day 21 of delivery in rats using a mixture of dimers and trimers extracted from polystyrene (Nagao, 2000). No increase in serum prolactin level was observed in the rats given the synthesized styrene dimers and trimers (Date et al., 2002). On the other hand, Ohyama et al. (2007) reported indications for estrogenicity in male offspring, but this study does not allow a firm conclusion due to methodological deficiencies like very low number of animals, inappropriate statistical evaluation, missing dose response relationships.

• Binding assays for estrogen receptor, androgen receptor and thyroid hormone receptor, estrogen reported gene assays, estrogenic assay on human breast cancer cell MCF-7 and the experiment on biosynthesis of testosterone using testicular cells were negative (Date et al., 2002; Ohno et al., 2003 and further references given in these publications). However, the growth of human breast cancer cells was noted in an in-vitro MCF-7 cell growth test and the binding to human estrogen alpha receptor was reported using synthesized styrene dimers and trimers at 1-10 μM, but the estrogenic activity observed in these tests was 1/68,000 or less of that of E2, and extremely weak (Ohyama et al., 2001). However there are discussions concerning also negative studies in these systems with dimers/trimers, and for the positive studies reasons are given, why they might be false positive, especially using concentrations exceeding solubility (Ohno et al., 2003). According to the OECD guidelines (TG 455, 458 and 498) test concentrations should not exceed the solubility limit.

• Various in vitro screening tests (e.g. Date et al., 2002; Ohno et al., 2003) to assess endocrine disrupting activity of styrene dimers and trimers have already been conducted. In addition, for highly pure synthesized, dimers and trimers most of research to detect estrogenic activity was negative. Although there are some reports showing endocrine activity, the activity was weak. Furthermore, neither estrogenic activity (uterotrophic assay) nor anti-androgenic activity (Hershberger assay) was noted in an in vivo experiment using rats (Date et al., 2002). Thus, no specific actions are judged necessary for the time being, since no convincing evidence indicating the endocrine disrupting activity of styrene dimers and trimers has been found from the test results obtained so far.

Based on extensive investigations, Japanese health authorities have removed styrene oligomers from the SPEED list (list of possible endocrine substances) in November 2000.

Since the Japanese Ministry of Economy, Trade and Industry (METI) report (2003) and EU Risk Assessment Report (EU, 2008), few studies have been published on the issue. Satoh (2007) and Ohyama et al. (2007) reported predominantly positive results at high in vitro concentrations for some trimers. Again the solubility limits were exceeded. Mertl et al. (2014) observed estrogenicity in reporter gene assays for 1,3-diphenyl propane again at a very high concentration. A weight of evidence assessment would lead to the conclusion that styrene dimers and trimers cannot be regarded as endocrine disruptors. However, the overall results are inconclusive for effects on endocrine system taking account of the positive in-vitro positive results only at very high concentrations.

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In summary, the vast majority of screening tests did not indicate to estrogenic or other endocrine effects of chemically synthesized dimers and trimers or extracts directly prepared from polystyrene. However, there are some positive results reported in studies, most of which were difficult to assess due to some important deficits. In consideration of such conflicting results, major emphasis should be placed on the in vivo study of Nagao et al. (2000- showing no endocrine activity of dimers and trimers extracted from polystyrene.

6.5 1,3-butadiene monomer

There is sufficient evidence of carcinogenicity of 1,3-butadiene in experimental animals and humans resulting in an IARC classification of carcinogenic to humans (Group 1) (IARC, 2008).

Based on the carcinogenic classification of 1,3-butadiene, the European Scientific Committee on Food (now EFSA) has placed it in List 4A Substances for which an ADI or TDI could not be established, but could be used if the substance migrating into foods or in food simulants is not detectable by an agreed sensitive method. This has resulted in a specific migration limit (SML) of Non Detectable (ND) in European Commission Regulation (EC) No 10/2011, and in addition a QM limit of 1 mg/kg (see section on Food Contact Regulations).

