**Abstract**

A Review of sample preparation and techniques used to determine Cadmium content in flexible films and biodegradable thermoformed products based on cassava. All determinations have been made using atomic absorption spectroscopy. The presence of this element in these matrices can be harmful if the maximum tolerated quantities are not complied by. The presence of Cadmium may be due, among other aspects, to the fact that it is present in the raw material, in industrial discharges or because it is found naturally. Its determination is an important parameter that needs to be considered as a good alternative for packaging.

**Keywords:** cadmium, thermoformed, flexible films, atomic absorption

## **1. Background and objectives**

#### **1.1 Introduction**

The accelerated pace of industrialization, combined with rapid population growth, intensive agricultural techniques, and inappropriate waste management in developing countries have increased the levels of micropollutants such as heavy metals, considered harmful or toxic to living beings [1, 2]. These heavy metals can enter the human body —causing serious damage— via food, water, air, soil, skin absorption, polluting emissions, anthropogenic sources (treated sewage discharges, mining operations), contact with industrial and agricultural products such as pesticide formulations, urban traffic, contamination from chemical fertilizers, and irrigation with poor quality water [3–8].

The migration of heavy metals induced by substances in contact with food is given by the negative interaction between packaging and food. Another risk factor is constituted by the fact that heavy metals are nonbiodegradable and cannot be metabolized and, thus, persist and accumulate in the environment and in organisms over long periods of time [1–3, 9–11].

#### **1.2 Biodegradable thermoformed and flexible films**

Thermoformed and flexible films are very popular in the food packaging market given their low cost, large surface area by volume, and outstanding performance

across a wide temperature range [12]. Thermoforming is a generic term that encompasses several processing techniques, by which plastic articles can be obtained from flat sheets of different polymers. Thermoformed products are classified into two major categories: permanent or industrial products (shelves for medical or electronic equipment, decorative panels for cars, planes, motorcycles, bathtubs and bathroom fixtures, helmets and seats for boats, and skylights) and disposable products (packaging for medicines, bubble wrap, cups for hot and cold beverages, baking trays, food containers, and clear packaging that is shaped like the product) [13, 14].

The films are defined as thin flexible sheets of synthetic or natural origin, that reach a thickness of 0.01 inches or less. The polymeric matrix that forms the film can be defined as the random arrangement of the chains that make up the structure. Flexible films used in the food industry are currently divided into two groups: synthetic or non-biodegradable materials and biodegradable materials. The manufacture of these products is important, as they break down quickly and easily, without producing residues that cause unfavorable impacts on environmental ecosystems [14].

Biodegradable thermoformed and flexible films can be made of cassava flour (given its high starch content, making it suitable for use in the manufacture of various products in the food industry, as well as for the production of biopolymers) and cassava starch (as it can be converted into a thermoplastic material by interrupting the molecular interactions of the double helix chain, formed by hydrogen bridges between the hydroxyl groups, in the presence of a plasticizer aided by suitable temperature and shear stress [15, 16], and by adding matter such as fique fiber, gelatin, poly(butylene adipate-coterephthalate), polylactic acid, glycerol, plasticizer, green composites, cellulose, chitosan, clay, pullulan, natural extracts, poly(vinyl alcohol), and kaolin [7, 8, 17–35].

Industries are currently striving to improve their products by using natural and renewable sources to store, package, and wrap food products [7, 8, 29, 32, 36]. These include thermoformed and flexible films (biopolymers) obtained from agricultural sources (cassava), and constitute a new and environmentally friendly industrial alternative (composting) given their rapid and easy biodegrading processes. Their main purpose is the replacement of regularly used petroleum-derived plastic polymers and their associated waste [8, 18, 20, 22, 23, 26, 31, 37, 38]. A common production method for thermoforming is the compression molding technique (**Figure 1**), in which the material is placed into an open mold to which pressure and heat are applied.

**Figure 1.** *Compression molding machine used for thermoforming.*

*Cadmium Contents in Biodegradable Films Made from Cassava DOI: http://dx.doi.org/10.5772/intechopen.96848*

Single screw extrusion —a continuous process that forms the plastic material is used to produce biodegradable flexible films, whereby turning the screw and applying heat pushes the material along while melting it [13, 21, 27, 32], turning it into a viscous material. Where the nozzle is positioned at the end of the cylinder, there is a hole shaped according to the use required (for films, the extrusion nozzle is round). From the extrusion hopper comes the plasticized mass, which is stretched, smoothed, and rolled by the rollers (**Figure 2**) [39].

The casting technique, using native and ozonated cassava starch, glycerol as the plasticizer, and water as the solvent is used for the elaboration of biodegradable films from cassava starch modified by ozone at different levels [40].

#### **1.3 A case study of heavy metal pollution: cadmium**

Biodegradable polymers may lead to heavy metal contamination during their manufacture if the raw material used to process them is contaminated (cassava flour and starch, fique fiber, polylactic acid, glycerin, etc.). They may also be subject to cross-contamination during production, for example, via petroleum- and nonpetroleum-associated activities, from containers used for cooking and storage, during drying, and from contaminated utensils or water [4, 41, 42].

Thus, tracking the manufacturing process is essential in determining the presence of toxic heavy metals in the biopolymers, in turn, to safeguard public health by limiting exposure [1, 9].

Among these metals, cadmium (Cd) is considered toxic to plants and animals; it is widespread in the atmosphere, soils, and water, and is a serious health hazard, affecting the gastrointestinal, cardiovascular, musculoskeletal, nervous, renal, and reproductive systems. Long-term exposure may cause mitochondrial damage and possible death. Cd bioaccumulates in individual organisms [4, 5, 43–46] and is likely to continue to do so due to the future use of biodegradable polymers in the packing and packaging of dry foods and other degradable products, as it enters the food chain.

The US Department of Health and Human Services has insisted that an excessive Cd accumulation in humans may be the cause of cancer as Cd and Cd salts are considered a "possible human carcinogen" [4, 44]. Certain plants can also accumulate Cd in their tissues, and levels are even more significant in plants grown in peri-urban areas with soil contaminated by irrigation using wastewater and sewage sludge [10, 47–50].

There are currently no studies reporting Cd found in thermoformed and biodegradable flexible films; however, the literature does report the presence of Cd in cassava tubers' cortex [42], cassava food crops [51], as well as Cd contaminated rice which causes the Itai-itai disease [52] by exposure to Cd-contaminated water

**Figure 2.** *Film extrusion machine.*

used for irrigation or from farms affected by petroleum- and nonpetroleum-related activities. The safety of the materials that come into contact with food is assessed by the amount of substances that migrate into it from the biopolymer and whether or not these meet the conditions established in the legislation on foods.

The legislation limits the migration of toxic pollutants from reaching unacceptable levels and helps to maintain the integrity of foodstuffs, thereby preventing health hazards, contamination, and alternations in food composition and sensory properties [9]. The current Colombian regulation NTC 4096 [53], allows a maximum level of Cd of 1 mg/kg for plasticizers while the Agency for Toxic Substances and Disease Registry [44] estimated that average Cd intake in Americans is 30 mg/day and that only one-tenth of this amount is absorbed into the tissues. Given that thermoformed and flexible film can be used as food containers, their Cd levels must be strictly monitored.
