Heliyon 8 (2022) e12255Contents lists available at ScienceDirect
Heliyon
journal homepage: www.cell.com/heliyonResearch articleOccurrence of microplastics in wild oysters (Crassostrea tulipa) from the Gulf
of Guinea and their potential human exposure
Samuel Addo a, Charles Mario Boateng a,*, Rhoda Lims Diyie b, Collins Prah Duodu a,
Anyan Kofi Ferni a, Ernestina Abbew Williams a, Akosua Ohemaa Amakye a, Obed Asamoah c,
Harriet Danso -Abbeam d, Elvis Nyarko e
a Department of Marine and Fisheries Sciences, School of Biological Sciences, University of Ghana, P. O. Box LG 99. Accra, Ghana
b Council for Scientific and Industrial Research, Water Research Institute (CSIR-WRI), P. O. Box AH 38, Accra, Ghana
c University of Development Studies, P. O. Box TL 1350, Tamale, Ghana
d Environmental Resources Research Centre, Ghana Atomic Energy Commission, Post Office Box LG 80, Legon, Accra, Ghana
e Regional Maritime University, Post Office Box GP 1115, Accra, GhanaA R T I C L E I N F O
Keywords:
Microplastics
Polymer
Fibers
Oysters
Human exposure* Corresponding author.
E-mail address: cmboateng@ug.edu.gh (C.M. Bo
https://doi.org/10.1016/j.heliyon.2022.e12255
Received 4 October 2022; Received in revised form
2405-8440/© 2022 The Author(s). Published by ElsA B S T R A C T
The high dependence on plastics in Ghana has resulted in the generation of large quantities of plastic waste which
are poorly managed and improperly disposed into the aquatic environments. This study assessed the spatial
distribution and abundance of microplastics in mangrove oysters (Crassostrea tulipa): a major fishery resource of
commercial importance in Ghana. The results showed that 84.0% of all individuals examined had ingested
microplastics. A total of 276 microplastic items were recovered from the 120 individual oysters. Densu (100%)
and Volta (93%), two estuaries situated in urban areas, had a greater incidence of microplastics than Whin (77%)
and Nakwa (66%), estuaries situated in peri-urban and rural settlements, respectively. The mean microplastic
abundance ranged from 1.4 to 3.4 items/individual and 0.34 to 1.7 items/g tissue wet weight. Fiber accounted for
69% of microplastic shapes, followed by fragments (27%) and films (4%). Polymer analysis showed polyethylene
(PE), polypropylene (PP) and polystyrene (PS) as the most common types in oysters. The estimated microplastic
intake per capita per year was one magnitude higher than the mean for other countries. This high rate of human
exposure to microplastics requires an eminent policy formulation to guide the use, management and disposal of
plastic waste in Ghana.1. Introduction
Global plastic waste generation threatens food security and the sus-
tainable utilization of marine resources (Campanale et al., 2020), as
developing countries with poor waste management strategies are more
likely to face severe impacts on human health and the environment
(Alpizar et al., 2020). Over the past few decades, Ghana has rapidly
expanded socio-economically, which has coincided with a significant rise
in the use of plastic products (Ghana National Plastic Action Partnership,
2021). The majority of the 840 thousand tonnes of municipal plastic
waste generated annually in the nation which is growing at a rate of 5.4%
each year comes from single-use plastics. This is exacerbated by the
country's poor waste management alternatives, which result from a low
recycling rate and a high proportion of illicit disposal (Effah, 2019; Kortei
and Quansah, 2016; Stoler et al., 2015). According to predictions made inateng).
22 November 2022; Accepted 2
evier Ltd. This is an open accessthe Ghana National Plastic Action Partnership (2021) report, for
instance, the amount of plastic that leaks into the nation's water bodies is
expected to rise by 190%, from about 78,000 tonnes per year in 2020 to
228,000 tonnes per year by 2040. Under suitable biophysical and envi-
ronmental conditions, the majority of the plastic waste in terrestrial and
aquatic systems disintegrates into small particles called microplastics
(plastic particles from 1 μm to 5 mm) (ISO, 2020), which could be easily
ingested by organisms such as invertebrates and fish (Wang et al., 2021).
