IDENTIFICATION OF MICROPLASTICS PRESENT IN POLYTHENE-SACHET WATER SIMPLY EXPOSED TO SUNLIGHT

ABSTRACT

Polythene and PVC are polymers used in production of packaging materials which are frequently used for food and water. Antioxidants, stabilizers, plasticizers, lubricants, antimicrobials, anti- static and anti-blocking agents, “slips,” or heat resistance agents are usually incorporated during the production of these packaging materials to improve functionality. A wide variety of synthetic and naturally occurring polymers absorb solar ultraviolet radiation and undergo photolytic, photooxidative, and thermooxidative reactions that result in the degradation of the material. Hence there is a high tendency that when packaging materials are heated by conventional means or exposed to sunlight, they may become brittle, or undergo both undesirable physical  and chemical changes. These undesirable chemicals may leach into the water content. Once these compounds  surpassed a  specified  limit,  quality and  safety of the packaged  content  may be compromised, thereby endangering the unsuspecting consumers. This work therefore evaluates the water quality/safety of consumption of polyethylene sachet-packaged water stored under varying environmental conditions such as direct sunlight, heat or indirect sunlight. GC-MS analyses of the packaged water were performed to ascertain the nature of compounds leached from the packaging material. Several organic compounds ranging from low molecular substituted hydrocarbons to polycyclic aromatic hydrocarbons (PAHs) were detected and a few of them include Trichloromethane (Chloroform), Naphthalene, Benzene, Xylene, Toluene, 2-Hexanone. These “micoplastics” that leached from polyethylene sachet package, of which many are possible human carcinogens, are listed on the Priority List of Hazardous Substances by Agency for Toxic Substances and Disease Registry (ATSDR).

CHAPTER ONE

LITERATURE REVIEW

1.0    INTRODUTION

Polythene products are identified as low (very low, linear low, medium, linear medium) and high density resins. They are used in the production of boil-in food packages, heat-sealed films, heat- sealed pouches, production of grocery bags, squeezable bottles, cable insulators and production of  flexible  food  packaging,  shrink-wrap,  stretch  film  and  overwrap  film  (NOVA,  2012). Polythene and polyvinylchloride (PVC) are the most frequently used polymer in packaging, an important prerequisite for food packaging materials (Thorbjörn  and  Bengt, 2002). Chemical additives are usually incorporated in polythene to improve functionality and these additives serve as antioxidants, stabilizers, plasticizers, lubricants, antimicrobials, anti-static and anti-blocking agents, “slips,” or heat resistance agents (Kanishka et al., 2013). However, polythene used for packaging are most times exposed to heat, either through conventional heating or solar radiation. Heat causes a degradation in polythene which occurs rapidly at higher temperatures (Lin et al.,2000). These degraded components termed microplastics could be in macro-, micro- and nanoscales (Carsten et al., 2005). A wide variety of synthetic and naturally occurring polymers absorb solar ultraviolet radiation and undergo photolytic, photooxidative, and thermooxidative reactions (Scott, 2000). Photooxidative degradation results in breaking of the polymer chains, radical  formation  and  reduction  of  molecular  weight,  leading  to  leaching  of  the  material (Gardella, 1988; Bottino et al., 2003; Emad and Raghad, 2013). Hence, additives that are incorporated within polythene packaging materials to improve functionality may interact or leach into water. This could have health and environmental implications and so effort is focused on hazardous compounds of polythene that leach into drinking water. Hawkers carry these packaged polythene-sachet water around for business, some marketers abandon the packaged water under sunlight due to lack of space for storage. Since sunlight radiation may cause the leaching of microplastic compounds, investigations were conducted to determine the quality of polyethylene- sachet water exposed to different durations of ultraviolet radiation to determine the microplastic components in the water and ascertain the nature of microplastics we are consuming.

1.1    POLYTHENE

Polythene (PE) is a clear-to-white, solid, plastic product made by reacting molecules of ethylene gas into long polymer chains in carefully controlled manufacturing processes. It is not known to occur naturally but the most common plastic. Polythene resins are used in many product end-use markets,  the  largest  of  which  is  packaging  (NOVA,  2012).  It  is  converted  into  packaging materials by thermal processes such as film blowing, sheet extrusion, or extrusion coating on substrates such as paper board. Many kinds of polyethylene are known. Usually, a mixture of similar polymers of ethylene with various values of n. Polyethylene absorbs no water. The gas and water vapour permeability (only polar gases) is lower in most plastics; oxygen, carbon dioxide and flavourings on the other hand can pass it easily (Michael et al., 2013).