6.6 Polystyrene plastics – safety in use

Polystyrene plastics which are intended for contact use with food and beverages in European Member States are manufactured with positive listed components and by processes, according to GMP and adequate quality management, which ensure that there is full compliance with the safety requirements in the relevant European Regulations and any other additional relevant national laws which are specific to individual Member States (see section on Food Contact Regulations).

To provide the necessary confirmation that individual types of polystyrene plastics comply with the legislative specifications and relevant restrictions which apply for the intended conditions of use, manufacturers and/or users of the plastics carry out prior use tests on representative samples. In most cases, any necessary migration testing is carried out with food simulants rather than food. The rules for such testing and the labelling requirements are given in Article 18 of Regulation (EC) No 10/2011 referring to the Annex III and V of this regulation.

When considered necessary, national government departments with responsibilities for food safety and national regulatory authorities may carry out tests and surveys on food, which have been packaged in, or which have come into contact with plastics, to establish that the safety of the foodstuffs is being maintained. UK MAFF (now called FSA) survey findings from 1992 and 1994 on styrene levels in packaging and migrations into packaged foods (see section on Polystyrene and Food Packaging Applications) revealed that the levels of styrene monomer in foodstuffs which had come into contact with various polystyrene plastics were similar to those reported in the 1983 survey. In the 1994 survey, 248 samples of foods were examined and, with the exception of two samples commonly referred to as “low-fat” table spread and 18 samples of milk and cream products sold as individual portions, the levels of styrene ranged from not detectable to 60 ppb (μg/kg). The limit of detection varied with the type of foodstuff but in most cases was 1 μg/kg. The comment was made that although levels of styrene in individual milk and cream portions were above those found in other foods, such portions are considered to make a very minor contribution to the daily diet and hence to styrene intake. It was further commented that the higher level of styrene found in two samples of “low-fat” table spread product was confined to a single batch and was not consistent with low levels found in other “low-fat” table spreads.

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This survey report did, however, point out that styrene is known to occur naturally in some foods. For example, it can be formed from cinnamon in the presence of certain yeasts (MAFF, 1995).

Styrene occurs naturally in some animal- and plant-based foodstuffs and it is a metabolite generated by microorganisms during production of foods such as wine, beer, grains, and cheese known to occur naturally in some foods. For example, it can be formed from cinnamon or strawberry jam in the presence of certain yeasts (Nieminen et al. 2008; Lafeuille et al., 2009),

Recent studies showed that styrene could be found in kiwifruit juice (Figoli et al., 2010), in olives and olive oil (Gilbert-López et al., 2010), in raspberry and blackberry cultivars (Isık et al., 2011). Phan et al. (2012) also demonstrated that styrene occurs during food decaying processes.

Lastly, Stadler (2009) established that the formation of styrene during the Maillard reaction is negligible.

Naturally occurring styrene levels measured in foods assumed not to be contaminated by plastic materials are summarized in the Table 2 (reviewed in CERHR report on styrene, 2005). With the exception of cinnamon, styrene levels in most foods were below 10 ppb.

Table 2: Naturally occurring styrene level according to CERHR report, 2005

Fooda Styrene Level in µg/kg (ppb)

Black currants 2 - 6

Wheat 0.4 - 2

Apples, cauliflower, onions, tomatoes < 1

Cinnamon 170 - 39,000b

Peanuts 1 - 2.2

Coffee beans 1.6 - 6.4

Strawberries 0.37 - 3.1

Beef 5.3 - 6.4

Oats < 0.65 - 1.6

Peaches < 0.18 - 0.3

Tomatoes, peaches, raw milk, chicken, pecans < 2

a Contact with packaging materials was avoided for these foods. Values were obtained from 2 or 3 samples of each

food, measured in duplicate.b Reported figures were rounded in the secondary source. The individual rounded values were 170, 180, 2300,

2700, 37,000, and 39,000 ppb in the paired samples.

