It is crucial for foods to reach the consumers in well condition, safe and in handy portion. In order to ensure a greater assurance of food safety, packagings have been widely used to protect it from microorganisms, biological and chemical reactions, promoting a longer shelf-life. Other than that, food packaging could also retard the food deterioration and retain the beneficial effects of processing (Marsh & Bugusu 2007).
Thus, it makes the packaging becomes a necessity in a food production process. We are able to see a very significant growth of the usage of food packaging in order to meet the industrial huge demand (Lau & Wong 2000). According to Coles (2003), the principles of food packaging are the ability of protecting food products from outside influences and damage, to contain the food and to provide the consumers with ingredients and nutritional information.
Package design and fabrication have an important role in determining the prolong-life of a food product. A good selection of packaging materials and technologies used can sustain the freshness and quality of the perishable product until its time of distribution and storage. Materials that have been regularly used as food packaging are of glass, metals, paper and paperboards and plastics (Marsh & Bugusu 2007).
At present, there are more than 30 different types of plastics that have been used as food packaging materials such as polystyrene, polyvinyl chloride (PVC), low density polyethylene (LDPE), high density polyethylene (HDPE), polyethylene (PE) and polypropylene (Lau & Wong 2000). Plastic are formed by condensation polymerization (polycondensation) or addition polymerization (polyaddition) of monomer units (Marsh & Bugusu 2007). According to EPA, there are two major categories of plastics that are, thermosets and thermoplastics (Marsh & Bugusu 2007). Plastics have been admirably used because of its lightness and excellent barrier protection characteristic (Rundh 2005).
Based on food packaging principle by Coles (2003), a food packaging should provide information on nutrition content, ingredients, date of manufacturing and expired date for the consumer to make a decision before buying the product. All the information needed have been printed on the packages by using inks, colors and waxes. Besides, the printings are also a part of a business strategy to attract consumers to buy theirs and yet to differentiate that particular product from other companies' goods.
It is almost impossible to sell a plain packaging food as it would not attract the consumer to buy it. Instead of that, all the printing inks used are not very safe at all as they can migrate into the layer of food at the interface. Various studies have been conducted to prove that migration did occur such as Aurela (2001) that stated most of the migrants that have been detected come from printing inks or adhesives used.
The word migration have been derives from the Latin verbs, migrare-prime meaning, to remove or depart (to another place) and the noun migratio-prime meaning, removal or changing of habitation. Both simulants that are food simulants (FS) and food simulating liquid (FSL) such as nitric acid and olive oil have been used in conducting research and in regulating control to ascertain the migration of substances as using the original food pose kind of problematic to researchers (Katan 1996).
Basically, a series of diffusion processes subjected to both thermodynamic and kinetic control could results in any migration of chemical substances from packaging into food (Conti 2008). Plastics that have been used as packaging materials also contain migrants such as additives that consists of antioxidants, stabilizers, lubricants, anti-static and anti-blocking agents (Lau & Wong 2000) to ensure a satisfactory product. Plastics itself that made up of polymers which is considered to be inert, contain various kind of low molecular weight component that tend to migrate into contacting food and could contaminate that particular foodstuff (Shepherd 1981).
Besides, packaging with plastic materials will also contain other components such as residual monomers that results from the polymerization reaction and oligomers and any other decomposition products or contaminants of intentional additives (Shepherd 1981).
All possible migrants could cause tainting or toxicological problems to the consumer if the migration occurs at a very high level (Shepherd 1981). This issue has caught lots of attention due to carcinogenic effect and potential estogenic effects to human as exposed by some studies on toxicological effects of migration (Lau & Wong 2000). On the other hand, stabilizers used in plastic manufacturing and printing ink used on the packaging surface would in the same way contaminate the food that come into contact with the plastic surface via migration.
Heavy metals are well-known as widespread of environmental contaminants and as accidental food contaminants. They enter the environment mainly as results of industrial pollution and find their way into the food chain through a series of routes (Wogan 1985). However, small amounts of heavy metals are actually required in our dietary intake but a large consumption of it would pose danger to human health, causing acute or chronic toxicity (International Occupational Safety and Health Information Centre 1999 cited by www.lef.org).
Apart from that, heavy metals poisoning could cause damaged or retard mental and central nervous function, lower energy levels, and damage to blood composition, kidney, liver and other vital organs. Long term exposure may result in slowly progressing physical, muscular and neurological degenerative processes that mimic Alzheimer's and Parkinson's disease. Allergies are common in heavy metals poisoning and repeated long-term contact with particular metals or their compounds may even cause cancer (International Occupational Safety and Health Information Centre 1999 cited by www.lef.org).
