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1.0         INTRODUCTION

1.1         BACKGROUND

Recently, there is an increasing concern about the quality of imported foods and food related products in several parts of the world (Maxwell and Neumann, 2009) particularly from China. This, as observed by the United States Congress, was due to the large size of shipments, the many different routes of entry, the variety of foods imported, and the large numbers of potential contaminants make effective interdiction of contaminated foods difficult (Congress Research Service (CRS) Report, 2008). Additionally, the US Congress observed that many products were brought into the United States by travelers especially residents travelling back and forth regularly to China. Among the common products imported were canned tomatoes, chocolates, candies, biscuits, bean paste, bean curd, teas and various nuts and spices (CRS Report, 2008).

According to the United States Congress Research Service Report (2008), in early 2007, evidence emerged that adulterated pet food ingredients from China had caused the deaths of many dogs and cats. However, toxicological and environmental studies have interest in the determinations of toxic elements in food. "Food safety" implies absence or acceptable and safe levels of contaminants, adulterants, naturally occurring toxins or any other substance that may make food injurious to health on an acute or chronic basis. Food quality can be considered as a complex characteristic of food that determines its value or acceptability to consumers. Besides safety, quality attributes includes nutritional value, organoleptic properties such as appearance, color, texture, taste and functional properties (World Health Organization (WHO), 1998).

Taking into consideration that products passed through different industrial processes


and are packaged to provide a means of protection, marketing or handling, and most of them have printed colour inks on the outer cover (Kim et al., 2008). Importantly, food products such as candies that are likely to be consumed frequently by small children are wrapped in colourful packages in order to induce them to purchase the products. Heavy metals, such as Pb, Cr, Ti, Zn and Cu can migrate from the printed surface to the food contact surface through four mechanisms: blocking, rubbing, peeling and diffusion (Bradley et al., 2005). Contamination of imported food products with heavy metals may cause a serious risk to human health because of the consumption of even small amount of metals can lead to considerable concentrations in human body. Metals that cannot be metabolized like cadmium, lead and mercury persist in the body and exert their toxic effects by combination with one or more reactive groups essential for normal physiological function and cellular disturbances or clinical manifestation may appear (Friberg and Elinder, 1988; Skerfving, 1988). The adverse toxic effects caused by lead (Subramanian, 1988), cadmium (Friberg et al., 1986), mercury (Manahan, 1989) and tin (Reilly, 1991) are widely recognized.

In spite of the hazard effects of heavy metals on public health, some of them are essential for normal physiological functions such as copper and zinc (Zaki, 1988; Hays, 1989). Also, copper sulphate exhibits clear reduction of cadmium residues in animal tissues (Ahmed et al., 1999), the dietary deficiencies of copper, zinc, calcium, iron, protein and an excess dietary fat cause an increase in the absorption and toxicity of lead (Goldfrank et al., 1990). Although there are standards set by the quality control bodies such as National Agency for Food and Drug Administration and Control (NAFDAC) and Standards Organization of Nigeria (SON) for permissible concentrations of these contaminants in imported products, the problem still exists because many Chinese manufacturers have two


or more versions of their products: one specifically designed to meet standards set by the import country, and a cheaper and poorer version for the native market (Medlin, 2004). Coupled with the fact that route of entry differs, therefore, monitoring of heavy metal content in these products is essential especially with their related health implications. The potential for exposure, though, is not completely understood due to the lack of data regarding heavy metal levels in various products and the extent of use within Nigerian communities. Canned tomatoes and candies, however, are of particular concern because of their potential for children consumption.


Tomatoes contribute to a healthy and well-balanced diet. They are rich in vitamins, minerals, proteins (Attia et al., 2000), essential amino acids (Gould, 1992), sugars and dietary fibers (Davies and Hobson, 1981). Tomatoes also contain vitamin C, vitamin E and low amounts of the water-soluble type B vitamins, thiamin, niacin and riboflavin (Beecher, 1998). Tomatoes and tomato products are used as ingredients in many traditional dishes, because of their compatibility with other food ingredients and due to the concentration and availability of several nutrients in these products and to their wide spread consumption by humans all over the world (Anonymous, 2008). However, heavy metals are one of a range of important types of contaminants that can be found on the surface and in the tissue of fresh tomatoes as well as processed tomato products. As a result, heavy metal accumulation in tomato and processed tomato products may pose a direct threat to human health.

Potentially toxic heavy metals including lead, cadmium, and arsenic have been found in chocolate products from a variety of origins (Mounicou et al., 2003; Rankin et al., 2005; Dahiya et al., 2005). These metals can be absorbed directly by the Theobroma


cacao tree or be introduced during the manufacturing process. But either way, they can still exist in the final product. Although the levels of these metals are often within acceptable ranges, it’s important to realize that they accumulate in the body and can become quite toxic over an extended period of exposure to small amounts. Many chocolate manufacturers claim that the amounts are small enough to not be a concern (Anonymous, 2002), but the American Environmental Safety Institute (AESI) considered it a large enough to file suit against a number of manufacturers in 2002 and petition for required contaminant labeling (AESI, 2002). The concentration of heavy metals may very well be too low to be of significant concern, but it’s definitely a legitimate reason to avoid eating sizable portions of chocolate on a regular basis. Furthermore, because the cacao beans used to make chocolate come from all over the world, the amounts of heavy metals that they contain can vary widely. Although there’s no guarantee, certified organic chocolate is less likely to be produced from cacao beans that have been grown in a contaminated environment or exposed to contaminants during processing (Carter-Pokras et al., 2007).