In 1999, MAFF (now called FSA) published the results from a survey, which examined five sets of UK Total Diet Study samples for the presence of styrene monomer (MAFF, 1999). The levels found were quite low, with the highest being only 14 μg/kg. The 14 μg/kg value was found in a sample from the oils and fats group and again confirms previous findings demonstrating that styrene migrates most readily into fatty foods. Dietary exposure to styrene was estimated at 0.03 to 0.05 μg/kg body weight per day. In the evaluation of the US ATSDR (2010), general population exposure via food is estimated to be 0.2 to 1.2 µg/person/day (equivalent to 0.0029 to 0.017 µg/kg body weight

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per day for a 70 kg adult). These estimates of styrene exposure via packaged food compare well with those of other authors: Tang et al. (2000) assessed human exposure to styrene for the general German population under the assumption that milk, milk products, fat and oil were all packed in PS materials. The daily intake was estimated to reach 0.03–0.17 µg/kg bw/d. A probabilistic approach was used by Holmes (2005) to calculate a median exposure for adults of 0.039 µg/kg bw/d. Vitrac and Leblanc (2007) also used a probabilistic method to estimate S exposure via consumption of yogurt, a food item often packed in PS. They assumed an average S concentration for the food containers of 500 mg/kg and calculated for the daily uptake a 50th percentile of 0.17 µg/kg bw/d.

These dietary exposure levels are much lower than the exposure limits proposed by different regulatory or scientific groups.

The acute-duration oral Minimal Risk Level (MRL) of 100 µg/kg body weight/day as elaborated by the ATSDR (2010). Health Canada (1993) and RIVM (2001) derived a TDI of 120 µg/kg bw/d based on the NOAEL in the study of Beliles et al. (1985) (125 ppm/12 mg/kg bw/d for females) using an AF of 100. The US EPA (1990) derived an oral Reference Dose (RfD) of 200 µg/kg bw/d based on effects observed on haematology and liver in the dog at exposure concentrations higher than 200 mg/kg bw/d (oral intubation) in a 19 months study (Quast et al., 1979). An AF of 1000 was applied. A much lower Tolerable Daily Intake (TDI) again based on Beliles et al. (1995) was set by World Health Organization (WHO, 2003): TDI = 7.7 μg/kg bw/d, based on a NOAEL of 7.7 mg/kg bw/d for decreased body weight observed in a 2-year drinking-water study in rats, and using an uncertainty factor of 1000 (100 for interspecies and intraspecies variation and 10 for the carcinogenicity and genotoxicity of the reactive intermediate styrene-7,8-oxide). However, the derivation of WHO has to be challenged for two mainly methodological reasons: i) The NOAEL was based on decreased body weight of high dose female rats, but the low dose of male rats was used (7.7 mg/kg/d) as starting point. The NOAEL for female rats was higher, 12 mg/kg/d. ii) The use of a factor of 10 to take into account a possible carcinogenic effect of styrene oxide is not any more justified in the light of the more recent mechanistic studies of Cruzan et al. (2009, 2012) and the toxicokinetic modelling of Filser and Gelbke (2016). If these points were taken into consideration, the appropriate starting point would be 12 mg/kg/d and the assessment factor should be 100, leading to a TDI of 120 µg/kg/d being in a similar range to the other above-mentioned limits.

In the EU no Specific Migration Limit (SML) has been established for styrene and therefore the Overall Migration Limit of 60 µg/kg food applies. Gelbke (2014) derived a somewhat higher health-based exposure limit for consumers of 90µg styrene/kg food. This assessment was based on the most relevant toxicological endpoints for styrene, namely ototoxicity and developmental toxicity in rats as well as ototoxicity and colour vision impairment in humans. The assessment factors proposed by EFSA for food contaminants and by ECHA for Derived No-Effect Level (DNEL) derivation for the general population were used.

7. ENVIRONMENTAL ASPECTS

7.1 EC Directives on packaging and packaging waste

The EU Packaging and Packaging Waste Directive 94/62/EC and its amendments in 2004, 2005 and 2009 places legislative obligations on all Member States to reduce packaging waste and specifies targets for recovery and recycling.