Thus, the purpose of this study was to determine the presence of possible heavy metals in plastic packaging food and whether these components would migrate into particular food.
1.1 Objectives of the Study
Specifically, the objectives of this study were:
- To determine the presents of heavy metals namely Lead (Pb), Cadmium (Cd) and Chromium (Cr) in food and plastic food packages.
- To determine the concentration of heavy metals (Pb, Cd and Cr) that migrates from plastic food packages into different pH solutions.
The word "package" refers to a container that provides a means of protecting, marketing or handling a product which comprises a unit package, an intermediate package, and shipping container (Kim et al. 2008). For the purpose of ensuring a reliable supply of safe and high-quality food products for the world's population, packaging becomes crucial. The requirements for packaging in modern urban society differ from those in societies in developing countries (Aurela 2001).
An insistent for ready-to-eat meals and takeaway food revolts explosively in urban communities, and consequently new packaging designs are needed. Among other things, packaging is a powerful marketing tool designed to be appealing to the senses of the eye and to provide information about its content. To whatever extent, the main reason of a packaging; protect its content, is global (Aurela 2001).
Packaging is a form of transfer engineering designed to collate contents and extend the duration of their shelf-life in a hostile environment. For many commercial purposes, a 'life' of 1 to 3 months is a satisfactory, and often this can be attained by wrapping in a plastic film. Such particular kind of films provides little protection against mechanical hazards, but they exclude most small, visible predators (Oswin 1982). Any packaging materials fulfill three broad functions; presentation, protection and preservation (Brown 1993).
Within all three areas, a thin polymer film or rigid container, fitted to the particular application while in the same time, satisfies the requirements of producer, retailer and consumer. In addition, packaging must be added the need to operate within a set of constraints. Other general examples would be well suited with the temperature requirements of the packaging process and the chemical nature of the product involved (Brown 1993). The main function of packaging is to control the internal micro-climate within a range that impedes microbial conquest (Oswin 1982). The principal roles of food packaging are to preserve food products from outside influences and other detrimental effect, keeping the food and provide consumers with ingredient and nutritional information (Coles 2003). The aims of food packaging is to keep food in a cost-effective way that meet the needs of industry requirements and consumer desires, maintains food safety, and reduces environmental impact (Marsh & Bugusu 2007).
Although one of the main functions of packaging is to protect the product during shipping, it is obvious that packaging is important both for marketing and logistic issues (Rundh 2005). The objective of food packaging other than marketing purposes, is to maintain foods' original state by protecting it from air (and oxygen), loss of gas (eg: carbonated oxygen), moisture loss or incorporation, light (and UV radiation), unfamiliar aroma compounds, microbial exposure, instability of temperature and mechanical influences (Muncke 2009). Development of food packaging plays an important role in keeping the food supply amongst the safest in the world (Marsh & Bugusu 2007).
Simply stated, packaging keeps the benefits of food processing after the process is complete, make possible for foods to travel safely for long distances from their point of origin and still be wholesomely by the time of consumption (Marsh & Bugusu 2007). In addition, packaging also makes food more convenient and gives the food greater safety assurance from microorganisms, biological and chemical changes such that the packaged foods can enjoy an extra longer shelf life. As a result, packaging became an indispensable element in the food manufacturing process (Lau & Wong 2000).
2.2 Plastic Material
Plastics are materials, the central of importance components which consist of those macromolecular organic compounds produced synthetically or by modification of naturally occurring products (Figge 1996). Plastics are the raw materials from whence films, plastic bottles and other products are produced. Plastics raw material manufacturers have significant, but limited scope for tailoring their products to the needs of many applications for which plastics are now used extensively (Birley 1982).
Plastics are some of the most critical and widely used materials in the industrialized world. Plastic films and packaging are widely utilized in the food industry due to their adaptability, variable sizes and shapes, relative light weight, stability, barrier properties, resistance for breaking, perceived high-quality image and cost effectiveness (Jenkins & Harrington 1991). Plastics can fulfill all the different functions necessary for packing, protection and food supply. On the other hand, they guarantee that, as far as possible the packaged foods reach the consumers in their original existing condition without the loss of primary ingredients and also prevent shortening of shelf-life and damage of the characteristic qualities of the products by outside influences (Figge 1996). For many food products, rigid or flexible plastics are primary choice as packaging media. Based on common thermoplastic polymers, they provide an unparalleled combination of performance, processability, convenience and low cost (Brown 1993).
2.3 Functional Barrier
A functional barrier can be generally described as a package construction that restricts the amount of migration of a component from the package into food or food simulating liquids in amounts below a thresholds value. This threshold value is usually set up by regulatory institutions and is generally derived from toxicological evaluations. The functional barrier concept can also be defined in practical food quality terms in place of toxicological terms (Piringer et al. 1998).