Also, essential elements are present in the industrial processes and agrotechnical operations, so disregarding their nutritive essence, their contents should be determined because they can often reach toxic level (Kim et al., 2008). Copper intoxication can be caused by its many chemical compounds which are components of fungicide used in agriculture and veterinary practice. Using vegetables and fruits grown on high copper soil (near smelters, industrial factories) is also a cause of copper intoxication. Zinc and iron used in the form of alloys in industry and in some inorganic fertilizer components, could lead to high concentration of these metals in soil and then in plants grown in the soils.

Canned foods offer a shortcut in meal preparation which is most favored by those


who are stretched for time. Canned fish, milk, tomatoes products manufactured either locally or imported, are very popular in supermarkets and small grocery retail outlets.


According to Dahiya et al (2005), the future of any nation depends on the health, prosperity and progress of the forthcoming generation. Presently, in the era of industrialization, development and inter-boundry trades, one concern should be the health of the future generation. Children are the most vulnerable age group to any kind of contamination in the food chain (Arreola et al., 1996). Lollipop, chocolate, biscuits and milk candy are some of the favourite items of children and are often presented to them as token of love and affection from their parents, relatives and friends (Dahiya et al., 2005). Many brands of these kinds of child-consumed favourite items are available in the market at variable prices, among them are those imported from Peoples’s Republic of China which are sold at a low price. Most of the packaging is so poorly designed that the inner coatings do not maintain structural integrity, allowing ink component in the outer packages layer to migrate into the products (Kim et al., 2008). This could be a possible route of heavy metals into the children body system.

Also, it is a common phenomenon to list ingredients on the wrappers. The most common ingredients listed are sugar, liquid glucose, milk solids, cocoa solids, hydrogenated vegetable oil, vegetable fats, cocoa butter, wheat flour, edible starches, added flavor, yeast and flavor improvers, buffering agents and permitted stabilizer. Out of the listed ingredients, hydrogenated vegetable oil, vegetable fats, permitted emulsifier, buffering agent and permitted stabilizer may be the source of trace metal contamination (Dahiya et al., 2005).


In September, 2008, at least 12 countries had banned Chinese dairy products and these products were even recalled from shelves throughout Asia and in some African countries (CRS Report, 2008). Food products such as biscuits, chocolates and milk candies could be made from contaminated milk powder and children who consumed such food products could potentially exceed the tolerable daily intake (TDI) by more than threefold (European Food Safety Authority (EFSA), 2008). It is therefore necessary to monitor the level of heavy metals in these products especially its health risk implications.

In Nigeria, tomato paste, which constitutes a significant volume among canned vegetable products are mainly imported. The processing plants for the tomato paste are depending on their farmland, most of which are irrigated, for the supply of raw materials (Jones, 1987). The plants use fertilizer and agricultural chemicals for the production of raw materials. Hence, the need to determine the levels of essential and toxic heavy metals in canned tomato paste imported into the country become essential due to their beneficial or damaging effects. Moreover, it has becomes necessary to know about the concentration of essential and toxic heavy metals in canned tomato paste to ensure the quality of the product and to comply with quality and specification standards developed by the Codex Committee on Processed Fruits and Vegetable (CCPFV).

Increase of metal contamination in food and food products over the allowed limits (either concerning non essential or essential metals in surplus), may cause toxic effects to the consumers of the products. The gravity of toxic effects depends on the nature, quantity and chemical form of metals and synergetic or antagonistic effects of other chemical contaminants. Children are mostly exposed to the toxic metal effects through food and some of the favourite gifts. Metal genoxic effects are more often in the children because


their organs grow faster, the metabolism is more intense and the cells are divided more quickly (Vitosevic et al., 2007).

Studies on the assessment and evaluation of safety of food products are mainly carried out in developed countries. Literature information on such studies in developing country like Nigeria where such “junks” are constantly circulated in the markets and consumed by families is scarce. Thus, this study is necessitated to identify and characterize imported candies and canned tomatoes paste from China into the country. This is because the safety of our food products supply is a shared responsibility, from the fork of the food producing industry, regulatory authorities, scientists and consumers. As part of this responsibility, this study was conceived to assess the potential risks posed by food ingredients (canned tomato paste) and candies imported from China.

1.4         HYPOTHESIS

The purpose of this study was to identify and determine the level of heavy metals in different imported canned tomato pastes and candies from China into the country, considering that these products are supplied to every market in the country. Therefore, the study is based on the following null hypotheses:

i.        Mean metal concentrations of candies and canned tomato pastes purchased from different zones of the country do not differ, and their heavy metal levels are within acceptable or safe limits.

ii.      Candies and canned tomato paste of different types do not have equal metal concentrations.



The aim of this study was to determine some heavy metals (Cu, Mn, Fe, Ni, Zn, Ti and Cr) which might be essential at low concentrations in some canned tomato paste (testi tomato paste and merysa concentrates de tomato paste) chocolates and candies (lollipop with pencil, milk candy, royal glucose and biscuits) imported from China and to provide data that may be used as the basis for preventive measures. This was set to be achieved through the following objectives:

i.        To determine the metal contents of canned tomato pastes, lollipop, biscuits, milk candy and chocolates from China sold in Nigeria major markets.

ii.      To compare the levels of the metals in canned tomato paste, lollipop, biscuits, milk candy and chocolates with international standards.

iii.    To determine the risk associated with the consumption of these products.


The study was limited to these brands of canned tomato pastes and candies due to their availability in all the selected markets from the six geographical zones of the country. Also, the sampling sites per zone were limited due to financial constraint as at the time of study.

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