ABSTRACT
This study investigated hazard indices and human health risks associated with consumption of bivalve mollusc from the Niger delta. The research was conducted in two phases; The first was the analysis of consumption pattern and perception of bivalve molluscs in the studied locations through the use of structured questionnaire while in the second phase, four species of bivalve mollusc; Bloody cockle (Anadara senilis), Donax clam (Donax rugosus), Knife clam (Tagelus adansonaii) and Mangrove oyster (Crassosstra gasar) collected from four different locations in the Niger delta were assessed for microbiological hazards, toxic element contents, concentrations and compositional pattern of polycyclic aromatic hydrocarbons (PAHs), levels of polychlorinated biphenyls (PCB) congeners in bivalves as well as the estimated human health risk associated with the consumption of bivalve with these chemical contaminants. Standard methods of analyses were employed in the determination of microbiological hazards and levels of toxic elements, PAHs and PCBs concentrations in bivalves were determined through the use of gas chromatography while the United State Environmental Protection Agency (US EPA) method was used to estimate the human health risk of chemical contaminants in bivalves consumed in the Niger delta. Results of consumption pattern and perception indicated that bivalve consumption were driven by attributes such as easy availability, low-price and pleasant flavor. A chi-square test indicated a positive significant relationship (p<0.05) between demographic variables of the respondents and the level of perception toward bivalve consumption. Microbiological hazards isolated from bivalve samples included; Vibrio cholerae, Vibrio parahaemolyticus, Salmonella spp, Shigella spp, Listeria monocytogenes and Escherichia coli in levels above the stipulated FDA standard for shellfish which rendered the product unsafe for human consumption. Lead concentration was within the 1.5mg/kg acceptable limits while cadmium, arsenic and mercury were higher than FAO limits of 0.5, 0, 0.5 mg/kg respectively. The individual tissue burden of PAHs indicated bloody cockle (53.75μg/kg), knife clam (50.00μg/kg), mangrove oyster (40.34μg/kg) and Donax clam (36.94μg/kg) while the compositional pattern of PAHs indicated the dominant of low molecular weight PAHs in Andoni location while other study locations were dominated with high molecular weight PAHs. The diagnostic ratio showed that the PAH burden originated from petrogenic source at Andoni while that of other locations were from pyrogenic or combustion processes. The result of analysis for PCBs indicated the presence of lower chlorinated PCB congeners in all the study location. The total concentrations of PCB congener were highest at Bonny (1.75ng/g) while Andoni had the least (0.36ng/g). The PCB burden in bivalve tissue indicated that mangrove oyster accumulated the highest concentration (1.38ng/g) followed by bloody cockle (1.11ng/g) while Donax clam (0.60ng/g) had the least. The estimated human health risk indicated a non-carcinogenic values and hazard indices higher than threshold value of one for cadmium, total arsenic and methylmercury while risk values for carcinogens were higher than the US EPA stipulated one in one million chances for developing cancer. This implies that toxic elements apart from lead, carcinogenic PAHs and PCBs in bivalves from these locations can induce potential deleterious health effects to the consumers.
