Determination Of Heavy Metals In Fermented Cassava

Project and Seminar Material for Food Science and Technology (FST)

Project / Seminar Research Material On – Determination Of Heavy Metals In Fermented Cassava


This study was carried out on the determination of heavy metals in fermented cassava. Analysis was carried out on the cassava flour to ascertain the levels of some toxic contaminants like cyanide and metals introduced into the food naturally or as a result of human activities such as industrial emission, effluent discharges, solid waste disposal, usage of agrochemicals and sewage sludge in agricultural practices, incineration, traffic pollution, atmospheric pollution, vehicular emission, combustion of plastics, fossil fuels etc., which are more prominent in urban areas where multitudes of stationary and mobile sources release large quantities of these toxic contaminants into the environment which are then taken up by man, soil, water, plant, food than in rural areas. At selected sites, 20 (twenty) samples were collected, digested and analyzed. Cyanide in the cassava flour was determined by UV-Visible spectrophotometer. Lead, cadmium and nickel were determined using Atomic Absorption Spectrophotometer (AAS) while arsenic and selenium were determined using Titrimetric method. The mean concentration levels in mg/kg of cyanide, lead, cadmium, nickel, arsenic and selenium in the cassava flour from the urban areas were 0.07±0.03, 0.13±0.14, 0.03±0.02, 0.60±0.18, 0.30±0.07 and 5.12±0.90. These were higher than the mean concentration levels, 0.03±0.02, 0.04±0.10, 0.02±0.02, 0.36±0.11, 0.20±0.03 and 4.50±0.80 respectively determined in the cassava flour from the rural areas. However, all the determined levels of these elements from both urban and rural areas are far below the WHO guideline values or permissible levels of cyanide and metal in food. This implies that cyanide and the metal toxicants are present in the cassava flour in such low concentrations that render the food non-toxic.

Chapter One

1.0 Introduction

1.1 Background of the Study

Pollution is the introduction of contaminants into an environment, soil, food, water etc. that causes instability, disorder, harm or discomfort to the ecosystem or living organisms[1]. Sources of pollution can be natural or man-made. The major sources of cyanide and metal pollution in urban areas are anthropogenic (human activities) while contamination from natural sources predominate in the rural areas[2]. High concentration of toxic contaminants like cyanide and heavy metals are generally found in the urban areas with large population, high traffic density and industries[2].

Consequently, their undue presence in the environment through industrial emission, effluent discharges, solid waste disposal, usage of agrochemicals and sewage sludge in agricultural practices, traffic pollution, atmospheric pollution, automobile activities, combustion of fossil fuels, coal, steel, plastics e.t.c, are more prominent in urban areas where multitudes of stationary and mobile sources release large quantities of toxic contaminants into the atmosphere.

Cyanide, a toxic contaminant, occurs naturally in most plants but has high concentration in cassava and bamboo shoot. It is released into the environment through volcanoes and natural biogenic processes from higher plants, bacteria, algae and fungi[3], biomass burning, discharges from industries, waste water treatment, tobacco smoke, wood smoke, smoke from burning plastics, vehicular emission, inadequately processed cassava products e.t.c. Exposure to small amounts of cyanide can be deadly regardless of the route of exposure. Cyanide is very poisonous, it stops cellular respiration by inhibiting an enzyme in mitochondria called cytochrome c. oxidase in the body.

The term heavy metals, is a group name for some metals and metalloids associated with pollution and toxicity, but also includes some elements which are essential for living organisms at low concentrations. Heavy metals like zinc, manganese, copper, chromium, iron, cobalt, selenium, magnesium and calcium are essential trace elements for man, animal and plants but become toxic if the homeostatic mechanisms maintaining their physiological limit are disrupted or they become toxic if their concentration is very high in the body while lead, cadmium, nickel, mercury, arsenic are potentially toxic at certain levels[4].

Despite the fact that some heavy metals are beneficial, essential and non-essential, they can cause morphological abnormalities, reduced growth, increased human mortality rate and mutagenic effect in human when present in excessive levels[5]. Also, excessive accumulation of heavy metals in the human body system usually results from increased human exposure to the metals and this may cause health problems such as cancer, anaemia, neurological problems, renal dysfunction, damage to the hepatic, hematological, neuromuscular, reproductive, renal and central nervous system [6,7].

Cassava flour, a processed product from cassava, popularly known as “lafu” in Yoruba language is a staple food in Nigeria which contains essential and beneficial minerals needed for the body morphological processes. It is a rich source of carbohydrate, often referred to as the major fuel of the body tissues[8] that releases energy needed by the body to function properly in its daily activities. Human activities (anthropogenic sources) could favour the presence of toxic contaminants like cyanide and heavy metals in cassava flour which may render it unfit for human consumption especially when they are in high concentration.

Research have it that particulate air pollution and vehicle emission are the main causes of heavy metals contamination in the urban areas[9]. Ano et al reported that atmospheric deposition of heavy metals on cassava and soils along express road is higher than on cassava and soils in remote villages (non road side environment) because of low vehicle emission in the remote villages[10]. Alloway reported that plants accumulate considerable amount of heavy metals in root and leaves[11]. Amusan et al also reported that there is high concentration of heavy metal in vegetables grown in waste dump soil[12]. Ugwu et al reported high concentrations of lead, cadmium and nickel in cassava flour sundried along a major highway[13].

Detailed studies of the fate and contents of these heavy metals in various food and human being have become a major task in research and there is continuos challenge to develop new methodology and optimize that already available.

1.2 Statement of Problem

In food processing, it is often necessary to carry out trace element analysis to ensure that harmful and non-essential elements are kept at low concentrations as much as possible. Most of these ions are toxic to human beings by interfering with enzyme functions while some may have stimulatory effects. When the metals intake is at low concentration, the body system might not be able to remove it and it will remain in the body as impurities for a short time.

The increase of cyanide and some metal toxicants in cassava flour can cause toxic effects for consumers. The gravity of toxic effect depends on the nature, quantity, chemical form on body resistance and on synergetic or antagonistic effects of other chemical contaminants. Sometime in 2008, it was widely reported about a family who was nearly wiped out after eating food prepared from fermented cassava flour in Ondo state. Such food poisoning could result from pollution by known and unknown toxicants.

1.3 Aim and Objectives of the Research Project

This research work focuses on the determination of heavy metals in fermented cassava from some urban areas and rural areas of Ekiti, Oyo, Lagos, Ondo and Osun states, all in South-West, Nigeria.

  1. To find out if there is any significant differences in the concentration levels of heavy metals in fermented cassava flour sourced from urban and rural areas of these states.
  2. To examine the dietary exposure to heavy metals through consumption of cassava flour and create public awareness.

1.4 Significance of the Study

This study on the determination of heavy metals in fermented cassava identify the heavy metals, and also ascertain the risk to public health owing to the fact that fermented cassava constitutes one of the major staple foods in Nigeria. The study will make people to know the inherent dangers of consumption of cassava flour and other food products that may contain heavy metals above the W.H.O (World Health Organization) guideline or permissible level.

Chapter Five

5.0 Conclusion

The results obtained from the study shows that the mean concentration levels of lead, cadmium, nickel, arsenic, selenium and cyanide in fermented cassava flour from both urban and rural areas are far below the World Health Organization (WHO) guideline or permissible safe levels of cyanide and metals in food. This shows that cyanide and metals are present in the cassava flour in such low concentrations that render the food non-toxic and not to cause any harmful effect.

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