ABSTRACT
Water, sediment and shellfish were collected from four locations (Slaughter, Aboluma, Okwujiagu and Oginiba) of the Azobie creek of River state Nigeria and were evaluated for microbiological, heavy metals, nutritional composition and physico-chemical parameters. Bacterial isolates consisting of ( total heterotrophic bacteria and hydrocarbon utilizing bacteria count) and fungal count (total fungal count and hydrocarbon utilizing fungi count) were analysed from the shellfish and its habitant (water and sediments). Data generated were subjected to analysis of variance (ANOVA) and mean were separated using fishers minitab 2017. The highest total coliform counts obtained from Slaughter (control) had a value of 1.52 during wet season and 1.23x105 CFU/g in dry season and in Aboloma it was 1.53x105CFU/g for wet season and 1.12x105 Cfu/g for dry season in periwinkle . These decreased to an acceptable limit of 0.02 x10 5CFU/g at different time intervals of 24-96h of soaking and depuration. Total heterotrophic bacteria count in periwinkle had the highest count in control at Slaughter, Oginigba and Abuloma at a value of 0.48 and 0.33X105 CFU/g This was reduced to acceptable limit of 0.12 x 105 CFU/g. Similar trend occurred in oyster sample at the same locations. Total hydrocarbon utilizing bacteria and fungal count in oyster had the highest count of 9.80 during wet season and 8.90x105 CFU/g for dry seasons at Slaughter and Abuloma at 9.17x10 CFU/g for wet season and 7.12x105 CFU/g during dry season. Oginigba did not record any bacteria count. Total faecal count was reduced at different time interval of 24-96h to an acceptable limit , while for depurated at different time intervals during dry season, it was not reduced. This could be as a result of the different depuration methods. The same trend was observed in periwinkle although it was not fast as in oyster. The different bacterial profiles are probably attributable to industrial activities of the sites. The moisture, protein, fat, crude fiber and ash content were the major constituents which had been considered in evaluating the nutritional value of these species. Soaking shellfish had no effect on the proximate composition except in fat where it increased the fat and protein content in the control. Physio chemical parameters varied among different locations. The levels of Cd ( 0.00-2.5ppm) recorded in these samples were higher than the maximum recommended limit of 2-0ppm in sea food. The value of Cr recorded was between 1.50 – 2.0 ppm and was found to be higher than the maximum recommended limits of 0.15-1.0ppm.The levels of Pb (0.001-2.50) recorded in this study was higher than the recommended limits of 2.0ppm in some locations. The micro nutrient (K, Fe, and Zn) were above the permissible limits for human consumption as recorded by the Food and Agricultural Organization. Depuration had little effect on contaminant while soaking had no effect at different locations and different time intervals. Depuration performed better than soaking during dry season than raining seasons. Oyster was faster than periwinkle in removing this contaminant during depuration than soaking in during dry seasons.