TABLE OF CONTENTS
CHAPTER TITLE PAGE
Title
Page .. .. .. .. .. .. .. .. .. i
Declaration .. .. .. .. .. .. .. .. .. ii
Certification .. .. .. .. .. .. .. .. .. iii
Dedication .. .. .. .. .. .. .. .. .. iv
Acknowledgement .. .. .. .. .. .. .. .. v
Table
of Contents .. .. .. .. .. .. .. .. vi
List
of Tables .. .. .. .. .. .. .. .. .. ix
List
of Figures .. .. .. .. .. .. .. .. .. xi
List
of Plates .. .. .. .. .. .. .. .. .. xii
Abstract .. .. .. .. .. .. .. .. .. xiii
CHAPTER 1: INTRODUCTION
1.1 Background of the Study .. .. .. .. .. 1
1.2 Statement of Problem .. .. .. .. .. 5
1.3 Justification .. .. .. .. .. .. 7
1.4 Objective of the study .. .. .. .. .. 8
CHAPTER 2: LITERATURE REVIEW
2.1 The Bivalve Mollusc .. .. .. .. .. .. 9
2.2 Global Bivalve Production,
Distribution and Consumption 10
2.3 Bivalve Production and
Consumption in Nigeria .. .. 12
2.4 Food Safety Issues Related to
Bivalve Molluscs Consumption 14
2.5 Benefits Associated with
Bivalve Molluscs Consumption 15
2.6 Risk Factors Associated with
Bivalve Molluscs Consumption 17
2.7 Toxic elements .. .. .. .. .. .. 24
2.8 Organic Contaminants .. .. .. .. .. 29
2.9 Food Safety Risk Assessment .. .. .. .. 35
2.10 Components
of Risk Assessment .. .. .. .. 37
2.11 Method
of Food Safety Risk Assessment .. .. 42
2.12 Determination of Human Health
Risk Assessment of
Chemical Contaminants .. .. .. .. .. 44
CHAPTER 3:
MATERIALS AND METHODS
3.1 Study
Area .. .. .. .. .. .. .. 47
3.2 Sample
Collection .. .. .. .. .. .. 49
3.3 Sample
Preparation and Treatments .. .. .. .. 52
3.4 Consumption
Pattern and Perceptions of Bivalve Molluscs 52
3.5 Proximate Analyses .. .. .. .. .. .. 53
3.6 Assessment
of Microbiological Composition of Bivalves .. 56
3.7 Determination
of Mineral Composition in Bivalve Mollusc .. 59
3.8 Determination
of Concentration of Organic Contaminants in
Bivalve Samples .. .. .. .. .. .. 61
3.9 Human
Health Risk Assessment Procedure .. .. 64
3.10 Experimental
Design .. .. .. .. .. .. 67
3.11 Analysis
of Data .. .. .. .. .. .. 68
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Consumption
Pattern and Perception of Bivalve Molluscs 69
4.2 Bivalve
Consumption Pattern .. .. .. .. .. 72
4.3 Perception
toward Bivalve Consumption .. .. .. 81
4.4 Food
Safety and Environmental Concerns .. .. .. 84
4.5 Proximate
Composition .. .. .. .. .. 88
4.6 Macromineral
Content of Bivalve Molluscs .. .. 97
4.7 Trace
Elements .. .. .. .. .. .. 103
4.8 Toxic
Elements .. .. .. .. .. .. 110
4.9 Microbiological
Composition .. .. .. .. 119
4.10 Polycyclic
Aromatic Hydrocarbons (PAHs) .. .. 126
4.11 Polychlorinated
Biphenyls (PCBs) .. .. .. .. 137
4.12 Human
Health Risk Assessment .. .. .. .. 146
4.12.1 Risk assessment of toxic elements
from consumption
of bivalve samples .. .. .. .. .. .. 146
4.12.2 Risk
assessment of PAHs from consumption of bivalve samples .. 151
4.12.3
Risk assessment of PCBs
from consumption of bivalve samples 153
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion .. .. .. .. .. .. .. 164
5.2 Recommendations .. .. .. .. .. .. 166
REFERENCES .. .. .. .. .. .. .. .. 168
APPENDIXES
.. .. .. .. .. .. .. .. 189
LIST OF TABLES
TABLE TITLE PAGE
4.1 Demographic characteristic of
the respondents .. .. 70
4.2
Showing the Rate of
Consumption of Bivalve Species 74
4.3
The preferred form of
consumption .. .. .. .. 78
4.4 The
preferred place of consumption .. .. .. .. 80
4.5
Reasons for consuming
bivalve molluscs .. .. 82
4.6 Health
related issues encountered while consuming bivalves 85
4.7
Effect of location
on Proximate composition(%) of bivalve samples 90
4.8
Effect of species on
Proximate composition of bivalve species(%) 91
4.9
Effect of location and
species on the proximate composition (%)
of bivalve samples .. .. .. .. .. .. 95
4.10
Effect of location on
Macro mineral content of
bivalve samples
(mg/100g) .. .. .. .. .. 98
4.11
Effect of species on Macro
mineral content of bivalve
Samples (mg/100g) .. .. .. .. .. .. 99
4.12
Effect of location and
specie on: Macro minerals content
of bivalve samples
(mg/100g) .. .. .. .. .. 101
4.13
Effect of location on
Trace elements content of bivalve
samples (mg/100g) .. .. .. .. .. .. 104
4.14 Effect of species on Trace
element content of bivalve
samples (mg/100g) .. .. .. .. .. .. 105
4.15 Effect of location and species
on Trace element content
of
bivalve samples (mg/100g) .. .. .. .. .. 107
4.16
Effect of Location on
Toxic element content of
bivalve samples
(mg/kg) .. .. .. .. .. .. 112
4.17
Effect of species on Toxic
element content of
bivalve samples(mg/kg) .. .. .. .. .. 113
4.18 Effect of location and species
on Toxic metal content
of bivalve samples
(mg/kg) .. .. .. .. .. 114
4.