Resolution defined the functional barrier as "Any integral layer which under normal or foreseeable conditions of use limits all possible materials transfer (permeation or migration) from any layer beyond the barrier into food to a toxicologically and organoleptically insignificant and technologically unavoidable level" (Aurela 2001).
Therefore, the efficiency of a functional barrier is eventually defined by a concentration of no concern (that is a conventional value) in a food or a food simulant (Aurela 2001). Moisture transfers from the "wet" to the "dry" component of these products affect the physical properties, mainly texture, and chemical composition of the food system, and subsequently affecting its quality and shelf-life (Katz & Labuza 1981). The highest barrier properties are not always needed as they can sometimes be harmful by promoting anaerobic conditions, thus the application of edible films and coatings can help reduced internal and external water transfer in slightly modified and processed food products (Oswin 1982).
Edible films must not only have good barrier properties, but also acceptable sensory characteristics (mouth feel, taste and aftertaste), a flexible and stretchable structure for an easy application onto the food and a composition conforming to the regulations (Guilbert 1986).
In many instances, plastic packaging contains many components in addition to the base polymer. Additives are required both for the manufacturing process to give adequate results for the finished product to have the desired characteristics (Shepherd 1982).
Apart from the high-polymers, plastics also contain low-molecular compounds, oligomers and monomers and particularly the so-called plastics additives such as heat and light stabilizers, anti-oxidants, UV-absorbents, lubricants and plasticizers which may be physiologically opposed. The addition of these auxiliaries is absolutely required for the processing and stability of the plastics as well as for attaining certain mechanical strength properties of the final plastics products (Figge 1980).
Food packaging can interact with the packaged foodstuff by diffusion-controlled processes which mainly dependent on chemical properties of the food contact material (FCM) and the foodstuff, temperatures at packaging during heat treatment and storage, exposure to ultraviolet (UV) light, and time storage of the product (Arvanitoyannis and Bosnea 2004). This interaction might lead to FCM compounds leaching from the packaging to the food, which also known as 'migration' (Muncke 2009).
The main source of potential migrants is the additives incorporated in all plastics for manufacture reason or use. Apart from possibly causing tainting or toxicological problems, migration could also be unpleasant because of consequent deleterious changes in the physical properties of the package itself (Shepherd 1982). The low molecular compounds frequently have a high mobility in the plastics and in contrast to the macro-molecules, they can easily migrate from plastic packaging into a foodstuff. According to the present interpretation, the migration of plastics components in packaging into foodstuffs is fundamentally a diffusion problem (Figge 1980).
During assessment of food contamination from packaging, it is not enough to only sample retail products and analyze them for certain contaminants. While this will give a good indication of real food pollutant levels, their presence in food cannot be clearly represents leaching from packaging because other contaminant sources, like processing prior to packaging are not taken into account. To ascertain the actual leaching from food packaging, contaminant levels need to be assessed over time. Such experiments are often carried out using food simulant such as water, 3% acetic acid, 10% ethanol and oils instead of actual foods (Muncke 2009).
However, the use of food simulants might cause an underestimation of actual migration into food (Grob 2008). Migration frequently assessed using chemical analysis of known single substances. Such studies in other way do not cover all possible migrants (Muncke 2009). Accordingly, the extent of migration of a plastics component depends on numerous variables such as density of the plastics, the concentration of the component in the plastics, contact time between plastics and foodstuff and the temperature in the system of 'plastic or foodstuff' (Figge 1980).
It would be perfect if the migration of each additive and monomer into the packed foodstuff could be determined when the package has been filled and stored under normal conditions of practice. This would ensure that no physiologically objectionable plastics material would be admitted and plus no suitable plastics material would be refused because of an excessively assessment (Figge 1980). Because of the heterogeneous nature of the foodstuffs, great analytical difficulties are involved in the determination of migrated low-molecular plastics components. Therefore, natural migration must be simulated in tests model to determine the migrated additives and monomers in food simulants, which is more easily to be analyzed (Figge 1980). However, the results of such migration or extraction studies are only suitable for the assessment of the health-safety of plastics packaging where it is in contact with the food in practice and simulated exactly the same. It is therefore necessary to fix test temperature and times that are closely related to those of the practice. Moreover, contact media must be used which are comparable with the different foodstuffs regarding their behavior in relation to the plastics (Figge 1980).
2.6 Heavy Metals
Heavy metals composition of foods is of interest because of the essential or toxic nature (Gopalani et al. 2007). Under certain condition, exposure to high levels of these metals in the environment has been relates to adverse effects on human health and the environment (Zagorska 2007). Heavy metals are potential environmental contaminants with the ability of causing human health problems if present to excess in the food we consume (Rayment undated). It is well defined as chemical elements with a specific gravity that at least five times the specific gravity of water (Lide 1992 cited in www.lef.org).