Coastal ecosystems particularly estuaries are sensitive to environ-
mental pollution and may serve as conduits for microplastic transfer and
accumulation. Plastic materials may enter estuaries from rivers through
spills, runoff, sewage discharges and municipal waste treatment plants
(Wagner et al., 2014). Several studies have reported significant occur-
rences of microplastics in the estuarine environment compared to near-
shore waters affirming its role in plastic pollution (Peng et al., 2017; ZhaoDecember 2022
article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
S. Addo et al. Heliyon 8 (2022) e12255et al., 2014). Hence, estuaries have become the most critical path for
microplastic transport to the ocean. Lebreton et al. (2017) reported that
between 1.5-2.4 million tonnes of macro and microplastic litter enter the
sea through estuaries worldwide. Therefore, studies on the microplastic
accumulation in estuarine organisms are important to understand their
spatial distribution and transfer into the ocean.
Oysters are good bioindicators of aquatic pollution because their
unique feeding strategy allows them to filter large amounts of water
through their gills, thereby exposing the organisms to filamentous
microplastics found in aquatic media (Wang et al., 2021a; 2021b; Teng
et al., 2019). The mangrove oyster is a popular seafood choice in West
Africa and may be found in many of the region's estuaries and lagoons.
The mangrove oyster fisheries is a lucrative industry in which women
who pick and process the catch play a disproportionately large role
(Asare et al., 2019). However, these organisms are often exposed to
microplastic pollution from human activities through the improper
disposal of plastic refuse near rivers and estuaries in Ghana. The prospect
of oyster culture within the West African region is not well exploited,
thus, forcing consumers to rely solely on oysters harvested from the wild.
Currently, shellfish consumption is the primary route of human dietary
exposure to microplastics (Vital et al., 2021).
Several studies have reported microplastic ingestion and toxicity in
marine organisms from various ecosystems worldwide (Lerebours et al.,
2022; Said et al., 2022; Zhang et al., 2022; Wang et al., 2021a; 2021b; Li
et al., 2018; Martinelli et al., 2020; Patterson et al., 2019; Teng et al.,
2019; Bour et al., 2018; Digka et al., 2018; Li et al., 2018; Murphy 2018;
Renzi et al., 2018 Avio et al., 2015, Cauwenberghe et al., 2015; De-Witte
et al., 2014) with little information on their impact on human health
when consumed. Nonetheless, the extent of exposure and toxicity may
vary depending on environmental conditions and geographic location.
Microplastics may contain endocrine-disrupting chemicals (Bisphenol-A)
which are normally added as additives during the polymerization process
of plastic production or serve as receptors for absorbing contaminants
such as Polychlorinated biphenyls (PCBs), Polybrominated biphenyl
ethers (PBDEs) and trace metals in the environment (Gallo et al., 2018).
These chemicals may leach into edible tissues of the marine organism
through translocation, increasing human exposure via the consumption
of contaminated seafood products (Fossi et al., 2012). Again, most people
consume whole oysters including the stomach content which may expose
consumers to microplastic intake, while the digestive tract of larger fin-
fishes which happens to be the repository for microplastics is discarded
during ingestion.
Despite reports of microplastic pollution in Ghana from Blankson
et al. (2022), Pappoe et al. (2022), Nuamah et al. (2022), Adika et al.
(2020), and Chico-Ortiz et al. (2020), there is a paucity of information on
the occurrence, distribution, and accumulation of microplastics in sea-
food particularly oysters from the coastal waters of Ghana and their
potential human health risk. Therefore, this study assessed the abun-
dance and spatial distribution of microplastics in the tissue of oysters and
categorized them into colour, size, shape and polymeric type. In addition,
the potential human exposure through the consumption of
microplastic-contaminated oysters was estimated.