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7.2 Recyclability and reuse

The European Commission has recognised the increasing recycling of packaging materials, including plastics. To ensure that the same high safety standards are applied to recycled plastic as to new / virgin plastic, when used in contact with food, the Commission has implemented Regulation (EC) No 282/2008. This Regulation sets specific criteria on the applied recycling process, especial the sorting and cleaning technology ensuring very pure recycled materials, meeting virgin quality. The most essential requirement is that EFSA has implemented an application process for the recycling technology being applied. Such recycling technology can be different for certain plastics. This new Regulation finds its way slowly for more and more recycling processes, although the main focus is currently on PET beverage bottles. Currently, although polystyrene can be reprocessed up to 20 times without a major loss of its mechanical and thermal properties, there is no recycling technology approved by EFSA for PS.

For much of the food packaging made from polystyrene plastics which ends up as consumer waste, it is not practical to attempt to either re-use or recycle the materials. Even if waste polystyrene plastics food packaging could be separated from other plastics by the consumer, a viable recovery system is unlikely to be achieved, with the various types of polystyrene plastics in use (e.g. crystal polystyrene, foamed polystyrene and HIPS, and the small individual quantities per household).

To assist in the identification of waste polystyrene plastics for recycling, the following symbol is used. This is often found printed or embossed on the base of the polystyrene containers and trays.

In the mid-1990s, research was carried out by a group of European laboratories in a European Commission-sponsored project to investigate the safety implications of plastic food packaging made from recycled waste plastic food packaging (European Commission, 1997). A particular part of the project looked at polystyrene food packaging plastics made from recycled vending cups and the possibility of safety being influenced if any of the vending cups contained toxic contaminants.

7.3 Incineration through energy recovery

Incineration through energy recovery is one of the processes used to dispose of consumer waste. More and more adequate incineration, with energy recovery will replace landfill. As polystyrene plastics burn easily when ignited, modern incineration units with efficient combustion provide an effective process with energy recovery for the disposal of waste polystyrene plastics packaging materials. The used additives do not pose a concern as they consist mainly of carbon and hydrogen.

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8. GENERAL CONCLUSIONS

T he family of polystyrene plastics is one of the major plastics types used for packaging of a wide range of food as well as beverage containers. Polystyrene plastics are particularly suitable for formation into food trays, pots and containers by thermoforming or injection

moulding processes, and they offer an attractive overall cost/performance balance. The properties of the basic polystyrene polymer have been modified and enhanced for particular applications, such as the incorporation of butadiene rubbers to produce HIPS and the use of blowing agents to form foamed polystyrene plastics.

Polystyrene plastics are easy to recycle. Closed loop re-cycling systems are in operation, which provide re-cycled polymers of good quality suitable for a wide range of non-food contact applications. However, these recycle systems are not yet approved under Regulation (EC) No 282/2008.

Polystyrene plastics have been used for more than 50 years as food packaging materials and the safe continued use is fully supported by today’s scientific knowledge on the polymer, the monomers and any possible exposure to low molecular weight residuals.

Current commercial polystyrene products, intended for food packaging applications, are fully compliant with EU Regulations, US FDA CFR’s and national legislation in many countries.

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GLOSSARY

ABS Acrylonitrile-butadiene styrene

ATSDR US Agency for Toxic Substances and Disease Registry

CEDI Cumulative Estimated Daily Intake

CEFIC European Chemical Industry Council

CERHR Centre for Evaluation of Risk to Human Reproduction

CFR US Code of Federal regulations

CLP Classification, Labelling and Packaging

COT Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment

DNEL Derived No-Effect Level

DSD Dangerous Substances Directive

EB Ethyl Benzene

EBHP Ethylbenzene Hydroperoxide

EBMS Ethylbenzene Styrene Monomer

ECHA European Chemicals Agency

EFSA European Food Safety Authority

EPS Expandable Polystyrene

EVOH Ethylene Vinyl Alcohol

FAP Food Additive Petition

FCNs Food Contact Notifications

FCS Food Contact Substances

FDA Food and Drug Administration

FFS Form-Fill-Seal

FSA Food Standard Agency

GLP Good Laboratory Practices

GPPS General Purpose Polystyrene

HIPS High Impact Polystyrenes

IARC International Agency for Research on Cancer

MAFF Ministry of Agriculture, Fisheries and Food (UK)

