TABLE OF CONTENTS
ATTESTATION ……………………………………………………………………………………………. iii CERTIFICATION ………………………………………………………………………………………….. iv ACKNOWLEDGEMENTS ……………………………………………………………………………… vi LIST OF TABLES ………………………………………………………………………………………….. ix LIST OF FIGURES …………………………………………………………………………………………. x LIST OF ACRONYMS …………………………………………………………………………………… xi SUMMARY ………………………………………………………………………………………………….. xii
CHAPTER ONE: INTRODUCTION ………………………………………………………………… 1
1.1 Background Information ………………………………………………………………………….. 1
1.2 Problem Statement ………………………………………………………………………………….. 3
1.3 Justification of the Study …………………………………………………………………………. 5
1.4 Research Questions …………………………………………………………………………………. 6
1.5 General and Specific Objectives ……………………………………………………………….. 7
1.5.2 Specific Objectives: …………………………………………………………………………. 7
CHAPTER TWO: LITERATURE REVIEW ………………………………………………………. 8
2.1 Heavy Metals …………………………………………………………………………………………. 8
2.2 Lead…………………………………………………………………………………………………….. 10
2.3 Sources of Lead…………………………………………………………………………………….. 11
2.3.1 Natural Sources ………………………………………………………………………………. 11
2.3.2 Anthropogenic Sources of Lead………………………………………………………… 11
2.3.3 Other Sources of Lead …………………………………………………………………….. 12
2.4 Toxico-dynamics of Lead ………………………………………………………………………. 13
2.5 Lead Poisoning……………………………………………………………………………………… 13
2.6 Epidemiology of Lead Poisoning…………………………………………………………….. 14
2.7 Lead Poisoning in Zamfara State …………………………………………………………….. 18 2.8 Lethal Levels of Lead in Animals ……………………………………………………………. 20
2.9 Traditional Livestock Breeds Used as Food Animals…………………………………. 20
2.9.1 Cattle …………………………………………………………………………………………….. 21
2.9.2 Sheep …………………………………………………………………………………………….. 23
2.9.3 Goat ………………………………………………………………………………………………. 24
2.9.4 Camels…………………………………………………………………………………………… 25
2.10 Lead Poisoning in Animals. ………………………………………………………………….. 26
2.11 Clinical Signs of Lead Poisoning in Animals ………………………………………….. 29
2.11.1 Acute …………………………………………………………………………………………… 29
2.11.2 Sub-acute……………………………………………………………………………………… 29
2.11.3 Chronic ………………………………………………………………………………………… 29
2.12 Lesions in Animals ……………………………………………………………………………… 30
2.13 Lead Poisoning in Children ………………………………………………………………….. 30
2.14 Diagnosis of Lead Poisoning ………………………………………………………………… 32 2.15 Treatment of Lead Poisoning ………………………………………………………………… 33 2.17 Prevention of Lead Poisoning ……………………………………………………………….. 35
2.18 Public Health Implications of Lead Poisoning ………………………………………… 36
CHAPTER THREE: METHODOLOGY ………………………………………………………….. 40
3.1 Area of Study ……………………………………………………………………………………….. 40
3.3 Study Population …………………………………………………………………………………… 42
3.3.1 Inclusion Criteria ……………………………………………………………………………. 42
3.3.2 Exclusion Criteria …………………………………………………………………………… 42
3.4 Sample Size Determination…………………………………………………………………….. 42
3.5 Sampling Technique ……………………………………………………………………………… 45
3.6 Sample Collection …………………………………………………………………………………. 45
3.7 Sample Preparation for Laboratory Analysis …………………………………………….. 45
3.7.1 Sample Digestion ……………………………………………………………………………. 45
3.7.2 Spectrophotometry Techniques for Lead ……………………………………………. 46
3.8 Data Analyses ………………………………………………………………………………………. 46
3.9 Ethical Considerations …………………………………………………………………………… 46
3.10 Limitations …………………………………………………………………………………………. 47 CHAPTER FOUR: RESULTS ………………………………………………………………………… 48 CHAPTER FIVE: DISCUSSION …………………………………………………………………….. 61
CHAPTER SIX: CONCLUSIONS AND RECOMMENDATIONS …………………….. 64
6.1 Conclusions ………………………………………………………………………………………….. 64
6.2 Recommendations …………………………………………………………………………………. 64 REFERENCES ……………………………………………………………………………………………… 65 APPENDIX 1 ………………………………………………………………………………………………… 73
APPENDIX 2 ………………………………………………………………………………………………… 74 APPENDIX 3 ………………………………………………………………………………………………… 75
LIST OF TABLES
Table 1: Proportionate allocation of samples based on slaughter figures ……………… 44 Table 2: Prevalence of lead residues in tissues of animals slaughtered at Gusau