An important prerequisite for food packaging materials is that they should not emit substances that interfere with the product, i.e., cause smell and taste but because of the high temperatures used in polymer processing degradation occurs (Wiik and Helle, 2000). PE can become brittle when exposed to sunlight, carbon black is usually used as a UV stabilizer.  Typical examples are low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and polypropylene (PP) (Kanishka et al., 2013).

1.1.1   Low Density Polyethylene (LDPE)

The branched-chain structure of LDPEs prevents close packing of monomeric units within the polymer chain, resulting in a relatively low molecular weight (density often ranges from 910 to 940 kg/m3) and low degree of crystallinity (55% to 70%) (Long-chain entanglement prevents

crystallization upon cooling) (Kanishka et al., 2013). Low-density polyethylene (LDPE) resins are used in the production of grocery bags, squeezable bottles, and cable insulation. LLDPE and VLDPE are other forms of LDPE. The polymer structure of LLDPE has no long-chain branches; the molecules are linearly oriented, resulting in a stiffer and more crystalline structure. Very low- density polyethylene (VLDPE) resins are used in the production of boil-in food packages and heat sealed films and pouches (NOVA, 2012).

1.1.2    High Density Polythene (HDPE) and Polypropene

Polypropene is a saturated linear polymeric structure with a lower density (900 kg/m3) and higher softening points (140 to 150 °C) compared to the other PEs. HDPE has a relatively high density (941 to 965 kg/m3) and higher degree of crystallinity (up to 90%) due to its nonpolar, linear, and relatively simple structure. The higher softening point of PP and HDPE allows it to withstand high temperatures, such as exposure during steam-sterilization (Kanishka et al., 2013). Unlike LDPE, HDPE has high water vapour and gas barrier properties due to its high crystallinity. Oriented polypropene (OPP), a type of PP, is in demand for food packaging because its bidirectional orientation facilitates diverse applications such as snack food packaging, candy-bar overwraps, beverage bottles, and soup wrappers (Robertson, 2006). For all plastics materials their

characteristics may be changed and improved by use of additives.

Figure 1: Drinking water packaged in polythene-sachet water

1.1.3 MICROPLASTICS

Microplastics are plastics debris made of Polyethylene (PE), Polypropylene (PP), Polyethylene Terephthalate (PET), Polymethyl methacrylate (PMMA) and Nylon. PE and PP are the most common (Carsten et al., 2015). It can also be particles intentionally produced for direct use e.g. in cosmetics and abrasives, or as raw materials for production of larger plastic items (GESAMP,

2015). Arthur et al. (2009) and The Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) (GESAMP, 2015) have defined microplastics as a size range between 333 μm-5 mm and 1 nm-5 mm, respectively. Some of the proposed size limits are based on pragmatic rather than scientific concerns and are determined by the techniques used for field sampling of microplastics. In the literature, a distinction is made between the plastics at macro-,  micro- and  nanoscales.  There is  no,  however, clear definition  of microplastics,  but

definitions for what could be termed “micro-”, “meso-”, “macro”- and “mega-”plastic debris have been proposed and generally accepted according to the US EPA (2011). “Micro-”, “meso-”, and  “macro”-plastic  debris  would  be defined  as  <5  mm,  5–20  mm  and  >20  mm  diameter, respectively, whereas “mega-” plastic debris would be >100 mm (US EPA 2011). The definition used by GESAMP (2015) is the only currently proposed definition that also covers what has been termed “nanoplastics”.

Microplastics have been classified into two main group based on GESAMP (2012; 2015)

1.   Primary microplastics: Microplastic particles intentionally produced for direct use e.g. in cosmetics and abrasives, or as raw materials for production of larger plastic items;

2.   Secondary microplastics: Microplastic particles originating from the fragmentation of larger plastic items by use, waste management or in the environment.

The mechanisms and rates of degradation of microplastics have been described in section 1.5; the overall degradation rates and the formation of microplastics from fragmentation of macroplastics. The breakdown of the macroplastics initiated by solar UV radiation is a very efficient mechanism in plastics exposed to air or lying on a beach surface (Carsten et al., 2015). It should also be noted that the estimated degradation rates vary substantially depending on environmental conditions such as sun exposure, particularly UV levels, temperature, oxygen level, wave energy and the presence of abrasive factors (sand, gravel or rock) (Cheshire et al., 2009).