Metals are the only group of pollutants that are biologically non-degradable, but undergo a biogeochemical cycle through various compartments of the environment (Golimowski 1979). Chronic low level intakes of heavy metals are known to have damaging effects on human being, since there is no good mechanism to get rid of them (Bahemuka et al. 1999). Metals such as lead, mercury, cadmium and copper are cumulative poisons, causing environmental hazards and are reported to be exceptionally poisonous (Ellen et al. 1990).
Throughout the course of the cycle, those toxic metals are taken up and accumulated by plants and thus enter the food chains and eventually reached to human, where the toxic metals tend to accumulate in vital organs, and display progressively increasing chronic toxic action over extended period of time. Besides the primary uptake from natural sources (e.g. soils and atmospheric precipitates), the secondary uptake due to the use of certain pesticides, fungicides and fertilizers (sewage sludge), as results of particular local or regional anthropogenic pollution (e.g. lead from automobile exhausts), and as a consequences of accidental metal contamination during food manufacturing and storage, could make severe hazards occur (Golimowski et al. 1979).
In small amounts, certain heavy metals are nutritionally essential for a healthy life (www.lef.org 2010). During consumption of food in the diet, the trace metal contents of foods are directly taken into the body (Tuzen et al. 2003 cited by www.lef.org). These elements are often to be found naturally in foodstuff, fruits and vegetables, and also commercially available multivitamin products (International Occupational Safety and Health Information Centre 1999 cited by www.lef.org). Heavy metals may enter the human body through food, water, air, or absorption through the skin when they come into contact with humans through agriculture and manufacturing, pharmaceutical, industrial, or residential settings. Industrial exposure accounts for a common route of exposure for adults whereas ingestion is the most common route of exposure in children (Roberts1999 cited in www.lef.org).
Children may develop toxic levels from the normal hand-to-mouth activity of small children who come in contact with contaminated soil or by incidentally eating objects of non-food (dirt or paint chips) (Dupler 2001 cited by www.lef.org). There may be no foreseeable sign of an illegal or unacceptable level of residue, specifically for toxic elements such as cadmium, lead and mercury. At higher concentrations heavy metals may harmed their hosts. Those which obviously harm their host before they adversely affect human health are of lesser anxiety to the wider community (Rayment undated).
Hazardous pollutants that are sets free into the environment persistently increases metal concentrations, thus contaminating the food supply. Metal contamination can take place throughout the handling and processing of foods, starting from the farm to the point of consumption (Morgan 1999). Thus, besides the growth of plants in contaminated soils and the feeding of animals on feeds containing toxic metals, other factors may also contribute to the food contamination. Physical contact between food and metal, such as processing equipment, storage and packaging containers, contribute to a significant source of metal in food. Once metals are exist in foodstuff, their concentrations are not often modified by traditional preparation and processing techniques, although in some cases washing may decrease the metal content (Morgan 1999).
Lead in the environment has long been identified as a risk factor for humans (Berg 1994). If consumed or inhaled, it can affect nearly all systems in the body. As a consequence of many years being used in production, gas and paint, lead can be found in lots of places. Lead poisoning is a very critical issue for young children and pregnant women. Lead is found to be very toxic for growing brains and nervous systems of fetuses and small children. It is also known to affect a number of different biochemical and physiological processes, cell types, tissues, and organ systems (Andrews 1992). The main targets for the toxicity of lead include the red blood cells and their stem cells, the central and peripheral nervous systems, and the kidneys. During the past few decades, levels of exposure to lead that were once thought not to pose any hazard have since been shown to elicit deleterious effects. Furthermore, lead may affect the neurobehavioral development of newborns, infants, and children exposed to lead either in utero or postnatal (Carrington & Bolger 1992).
There are lots of sources of lead in our environment. Primary sources come from lead-based paint and contaminated soil, dust, drinking water, air, food and other related products. Food grown on lead-contaminated soils could also contain high lead levels (Andrew 1992).
On the other hand, most lead contamination from food does not start with the food itself. Packaging or the dishes used to serve food are the main cause of most food-related lead contamination. By reducing lead in packaging and dishware, food sources of lead might be reduced (Andrew 1992). Weisel (1991) found that bread wrappers imprinted with lead-based inks could be a source of lead. If the bread bag is turned inside out and reused, lead could become part of stored food. While this source of lead was not major, bread bags are now imprinted with new dyes with very small amount or no lead. Now, bread wrappers used inside-out for food storage is of little concern as a source of lead (Weisel et al. 1991).