TABLE OF CONTENTS
Title page ii
Declaration page iii
Certification iv
Dedication v
Acknowledgements vi
Table of contents vii
List of Tables xiv
List of figures xiv
List of plates xxi
Abstract xxii
CHAPTER 1: INTRODUCTION
1.1 Background of the study 1
1.2 Statement of Problem 5
1.3 Justification of the Study 6
1.3 Objectives of the Study 7
1.3.1 General objective of the
study 7
1.3.2 The specific objectives of
the study 7
CHAPTER 2
2.0 Review of Related
literature 9
2.1 Sea Food: Meaning and Component 9
2.2 Sources, Distribution and Components of Shellfish 9
2.3 Shellfish Nutritional Value and Food Uses 10
2.4 Food Uses and
Industrial Application of Shell Fish 15
2.5 Creeks
of River State- Geographical location, Vegetation and Weather
Condition 15
2.6 Industries
in the Creeks-Distribution, Raw Materials, Human Faeces 17
Discharge and Management in creek 16
2.7 Impact
of Waste Discharge into the Water Bodies on Aquatic and Human
life in the Creek 19
2.8 Microbial
Contaminants in the Water and their Impact on Human Health 19
2.9 Shellfish and
Heavy Metal Absorption 22
2.10 Nutritional
Composition of Seafood 23
2.11 Reduction
of risks Associated With Contaminated Shellfish 24
2.12 Shellfish
Contamination 24
2.13 Infectious Risk Related
to Shell Fish Consumption 25
2.14 Pathogenic
Organisms Associated In Shellfish Disease Outbreaks 27
2.15 Disease outbreaks
associated with shellfish 31
2.16 Proximate
Composition Of Shellfish 31
2.17 Depuration and
Relaying (Soaking) 32
2.18 Origin of Depuration 34
2.19 Pollution limit for
Shellfish Depuration and Relaying 36
2.20 Basic Principles of
Depuration 36
2.21 Quality of a Good
Depuration Stand 37
2.22 Heavy Metals 37
2.23 Cadmium Toxicity 42
2.24 Effects of Heavy Metals 43
2.25 Types Of Heavy
Metals That Can Be Dangerous To The Body 44
CHAPTER THREE
3.0 Materials and
Methods 48
3.1 Shellfish 48
3.2 Study Area
Description 48
3.3 Water Sample
Collection 49
3.4 Collection of
Sediments 50
3.5 Shellfish
Collection 51
3.6 Stocking and
Managing the Shellfish in the Soaking and Depuration Tanks 52
3.6 Determination
of Heavy Metals in Soft tissue of Shellfish 57
3.7 Determination of
Heavy Metals in Sediments 57
3.8 Determination of
Heavy Metals in Water 58
3.9 Analysis
of Physical and Chemical Parameters of the Sampling Area Water
sample 59
3.9.1 Temperature 59
3.9.2 pH 59
3.9.3 Salinity 60
3.9.4 Turbidity 60
3.9.5 Dissolved oxygen
(DO) 60
3.10 Proximate Analysis 62
3.10.1
Moisture
content analysis: 62
3.10.2
Ash
content analysis: 62
3.10.3Fat content analysis: 63
3.10.4 Crude protein
analysis: 63
3.10.5 Carbohydrate analysis 64
3.10.6 Crude fibre analysis 64
3.11 Microbiological
Analysis 65
3.11.1 Sample preparation 65
3.11.2 Total heterotrophic
bacteria count 65
3.11.3 Hydrocarbon utilizing
bacteria count 66
3.11.4 Total heterotrophic
fungal count 66
3.11.5 Hydrocarbon utilizing
fungi count 66
3.11.6 Vibrio count 67
3.11.7 Faecal coliform count 67
3.11.8 Isolation and
purification 67
3.11.9 Identification of
microorganisms 67
3.12 Identification and
characterization of the isolates 69
3.12.1 Bio chemical test 69
3.12.2 Catalase Test 70
3.12.3 Coagulase test 70
3.12.3 Motility in dole
urease (MIU) agar. 70
3.12.4 Preparation of MIU
agar 71
3.12.5 Klinger Iron Agar
(KIA) 71
3.12.6 Preparation of KIA 72
3.12.7 Inoculation 72
3.12.8 Preparation of
simmons citrate 72
3.12.9 Oxidase 72
3.12.10 Indole 73
3.12.11 Methyl red 73
3.12.12 Voges Proskauer 73
3.12.13 Urea utilization 74
3.12. 14 Citrate 74
3.13 Molecular Analysis 75
CHAPTER 4: RESULT
AND DISCUSSION
4.1 Effect
of Soaking and Depuration Time on Bacterial load of Oyster
Harvested From Different locations of the Creek at Different Seasons
of
The Year 80
4.2 Effect of Different Time Intervals
of Soaking and Depuration at
Different
Locations on Total Heterotrophic Bacteria (THBC) X105cfu/G
Of
Periwinkle Sample at Different Season 83
4.3 Effects of Different Time Intervals of
Soaking and Depuration on
Hydrocarbon
Utilizing Bacteria (HUBC) x105Cfu/g at Different location in
Oyster
Sample at Different season x105Cfu/g 86
4.4 Effects Of Different of Soaking