19 Effect of Location on
Microbiological
composition (log CFU/g)
of bivalve tissue .. .. 120
4.20 Effect of species on
Microbiological composition
(log CFU/g) of bivalve tissue .. .. .. .. .. 121
4.21 Effect of Location and species
on Microbiological
composition (log CFU/g)
of bivalve tissue .. .. 122
4.22
Effect of location on the
concentrations and compositional
patterns of PAHs (μg/kg)
in bivalve samples .. .. .. 127
4.23
Effect of species on the
concentrations and compositional
patterns of PAHs (μg/kg)
in bivalve samples .. .. .. 128
4.24
Effect of location and
species on the concentrations and
compositional patterns
of PAHs (μg/kg) in bavalve samples .. 131
4.25
Effect of location on the concentrations of
PCBs (ng/g) in bivalve
samples .. .. .. .. 138
4.26
Effect of species on the
concentrations of
PCBs (ng/g) in bivalve
samples .. .. .. .. 139
4.27
Effect of location and
species on the concentrations of
PCBs (ng/g) in bivalve
samples .. .. .. .. 141
4.28
Non-carcinogenic risk
value of toxic elements in bivalves samples 147
4.29
Carcinogenic risk value for toxic
elements during bivalve consumption 152
4.30
Non carcinogenic risk
value for PAHs during consumption
of bivalve samples .. .. .. .. .. .. 154
4.31
Carcinogenic risk value
for PAH during consumption
of bivalve samples .. .. .. .. .. .. 157
4.32
Non carcinogenic risk
value for PCBs during bivalve consumption 160
4.33
Carcinogenic risk value
for PCBs during bivalve consumption 162
LIST OF FIGURES
FIGURE TITLE PAGE
3.1 Section
of Niger Delta coastal area showing the
sampling
locations .. .. .. .. .. .. 48
4.1 The
source of bivalve species by the respondents in Niger Delta 76
4.2 Possible source of Risk Factors in Bivalve Species .. .. 87
4.3 Accumulated toxic element concentrations in bivalve
species
from study locations .. .. .. .. .. .. 115
4.4 Accumulated PAH concentration in bivalves species from
study locations .. .. .. .. .. .. .. 133
4.5 Accumulated PCB
concentration in bivalve species from
study locations .. .. .. .. .. .. .. 142
4.6 Hazard index of toxic elements of bivalve species in the
study locations .. .. .. .. .. .. 150
LIST OF PLATES
PLATE TITLE PAGE
1
Bloody
cockle (Anadara senilis) .. .. .. .. 50
2 Donax
clam (Donax rugosus) .. .. .. .. .. 50
3
Knife
or Razor clam (Tagelus adansonaii) .. .. .. 51
4
Mangrove
oyster (Crassosstrea gasar) .. .. .. 51
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Feeding an
expected global population of 9 billion by 2050 is a daunting task that is
engaging researchers, technical experts and leaders of the world over. A
relative unappreciated, yet the promising fact is that seafood plays an
important function in satisfying the plates of the world’s growing
middle-income group while also meetings the food security need of the poor (World
Bank, 2013). Already seafood including bivalve mollusc represent 20% of all animal
protein consumed globally, and this proportion of the world’s food basket is
likely to increase due to higher demand by middle income earners who seek
higher-value seafood and as aquaculture step-up to make up with rising demand
for bivalve shellfish (FAO, 2016).