1.2    ADDITIVES FOR PLASTICS

Plastics materials have become indispensable in our everyday lives. Although they offer many benefits, hazardous chemicals may be present in these materials. These hazardous materials can be introduced either intentionally as additives, or unintentionally as pollutants (Michael et al.,

2013). Plastic materials consist of plastic polymers and additives. In all cases the producer has made a formulary (plastic compound) with different additives to improve the performance and ageing properties as well as the processing properties of the plastic compound for the shaping process (injection moulding, extrusion, blow moulding, vacuum moulding, etc.) (Kanishka et al.,

2013). These additives can be used to tune a plastic material to a definite application, imparting high temperature oxidation resistance, improved flexibility, colour retention, anti-static performance,  or  adding  impact  resistance  (Michael  et  al.,  2013).  Only the reactive organic

additives e.g. some flame retardants are polymerised with the plastic molecules and become part of the polymer chain (Kanishka et al., 2013).

It should be noted that substances used as monomers, intermediates or catalysts in plastic manufacturing are not considered additives. Attention should also be paid to hazardous residues of monomers and degradation products present in end products since most of these compounds are not chemically bound in plastics, but are able to migrate (COWI, 2013). The migration rate of chemical substances depends on their size, boiling point, vapour pressure and their solubility in the plastic as well as in the environment or material surrounding the plastic (Kanishka et al.,

2013). Migration thus depends heavily on the physico-chemical characteristics of the substance. Small molecules, typically monomers and residual solvents, will migrate fast as they have low boiling point. Some monomers such as formaldehyde, vinyl chloride, ethylene and butadiene are all gases and have a high tendency to migrate quickly even at ambient temperatures (COWI,

2013). In all cases migration will decrease with time as the concentration of the migrating substances get lower in the plastic (Kanishka et al., 2013).

In many cases the plastic polymers alone have sufficient properties to “do the job” for a number of applications. Especially for one time use packaging plastic materials, only small amounts of additives are added to reduce oxidation and to improve slip properties. In other applications it is necessary to improve the basic properties of the plastic polymer by using higher amounts of additives (Michael et al., 2013). There are large number of additives which can be used to improve different properties of the plastic. Some are added to prevent degradation of the polymer during processing (typically for PVC), others to improve resistance to fire or to prevent degradation in the environment (UV, temperature, humidity, microorganisms) (Kanishka et al.,

2013). Other polymers are compounded for economic reasons, where a costly base polymer may be extended by addition of lower cost additives such as clays, reground polymer, other polymers, or a blowing agent that reduces density (Michael et al., 2013).

The leaching of these additives is temperature dependent which may or may not affect humans since its concentration in different plastics compounds is regulated by European Food Safety Authority on the basis of their toxicological properties in food/water contact applications, REACH, US EPA and other regulatory bodies. Even though food/water contact plastics have undergone a robust safety assessment for consumer use, consideration should be given to the fact that certain food/water contact materials may give rise to concern because of the use of certain

substances that have been placed on the REACH candidate list because they are considered to have met the definition of Persistent, Bio accumulative and Toxic or Very Persistent and Very Bio accumulative. However if such substances are present below the SVHC declaration of 0.1% w/w they can continue to be used unless otherwise (REACH, 2013).

Additives in plastic can be divided into:

    Functional   additives   (stabilisers,   antistatic   agents,   flame   retardants,   plasticizers, lubricants, slip agents, curing agents, foaming agents, biocides, etc.)

        Colorants (dyes and pigments).

        Fillers (mica, talc, kaolin, clay, calcium carbonate, barium sulphate)

        Reinforcements (e.g. glass fibres, carbon fibres).

1.2.1    Functional Additives

1.2.1.1 Plasticizers

Plasticizers are generally medium to high molecular weight esters of aliphatic or aromatic carboxylic acids, or phosphoric acid. The phosphate esters are used for their flame retardant properties  (Michael  et  al.,  2013).  Adipates  and  phthalates  are  also  very  common,  but  are becoming highly regulated due to concern that they may act as endocrine disruptors. The US EPA controls many Phthalates and Adipates by Methods 606, 506-1 and 8061 (Michael et al.,

2013). Plasticizers are the group of compounds used to improve flexibility, workability, and stretch-ability of polymeric films as a process aid, reducing melt flow (Page and Lacroix, 1995; Cano et al., 2002). Plasticizers also give a Plasticizers reduce shear during mixing steps in polymer production and improve impact resistance in the final plastic film. Selection of plasticizers depends on important parameters, such as compatibility with other components in the plastic matrix, low volatility, and lack of coloration (Crompton, 2007).