and Depuration Time on Total Fungal
counts
(Tfc) X105cfu/G of Periwinkle Sample Harvested from Different
location
at Different Season 89
4.5 Effect of different Time Interval
of Soaking And Depuration on Total
Fungal counts (Tfc) X105cfu/G
Of Oyster Sample Harvested from
Different location at Different
Season 93
4.6 Effect of Different Time Interval of
Soaking and Depuration Methods at
Different
locations on Hydrocarbon Utilizing Fcounts (HUFC)
X105cfu/G
Of Periwinkle at Different Season 97
4.7 Effects of Different Time Interval of
Soaking and Depuration at Different
locations
on Hydrocarbon Utilizing Fungal Counts (HUFC) x105cfu/g of
Oyster
sample at Different Season x105CFU/g 100
4.8 Effect of Different Time Interval of
Soaking and Depuration in Faecal
Coliform
Count of Oyster Sample Harvested at Different Locations at Different
Season x105cfu/g 104
4.9 Effect of Different Time Interval of
Soaking and Depuration Methods in
Faecal Coliform Count of Oyster
Sample Harvested from Different Locations at
Different Season x105cfu/g 107
4.9.1 Total load of different microbial contaminants
on sediment and water Body
from different locations 110
4.10 Organisms Isolated 122
4.11 Result
and Discussion of Proximate Composition of Shellfish
Harvested at Different Location During Different Season 131
4.12 Physicochemical Parameter Of Water 150
4.13 Heavy Metal Concentration of Shellfish
Harvested from Different
Locations at Different Seasons 166
4.13.1 Effect of different
time intervals of soaking and depuration on six heavy 166
metals for periwinkle at Abuloma location
4.13.2 Effect of different time intervals of soaking and depuration on
six heavy
metals for periwinkle at slaughter
location 170
4.13.3 Effects of different time intervals of soaking and depuration on
six
heavy metals for Periwinkles at Oginigba
location 172
4.13.4 Effect of different time intervals of
soaking and depuration on six (6) heavy
Metal for Okwujiagu location 175
4.13.5 Effect of different
time intervals of soaking and depuration on the level of
six heavy metals in oysters at different season for Slaughter
location 180
4.13.6 The effect of different time intervals of
soaking and depuration on
six heavy metals of
oyster at different season Aboluma location. 183
4.13.7 The effects of different time intervals of
soaking and depuration on six
heavy
metal on oyster at different seasons for Okwujiagu. 187
4.13.8 Effects of different time intervals of
soaking and depuration of oysters on
six heavy metal at Oginigba location
different seasons 190
4.13.9 Heavy metal concentration
in water and sediment 196
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1
Conclusion 198
5.2
Recommendation 199
References 201
Appendices 222
LIST
OF TABLES
2.1 Vitamin contents of some shellfish meat 13
2.3 Mineral contents of some
shellfish meat 14
2.4 Potential enteric
and water-based microbial pathogens 20
2.5 Seafood borne illnesses associated
with bacterial pathogens 21
2.6 Proximate composition of some shellfish species from Indian
waters 33
4.1 Effect of different time interval of
soaking and depuration at different
locations
on total heterotrophic bacterial count (THBC) x105 CFU/g in
oyster
sample at different Seasons 82
4.2 Effect of different time intervals of
soaking and depuration At different
locations on total heterotrophic
bacteria (THBC) x105cfu/g
in periwinkle 85
4.3 Effects of different time intervals of
soaking and depuration on
hydrocarbon
utilizing bacteria (HUBC) x105Cfu/g at different location in
oyster
sample at different season x105cfu/g 88
4.4 Effects of different time interval of
soaking and depuration on total fungal
counts
(TFC) x105cfu/g at different location in periwinkle sample at
different
Season 92
4.5 Effect of different time interval of
soaking and depuration at different
locations
on total fungal counts (TFC) x105cfu/g of oyster sample at
different
Season 96
4.6 Effect of different time interval of
soaking and depuration methods at
different
locations on hydrocarbon utilizing fungal counts (HUFC) x
105cfu/g
in periwinkle at different Season 103