Molluscs are
soft-bodied invertebrate which are enclosed in a hard shell. There are six
major classes of molluscs of which bivalves are the most organized and
specialized (Gosling, 2003). Bivalve mollusc inhabits fresh and marine waters
from the abyssal depths of high intertidal areas in tropical to warm temperate
waters. They are considered as delicious and healthy food items in several
dietary regimes in a different part of the world. The most important species
are the clams, mussels, oysters, and scallops (Gosling 2003, Gopalsamy et al., 2014). The pattern of their
distribution is characteristically different from one location to another
depending on the sediment types, variations in water salinities and tidal
movements (Sarker et al., 2008).
Globally,
bivalve production has consistently increased in the last sixty-six years
growing from nearly 1 million tonnes in 1950 to about 17.1 million tonnes in
2016, contributing to over 10% of the total amount of income in 2016 (FAO,
2018). China was by far the leading producers of bivalve molluscs with 13.4 million
tonnes in 2014 representing 83.3% of the global production and 81.9% of the
global aquaculture production in that year. Japan and the Korea Republic were
the second and third largest producers far behind China with a production of
376 and 359 thousand tonnes respectively (FAO, 2016). In Nigeria, finfish
farming dominates the scanty literature on aquaculture, with much less on
bivalve molluscs. Although there is no statistic on the production of bivalve
mollusc by species, the Nigeria Bureau of Statistic (NBS) reported that Nigeria
produced 5.8 million tonnes of fish including bivalve molluscs between 2010 and
2015 (NBS, 2017).
As the global
human population is increasing, seafood consumption including bivalve is also
rising steadily due to the health consciousness of modern-day consumers who are
interested in seafood because of their nutritional superiority and the health
benefits (Gopalsamy et al., 2014).
The consumption of bivalves and other seafood is believed to provide an
inexpensive source of protein with high biological value, essential minerals
such as selenium, calcium, iron, phosphorus as well as vitamins (Astorga-Espana
et al., 2007). The nutritional
characteristics of bivalves vary among species, and between individuals of same
species. Other factors that affect their nutritional qualities include age,
sex, maturation stage, origin, season, seawater, physical/chemical properties
and feed composition (Orban et al.,
2002).
Despite the
numerous advantages of seafood-based diet, adverse health effects can also
exist and seafood harvested from polluted aquatic environments can contain
biological and chemical contaminants (FAO/WHO, 2011a). Bivalves molluscs being
sedimentary filter feeders, feed by opening their shells for absorption of food
particles. Due to their feeding pattern, they filter tiny particles of aquatic
plants, animals and inorganic matter. It also accumulates the diversities of
other contaminants from the surrounding seawater (Huss et al., 2003, Lees, 2000). These feeding pattern render the bivalve
shellfish easily prone to bacteria, heavy metals, biotoxins and other
environmental contaminations (Sarkar et
al., 2008).
Most species of
bivalve molluscs consumed in Nigeria are harvested from the brackish water that
is exposed to varying amounts of chemical and environmental contaminants such
as industrial chemicals, toxic residues from various anthropogenic activities.