MCF-7 Breast cancer cell line, acronym of Michigan Cancer Foundation-7

METI Ministry of Economy, Trade and Industry (JP)

MFR Melt Flow Rate

ND Non Detectable

NOAEL No Observed Adverse Effect Level

NTP US National Toxicology Program

OECD Organisation for Economic Co-operation and Development

OML Overall Migration Limit

PCBs Polychlorinated Biphenyls

PET Polyethylene Terephthalate

PETG Polyethylene Terephthalate Glycol

POSM Propylene Oxide Styrene Monomer

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PP Polypropylene

PS Polystyrene

PVC Polyvinyl Chloride

RAC Risk Assessment Committee

RAR Risk Assessment Report

RIVM National Institute for Public Health and the Environment (NL)

SAN Styrene-acrylonitrile

SCF EC Scientific Committee for Food

SML Specific Migration Limit

SO Styrene-oxide

TDI Tolerable Daily Intake

Tg Glass Transition Temperature

VOC Volatile Organic Compounds

WHO Word Health Organisation

XPS Foamed Polystyrene

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Possible websites with additional information:

FDA: http://www.fda.gov (Ref. FDA correspondence dated March 22 2011).

FDA: http://www.fda.gov/Food/IngredientsPackagingLabeling/PackagingFCS/default.htm

FDA: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfCFR/CFRSearch.cfm?CFRPart=177 (Polymers)

FDA: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm?cfrpart=178 (Polymer additives)

FDA: http://www.fda.gov/Food/FoodIngredientsPackaging/ucm112642.htm (Inventories of cleared substances)

FDA: http://www.access.gpo.gov/nara/cfr/waisidx_01/21cfr.177_01.html

EU: http://ec.europa.eu/food/food/chemicalsafety/foodcontact/legisl_list_en.htm

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• Addition of Nutrients to Food: Nutritional and Safety Considerations (1999)

• An Evaluation of the Budget Method for Screening Food Additive Intake (1997)

• Animal-Borne Viruses of Relevance to the Food Industry(2009)

• Antioxidants: Scientific Basis, Regulatory Aspects and Industry Perspectives (1997)

• Applicability of the ADI to Infants and Children (1997)• Application of the Margin of Exposure Approach to

Compounds in Food which are both Genotoxic and Carcinogenic (2009)

• Approach to the Control of Entero-haemorrhagic Escherichia coli (EHEC) (2001)

• A Scientific Basis for Regulations on Pathogenic Microorganisms in Foods (1993)

• Assessing and Controlling Industrial Impacts on the Aquatic Environment (2001)

• Assessing Health Risks from Environmental Exposure to Chemicals: The Example of Drinking Water (2002)

• Beta-Carotene, Vitamin E, Vitamin C and Quercetin in the Prevention of Degenerative Disease: The Role of Foods (1994)

• Beyond PASSCLAIM – Guidance to Substantiate Health Claims on Foods (2010)

• Campylobacters as Zoonotic Pathogens: A Food Production Perspective (2007)

• Considering Water Quality for Use in the Food Industry (2008)

• Consumer Understanding of Health Claims (2007)• Detection Methods for Novel Foods Derived from

Genetically Modified Organisms (1999)• Emerging Technologies for Efficacy Demonstration (2009)• Evaluation of Agronomic Practices for Mitigation of Natural

Toxins (2010)• Evaluation of the Risks Posed in Europe by Unintended

Mixing of Food Crops and Food Crops Developed for Non-Food Uses (2011)

• Exposure from Food Contact Materials (2002)• Foodborne Protozoan Parasites (2003)• Foodborne Viruses: An Emerging Problem (2002)• Food Consumption and Packaging Usage Factors (1997)• Food Safety Management Tools (1998)• Food Safety Objectives – Role in Microbiological Food

Safety Management (2004)• Frontiers in Food Allergen Risk Assessment (2011)• Functional Foods in Europe – International Developments

in Science and Health Claims (2008)• Functional Foods – Scientific and Global Perspectives