4.7 Effects of different time interval of
soaking and depuration at different
locations
on hydrocarbon utilizing fungal counts (HUFC) x105cfu/g in
oyster
sample at different season x105cfu/g 106
4.8 Effect of different time interval of
soaking and depuration methods in
faecal
coliform count of oyster sample harvested from different location at
Different
Season x105cfu/g 109
4.9 Effect of Different Time Interval of
Soaking and Depuration Methods at
Different
Locations on Faecal Coliform in Periwinkle Sample at Different
Season
x105cfu/g
4.10 Biometric data of bacteria isolates 128
4.11 Effect of different time intervals of
soaking and depuration On Six
Heavy
metals for periwinkle at Abuloma Location 133
4.12 Effect of different time intervals of
soaking and depuration on six heavy
metals
for periwinkle at slaughter location 134
4.13 Effect of different time intervals of
soaking and depuration On six
heavy
metals for periwinkle at Oginigba Location 136
4.14 Effect of different time intervals of
soaking and depuration of periwinkle
on Six
(6) heavy metal for Okwujiagu Location 137
4.15 Effect of different time intervals of
soaking and depuration on the level of
six (6)
heavy metals in myster at different season for slaughter location 139
4.16 Effect of different time intervals of
soaking and depuration on six heavy
metals
at different season Aboluma Location 140
4.17 Effect of different time intervals of
soaking and depuration on six heavy
metal
on oyster at different seasons for Okwujiagu. 142
4.18 Effect of different time intervals of
soaking and depuration on six heavy
metal at Oginigba location different Seasons. 143
4.19 Heavy metal analysis in water and sediments 145
LIST
OF FIGURES
3.1 Map of the
sampling stations along the Azonie Creek in River State 49
4.1 Total hetrotrophic bacteria count in
sediment and water body from
different locations at different
seasons 111
4.2 Hydrocarbon utilizing bacteria in
sediment and water body from different
locations
at different seasons 113
4.3 Total fungal counts in sediment and
water from different locations at
different
seasons. 115
4.4 HUF counts in sediment and water from different location at
different 117
4.5 Total vibro parahaemolyticus counts in sediment and water from
different locations at different
seasons 119
4.6 Total Faecal coliform counts in
sediment and water from different
locations at different seasons. 121
4.7 Escherichia Coli Strain 124
4.8 Vibrio Stylophorae Strain 125
4.9 Candida albican strain 125
4.10 Meiothermus grandicius Strain 127
4.11 Biometric data of bacteria count.
130
4.11 The moisture content of soaked and
depurated shellfish for different
locations at different time
intervals for raining seasons 133
4.12 The moisture content of soaked and
depurated shellfish for different
locations
at different time intervals for dry seasons 134
4.13 The fat content of soaked and depurated
shellfish for different locations at
different
time intervals during raining seasons
136
4.14 The fat content of soaked and depurated
shellfish for different locations at
different
time intervals during dry seasons
137
4.15 The protein content of soaked and
depurated shellfish for different
location
at different time intervals during raining seasons 139
4.16 The protein content of soaked and
depurated shellfish for different
locations
at different time intervals during dry seasons 140
4.17 The Ash content of soaked and depurated
shellfish for different location at
different
time intervals during raining seasons 142
4.18 The ash content of soaked and depurated
shellfish for different locations at
different
time intervals during dry seasons
143
4.19 The crude fibre content of soaked and
depurated shellfish for different
locations
at different time intervals during raining seasons 145
4.20 The Crude fibre content of soaked and
depurated shellfish for different
locations
at different time intervals during dry season 146
4.21 The carbohydrate content of soaked and
depurated shellfish for different
location
at different time intervals during raining seasons 148
