Description
TABLE OF CONTENTS
Title page i
Certification ii
Dedication iii
Acknowledgement iv
Abstract
v
Table of content vi
CHAPTER ONE: INTRODUCTION
1.1 Heavy metals
1
1.2 Heavy metal pollution
2
1.3 Essential trace metals
4
1.4 Toxic trace metals
4
1.5 Objectives 6
6
CHAPTER TWO: LITERATURE REVIEW
2.1 Origin and Domestication of Swine (pigs)
7
2.2 Breeds of pigs
9
2.2.1 Berkshire 9
2.2.2 Chester White 9
2.2.3 Duroc 10
2.2.4 Hampshire 10
2.2.5 Poland China 11
2.2.6 American Land Race 11
2.2.7 Tamworth 11
2.2.8 Yorkshire 12
2.2.9 Feeds for Pigs 12
2.3.0 Biological functions and health effects associated with a
deficiency or excess of heavy metals 12
2.3.1 Zinc (Zn) 13
2.3.2 Iron (Fe) 15
2.3.3 Copper (Cu) 16
2.3.4 Chromium (Cr) 17
2.3.5 Nickel (Ni) 18
2.3.6 Lead (Pb) 20
2.3.7 Cadmium (Cd) 21
2.4.0 Methods of Analysis 24
2.4.1 Atomic Absorption Spectroscopy (AAS) 25
2.4.2 Sample Digestion Methods 27 CHAPTER THREE:
EXPERIMENTAL
3.1 Apparatus 31
3.2 Reagents and Reference Solutions 31
3.3 Sample Collection and Preservation 31
3.4 Determination of Moisture Content 32
3.5 Sample Digestion 32
CHAPTER FOUR
4.1 Results and Discussion 34
4.2 Conclusion 41 References 42
LIST OF TABLES
Table 2.1 Health effects associated with a deficiency or excess of
heavy metals 23
Table 4.1 Moisture and Dry matter content in muscle of free ranger pigs 34
Table 4.2 Moisture and Dry matter content in muscle confined pigs 35
Table 4.3
Concentration (µg/g) of Heavy metals in muscle of free Ranger
pigs 36
Table 4.4
Mean and Range (µg/g) of Heavy metals in muscle of free Ranger
pigs 37
Table 4.5
Concentration (µg/g) of Heavy metals in muscle of confined pigs
38
Table 4.6
Mean and Ranges (µg/g) of Heavy metals in muscle of confined
pigs 39
Table 4.7 WHO Guideline values of Heavy metals in pork 41
CHAPTER ONE
1.0 INTRODUCTION
Heavy metals are metals having density greater than 5g/cm 3 (or
5kgm -3 ). These are found mostly in groups III – V of the periodic table
(1). Many different definitions have been proposed – some based on
density, some on atomic number or atomic mass and some on chemical
properties or toxicity. (1) The term heavy metal has been described as
„meaningless and misleading‟ in an International Union of Pure and
Applied Chemistry (IUPAC) technical report due to the contradictory
definitions and its lack of a “coherent scientific basis” (1). There is an
alternative term, toxic metal, for which no consensus of exact definition
exists either. Depending on context, heavy metals can include elements
lighter than carbon and may exclude some of the heaviest metals. One
source defines “heavy metal” as ….common transition metals such as
copper, lead and zinc. These metals cause environmental pollution
(heavy-metal pollution) from a number of sources, including lead in
petrol, industrial effluents and leaching of metal ions from the soil into
lakes and rivers as well as acid rain (2).
In medical usage, heavy metals are loosely defined (2) and include
all toxic metals irrespective of their atomic weight. “Heavy metal
poisoning” can possibly include excessive amount of iron, manganese,
aluminum or beryllium (the fourth lightest element) or such semimetal as
arsenic. This definition excludes bismuth, the heaviest of stable element
because of its low toxicity.
Living organisms require varying amounts of some heavy metals”.
Such as iron, cobalt, copper, manganese, molybdenum and zinc (3).
Other heavy metals such as mercury, plutonium, and lead are toxic
metals that have no known vital or beneficial effect on organisms, and
their accumulation over time in the bodies of animals can cause serious
illness. Certain elements that are normally toxic are, for certain
organisms or under certain conditions, beneficial (4). Examples include
vanadium, tungsten, and even cadmium (3,4).
Analysis for trace heavy metals in food has become increasingly
important in medical, ecological and pollution studies due to the toxicity
of these metals. The environmental contamination from heavy metals is
of concern because they exhibit behaviour consistent with persistent
toxic chemicals unlike many organic contaminants that lose their toxicity
as a result of biodegradation. Metals cannot be degraded further and
their toxic effects can be long lasting (5). Whilst the concentrations in
biota can increase through bioaccumulation, heavy metals are also
known to have toxic effect at low concentration (6).
Heavy metal pollution can arise from many sources but most
commonly arises from the purification of metals, e.g. the smelting of
ores and the preparation of nuclear fuels. Electro plating is the primary
source of chromium and cadmium. Though precipitation of their
compounds or by ion exchange into soils and muds, heavy metals
pollutants can localize and lay dormant. Unlike organic pollutants,
heavy metals do not decay and thus pose a different kind of challenge for
remediation (5.6).
Advancement in technology has led to high levels of
industrialization leading to the discharge of effluents containing heavy
metals into out environment(7). Various activities by man in recent
years have increased the quantity and distribution of heavy metals in the
atmosphere, land and water bodies. The extent of this widespread, but
generally diffused contamination has caused concern about its possible
hazard on plants, animals and human beings.
The overall role of trace elements in living organisms is directly
related to the interactions within all environmental, geological,
biological, or marine systems. For example, the trace element
composition of soil may significantly influence the elemental
composition of the vegetation, which in turn influences that of animal or
human tissues or fluids via the food chain (8).
Some elements such as; copper, iron, nickel, chromium, zinc,
cobalt, iodine etc are essential in very low concentrations for the survival
of all forms of life, and are rather known as essential trace elements (9).
However, in higher concentrations, these essential trace elements can
also be quite toxic.
In addition to the essential elements, there are several others which are
always found in body tissues and fluids but for which no proof of
essentiality has been established. These elements are often referred to as
non-essential, e.g. lithium, boron, etc.
Some elements such as cadmium, mercury and lead are
prominently classified as toxic. This is because of their detrimental
effect even at low levels (8,9). It should be noted, however that all trace
elements are predominantly toxic when their levels exceed the limits of
safe exposure. These limits vary widely from one element to another.
There is a range of normal background concentration of these elements
in soils, sediments, water and living organisms. Pollution therefore is
the addition of a substance by human activity to the environment which
can cause injury to human health or damage to natural ecosystems (20).
Ingestion of heavy metals in food stuff contributes a substantial
proportion to total contamination in humans. Heavy metals are ingested
through the food chain directly or indirectly by humans and partially
accumulate in the human body. Exceeding toxic threshold values can
affect heath. For example cadmium disturbs kidney functions and has
cancerous effect (10). High levels of lead in children blood have been
known to have an inhibiting effect on certain enzymes (11).
World Health Organization and Food and Agricultural
Organization (WHO/FAO) have set some standards for heavy metals in
food stuffs. Therefore, constant analysis / investigation of food stuffs is
necessary to evaluate the magnitude and impact of trace element
contamination of the environment and to ensure compliance with the set
standards.
1.5 OBJECTIVES
i. Determine the concentration of heavy metals in pork.
ii. Determine the safety of pork sold in Nsukka and Enugu for human
consumption by comparing the levels of heavy metals in the muscle
with the WHO/FAO heavy metals