abattoir ………………………………………………………………………………………………………… 51
Table 3: Mean concentration of lead (mg/kg) in different species of animals
slaughtered at Gusau abattoir …………………………………………………………………………… 54
Table 4: Mean concentration of lead (mg/kg) in goats of different ages slaughtered at
Gusau abattoir ……………………………………………………………………………………………….. 55
Table 5: Mean concentration of lead (mg/kg) of different ages in camels slaughtered
at Gusau abattoir ……………………………………………………………………………………………. 56
Table 6: Mean concentration of lead (mg/kg) of different ages of sheep slaughtered at
Gusau abattoir ……………………………………………………………………………………………….. 57
Table 7: Mean concentration of lead (mg/kg) of different ages of cattle slaughtered at
Gusau abattoir ……………………………………………………………………………………………….. 58
Table 8: Prevalence of lead residues in different breeds of cattle and sheep at Gusau
abattoir …………………………………………………………………………………………………………. 59
Table 9: Association between length of stay in Zamfara and tissues lead residues in
animals slaughtered at Gusau abattoir, …………………………………………………………….. 60
LIST OF FIGURES
Figure 1: Map of Nigeria showing the position of Zamfara State and Gusau LGA in
Zamfara State ………………………………………………………………………………………………… 41
Figure 2: Sex distribution of animals slaughtered at Gusau abattoir ……………………… 48
Figure 3: Source of animals slaughtered at Gusau abattoir ………………………………….. 49
Figure 4: Distribution of animals slaughtered at Gusau abattoir by LGA of purchase in
Zamfara State ………………………………………………………………………………………………… 50
Figure 5: Chart indicating the three levels of lead residues found in all species
slaughtered at Gusau abattoir …………………………………………………………………………… 52
Figure 6: Prevalence of lead residues in different animal species slaughtered at Gusau
abattoir …………………………………………………………………………………………………………. 53 LIST OF ACRONYMS
| AAS | Atomic Absorption Spectrophotometer |
| ANOVA | Analysis of Variance |
| BAL | British Anti Lewisite |
| BLL | Blood lead level |
| CDC | Centres for Disease Control and Prevention |
| EC | European Commission |
| EDTA | Ethylene diamine tetra acetic acid |
| EPA | Environmental Protection Agency |
| EU | European Union |
| FAO | Food and Agriculture Organisation |
| FSIS | Food safety and inspection service |
| LGA | Local Government Area |
| MSF | Medecins sans Frontieres |
| NARICT | National research Institute for Chemical Technology |
| NFELTP | Nigeria Field Epidemiology and Laboratory Training Programme |
| OECD | Organisation for Economic Cooperation and Development |
| PPM | Parts per Million |
| PVC | Poly vinyl Chloride |
| SD | Standard Deviation |
| UNEP | United Nations Environmental Programme |
| WAD | West African Dwarf |
| WHO | World Health Organisation |
SUMMARY
Lead is a bioaccumulative heavy metal usually found in nature combined with other elements to form lead compounds. Over 400 children were reported to have died as a result of lead poisoning outbreak in Zamfara State, Nigeria and about 2000 children are currently on treatment. The prevalence of lead residues in tissues of animals slaughtered at Gusau abattoir, Zamfara State was determined using Atomic Absorption Spectrophotometer. A total of 384 tissue samples were collected and their lead content determined. About 95% of the 384 animals were purchased from markets within Zamfara State and out of all the samples investigated 324(84.4%) had lead residues. The lead residues in 314(81.80%) of the animals were above the permissible limit of 0.1mg/kg recommended by World Health Organisation and European Commission. Lead residues were not detected in about 60(16.60%) of the animals sampled. There was no significant difference (p>0.05) observed in tissue accumulation of lead in animals based on difference in age, sex, species or breed of the animal. Gross contamination of the environment from where these animals were sourced could therefore be inferred.