Plasticizers of PE include dipentylphthalate (DPP), di-(2-ethylhexyl) adipate (DEHA), di- octyladipate  (DOA),  diethyl  phthalates  (DEP),  diisobutylphthalate,  and  di-n-butyl  phthalate (DBP) (Kanishka et al., 2013). Plasticizers such as phthalate and adipate are commonly used in PVC and PE, and their migration to food/food simulants under different study conditions have been reported (Castle et al., 1990; Lau and Wong 1996; Goulas et al., 2000; Fankhauser-Noti and Grob, 2006; Biedermann et al., 2008; Wei et al., 2009; Guo et al., 2010; Fasano et al., 2012). Plasticizers have a low molecular weight and can migrate from packaging materials into wrapped food (Goulas et al., 1998).

1.2.1.2 Antioxidants

Oxidation during compounding or processing can cause problems such as loss of strength, breakdown and discoloration. Oxidation can also occur in the final product causing discoloration, scratching, loss of strength, flexibility, stiffness and gloss (Michael et al., 2013). Antioxidants are used in most hydrocarbon polymers including polyethylene, polypropylene, polystyrene, and ABS. Antioxidants are added to a variety of polymer resins to slow the onset of oxidative degradation of plastics from exposure to UV light (Arvanitoyannis and Bosnea, 2004; Sablani and Rahman, 2007).

Polymer degrades due to the action of highly reactive free radicals generated by heat, radiation, and  mechanical  shear,  enhanced  by the presence of metallic impurities.  In  food packaging, oxidation increases at high temperatures, including contact with hot foods or exposure to infrared heating,  retort  processing  and  microwave  heating  (Kanishka  et  al.,  2013).  Arylamines  are common antioxidants used in plastic food packaging. Butylated hydroxytoluene (BHT), 2- and 3- t-butyl-4-hydroxyanisole (BHA), tetrakismethylene-(3,5-di-t-butyl-4-hydroxyhydrocinnamate) methane (Irganox 1010), and bisphenolics such as Cyanox 2246 and 425, and bisphenol A are the most  common  phenols  used  as  antioxidants  (Kattas  et  al.,  2000).  The  amount  depends  on chemical  structure  of  additive  and  plastic  polymer.  Phenolic  antioxidants  are  used  in  low amounts, lowest amounts in polyolefins (LLDPE, HDPE), higher in HIPS and ABS Used in PVC.

1.2.1.3 Heat stabilizers

Heat stabilizers are added to plastics to prevent thermal degradation of resins from exposure to elevated  temperatures  during  thermal  processing  of  foods.  PVC,  PVDC,  vinyl  chloride copolymers (for example, vinyl chloride/vinyl acetate), and PVC 528, blends (PVC) require the addition of heat stabilizers to retain functionality (Kanishka et al., 2013). LDPE and polyamides usually do not require the incorporation of heat stabilizers, since these polymers remain stable under severe heat conditions (Crompton, 2007).

There are three major types  of primary heat stabilizers: mixed metal salt blends, organotin compounds, and lead compounds, and three secondary heat stabilizers: alkyl organophosphites, epoxy compounds, and beta diketones (Kattas et al., 2000). Generally, epoxy stabilizers are derived from epoxidized soybean oil (ESBO), linseed oil, and sunflower oil and are used in various food packaging plastics as heat stabilizers, and also as lubricants and plasticizers (Kattas et al., 2000; Arvanitoyannis and Bosnea, 2004; Boussoum et al., 2006). Other heat stabilizers, although more effective, are not suitable for use in food-contact plastics due to their potential toxicity (Kanishka et al., 2013).

1.2.1.4 Slip agents

Slip compounds significantly reduce the coefficient of friction of the surface of a polymer. Besides providing lubrication to the film surface, slip agents also impart lower surface resistivity (antistatic properties), reduced melt viscosity, better mold release, and antisticking properties (Sablani and Rahman, 2007). Common slip compounds are fatty acid amides (primary erucamide and oleamide), fatty acid esters, metallic stearates (for example, zinc stearate), and waxes (Kanishka et al., 2013).

1.2.1.5 Flame retardants

Flame retardants are added to inhibit ignition or flammability of the end-use product. Flame retardants  generally  function  by  inhibiting  the  mechanisms  of  burning.  Typical  chemical elements  found  in  compounds  used  as  flame  retardants  are:  aluminium,  bromine,  chlorine, fluorine and sulphur (Michael et al., 2013). Brominated flame retardants are used in polystyrene, polyesters,  polyolefins,  polyamides,  and  epoxies.  Decabromodiphenyl  oxide  is  the  most frequently used brominated flame retardant (Michael et al., 2013). The bromodiphenyl ethers are the most highly regulated of these compounds. Some of these flame retardants are not added to polymers during processing, but are found are incorporated in the polymer matrix. The largest example of this type is the Aroclors, found in a plastic matrix from having contact with fluid containing the materials (Michael et al., 2013).