Cadmium is naturally present in all components of the environment; it is present in all soils and sediments, unpolluted seawater and also in air of non-industrializes areas (Sherlock 1984). It is widely distributed throughout environment and is readily absorbed when eaten. A small proportion of ingested cadmium is accumulated in the kidneys in the form of a metal-protein complex. Continuous exposure to excessive amounts results in damage to the renal tubules in animals and human. Other long-term effects include anaemia, liver-dysfunction and testicular damage (Wogan 1985). Cadmium is also a byproduct of the mining and smelting of lead and zinc. Cadmium is a naturally occurring metallic element, which is one of the components of the earth's crust and present everywhere in our environment. It can also be found in soils because of insecticides, fungicides, sludge and commercial fertilizers that use cadmium are used widely in agriculture (www.lef.org 2010). Cadmium is considered as the greatest serious contaminant of the modern age because its toxicity is a major problem in foodstuffs. Cadmium also regarded to be similar to lead, as it is a cumulative poison and the danger lies in regular consumption of foodstuffs that contain cadmium at low levels of contamination (Zagorska 2007).
Cadmium emissions occur as results from two major source categories, natural sources and man-made or anthropogenic sources (www.cadmium.org 2010). Cadmium emissions to soils can be categorized in three different categories that are agricultural soils, non-agricultural soils and controlled landfills (Eggenberger and Waber 1998). According to Chandler (1996), the amount of cadmium in controlled landfills may arise from disposal of spent-cadmium containing product, non-cadmium containing product which may contain some cadmium impurities and naturally-occurring waste such as soils, food waste and grass which inherently contain trace levels of cadmium.
Because cadmium is a naturally occurring component of all soils, all food stuffs will contain some cadmium and therefore all humans are exposed to natural levels of cadmium. Cadmium levels can vary widely in various types of foodstuffs. Leafy vegetables and certain staples and grain foods exhibit relatively high values from 30 to 150 ppb. Meat and fish normally contain lower cadmium contents ranges from 5 to 40 ppb. Animal offal such as kidney and liver can exhibit extraordinarily high cadmium values; up to 1000 ppb as these are the organs in animals where cadmium concentrates (WHO 1992). Cadmium sulphide and cadmium sulphoselenide are utilized as bright yellow to deep red pigments in plastics, ceramics, glasses, enamels and artist colors. They are well known for their ability to withstand high temperature and high pressure without chalking or fading, and therefore are used in applications where high temperature or high pressure processing is required (Cook 1994). Consequently, all food, whether it be of plant or animal origin, is exposed to and contain cadmium (Sherlock 1984).
Chromium is remarkable among other regulated toxic elements in the environment in that different species of chromium, specifically chromium (III) and chromium (VI), which they are regulated in different ways based on their differing toxicities. All other toxic elements, such as lead, cadmium and arsenic are regulated based on their local concentrations, irrespective of their oxidation state (Kimbrough 1999).
Emissions occur to the three primary compartments of the environment which consists of air, water and soil, but there may be considerable transfer between the three compartments after initial deposition (Kimbrough 1999). The elemental composition of soils and sediments are affected by the composition of the parent rock from which they are formed. Thus, the natural concentration of chromium varies very much (Cary 1982). Several studies have estimates the chromium content in variable types of foods. Gibson (1998) for instance found that foods that rich in chromium are including brewers yeast, nuts, prunes, asparagus, mushrooms, beer and wine; meat, fresh fruits and vegetables. Cheeses were found to be good sources, while refined cereals were poor sources of cadmium.
Shils et al. (1994) noted that the daily intake of chromium can vary greatly depending on the amounts of various foods present in the diet such as processed meats, whole grain products including some ready-to-eat bran cereals, and spices were found to be the best sources of chromium. Conversely, Shils et al. (1994) also stated that dairy products, fruits and vegetables contained low concentration of chromium. In most cases, wide variations in chromium levels have been found in cereals depending on their distinct origins, species and chemical forms of chromium absorbed. It is well known that chromium (VI) is absorbed effectively and more rapidly than chromium (III), but it is not converted to chromium (III) (Bratakos et al. 2002). Higher concentrations of chromium have been reported in plants growing in high chromium-containing soils (e.g., soil near ore deposits or chromium-emitting industries and soil fertilized by sewage sludge) compared with plants growing in normal soils (Grubinger et al., 1994).
Different kinds of technologies that are used in food and beverage processing can also increase the chromium content in such products. The leaching of chromium from stainless steel, which has been greatly used in the food industry, is most likely the main source of chromium contamination of foods and beverages (Concon 1988). In accordance to Bratakos et al. (2002), food processing industry uses almost exclusively stainless steel containing 13-30% chromium in its processing equipment material which might leach into food during their manufacturing process.