KEY WORDS: Lead residues, Animal tissues, Atomic Absorption
Spectrophotometer
CHAPTER ONE: INTRODUCTION
1.1 Background Information
Lead is a bluish soft metal with atomic number 82; atomic weight 207.19, specific gravity 11.34, melting point 327⁰C and boiling point 1740⁰C. It is the most common industrial metal that has become widespread in air, water, soil and food.1 Metals are often characterized and distinguished from non-metals by their physical properties which include the ability to conduct heat, and an electrical resistance that is directly proportional to temperature, malleability, ductility and even luster.2
Heavy metals can be classified into four major groups based on their health importance.3, 4 Copper, zinc, cobalt, chromium, manganese and iron are essentialandalso called micronutrients but are toxic when taken in excess of requirements.4, 5 Barium, lithium and zirconium are non – essential. Tin and aluminium are less toxicwhereas mercury, lead, cadmium and arsenic are highly toxic.
They are (lead, cadmium, mercury and arsenic) among the main toxic metals that remain in the environment permanently because they cannot be degraded and thus find their way into the food chain and ultimately into the tissues. They have direct physiologically toxic effects when stored or incorporated in living tissues.6
Heavy metals are kept under environmental pollutant category due to their toxic effects on plants, humans and food. Heavy metals such as lead, arsenic, cadmium and mercury are persistent, accumulate and are not metabolized in to other intermediate compounds and do not easily break down in environment.1
Poisoning by toxic chemicals can cause serious stock losses. Historically, lead and arsenic have been the most common causes of inorganic chemical poisoning in farm animals.7 The increase in industrial and agricultural processes has resulted in increased concentrations of metals in the environment. These metals are taken in by plants and consequently animals that graze on such contaminated plants and animals that drink from polluted water also accumulate such metals in their tissues.8 Some heavy metals like arsenic, cadmium and lead have been reported to have no known bio-importance in human biochemistry and physiology and consumption even at very low concentrations can be toxic.9, 10
Several organisations have pointed out the need for monitoring heavy metal concentrations in the environment because of their persistence and accumulation in the biota.11
Lead is a metabolic poison and a neurotoxin that binds to essential enzymes and several other cellular components and inactivates them.12 Toxic effects of lead are seen in haemopoeitic, nervous, gastrointestinal and renal systems.6
Lead poisoningis a medical condition caused by increased levels of the heavy metal lead in the body. Lead interferes with a variety of body processes and is toxic to many organs and tissues including the heart, bones, intestines, kidneys, reproductive and nervous systems. It interferes with the development of the nervous system and is therefore particularly toxic to children, causing potentially permanent learning and behavior disorders. Symptoms include abdominal pain, confusion, headache, anemia, irritability, and in severe cases seizures, coma, and death.13 Toxicity of lead is closely related to age, sex, route of exposure, level of intake, solubility, metal oxidation stage, retention percentage and duration of exposure, frequency of intake, absorption rate and mechanisms and efficiency of excretion.14
In a survey of lead residue in kidney and liver of slaughtered cattle in Sokoto central abattoir, Nigeria, Bala et al15 reported a prevalence rate of 100%. The presence of lead in the liver among different age groups was above the permissible limits of
0.1mg/kg set by the Food and Agricultural Organisation (FAO) but in the kidney the concentration was within the permissible level in all age groups except for 0 – 2 years of age.