Flame  retardants  can  migrate  from  the  plastic  if  they  are  halogen  containing  additives. Phosphoric acid esters do migrate as well. These two groups of flame retardants can be added in amounts up to 50 % Polymer (Kanishka et al., 2013). Inorganic flame retardants contains aluminium   trihydrate,   antimonium   trioxide,   zink   borate   and   other   borate,   barium   and

phosphorous containing inorganic substances. They may not migrate but can as other inorganic additives be liberated by ageing/ abrasion of the plastic polymer (Kanishka et al., 2013). It is possible to make a copolymerisation of the plastic with halogen containing reactive monomers, e.g.   vinyl   bromide,  tetrachlorobisphenol   A  and  tetrachlorophthalic  acid  anhydride.   The copolymer will not migrate, but might be left as residual monomer (Kanishka et al., 2013).

1.2.1.6 Biocides

According to the European legislation, biocide is defined as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism by chemical or biological means. The US Environmental Protection Agency (EPA) uses a slightly different definition for biocides as “a diverse group of poisonous substances including  preservatives,  insecticides,  disinfectants,  and  pesticides  used  for  the  control  of organisms that are harmful to human or animal health or that cause damage to natural or manufactured products”. When compared to the two definitions, these imply the same, although the US EPA definition includes plant protection products and veterinary medicines. Biocides can be added to other materials (typically liquids) to protect them against biological infestation and growth (Kanishka et al., 2013). Soft PVC and foamed polyurethanes are the major consumers of biocides. They are of different chemical structures and include chlorinated nitrogen sulphur heterocyclic compounds and compounds based on tin, mercury, arsenic, copper and antimony, e.g. tributyltin and 10,10´-oxybisphenoarsine; Organic tin compounds; Triclosan (Kanishka et al., 2013).

1.2.2    Colorants and Fillers

Colorants are used in many industries – to colour clothes, paints, plastics, photographs, prints, and ceramics.  Colorants  can  be  either  dyes  or  pigments.   Dyes  are  soluble  coloured  organic compounds that are applied to textiles in a solution of water.  They are designed to bond strongly to the polymer molecules that make up the textile fibre. Pigments are insoluble compounds used in  paints,  printing  inks,  ceramics  and  plastics.     Many  organic  pigments  are  based  on  azo chemistry and  dominate  the  yellow,  orange  and  red  shade  areas.   An  example of  a simple monoazo pigment is Pigment Yellow (Kanishka et al., 2013).

Fillers are widely used  in plastics and the trend  of usage is increasing.  Fillers are used to reinforce plastics, for example, talc and glass fibre permit polypropylene to compete successfully in the engineering polymers market. Almost all plastics are made from petroleum feedstock and the price of plastics inevitably increases as abundance of oil and gas declines. Therefore, plastics are usually compounded mineral fillers to reduce cost (Michael et al., 2013).

1.2.3   Unreacted monomers and oligomers

The macromolecular structure of plastic is formed through the chemical reaction of monomers. Monomers and oligomers both tend to migrate from packaging materials into foods (Lau and Wong, 1996). Serious health risks may arise when the amount of unreacted monomers or low- molecular-weight substances in food reaches to a specified limit and absorbed by the human body (EU, 2006). The use of high volume of polystyrene food packaging may pose health concern as residual styrene can migrated from polystyrene (Arvanitoyannis and Bosnea, 2004). Epoxy resins of BPA, also known as bisphenol A diglyceride ether (BADGE), have cytotoxic effects in living tissues,  and  have been  shown  to  increase  the  rate of  cell  division  (Lau  and  Wong,  1996). However, recent FDA (food contact application) studies in collaboration with the National Centre for Toxicological Research (NCTR) state that the use of BPA in containers and other food- packaging materials is safe (FDA, 2013).

The fractional concentration of unreacted epoxy groups decides the degree of toxicity of the compounds. According to CEC (2011), the vinyl chloride monomers in PVC plastic can pose acute toxicity in the human body. Therefore, the materials and articles contacting food must not contain vinyl chloride monomers exceeding 1 mg/kg. The isocyanates used in polyurethane polymers and adhesives carry a low risk of oral toxicity, but a high risk of toxicity from dermal or inhalation exposure (Kanishka et al., 2013). BADGE is a monomer and the main component of epoxy  resins  for  internal  cans  linings.  Unreacted  BPA  in  the  plastic  lining  of  the  cans  or containers can migrate into foods during heating and storage. BADGE is added to the polymers to serve as antioxidant, but may contain unreacted BPA. It is not harmful to humans, as long as the amount of substances is below the specified limit (Kanishka et al., 2013). Polyethylene terephthalate (PET) contains small amounts of low-molecular-weight oligomers and the oligomer may vary from dimers to pentamers (Kanishka et al., 2013).