Pollution of the coastal waters in the Niger delta has continue to attract
greater attention. This is due to the high level of environmental degradation
posed by petroleum production and exploitation in along the coastline (Wala et al., 2016; Zabbey and Babantunde,
2015). Petroleum hydrocarbon from oils spills and human-mediated activities are
usually incorporated into sediments where they can persist for years gradually
releasing toxic substances into the immediate and remote environments (Zabby
and Babatunde, 2015). Some of the deleterious effects associated with dietary
intake of these contaminants include diarrhoea and gastrointestinal disorders,
immune suppression, neurological disorder, reproductive impairment,
developmental retardation, cardiovascular disorder, liver disease, infertility
and miscarriage (ASTDR, 2002; De Jager et
al., 2012). The groups most vulnerable to dietary exposure of the
contaminants are child-bearing women, children below twelve years, and
subsistence fish farmers (FAO/WHO, 2011a). For better understanding and
characterization of the risk presented by chemical toxins in the environment to
human and ecological receptors, most researchers used benthic organisms such as
bivalves as biomonitors of the levels and long-term influences of chemical
toxins within the ecosystem (Sarker et al.,
2008).
The risk
factors that are associated with bivalve mollusc consumption are mostly from
the contaminated water body where they live, particularly when they are to be
consumed fresh or slightly cooked (Lees et
al., 2010). These circumstances make them important sources of foodborne
diseases which represent a significant health risk to consumers. The hazards
usually encountered include those due to pathogenic bacteria, viruses,
parasites as well as intoxication due to chemicals from metallic elements such
as methyl mercury, cadmium, arsenic, lead and others. There are also organic
pollutants such as dioxins, furans, polychlorinated biphenyls (PCBs), pesticide
residues among others (Lees et al.,
2008). Marine bivalves are also implicated to be a major source of biotoxins or
shellfish toxins which are contacted from species of micro-algal cells
(phytoplankton) when consumed (Huss et al.,
2003). These toxins, usually linked to microalgae bloom are not harmful to the
bivalves but might pose a safety problem to consumers particularly when the
bivalves are cooked since the toxins are heat resistant.
According to
Conte et al (2014), seafood generally
is perceived as healthy food and as an alternative source of proteins. However,
consumers also have the consciousness of some safety risks, e.g. potential
adverse effects of shellfish contaminants on health. Also, the ability of
bivalve to bioaccumulate and bioconcentrate contaminants leaves those at the
highest trophic level at the greatest concentration and risk and depending on
the contaminants in contact with, a wide variety of harmful effects have been
reported (US EPA, 2009). Fishery products are considered the major sources of
human contact to pollutants such as polychlorinated biphenyls, dioxins,
organochlorines polycyclic aromatic hydrocarbons, some heavy metals and other
environmental toxic substances and according to Conte et al (2014), some differences exist in the type and levels of
contaminants among regions and as such risk assessment must be performed locally.
1.2 STATEMENT OF PROBLEM
The Niger Delta
coastal waters are an exceptional breeding ground for a vast variety of fish
and shellfish. They provide excellent habitat for a diversity of shellfish such
as bloody cockle (Anadara senilis)
mangrove oyster (Crassostrea gasar),
razor or knife clam (Tagelus andansonii)
and others. But the prevailing pollution occasioned by exploration and
production of petroleum have impacted negatively to the quality and quantity of
shellfish in the area (Yakubu, 2017).
According to
Amnesty International (2018) reports, Niger Delta is the most recognized
oil-producing region in Africa. It is also known to be the most polluted area
on earth. The prevailing widespread pollution has severally impacted negatively
on the food product especially seafood obtained from the coastal waters of this
area. Amnesty International (2009), reported a study carried out by Friends of
the Earth in Akwa Ibom State in 2008, which discovered elevated heavy metals in
fish tissue. Natives also complained that fish and fishery products obtained
from the coastal waters caused stomach upsets when consumed.
Research has
determined that there is bioaccumulation of Benzo (a) pyrene (BaP), other
hydrocarbons and heavy metals has occurred in a toxic amount in major high
protein contents seafood such as periwinkle (Tympanotonus fuscatus), mudskipper (Periophtalalius papillio) and other seafood (Ordinioha and Brisbe,
2013). Yakubu (2017), reported a benzene concentration of 0.155-48.2μg/m3
in this area and this concentration to represent 1:10,000 cancer risk as
benzene and its associated compounds
such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls
(PCBs) are known carcinogens. Also, Gobo et
al (2010) argued that the prevalence of diarrhoea in coastal communities of
Nigeria is on the rise because of consumption of sea food and other animals
products which have been in contact with pathogenic microorganisms.