4.22 The Carbohydrate content of soaked and
depurated shellfish for different
locations
at different time intervals during dry seasons 149
4.23 Variation in temperature of the water body at different
locations in Azobie
creek during different month and seasons
of the year 151
4.24 Variation in Dissolved oxygen of the water body at different
locations in
Azobie creek during different
month and seasons of the year 154
4.25 Variation in pH of the water body at different locations in
Azobie creek
during different month and seasons of the
year 156
4.26 Variation in Nitrite content of the water body at different
locations in
Azobie creek during different month and
seasons of the year. 158
4.27 Variation in Nitrate of the water body at different locations
in Azobie creek
during different month and seasons of the
year. 159
4.28 Variation
in salinity content of the water body at different locations in
Azobie creek during different month and seasons of the year 161
4.29 Variation in Amonia content of the water body at different
locations in
Azobie creek during different month and
seasons of the year 163
4.30 Variation
in Chloride content of the water body at different locations in
Azobie creek during different month and seasons of the year 165
LIST
OF PLATES
3.1 Water Sample
Collection from Azobie creek at monthly interval. 50
3.2 Collection of the
Sediment from Azobie creek 50
3.3 Collection of the
Oyster from the root of mangrove in Azobie creek 51
3.4 Collection of the
Periwinkle from the sediment 51
3.5 Depuration Stand 53
3.6 Oyster shell 53
3.7 Oyster without
shell 54
3.8 Periwinkle in
shell 54
3.9 Periwinkle in the
soaking tank 55
3.10 Periwinkle in the
depuration tank 55
3.11 Oyster in the
depuration tank 56
3.12 Oyster in the
soaking tank 56
3.13 ZR Fungal/Bacterial
DNA Kit 75
CHAPTER 1
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Environmental pollution
is a major problem facing many
settlements in Rivers State, especially Azobie creek where there was recent oil vandalization., repairs of
vessels, human faces, and increased in domestic wastes .The water and the shellfish quality from this creek had
been affected due to increase in environmental pollution. The increase in human
population also in this area has led to increase in rate of pollution and
contamination of most shellfish (Obodaiet al., 2010).
During soaking and
depuration of shellfish harvested from a polluted area, the shellfish is
dipped in clean water in a container
(unpolluted water) to allow the shellfish to cleanse or purge themselves by
continuation of their normal filter-feeding and digestive process. This is a
natural cleansing process that can be performed in a controlled environment by
immersion in tanks of clean seawater to allow sewage contaminants to be purged
(le Guyaderet al., 2006).
Depuration unlike
cooking allows bivalve shellfish to be marketed as a live or fresh product.
This is very common with species such as oyster, clams, periwinkles and mussels
which are traditionally eaten live or are slightly cooked prior to consumption
.It is the trust of this study to investigate the effect of depuration and
soaking of live shellfish on heavy metal content, nutrient composition and
microbial load of shellfish harvested from polluted creek of Rivers state.
Most water bodies in Rivers State are
polluted. They receive indiscriminate effluent discharge of oil spill from
heavily industrialized and highly populated Port-Harcourt metropolis.
These are some of
the reasons why pollution occur frequently in RiverState. These also occur as a
result of geological weathering, industrial processing of ore, metals,
petroleum exploitation, vessel repair facilities, industrial wastes, oil spill
and humanfaces(Chaerunet al., 2004;Muniaine Mujika et al., 2002;Loisyet
al., 2005;Lees, 2000) These can impact negatively on the aquatic organisms,
water and sediment. This causes most residents to eat contaminated
seafoods.Clean-up of oil pollution in Rivers state is not frequent, and
inadequate,leaving many people to cope with ongoing impacts of pollution
to humans (Chaerunet al.,2004).