In addition, other chemical substances can be formed during processing by degradation of the plastic polymer or of some additives or during the use of the plastic materials (ageing). This means that the chemistry of plastics and environmental health impacts can be difficult to predict.

1.3      Hazardous substances in manufactured plastic materials

Two  recent  reports  for  the Norwegian Environment  Agency and  the  Danish  Environmental Protection Agency have reviewed the knowledge on hazardous substances in plastic materials (Hansen et al., 2013; Hansen et al., 2014). Hansen et al. (2013) describes the use in plastics of 43 hazardous substances adopted on the Norwegian Priority List of hazardous substances or the REACH Candidate list of SVHC-substances. The report provides information about plastic types in which the substances are used and the main applications of these plastics. Hansen et al. (2014) provides information on 132 hazardous substances used in plastic materials selected from a gross list  of 330  substances  from  the Danish  EPA’s  List  of Undesirable Substances  (LOUS),  the REACH Candidate List, Carcinogenic, mutagenic or reprotoxic (CMR) substances likely to be present in plastic toys and several other lists. Examples of the main hazardous substances used in plastics are shown Table 7 below. Many of the same substances are used for similar applications in various coatings (paint, lacquer. varnish, etc.). It should be noted that the table below does not contain comprehensive list of hazardous substance used in plastic.

Table 1: Examples of hazardous substances used in plastics (Hansen et al. 2013; 2014)

Substance group	Examples	of	hazardous	Application in plastics		Typical concentration in   material, percent
	substances
Organic compounds
Alkylphenols	Nonylphenol  (NP),  octylphenol			Unreacted                raw		Some 3-4% of the AP is
(AP)	(OP),    4-tert-butylphenol    (4-t-			materials;          Catalyst		present as unre-acted AP
	BP)			(nonylphenol);       Heat		in  phenolic  resins,   the
				stabilizers  (barium  and		concen-tration   in   final
				calcium salts of NP)		plastics is approximately
						0.2-2%     residual     NP
						(Lassen et al. 2015)
Bisphenol A	Bisphenol A			Unreacted                raw		Up  to   0.0003-0.1%	as
				materials; Antiox-idant		unreacted  mono-mer	in
						polycarbonate
						0.2%  as  antioxidant   PVC	in
Brominated flame	Decabrominated    diphenylether			Flame retardants		2-28%                 (various
retardants	(DecaB-DE),					applications)
	hexabromocyclododecane					0.7%  in  EPS,  1-3%  in
	(HBCDD), tetrabromo bisphenol					XPS (HBCDD)
	A                                 (TBBPA),
	decabromodiphenyl          ethane
	(DBDPE),                      ethylene
	(bistetrabromophthalimide)
	(EBTEBPI)
Chlorinated	Medium-chain           chlorinated			Plasticizers;	Flame	MCCP: 9-13%
paraffins	paraffins (MCCP)			retardants		SCCP:      10-15%	(in
	Short-chain chlorinated paraffins   (SCCP) (mainly historic use)					sealants)

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Table 1 contd.

Chlorinated	Tris(2-chloroethyl)phosphate		Flame  retardants;		TCEP:  1-10%  in  PMMA   and PA, 0-6% in   PUR, 0-20% in unsaturated polyester (UPE)
phosphates	(TCEP),		Plasticizers
	Tris(2-chlor-1-
	methylethyl)phosphate (TCPP)
Phenylmercury	Phenylmercury	acetate,	Accelerators,		0.1-0.3% mercury in PUR
compounds	phenylmercury	propionate,	curing agents
	phenylmercury	2-ethylhexanoate,
	phenylmercuric	octano-ate,
	phenylmercury	neodecanoate
	(mainly historic)
Phthalates	Bis (2-ethylhexyl)phthalate		Plasticizers		10-40% (total phthalates)
	(DEHP),  dibutyl  phthalate  (DBP),
	benzyl     butyl     phthalate     (BBP),
	diisononyl     phthalate     (DINP     ),
	diisobutyl phthalate (DIBP)
Inorganic compounds
Boric	Boric acid		Flame retardant		Up to 8%
compounds
Antimony	Antimony   trioxide   (together   with bromin-ated flame retardants		Flame retardant		4-10% (Lassen et al. 2014)
trioxide
Lead	Lead chromate molybdate sulphate red, lead sulfochromate yellow, lead stearate		Stabilizers;	Col-	0- 5% (colourants)   ~2% (Stabilisers)
compounds			ourants
Cadmium	Cadmium chloride, cadmium oxide		Stabilizers,	col-	~0.01-1% (colourants)
compounds			ourants		~0.1% (stabilizer)
Cobalt(II)	Cobalt(II) diacetate		Catalyst,		<1% (pigments)
compounds			pigments		no   information	regarding
					use as catalyst