Meat products showed a wide variation in chromium content but were generally lower than that of fresh meat; this was dependent on product composition and added materials such high fat content in sausages. Guthrie (1975) reported higher chromium concentrations in meat products for example salami, is due to contamination during processing. Increased levels of chromium were also detected in dairy products that used eggs as addition ingredient (as custard samples) and chocolate; it was proposed by Fennema (2000), that cocoa may contribute considerable amounts of chromium element to the samples analyzed. There are four main routes of exposure of interest for chromium which are dermal absorption, ingestion, inhalation, and ingestion secondary to inhalation. Chromium can act directly at the site of contact or be absorbed into, or through, human tissues.
MATERIALS AND METHODS
3.1 Sample preparation
Six different types of foods were selected for this study. All samples were chosen by randomly sampling and bought at local supermarket (Giant Hypermarket Shah Alam). Three packages were bought for every single sample to get the mean reading of the sample. Sample descriptions are stated as in Table 1.
3.2 Ashing of food packages
This test was carried out to determine the content of heavy metals in the food packages that also indicates the total heavy metals that contained in the particular food packages. This test is important in calculation of percentage of heavy metals that leached out in migration test by using three different food stimulant that will be discuss further in this thesis.
Each food packages was placed in the ceramic crucible and also covered with ceramic crucible. All three crucibles were labeled by using pencil. Muffle furnace temperature were slowly heated from room temperature to 500°C over a 1 hour period. The samples in the crucible were ashed for about 3 hour and 50 minutes until white or grayish ash residues were obtained.
The ashes were dissolved in 10 ml concentrated HNO3 before it is covered with parafilm for 24 hour. The clear solution was then heated on a hot plate in a fume cupboard until it becomes almost dry. Another 10 ml of HNO3 were added into the crucible. The digested samples were filtered with Whatman 42 Ashless filter paper. The filtered samples were transferred into 20 ml volumetric flask and made up to volume. The blank was performed in the same way. (Method adapted from Khunprasert et al. 2006)
3.3 Analysis of heavy metals in food
This test was carried out to determine the content of heavy metals in the food. Each 2 g of food samples were weighted into 150 ml beaker and dried in the oven for one hour. The dried samples were kept in the desiccators to balance the temperature until it reached constant weight. The samples were then digested using 10 ml of HNO3 and covered with parafilm before it is allowed to stand for 24 hour.
After 24 hour, the samples were heated on the hotplate in a fume cupboard until it becomes almost dry before it is filtered with Whatman 45 filter paper. 5 ml of filtered sample were pipette and transferred into 50 ml volumetric flask and made up to volume for dilution purpose.
A blank was performed in the same manner in this treatment (Method adapted from Zaharin unpublished)
3.4 Extraction Test
This test was conducted to determine the amount of heavy metals leached from the food packages into solution of pH 6.5. The food packages of 5 cm x 5 cm were immersed in the 100 ml of metals-free deionized water at 26.5°C for 24 hour. The beaker were covered by using parafilm in order to avoid any cross contaminant during the treatment period.
A blank was prepared in the same manner in this treatment (Method based on Conti and Botrč 1997)
3.5 Migration Test
This test was conducted to determine the amount of heavy metals migrate from the food packages into solution of two different acid concentration. Two different packages of the same sample (5 cm x 5 cm) were immersed into both 100 ml of 3% and 4% v/v metal-free solution of acetic acid at 40°C for 24 hour. Table 3 states the pH condition of every solution used in these tests.
A blank was prepared in the same manner for this treatment. (Method based on Conti and Botrč 1997
3.6 Laboratory glassware, reagents and standards of heavy metals
All reagents used during analysis were of analytical reagent grade. Deionized water was used throughout the study. All the plastic and glassware to be used were decontaminated by overnight treatment using 5% nitric acid.
3.7 Standard Preparation
3.7.1 Lead (Pb) Standard Preparation
Concentrations of lead solution that have been used for sample analysis are 1.0 ppm, 3.0 ppm and 6.0 ppm. From the original bottle of lead standard solution, 10 ml have been taken by using extremely clean pipette and transferred into 100 ml volumetric flask and made up to volume.
After dilution of the original solution, 1 ml, 3 ml and 6 ml of solution are taken and transferred into three different 100 ml volumetric flask and made up to volume. All three concentrations are transferred into separate plastic tubes for analysis.
3.7.2 Cadmium (Cd) Standard Preparation
Concentrations of cadmium solution that have been used for sample analysis are 0.5 ppm, 1.0 ppm and 2.0 ppm. From the original bottle of cadmium standard solution, 10 ml have been taken by using clean pipette and transferred into 100 ml volumetric flask and made up to volume.