Some shellfish
such as oyster and periwinckle (Ifon and Umoh,2007) have the ability to
accumulate contaminants such as heavy
metals, micro-organisms and polycyclic aromatic hydrocarbons in the
environment. The ingestion of these contaminants by these organisms will not
only affect the productivity and reproductive compatibility of these organisms
but also affect the health of humans who depend on these organisms for food
(Chaerunet al., 2004:Ifon and Umoh,2007)
The mangrove
oysters (Crassostergasar are filter feeders, capable of accumulating
micro-organisms in high concentration. They filter water at a rate of 2 to 5
litres/hour and also absorbs biotic and abiotic contaminant in their habitat
(Nunes and Parsons,1998). They are one of the popular edible bivalves in Niger
Delta. They have been identified as important vehicles of food-borne diseases
because of their ability to absorb bacteria and viruses despite their
nutritional benefit. These species may be eaten raw or
lightly cooked and this increases the risk of food borne diseases.Shellfish
like oysters feed by filtering large volumes of water and sediments. If the
water contains microbiological and chemical contaminants and natural toxins,
these will concentrate in their gut. As people normally eat shellfish raw,
slightly cooked and without removing the gut, they are likely to become ill if the shellfish is harvested from heavily contaminated areas (Adeyerne,
2002). Oysters could be used as
vectors for indicator of water
quality since they harbor micro-organisms used as indicators of water quality
One group of water and sewage indicators is the enteric bacteria,-fecal
coliforms, which naturally inhabit the intestines of humans and are therefore
used as surrogates in water quality assay (Nester et al., 2004).The
range of bacteria commonly found in
waste water, tissues and over flows
discharges in a contaminated environment include Salmonella spp, Yersinia
enterocolitica, Shigella spp Enterococcus spp, Escherichia
coli, Clostridium perfringens, Staphylofcoccus spp,
and Campylobacter spp (Scott, 2002) When enteric bacterium (Escherichia
coli) is excreted into the water, they die at a slower rate than pathogenic
bacteria such as Salmonella and Shigella and their presence might
indicate presence of other pathogens in the water (Madigan et al.,
2000).Periwinkle Tympanotonus Fuscatus is the most common gastropod in
the Niger Delta Nigeria and are used for delicacy by most communities. They
survive in a salinity range of 0.5 to 27.5ppt. They inhabit in stagnant waters
where the substratum is muddy and rich in nutrients (Jamabo and Abowei, 2010).Tympanotonus
Fuscatus var fuscatus and
Crastora gassar has been with high level of contaminant, and is the one of
interest in this study (Davis et al.,2006).
Some heavy metals that are discharged into
aquatic ecosystems are likely collected as particles and accumulate in sediments
and water (WHO,2006). A large reservoir of the metals in sediments exist and
act as overlying water column (WHO,
2006) and lead to adverse ecologic
effects and danger to human health. The
release of these contaminants from sediments and water may not only result from
re-suspension of particulates, but also from the activities of microorganisms
on the sediment and also on sediment-water interface. The extent of the risks
of heavy metals and microorganisms is difficult to assess because of the
complexity of biochemical activities that alter availability of metals in
water, tissues and sediments. This is
why there is need for effective
depuration systems, to ensure that contaminant are washed out from the tissue
(Obodai et al., 2010).
Depuration is a process by which shellfish are
placed in a clean water environment for a period of time to allow purging of
its contaminants (Annon, 2006). Most researches and publications focus
primarily on depuration of seafood rather than fresh water animals. Modern seafood depuration, are segregated
physical tanks using treated sea water sterilized either by chlorine,
ultraviolet or Ozone.
Depuration helps in preventing water and food
borne diseases such as typhoid fever and other illness associated with sewage–
borne bacteria and other contaminant (le Guyer, 2006). Depuration has been in
practice globally within the last century but Nigeria has not recorded any
depuration facilities, although the rate of consumption of these shellfish is
increasing yearly in most parts of Nigeria. In research publications and
government regulations, depuration is more embraced as “public protection”
rather than as public awareness. In this study, depuration is embraced as both
public protection and public awareness in some countries. It is now known that
the success of depuration depends on
understanding of the environment, good monitoring practice, levels of pollution
in the harvested area, and quality of water and shellfish (FAO, 2008). Although depuration confer a
level of additional food safety assurance to shellfish harvested from areas which may be highly polluted, it will not render shellfish
grown in heavily polluted waters a safe product. Literature shows that depuration successfully
reduces bacteria, heavy metals and viral load in moderately polluted area.