(2002)• Guidance on Best Practices on the Risk Assessment of Non

Intentionally Added Substances (NIAS) in Food Contact Materials and Articles (2015)

• Guidance for Exposure Assessment of Substances Migrating from Food Packaging materials (2007)

• Guidance for the Safety Assessment of Botanicals and Botanical Preparations for Use in Food and Food Supplements (2003)

• Impact of Microbial Distributions on Food Safety (2010)• Markers of Oxidative Damage and Antioxidant Protection:

Current status and relevance to disease (2000)• 3-MCPD Esters in Food Products (2009)• MCPD and Glycidyl Esters in Food Products (2012)• Micronutrient Landscape of Europe: Comparison of Intakes

and Methodologies with Particular Regard to Higher Consumption (2009)

• Mycobacterium avium subsp. paratuberculosis (MAP) and the Food Chain (2004)

• Nutrition in Children and Adolescents in Europe: What is the Scientific Basis? (2004)

• Overview of the Health Issues Related to Alcohol Consumption (1999)

• Overweight and Obesity in European Children and Adolescents: Causes and consequences – prevention and treatment (2000)

• Packaging Materials: 1. Polyethylene Terephthalate (PET) for Food Packaging Applications (2000)

• Packaging Materials: 1. Polyethylene Terephthalate (PET) for Food Packaging Applications- Updated version (2017)

• Packaging Materials: 2. Polystyrene for Food Packaging Applications (2002)

• Packaging Materials: 3. Polypropylene as a Packaging Material for Foods and Beverages (2002)

• Packaging Materials: 4. Polyethylene for Food Packaging Applications (2003)

• Packaging Materials: 5. Polyvinyl Chloride (PVC) for Food Packaging Applications (2003)

• Packaging Materials: 6. Paper and Board for Food Packaging Applications (2004)

• Packaging Materials: 7. Metal Packaging for Foodstuffs (2007)

• Packaging Materials: 8. Printing Inks for Food Packaging Composition and Properties of Printing Inks (2011)

• Packaging Materials: 9. Multilayer Packaging for Food and Beverages (2011)

• Persistence and Survival of Pathogens in Dry Foods and Dry Food Processing Environments (2011)

• Practical Guidance for the Safety Assessment of Nanomaterials in Food (2012)

• Recontamination as a Source of Pathogens in Processed Foods – A Literature Review (2005)

• Recycling of Plastics for Food Contact Use (1998)• Risk Assessment Approaches to Setting Thermal Processes

in Food Manufacture (2012)• Safety Assessment of Viable Genetically Modified

Microorganisms Used in Food (1999)• Safety Considerations of DNA in Food (2001)• Safety Implications of the Presence of Nucleic Acids of

Inactivated Microorganisms in Foods (2013)• Significance of Excursions of Intake above the Acceptable

Daily Intake (ADI) (1999)• The Enterobacteriaceae and Their Significance to the Food

Industry (2011)• The Safety Assessment of Novel Foods (1995)• The Safety Assessment of Novel Foods and Concepts to

Determine their Safety in use (2003)• Threshold of Toxicological Concern for Chemical

Substances Present in the Diet (2001)• Tools for Microbiological Risk Assessment (2012)• Transmissible Spongiform Encephalopathy as a Zoonotic

Disease (2003)• Using Microbiological Risk Assessment (MRA) in Food

Safety Management (2007)• Validation and Verification of HACCP (1999)• Water Use of Oil Crops: Current Water Use and Future

Outlooks (2011)

ILSI Europe Reports Series

36> contents

ILSI Europe Reports can be downloaded from:http://ilsi.eu/publications/report-series/

ILSI Europe publishes also Concise Monographs in its Concise Monograph Series. They can be downloaded from: http://ilsi.eu/publications/concise-monograph-series/

Predominantly, ILSI Europe publishes articles and proceedings in peer-reviewed journals. Most of them can be downloaded from:http://ilsi.eu/publications/peer-reviewed-publications/

Keep up-to-date with all the latest activities from ILSI Europe by checking out our website at www.ilsi.eu, connecting with us on LinkedIn and following us on Twitter.

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ISBN 9789078637448