After dilution, another 10 ml of solution were taken and transferred into three different 100 ml volumetric flask and made up to volume. From dilution of 10 ml, another 5 ml of solution was taken and transferred into another 100 ml volumetric flask and made up to volume. The solution that are made up of 5 ml, 1 ml and 2 ml solution are transferred into separate plastic tubes for analysis.
3.7.3 Chromium (Cr) Standard Preparation
Concentrations of chromium solution that have been used in this study are 0.1 ppm, 0.2 ppm and 0.4 ppm. 10 ml of solution from the original bottle of chromium was taken and transferred into 100 ml volumetric flask and made up to volume.
Another 10 ml from diluted solution was taken and transferred into another 100 ml volumetric flask and made up to volume. From newly diluted solution, 1 ml, 2 ml and 4 ml solution were taken and transferred into three different 100 ml volumetric flask and made up to volume. All three solutions were transferred into three separate plastic tubes for analysis.
3.8 Sample analysis
The heavy metals in the samples were analyzed using Perkin Elmer 3300 Atomic Absorption Spectrometry under the conditions shown in Table 4.
Calibration curves were constructed by running the standard solutions of each element as in the Table 5. The amounts the standards absorbed were compared with the calibration curve and this enabled the calculation of the heavy metals concentration of the samples.
3.9 Data analysis
All the results achieved from the various analyses conducted in this study were transformed into graphs. The contents of heavy metals in different food packages were compared and the amounts of heavy metals in different solutions were analyzed. The values were also compared to the safety levels recommended by the regulatory authorities.
RESULTS AND DISCUSSIONS
All results of the study are reported in Table 6 and Figure 1 (Content of heavy metals in food packages), Table 7 and Figure 2 (Content of heavy metals in foods), Table 8 and Figure 3 (Amount of heavy metals leached from food package in 3% Acetic Acid), Table 9 and Figure 4 (Amount of heavy metals leached from food pacakage in 4% Acetic Acid), Table 10 and Figure 5 (Amount of heavy metals leached from food package in deionized water). All data are expressed in mgkg-1.
4.1 Content of heavy metals in food packages
FP 5 contained low concentration of lead (0.103 mgkg-1) but high in concentration of cadmium (8.955 mgkg-1) and chromium (2.989 mgkg-1). While in FP 6, there is a little bit high in concentration of lead (1.273 mgkg-1) but low in concentration of cadmium (0.801 mgkg-1) and chromium (0.754 mgkg-1).
Those packages that contain high concentration of heavy metals are mainly because of the printing inks that have been used on its surface. Lead-based pigment could confer the colors of white, red and yellow, while chromium could confer colors of chrome yellow, green and red (Bradley et al. 2005). As cadmium have been used widely in plastic stabilizer, it would be possible that packages with high concentration of cadmium were come from this source.
4.2 Content of heavy metals in food
Andrew (1992) has stated that, packaging is the most reason to food which gives an account to lead contamination. The used of lead-based ink on the surface of food packaging could migrate the lead substance into food itself. Apart from that, WHO (1992) says that grains contain lots of cadmium if compared to meat. That is why we can see that the cadmium content of FP 1 (2.574 mgkg-1) is much higher than concentration of cadmium in FP 3 (0.399 mgkg-1).
Besides, it is noticeable that concentration of cadmium in FP 5 (0.175 mgkg-1) is much more lower compared to FP 3 eventhough the FP 5 substance is of grain. It could be of other product composition or added material into the meat product that contribute to higher concentration of cadmium. As in chromium, Fennema (2000) states that cocoa-based product could contribute to the higher concentration of chromium in its product. This statement explained well why the FP 2 and FP 6 product contains highest concentration of chromium subsequently, (1.179 mgkg-1) and (0.967 mgkg-1).
According to Food Regulation 1985, milk product should only contained 1.0 mgkg-1 of lead and chromium while 2.0 mgkg-1 of lead and 1.0 mgkg-1 of cadmium in meat (other than edible gelatin), cocoa product and any food which no other limit is specified (excluding water and food additives). On top of that, only FP 6 (0.559 mgkg-1) does not exceed the lead concentration limit while both FP 1 (2.574 mgkg-1) and FP 2 (2.538 mgkg-1) do exceed the chromium permissible limit, whilst there is no limit for chromium concentration in food is stated in any part of the regulation.
4.3 Amount of heavy metals leached into food simulants
The solution of 3% acetic acid was a food simulant which simulate the acidic condition which represents vinegar, pickles and fruit juices (Crosby, 1981). It indicates that, the metals would migrates in such amount when the package contact physically with the foodstuff having a pH in the exact of the food simulant. Besides, a migration could also happen towards human skin especially when the consumer deals with food which has similar pH condition of acetic acid before touching the food package.