Furthermore,
the Nigerian Government recently seek European Union to help to counter cancer
outbreak in the polluted Niger Delta. This is as a consequent of the reported
cases of health issues such as breathing problems, skin lesions and many cases
of cancer resulting from oil pollution from water, air and agricultural
products. The government explained the “enormity of the menace” and called for
immediate action as the capacity of the Nigerian government was inadequate
(Euroactiv, 2017). Also, the former Bayelsa State Governor, Hon. Henry Seriake
Dickson in 2018 during his mother's death expressed worry over the increasing
numbers of illnesses paticularly respiratory problems and cancer in Niger
Delta. He stressed that cases of illnesses in the Niger delta were traceable to
environmental degradation and called for a serious action to reverse this
condition (The Guardian, 2018). Bivalve including mangrove oysters, bloody
cockle, clams among others are suspension or filter feeders takes in chemical
contaminants and microbes from the polluted Niger delta waters can accumulate
in their tissue posing serious concern in their quality and safety. Therefore,
the continuous consumption of bivalve molluscs from the Niger Delta waters
posits or exemplify the conflict between food benefits and food risks. The State
(Government) are encouraged by international law and other Charters to improve
upon, protect and provide its citizens with different sources of food. The
major food sources should therefore be
seriously protected, not abused or comtaminated by private individuals or
organisations thereby preventing peoples’ ability at feeding themselves. The
multidisciplinary and multisectoral approach to the sustainable mitigation of
health risks resulting from pollution in Niger Delta region is paramount and the assessment of food safety risks that are
associated with the consumption marine bivalve mollusc shellfish offer a
valuable strategy.
1.3 JUSTIFICATION
The foodborne disease presents a serious public health problem
to every country in the world of which a little over 10% is attributable to
fish and shellfish product. Reports show that when muscle foods are considered
separately over 56% of illnesses are connected to seafood (CDC, 2008). Seafood
is not only a high internationally traded commodity but an important component
of diets worldwide. According to FAO/WHO (2011a), it is estimated that over one
billion people around the globe rely on seafood products as their main source
of animal protein. Fishing is also a major occupation of the people of the
riverine communities of Nigeria, and various fisheries resources are also
important delicacies including bivalve mollusc which are common among
small-scale fisheries. Contamination of aquatic ecosystem in the Niger delta region
cannot be overemphasized as most of the contaminants can bioaccumulate and
become significant along the food chain giving concern on seafood safety to
consumers (Davidson et al., 2006).
Risk assessment and hazard identification are established protocol or framework
that defines an appropriate level of public health hazards in food products and
ensures the presentation of foods that
are safe. Since bivalves are economically and nutritionally very important for
human consumption, playing a central role in the gastronomy of this region,
assessing risk factors relating to its consumption and their health
implications are indeed very important. This research work is aimed at
correctly predicting food safety risk associated with chemical contaminants
in bivalve mollusc.
1.4 OBJECTIVE OF THE STUDY
The broad
objective of the study is to assess the food risks associated with bivalve molluscs harvested from the coastal
waters of Niger Delta,in Nigeria. The specific objectives of the study are as
follows:
1. To
analyse the consumption pattern and perceptions of bivalve molluscs in Niger Delta through the use of a structured
questionnaire.
2. To assess the
microbiological composition of bivalve species harvested from this area and identify inherent hazards in fresh
bivalve.
3. To
access proximate composition of bivalve
species consumed in the Niger Delta.
4. To
assess the macrominerals and trace elements content of bivalve species from the
region.
5. To determine the
level of toxic elements accumulated by bivalve molluscs.
6. To investigate
the concentrations and patterns of
composition of the 16 priority PAHs
accumulated by bivalve molluscs
7. To assess the
distribution pattern and bivalve tissue burden of PCB congeners in the study locations.
8. To use the US
EPA method to estimate the human health risk of toxic elements, PAHs and PCBs contaminants in bivalve samples
consumed in Niger delta.
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