Depuration is capable of removing many bacterial species including faecal
coliform from shellfish (Kelly et al., 1991). The efficacy of depuration
is influenced by water temperature, salinity and turbidity which must be
optimized to maintain the health status of shellfish (Annon, 2006). The success
of depuration varies with species of shellfish, initial pathogen load, length
of exposure to pathogens and pathogen distribution within shellfish tissues. It
also depends on other factors such as mode of contamination and also the
environmental conditions
1.2THE STATEMENT OF PROBLEM
Shellfish which constitute major source of
protein to rural communities of River State is harvested from the stream,
rivers and sea in this area. These water bodies are continually contaminated
with highly polluted industrial waste heavily loaded with oil spill, heavy
metals, human faeces, agricultural waste and several hydrocarbon polymers. The
shellfish harvested from these water bodies are consumed without any treatment
to reducethese contaminants. Consequently cases of food infection and
intoxification relating to pathogenic microorganisms and heavy metals
contaminants have been reported severally among these people. The major source
of these food associated diseases could be from the sea food that they consume
heavily. It became necessary to investigate the level and types of contaminants
in the water bodies and the shellfish and the effect of depuration and soaking
in reducing these contaminants in harvested
shellfish (periwinkle and oysters). This approach could be simple and
affordable than checking the effluents in the water bodies within the
depuration plan.
1.3 JUSTIFICATION OF THE STUDY
Shellfish,
particularly Periwinkles and oysters are one of the major foods used for
special delicacy in Rivers State. They are the cheapest and principal source of
animal protein for the low-income group in the state. Periwinkles and oysters
are of commercial value because most people use it in soups and as a delicacy.
Most resort to shellfish as a healthy alternative to meat today because they
are cheaper, provides high quality proteins and good profile of fatty acids and
easily digestible mineral salts (Andrew, 2001).
Unfortunately,
shellfish grow naturally in coastal waters and are exposed toseries of
contaminants including pathogenic enteric micro-organisms, cyclic hydrocarbons
and toxic heavy metals. Thus microbial quality and levels of heavy metals and
polycyclic hydrocarbon content of the inhabiting water body determine safety of
the shellfish (Offen et al., 2009). River state is highly industrialized
in Nigeria with discharge of oil spill, human faeces, heavy metals
contaminants, cyclic hydrocarbons, mining residues, other mineral pollutants in
the water bodies where the fishes inhabit (Koopmans et al., 2002).
Several cases of food poisoning and untimely death of eating contaminated shell
fish have been reported in this area (Davis et al., 2006; Chaerun et
al., 2004; Jackson and Ogburum, 1996; Otsu, 1999; Bahir et al., 2012)
Many communities in River State are
affected and people in these communities are reluctant and scared to eat
locally caught shellfish. The people have no idea of any method to
decontaminant their shellfish before consumption .Again, they sell their fish
to buyers in the same level of
contamination. Depuration and soaking is one of the simplest cost effective approach that processors can
use to make shellfish safe for consumers .The people are unaware of this
approach. Depuration in this study could be used to produce natural safe
shellfish to ensure consumer safety and sustainable supply of high quality
flesh protein to the common man in Rivers state and its environment. This will
improve food security.
1.3 OBJECTIVE OF THE STUDY
1.3.1
General objective of the study
The main objective is to
investigate the effect of different time intervals of soaking and depuration on
microbial load, heavy metal, nutritional composition of shellfish harvested
from polluted creek in rivers state at different seasons
1.3.2
The specific objectives
of the study are to:
1.
To construct depuration
system
2.
To determine the concentration of heavy metal
present in the harvested periwinkle and oyster
3.
To evaluate the microbial
quality and proximate composition of the harvested periwinkle and oyster
4.
To determine the effect
of depuration and soaking time on heavy metals load on periwinkle and oyster
harvested at different location from a polluted creeks of Rivers state, Nigeria
at different seasons.
5.
To determine the effect
of soaking and depuration time on nutritional composition of periwinkle and
oyster harvested at different location from a polluted creeks of Rivers state, Nigeria at different seasons
6.
To determine the effect
of depuration and soaking time on microbial quality of periwinkle and oyster
harvested from different location from a polluted creeks of Rivers state,
Nigeria at different seasons .
7.
To evaluate the variation
in physical and chemical parameters of the shellfish habitat at different
location of the Azobie Creek.
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