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For substances intentionally used as additives in plastic materials or present in plastic materials due to their use in the manufacture of the materials, the plastic items/particles are not only a vector of pollutants transfer, but a primary source. Examples of substances demonstrated in plastics in the environment are PAHs, PBDEs, HBCDD and alkylphenols (e.g. nonylphenol and octylphenol), though it is not known how much of the measured concentrations can be attributed to sorption within the environment. The bioavailability of the substances embedded in the matrix (and present in an even concentration all through the particles) may likely be different from the availability of substances absorbed to the particles in the environment (Carsten, 2015).

1.4      Temperature effect on plastics

Leaching of chemical compounds from packaging polymers into foods and water must be evaluated to ensure that the amount of migrating components meet compliance standards set by regulatory agencies. This migration is influenced by several parameters, such as temperature of contact, duration of contact, surface area of contact, types of components in packaging material, and foodstuff (fatty, acidic, or aqueous) (Barnes et al., 2007; Veraart and Coulier, 2007; Khaksar and Ghazi-Khansari, 2009). As temperature increases, the diffusion of monomers, oligomers, and other compounds increases, and are accumulated.

Plastic materials will slowly degrade during use. How fast depends on the chemical structure of the plastic, the amount of stabilizers and the environment it is exposed to (mechanical wear, weather conditions, chemical attack) (Kanishka et al., 2013). Some plastics such as polyurethane and polyamide can hydrolyse when in contact with water especially if the water is acidic or basic or at high temperature (Kanishka et al., 2013). The migration rate of organic chemical substances depends on their size. Small molecules, typically monomers and residual solvents, will migrate fast as they have a low boiling point. Some monomers such as formaldehyde, vinyl chloride, ethylene and butadiene are all gases and have a high tendency to migrate quickly at ambient temperatures and for sure at 100 °C (COWI, 2013). The molecular weight of substances used as additives in the plastic are estimated to be in the range of 200 – 2000 g/mol. A high molecular weight means a large molecule and a slow migration rate and vice versa. The types of contact media are also important: gas, liquid or solid. Finally, the contact time determines how much will leach into the contact media (Kanishka et al., 2013).

Health assessments are carried out and based on data from these contact migration studies. In Klif (2010), it is stated that only the fraction of additives with molecular weight less than 1000 g/mol is regarded as toxicologically relevant as it is very unlikely, that the molecules with more than

1000 g/mol will be absorbed by the gastro-intestinal tract and thus is not considered to present a toxicological risk. Below 600 g/mol most substances are absorbed and the rate of absorption is determined by other factors than size and shape of the molecule.

1.5      Effect of UV Radiation on Polymeric Polymers

UV light is part of the electromagnetic spectrum. It is at the higher end of energy compared to visible light and is followed in energy by X-rays and the Gamma rays. UV radiation is split into three different types; UV-A, UV-B and UV-C.

Solar radiation reaching the surface of the earth is characterized by wave lengths from approximately 295 up to 2500 nm. The solar radiation classified as UV-B (280 – 315 nm) has an energy of 426 – 380 KJ mol-1. Fortunately, the higher energetic part of UV-B; 280 – 295 nm, is filtered by the stratosphere and does not reach the earth’s surface, UV-A (315 – 400 nm), has energy between 389 and 300 KJ mol-1 and is less harmful for organic materials than UV-B (Emad and Raghad, 2013). Exposure to ultraviolet, UV, radiation may cause the significant degradation of many materials. Damage by UV radiation is commonly the main reason for the discoloration of dyes and pigments, weathering, yellowing of plastics, loss of gloss and mechanical properties (cracking), sun burnt skin, skin cancer, and other problems associated with UV light. The manufacturers of paints, plastics, contact lenses, and cosmetics have a great interest in offering products that remain unaltered for long periods under conditions of light exposure (Bojinov and Grabchev, 2005; Pospisil et al., 2006; Galdi et al., 2010; Goldshtein and Margel, 2011). Photooxidation of organic materials is a major cause of irreversible deterioration for a large number of substances. It is responsible not only for the loss of physical properties of plastics, rubber,  but  for  foodstuffs  (Grassie  and  Scott,  1985).  In  most  polymers,  photooxidative degradation may be induced by UV radiation or catalytic process (or both) and can be accelerated by elevated temperature.