In another study of metal composition of livers and kidneys of cattle from Southern Nigeria, Iwegbue16 reported levels of various metals were generally low and within international statutory safe limits.16 However, Nwude et al17 in a study of metal quantification in cattle: a case study of cattle slaughtered at Ota abattoir, Nigeria observed that the level of six metals quantified were higher than the WHO standards and gross contamination of cattle could be inferred; and the levels of metals in cattle parts could be used as biomarkers of metal pollution, though highly influenced by other factors.17
In a study of outbreak of fatal childhood lead poisoning related to artisanal gold mining in Zamfara State, Doyeema et al18 reported that venous blood lead samples were obtained from 59% (204 of 345) of children < 5 years of age. All blood samples indicated lead poisoning, blood Lead level (BLL) ≥ 10 μg/dl. In 97% of children, BLLs were ≥ 45 μg/dl which is the CDC-recommended threshold for initiating chelation therapy.19 Eighty-five percent of blood samples exceeded 65μg/dl, the maximum detection limit of the Lead Care II instrument.18
1.2 Problem Statement
Lead poisoning accounts for about 0.6% of global burden of diseases.20 Lead has been impacting the health of humankind since the Romans began mining it 2500 years ago, and despite early knowledge of its harmful effects, exposure to lead from a wide variety of sources persists to this day.21
Lead bio-accumulates in many organs of the body after ingestion, it adversely affects many organs and systems which results in conditions such as anaemia, kidney damage, high blood pressure, impaired hearing and mental retardation22 and elevated levels can cause abortion in female animals and humans.22 Consumption of carcass containing lead can cause lead poisoning as a result of bioaccumulation in body tissues, and this varies with individual and the duration of lead exposure.23, 24
In an assessment of metal levels in fresh milk from cows grazed around Challawa Industrial Estate, Kano, Nigeria, Ogabiela et al25reported that the concentrations were very high as the metals of samples exceeded the World Health Organisation permissible limits.25 Another study by Okoye and Ugwu26 on the impact of environmental cadmium, lead, copper and zinc on quality of goat meat in Nigeria reported high levels of cadmium, copper and zinc in the liver, kidney and muscles of goats.26 However, lead levels determined were relatively within safe limits. Akan et al27 in a study of heavy metals in the liver, kidney and meat of cattle, sheep, goat and chicken from Kasuwan Shanu, Maiduguri, Nigeria reported that the concentrations of all metals were within the tolerance limits with the exception of chromium and lead which were higher than standard limits.27 Nwude et al28 also reported varying levels of heavy metals in different seasons indicative of the effect of season as a factor in accumulation of heavy metals by animals.28
Environmental levels of lead have increased more than a thousand fold over the past three centuries as a result of human activity. The greatest increase occurred between the years 1950 and 2000 and reflected increasing world wide use of leaded gasoline. Lead is released into the air in the form of metal fumes or suspended particles from fuel combustion or smelting and disposal of wastes, however, most of the lead poisoning is from leaded gasoline.6
Dioka et al29 and Kamala and Kumar30 reported that some of these waste materials may contain some heavy metals such as lead and others that are dangerous to human and animal health.29, 30
Results of a recent study conducted in Macedonia indicate that Lead concentration in animal tissues is dependent on sampling locality, the organ and animal species. The concentrations of lead in the liver and kidney tissues taken from industrial area were higher as compared to other localities from which samples of tissues were taken for analysis.31
It is evident from available information that lead poisoning in man could result from consumption meat and milk of poisoned cattle, camel, sheep, goats and birds. Man can also be poisoned by lead through mining activities as is obtained in Zamfara State due to illegal, informal or unsafe mining of lead. Environmental poisoning is another risk for human especially from leaded petrol, diesel and even water.
The current study will provide information on lead poisoning in cattle, camel, sheep and goats as a risk for consumers of these various meats. This will serve as a guide to the public.
1.3 Justification of the Study
From a public health point of view, consumption of lead-contaminated animal products from lead-poisoned animals poses a food safety concern especially in children less than five years of age. Lead concentrations in the liver and kidneys are usually the highest and can be detected within few days before it is redistributed for storage in bones.
The primary route of lead exposure for humans is through ingestion of contaminated foods. The recent outbreak of lead poisoning and other heavy metals amongst local miners in Zamfara State calls for investigations of animals in that locality and other locations as they may have ingested the heavy metals. According to Doyeema et al18prevalence of lead poisoning is very high in Zamfara State. Over 400 children were reported to have died as a result of the lead poisoning outbreak in Zamfara State; about 2000 children are currently on treatment. In 2010, WHO stated that over 4000 children are at risk of lead poisoning and this is entirely preventable.
The habitats of animals are continually being polluted with lead metal as a result of indiscriminate dumping of waste materials on the land and in water bodies, illegal mining of ores, painting of animal‟s houses, and the use of tetra ethyl lead as an antiknocking additive to improve the quality of petrol in Nigeria and many other developing countries.
In Nigeria and Zamfara State in particular, most cattle are free grazing and drink water from ditches, streams, rivers and other possible contaminated water sources. They graze along roads, runways and other sites that might have been contaminated with toxic substances. Animals in the process could be liable to exposure to high levels of contaminants in the environment. These metals accumulate in the organs and other tissues which are sold for consumption by man. A primary source of lead exposure for human beings is through ingestion of contaminated foodstuff, consumption of contaminated animal products from lead – poisoned animals therefore poses a public health food safety concern especially among children less than five years. In view of the fact that there are very little or no available original data on lead residues in tissues of domestic and wild animals in the study site, this study will be undertaken in order to determine the levels of lead in meat of animals slaughtered at Gusau abattoir, Zamfara State.