In a manner corresponding to Food Regulations 1985 in Thirteenth Schedule, the leachate of heavy metals from food packaging should not exceed the permissible limit, which was 0.2 mgkg-1 for cadmium and 2.0 mgkg-1 for lead. In this case, there was no limit exceeded by any of the samples.
Once more, the FP 1 represents the second highest migration of lead (0.39 mgkg-1) and cadmium (0.155 mgkg-1).
The purpose of doing the migration test simulated by 3% and 4% of acetic acid is to do a comparison whether there are any significant difference between both concentrations as Malaysian Food Regulation 1985 has come out with the test of using 4% acetic acid instead of standard method which used 3% acetic acid as food simulant.
Obviously, there are no extensive differences between results produced by both concentrations. Thus, it is much better to do the migration test by using the standard method as it can save up the chemical being used.
Deionized water simulate a condition which is closely similar to our skin. To this point, any contact between human skin (usually of palm and fingers) and the surface of food package at significant period of time, there will be a migration of heavy metals to contacted skin.
After taking everything into account, it can be concluded that heavy metals does exist in the food packaging so do the food itself. According to Reilly (1991), print and color that applied to the plastic packages are capable of contaminating its food. Besides, pigments used for coloring and printing on packaging surface might also a good source of metals that leached into the food.
Apart from that, tests using food simulant such as 3% and 4% acetic acid and deionized water, shows some variables in heavy metals migration. It is not a denial that migration of heavy metals from 4% acetic acid is much more higher compared to the other two. But, in consideration that there is no significant difference between both migrations, 3% of acetic acid would be more desirable in conducting the migration test using acidic food simulant as both pH also does not differ much.
Other than simulating the pH condition of fruits and juices (Crosby 1981), the acidic condition also simulates the condition of a landfill. According to Hunt et al. (1990), food packaging accounts for almost two-thirds of total packaging waste by volume.
Thus, those packaging dumps in a landfill could leached significant amount of heavy metals that they contained as they are exposed to the conditions as simulated by food simulants. Leaching of heavy metals could cause harm to the environment and its living creatures. Improperly designed landfills such landfill without leachate collection system and HDPE liner would contaminate groundwater sources when water from rain or the waste itself permeates the landfill and dissolves substances in the waste including toxic heavy metals. The acidic or alkaline conditions can enhance rapidly the extraction of these substances in the waste allowed them to seep into the ground, reaching for natural groundwater sources.
According to Marsh and Bugusu (2007), lead and cadmium based additives for plastics and colorants contribute to the heavy metals content of MWC ash. Although the substances used is only small in amount, these metals concentrate in the ash as the polymers are burned off. The statement shows how much these heavy metals are persistent in our environment. Not only landfills that gather a number of heavy metals, but the worst are we are accumulating these kind of heavy metals in our body day by day through the consumptions of foods in packaging. In accordance to Marsh & Bugusu (2007), we as a consumer drives the packaging design as our desires becomes sales' significant. As we are the significant sales tools, would we change our desire for the sake of our own health?
CONCLUSION AND RECOMMENDATION
The use of heavy metals in printing inks and manufacturing of plastic used for food packaging are of great concern. Consumers are likely to be exposed to the migration of heavy metals through the consumption or come into contact of packaging food. Three tests have been carried out to determine the heavy metals namely lead, cadmium and chromium contained in food packaging, food itself and the ability of those heavy metals to migrate into food simulants. For the first test, four out of six samples contained high concentration of lead ranging from 4.159 mgkg-1 to 15.950 mgkg-1. The source of lead could come from the inorganic inks and pigments used (Kim et al. 2008). Food test show variables of heavy metal concentration contained by food. The concentrations vary according to source of food that could contribute to metal contents. Heavy metals contamination could also occur during the manufacturing process of food which comes from the stainless steel being used. Migration test using food simulant also shows varies concentration of heavy metals leached out from the food packages but none of them exceeded the permissible limit fixed by Malaysian Food Regulation 1985. Nevertheless, we should bear in mind that heavy metals do accumulates in human body especially targeted organs such as kidney and liver that could contribute to vital organ damage. Therefore, the metal-based pigment and inks used in printing on food package surface should be strictly regulated by Malaysian Food Regulation 1985.
It is highly recommended for future study to come out with toxicological assessment specifically, Exposure Assessment to make a comparison with Tolerable Daily Intake (TDI) in order to estimates the dietary intake of targeted group (Nasreddine 2002). It is crucial to actually determine if there are any risks related to an accidental consumption of a commodity with a level of heavy metal residue superior to the TDI sets by regulation (Nasreddine 2002).
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