1.5.1     Photodegradation

Photodegradation of molecule is caused by the absorption of photons, particularly those wavelengths found in sunlight, such as infrared radiation, visible light, and ultraviolet light (Emad and Raghad, 2013). However, other forms of electromagnetic radiation can cause photodegradation. Photodegradation includes photodissociation, the breakup of molecules into smaller units by photons. It includes the change in shape of a substance or molecule by making it irreversible, such as the denaturing of proteins, and the addition of other atoms or molecules. A common photodegradation reaction is oxidation. Light – induced polymer degradation, or photodegradation, includes the physical and chemical changes caused by irradiation of polymers with ultraviolet or visible light. In order to be effective, light must be absorbed by the substrate (polymeric system). Thus, the existence of chromophoric groups in the macromolecules is a prerequisite for the initiation of any photochemical reaction (Andrady, 2011).

Ketones, quinines, and peroxides are initiators for different reaction degradation or chemical modification occurring in organic compounds (Kaczmarek et al., 1999). They absorb light up to about 380 nm, which causes their excitation or cleavage to radicals. One may initiate polymer degradation and other transformation by abstruction of hydrogen atom from a macromolecule (PH) and formation of polymer alkyl radical (Rabek 1993; Rabek 1996).

The influence of low-molecular weight organic compounds such as benzophenone (BPh), anthraquinone (AQ) and benzoyl peroxide (BPo) on the photo-processes of polystyrene has been studied. The results indicate that additives accelerate and increase the photodegradation and photooxidation of polystyrene (Kaczmarek et al., 1999). Photodegradation may occur in the absence of oxygen (chain breaking or cross-linking) and the presence of oxygen (photooxidative) degradation. The photooxidative degradation process is induced by UV radiation and other catalysts (or both) and can be accelerated at elevated temperatures. Photodegradation of polymers (e.g. embrittlement and color change) can take place on irradiation with a portion of UV light that is contained in sun light. The term of photodegradation might be distinguished from photooxidation of the polymer. In the latter, oxygen is involved in the process while in the former light energy (E=hv) only is responsible for the photodegradation.

1.5.2 Factors triggering Photodegradation

Generally, many factors are responsible for causing Photodegradation of polymeric materials. They may be divided into two categories

i.      Internal impurities, which may contain chromophoric groups that are introduced into macromolecules during polymerization processing and storage; they include:

        Hydroperoxide.

        Carbonyl.

        Unsaturated bonds (C=C).

        Catalyst residue.

        Charge–transfer (CT) complexes with oxygen.

ii.      External impurities, which may contain chromophoric groups, are:

        Traces of solvents, catalyst, etc.

    Compounds from a polluted urban atmosphere and smog, e.g. polynuclear hydrocarbons such as naphthalene and anthracene in polypropylene and polybutadiene.

        Additives (pigments, dyes, thermal stabilizers, photostabilizers, etc.).

    Traces of metals and metal oxides from processing equipment and containers, such as Fe, Ni or Cr.

1.5.3 Mechanism of photooxidative degradation of polymers

Photooxidative degradation of polymers, which include processes such as chain scission, crosslinking and secondary oxidative reactions, and takes place via radical processes, similar to thermal oxidation reactions (Rabek, 1995; Feldman, 2002)

Two mechanisms have been proposed to explain the photooxidation of polymers in conformity with  observations  made  on  low  molecular weight  compounds.  One proceeds  through  direct reaction of singlet oxygen with the substrate while the other involves the production of radicals and subsequent reaction with oxygen (Rabek, 1994).

1.5.3.1 Singlet oxygen mechanism of oxidation

It has been clearly demonstrated that many photosensitized oxidation reactions proceed with participation of oxygen in an electronically excited singlet state. The photochemical production of singlet oxygen is mainly due to quenching of the excited triplet state of suitable sensitizers:

3S + 3O2                  1SO + 1O2

Singlet oxygen exhibits several specific reactions and the one that has been most often invoked in the photooxidation of polymers is the formation of a hydroperoxide by oxidation of an olefin containing an allylic hydrogen, and which could further decompose and lead to chain scission and formation of a terminal of carbonyl group.

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