Assessment of heavy metals in food and drug packaging materials

Introduction

Packaging materials are defined as any substance or item that comes in contact with food and drug including containers, cans, bottles, cartons, boxes, cases and covering material such as foil, film, metal, paper, wax paper or cloth.¹ The main objective of packaging is to provide protection from foreign materials while in-transit and help in maintaining the shelf life of food products. Packaging is a field combining science and technology used for protecting products during distribution, storage, sale and use. It can also be applied to the procedure of evaluating, designing and manufacturing a packed item. Storage and preservation instructions, directions for use, expiry or use by date, and design of packaging materials among others are crucial information which give cognoscibility to the brand and increase the visibility on the shelf.^2,3

All the above processes result in migration of additives, adulterants and toxins such as colourants and adhesives from packaging material into the food, as shown by previous research.^4–6 Leaching can be explained as any process that allows transfer from surface to the core particles.⁷ With reference to food packaging, the term “leaching” can be defined as the movement of undesirable particles from packaged materials to the packaged particle. The European Council Standard requires that various contaminants like aromatic amines, benzophenones, polyaromatic hydrocarbons, plasticizers and heavy metals be controlled and analyzed in food packages.⁸ Heavy metals are a huge source of environment pollution.⁹ The toxicity of heavy metals has harmful effects on biological systems as they do not undergo biodegradation. They accumulate in living organisms, causing several diseases and disorders even when present in very low concentrations.¹⁰

The toxic effects of vanadium are particularly seen in lung and stomach tissues, resulting in pneumonia, bronchitis and breach in the gastric mucosal lining.¹¹ Increased concentration of arsenic in humans can induce epigenetic changes and genetic mutations causing cancer.¹² Cadmium has been used in industries for a long time. Toxicity due to cadmium can affect kidneys, and the reproductive, skeletal, and respiratory systems, causing proteinuria, kidney stones, loss of bone density and mineralisation, destruction of mucous membranes, pneumonitis, testicular necrosis, and affects steroid hormone synthesis.¹³ Mercury pollution impacts human health leading to developmental flaws in children and Minamata disease¹⁴ Metals like vanadium and mercury may be added as additives as a part of manufacturing process or may be an unintentional adulterant released from the moulds used specifically in the plastic industry.¹⁵

Considering the wide applications of the packaging material, the concentration of high amounts of heavy metals in them requires fine regulation. The Environmental Defence Fund¹⁶ states that these heavy metals can be toxic and the route of ingestion can be packaging materials.¹⁷ Sometimes, odorous compounds from the food packaging may get transferred to the food items and affect the foods’ flavour. This results in considerable nutritional loss and consumer dissatisfaction. Although food and drug packaging are a multi-billion industry, studies on the presence of heavy metal in these packaging materials in India are lacking. The interest of the present work lies in qualitative and quantitative assessment of arsenic, vanadium, cadmium and mercury levels in locally procured food and drug packaging materials.

Methods

This study was conducted at the Department of Biochemistry, Kasturba Medical College, Mangalore, Karnataka and Department of Chemical Engineering, National Institute of Technology, Suratkal, Karnataka. The Institutional Ethics Committee (IEC) approval was obtained prior to the conduct of the study.

A total of eleven food packaging samples and two drug packaging materials were bought from the local market.

The samples included aluminium cans, leak-proof bags, cardboard, tetrapaks, cellophane, tissues, sachets, aluminium bags and boxes, plastic bags and containers, as well as medicinal blister packets and medicinal closures.

The packaging materials were collected, cleaned with distilled water and dried in a hot air oven. The samples were cut into small pieces using scissors and metal cutters, and 10 grams each of the sample were weighed using a calibrated electronic weighing scale. The following tests were performed in triplicates.

Results

All tests were run in triplicates to ensure consistency in results. The average of the three readings was taken for computation and analyses.

Extraction

Microwave-assisted extraction was carried out using hydrochloric acid and sulphuric acid in a concentration of 80:20 used for samples like aluminium can and leak-proof bag. Dehydrator aid proof extraction using a combination of sulfuric acid and nitric acid in the ratio of 80:20 was used for medicinal blister packets, tetrapak, sachets, plastic containers and medicinal closures. Acid digestion with a combination of hydrochloric acid and nitric acid in ratio of 80:20 respectively was employed for the extraction of cellophane, tissue cardboard, aluminium bags, box and plastic container. The time taken for extraction ranged from 210 minutes to 34 minutes (Table 1).

