**1. Introduction**

Many food-insecure nations are located in Africa, which happen to be the net importer of fish in terms of volume [1]. The Nigeria population which is estimated to be growing at 2.41% annually, depends massively on fish to meet the over 40% animal protein intake needs of its population. Demand for fish from industrial fishing countries around the world in the form of frozen and canned fish is valued at about \$500 Million US Dollars or N250 Billion Naira per annum [2]. The state of World Fisheries and Aquaculture in 2022 reported that that global merchandise trade which increased at a rate of 6.8% per year in nominal terms between 1976 to 2020 and by 3.75% in real terms.

Fish consumption can supply over 50% high quality protein, low fat, essential poly unsaturated fatty acids, micro and macro nutrients [3]. World population growth has

### *Heavy Metals – Recent Advances*

outweighed fish production due to increased fish and sea food consumption which have increased per capita across the world from as reported for as at 2017 [4].

Federal Department of Fisheries (FDF) and Food and Agriculture Organization (FAO) has previously reported Nigeria's self-sufficiency in fish production ratio of 98.8% in 1983, which dwindled to between 40% and 19.2% in 2005–2014. And with the present economic realities in Nigeria foreign exchange, weak institutional reforms and economic measures without the well withal to implement them; the challenge to increase protein consumption in Nigeria appears to be more urgent [5].

According to FAO statistics as reported [6], 6% of the 11% global population's animal protein intake is derived from fish. Presently, more than 30% of the world population is suffering from malnutrition, this is more evident in developing countries like Nigeria, where people experience just over one quarter of all possible deprivation as highlighted in the 2022 multidimensional poverty index survey which revealed that 63% (133 million people) of persons living within Nigeria are multidimensionally poor [7].

Carbohydrate which is the stable food in Nigeria is complemented richly with fish because of its provision of fatty amino acids, minerals and trace metals and it is also believed to be a healthier alternative to many other sources of animal protein. Until recently in Nigeria, fish was regarded as the cheapest and easily accessible animal protein source. And canned fish which has become very popular, makes marine fish available in different part of the world irrespective of season.

Humans are usually more exposed to toxic elements via food as they tend to absorb many of these pollutants from the natural environment, storage medium, storage conditions before sales among others [8]. Therefore, the determination of safety levels has become paramount due to the health challenges which hereto were not frequently diagnosed, but has become a recent trend in the poorly revitalized health sector of the country coupled with the dwindling value of the naira due to the high demand for dollars as a result of Nigeria's mono-economy.

Studies on the quality of frozen and canned fishes has attracted attention from relevant agencies and experts, as the beneficial and toxic level range of any product are very small [9]. Therefore, effects of exposure above certain threshold can be potentially life threatening especially if not properly diagnosed for immediate medical treatment.

Canned food are popular food sources all around the world [10], and it is a modern technological advancement in food processing, helps to increase shelf life and allow storage for several years. Operations in canning industries are manually and mechanically carried out, the final heat treatment gives protection from spoilage organisms. But this process of heat treatment is done in such a way as not to alter the flavor and texture of fish considerably [11].

Most of the marine fish are canned, thus, making it more available for consumption by humans living far away from sea sites [12]. Fish are constantly exposed to chemicals in polluted and contaminated waters; therefore, fish products need to be well established to be relatively free of excessive metals as some metals according to [13] can act as catalysts in the oxidative reactions of biological macromolecules resulting in induced alterations in almost all body functions and organ integrity. Metals can be classified as potentially toxic, probably essential and essential [14].

Many priority pollutants as classified by the United States Environmental Protection Agency (US EPA) have made their way into aquatic systems through anthropogenic sources and natural weathering. The major sources of pollution

### *Some Metals Found in Stored Canned Fish Products Sold in Nigeria DOI: http://dx.doi.org/10.5772/intechopen.110214*

of surface waters include effluent discharges by industries, agricultural run offs, atmospheric depositions of pollutants and accidental spillage. Trace elements may be immobilized within the stream sediments and result in absorption, co-precipitate and form complexes by co-absorbing with other elements or form particulates as oxides hydroxides of Fe, Mn.

Toxicity and the resultant adverse effect based on its' concentration on humans has been of concern especially in developed countries which has resulted in the imposition of new and more restrictive regulations [15, 16]. Regulations in Nigeria are still not strictly followed due mostly to poor will-power and inadequate manpower. This has resulted in increased level of health concerns in the country, as more and more persons now embark on medical pilgrimages and increase pressure on the available medical facilities and personnel.

Canned fish and fish products considered by Nigerians as conventional, hygienic and tasty has resulted in their preference and patronage, but some of these products may be laden with deleterious contaminants whose effects may take a long time to manifest especially when consistently taken in large quantities.

During these last decades, environmental research on metal pollution on marine and freshwater environments has been conducted, focusing especially on the distribution of trace metals in freshwater as well as in seawater fish [17]. Since most of the marine fish are canned, it therefore becomes more available for consumption by humans living far away from sea sites [12].

Since metals present in seafood, at low concentration may be essential; however, they can become toxic having harmful effects when their intake exceeds the recommended quantities significantly [18–20].

Human exposure to heavy metals has risen dramatically in the last 50 years as a result of an exponential increase in the use of heavy metals in industrial processes and products [21]. Therefore, the lethal thresh of substances like zinc while working on the toxicity of zinc to *Clarias gariepinus* can be defined after a long period of exposure [22], which is characteristic of substances that may be slowly excreted or metabolized and at the same time a decreasing concentration may not appreciably increase the survival period of the fish. It is essential to identify the interaction between the foodstuff and its package, particularly when it is being purchased and consumed nationwide on a regular basis [23]. The most important heavy metals causing severe toxicity to fish are arsenic, lead, nickel, zinc, tin among others, as they are considered the most important form of pollutants of the aquatic environment because of their toxicity and accumulation by marine organisms [24]. Heavy metal pollution of the marine environment has long been recognized as a serious environmental concern as toxic elements can become very harmful even at low concentration when ingested over a long period of time [25, 26]. Heavy metals can be accumulated by marine organisms through a variety of pathways, including respiration, adsorption and ingestion [27, 28].

The aquatic environment is a major place for contamination by metals, as a result of bio-accumulation by fish during feeding, it may become bio-magnified in consumers of such contaminated fishes. The growing concern over the increasing level of heavy metals contamination, in agricultural, sea foods and industrially processed food products has therefore birthed this study. This study therefore aims to determine the levels of some metals (Fe, Zn, Mn and Ni) in six different brands of canned fish products stored in curry sauce, tomato sauce and soybean oil with a view to evaluating how safe these canned fish products in these storage media, sold in the Nigerian market are against set safe standards.