Table 1. Extraction of heavy metals from the samples.

Packaging material	Type of extraction	Time taken for extraction (in minutes)
Leak proof bags	Microwave assisted extraction HCl and H2SO4	210
Plastic container	Dehydrator aid proof extraction H2SO4	190
Aluminium can	Microwave assisted extraction HCl and H2SO4	140
Cellophane	Acid digestion 80:20 HCl and HNO3	140
Tetrapak	Dehydrator aid proof extraction H2SO4	130
Sachet	Dehydrator aid proof extraction H2SO4 and HNO3	80
Plastic bag	Acid digestion 80:20 HCl and HNO3	60
Cardboard	Acid digestion 80:20 HCl and HNO3	60
Medicinal closure	Dehydrator aid proof extraction H2SO4 and HNO3	46
Medicinal blister packet	Dehydrator aid proof extraction H2SO4 and HNO3	46
Aluminium bag	Acid digestion 80:20 HCl and HNO3	45
Aluminium box	Acid digestion 80:20 HCl and HNO3	42
Tissue	Acid digestion 80:20 HCl and HNO3	34

• A) Qualitative analysis

Cardboard, medicinal blister packets and closures were positive for the presence for vanadium. Mercury was qualitatively identified in eight samples viz. aluminum can and bag, leak-proof bags, sachet, plastic bag, cellophane, medicinal blister packets and closure. Arsenic was present in samples: aluminum bag and box, sachet, cellophane and leak-proof bags. Cadmium was detected in plastic bag, aluminum bag, sachet, cardboard and leakproof bag (Table 2).

Table 2. Presence of heavy metals using qualitative analysis.

Sl No	Packaging material	Vanadium	Mercury	Arsenic	Cadmium
1	Leak proof bags	-	+	+	+
2	Plastic container	-	-	-	-
3	Aluminium can	-	+	-	-
4	Cellophane	-	+	+	-
5	Tetrapak	-	-	-	-
6	Sachet	-	+	+	+
7	Plastic bag	-	+	-	+
8	Cardboard	+	-	+	+
9	Medicinal closure	+	+	-	-
10	Medicinal blister packet	+	+	-	_
11	Aluminium bag	-	+	+	+
12	Aluminium box	-	-	+	-
13	Tissue	-	-	-	-

Figure 1. Spot test for vanadium.

Figure 2. Turquoise colour indicating positive test for vanadium.

Figure 3. Mercury Boris’s SenSafe strips tested for presence of mercury.

Figure 4. Ochre colour indicates positive test for mercury.

Figure 5. Cotton swab test for cadmium.

Figure 6. Negative test for cadmium.

Figure 7. Violet colour indicates positive test for cadmium.

Figure 8. Aquasol arsenic detector test.

Figure 9. Yellow to ochre indicates positive test for arsenic.

Discussion

In the current study, eleven commercially available food packaging materials and two drug packages were analysed for the presence of four heavy metals, namely vanadium, arsenic, mercury and cadmium. Packaging materials constitute the mainstay of the modern food industry. Hence, it is important to study their interference with food/drug present within the packaging material. As research has shown leaching of toxins from packaging materials, monitoring the heavy metal leaching is essential to prevent harmful effects to the human body.⁶

Vanadium is a heavy metal which is used as an additive in stainless steel as well as a catalyst for manufacturing sulfuric acid. It is also used in glass coating and lacquering in aluminum cans to give strength to the material. Vanadium is used as an amalgam in manufacturing cans with stainless steel to give it tensile strength. Vanadium toxicity is known to cause abdominal discomfort by interfering with mucosal lining leading to nausea, bloating, diarrhea and vomiting in the initial stages. Prolonged exposure can result in renal and neural damage.²⁴ Qualitative tests detected the presence of vanadium in only three samples. However, ICP-OES values showed presence of vanadium higher than permissible amounts in 10 samples. The study by Imtiaz et al.²⁵ stated that vanadium causes oxidative stress in human cells and alteration in human metabolism, reduces enzymatic activities and disturbs membrane integrity in humans.²⁵ This oxidative stress leads to the formation of pentavalate vanadium which is its most toxic and mobile form.

Arsenic, found in higher concentration in all the study materials (detected by six samples qualitatively), is a heavy metal that can act as a toxin due to its high presence in water which is used for material cleaning and lacquering processes.²⁶ Arsenic is also known to be present as one of the food packaging colorants used in the packaging industry.²⁷ Arsenic could enter the food packaging material during the cleaning process or as an adulterant of iron source. Arsenic has been used as a common ingredient in many pesticides and herbicides in the past. It is known to cause skin lesions and cancer in humans.²⁸ The International Agency for Research on Cancer (IARC), a part of the World Health Organisation (WHO) has stated that exposure to arsenic is the leading cause of lung, bladder and skin cancer.²⁹ The National Toxicology Programme (NTP) is composed of several different government agencies, including the National Institute of Health (NIH), the Center for Disease Control and Prevention (CDC), and the Food and Drug Administration (FDA). In its most recent Report on Carcinogens, the NTP classifies arsenic and inorganic arsenic compounds as known to be human carcinogens. The study by Park et al. stated that arsenic is present in paper in contact with food such as any kind of wrapping, and paper board, and presents a risk to consumer safety as increased ingestion in humans can cause skin lesions and gastric cancers.³⁰

Mercury dissolves in aluminum at room temperature and is added as an additive in aluminum cans and foils to enhance the shelf-life of the seafood packed inside.³¹ Ingestion of mercury is the leading cause of Minamata disease. Mercury was detected qualitatively in eight samples and quantitatively in amounts greater than those permissible in sachet and plastic bag only. The mercury absorbed in the body mainly concentrates in the kidneys and brain.³² The half-life of mercury in the body is about 70 days. Inorganic mercury is mainly absorbed through the respiratory tract, but is also absorbed through the skin to a small extent (3-4%) or gastrointestinal (GI) tract (2–10%). Methylmercury is easily absorbed into the GI tract (≥95%) and into the respiratory tract (≈80%). About 90% of methylmercury is excreted through the faeces via bile, and less than 10 % through urine. The absorbed mercury is distributed throughout all tissues within 30 hours. Its half-life ranges from 45 to 70 days.³³ Higher concentrations (more than 100 ppm) of mercury have been known to cross the placenta and result in foetal defects.¹⁴ Toxic effects of mercury have been reported even at lower concentrations in humans.^34–36 Therefore, it would be worthwhile to study the leaching from the packaging material and reconsider the admissible limit if proven.

Ingestion of cadmium in higher concentration creates oxidative stress in the cells and increases the level of antioxidant uptake to protect against macromolecular cell damage, thus leading to prolonged exposure to cadmium, causing depletion of antioxidant levels in the body. Cadmium is generally a contaminant present as residues of the recycling and manufacturing processes, and hence determining their suitability in packaging materials coming in direct contact with foodstuffs is imperative. During the recycling process and cooling of cans, cadmium enters the food production system due to changes in temperature or as an additive used in the metal and glass industry. Cadmium can cause respiratory illnesses, lung fibrosis and cancer.³⁷ Huff et al., found cadmium to be the major causative agent of lung cancer, and possibly prostate cancer. Studies in experimental animals have demonstrated that cadmium concentrations higher than those set by regulations (100 ppm) cause tumours at multiple tissue sites, by various routes of exposure, and in several species and strains.³⁸

It is alarming to find high concentrations of toxic metals in several of the packaging materials studied. While cadmium seemed to be the least abundant contaminant, arsenic was the most prevalent heavy metal contaminant. Of all the types of packaging materials studied, sachets, which are manufactured using a plastic and aluminium amalgam, had the highest concentration of all the heavy metals.

Conclusions

In summary, a wide variety of food and drug packaging materials from an Indian market were tested for the presence of heavy metal, namely vanadium, arsenic, cadmium and mercury. Our study shows the presence of heavy metals in routinely used food packaging materials, measured quantitatively and qualitatively. All samples, irrespective of the results of qualitative analysis, were subjected to quantitative analysis, as ICP-OES is a sensitive technique for the detection of heavy metals. Of the thirteen samples analysed, arsenic was found in all samples at concentrations above regulated limits; cadmium was present in higher than regulated concentrations only in sachets. Arsenic was present in all samples, whereas vanadium was present in lower concentration in tissue, cellophane and sachets; mercury was present in higher concentration in sachets and plastic bags. Leaching of these heavy metals into the packaged food/drug may be potential health hazard that severely compromise the well-being of humans. This study calls for stringent regulatory guidelines and strict monitoring of packaging materials at all stages, starting from raw material selection, storage and production until it reaches the consumer. The post-packaging handling, transport, storage and conservation of the supply chain requirements further add to prospective leaching, which may be the scope of future studies.

Data availability