2. Methodology
2.1. Study area
Live oysters were collected from Volta, Densu, Nakwa and Whin es-
tuaries along the coast of Ghana fromMarch to April 2021 (Figure 1). The
selection of these sites was based on their vibrant oyster harvesting ac-
tivities. The Volta River flows through a distance of about 670 km from
the northern to the southern part of Ghana with its lower arm towards the
estuary becoming a hub for tourism yet provides over 60% of inland fish
catch (Nunoo et al., 2014). The Densu River flows from the Atiwa forest
in Ghana's Eastern Region and spans about 120 km, passing through over
300 communities and industries. Industrial activities include a water2
treatment plant that supplies potable water to about 4.8 million Gha-
naians. Due to its ecological importance, the Densu estuary is designated
as a RAMSAR site despite the influx of anthropogenic activities such as
mining and intensive agriculture within its buffer zone, coupled with
rapid urbanization (Kasei et al., 2014). TheWhin estuary is located in the
Western Region of Ghana and provides livelihood support through finfish
and shellfish trade to the surrounding communities. The Nakwa estuary,
a 3.6 square kilometer water body in the Central Region of Ghana along
the coast, is a shallow water body adorned with mangroves, and exten-
sive swaths of Paspalum vaginatum marshlands.2.2. Sample collection
Mangrove oysters were collected randomly from each estuary with
the assistance of oyster pickers. A total of one hundred and twenty (N ¼
120) individuals (30 per site) of varying sizes were collected and placed
in a locally manufactured metal case. Samples were washed thoroughly
with distilled water to remove sand particles and transported on ice to the
laboratory where they were stored at –20 C until analysis.2.3. Microplastic extraction
Prior to the extraction of microplastics, the oyster samples were
thoroughly thawed at room temperature and the shell length and height
were measured with a vernier calliper. The shells were opened from the
posterior end, and the muscle was shucked out with a stainless-steel knife
into a clean glass beaker. The soft tissue was weighed using a precision
balance (Philip Harris, England) to the nearest 0.01 g. Microplastic
extraction was carried out in accordance with the protocol by Hara et al.
(2020), Phuong et al. (2018), and Karami et al. (2017) with minor
modifications. The whole oyster tissues were digested separately with 30
mL of 10% KOH (analytical grade). The digested sample was covered
with aluminium foil and incubated at 60 C for 48 h. Density separation
was performed three times to enhance the maximum recovery of
microplastics after incubation by the addition of 150 mL saturated ZnCl2
solution (1.6 g/cm3) and agitated for 10 min with a mechanical shaker
(Rodrigues et al., 2018; Zobkov and Esiukova 2017). The mixture was
allowed to stand undisturbed for 3 h at room temperature, and the su-
pernatant was filtered through a 1.2 μm glass filter (CHMLAB GF3) using
a vacuum filtration system. The glass filters were then placed in a clean
Petri dish, dried at 40 C for 60 min, sealed, and kept in a desiccator for
examination. Procedure blank samples, consisting of the extraction so-
lution (10% KOH) without samples, were analyzed in parallel with the
digested fish samples. Such blanks were necessary to evaluate any po-
tential contamination from the laboratory atmosphere that might have
happened during digestion procedures despite all precautions being
taken.2.4. Microplastics examination
Filters were examined and counted for microplastics with Stereomi-
croscope (Leica EZ4D) equipped with an inbuilt camera (Leica ICC550E).
To avoid overestimation, the filters were examined in a Z-shape, ac-
cording to the method by (Teng et al., 2019; Peng et al., 2017). All
plastics were separated and photographed to determine their size and
shape using the Spotter Guild protocol developed by the Civil Laboratory
for Environment Action Research (CLEAR) for microplastic identification
and shape guide by Frias et al. (2019). The shape of the plastics was
categorized as fragments (irregular and angular pieces mainly from the
degradation of large plastic materials), fibers (long and elongated), pel-
lets (spherical shapes) and film (thin and transparent). The colours of
microplastics were classified into black, blue, white, red, yellow and
others according to Edo et al. (2019). Size categorization was based on
the recommendation by Frias and Nash (2019).
S. Addo et al. Heliyon 8 (2022) e12255
Figure 1. Map of Ghana showing the location of the four water bodies along the coast of Ghana.2.5. Polymer identification
Fourier Transform Infrared Spectroscopy was used to identify the
polymer (FT-IR). Background scans were performed before analysis to
account for any potential distortions in the data. Eighty isolated
microplastics (20 per estuary) were then examined using an FT-IR
microscope (PerkinElmer Spotlight i200) and a spectrometer (Spec-
trum Two, PerkinElmer). Using spectrum 10 software, each sample was
subjected to 16 scans at a resolution of 4 cm1. The OMNIC v9.0
spectra software (Thermo Fisher Scientific Inc.) was used to evaluate
the output spectra and compare them to its polymer libraries. Finally,
reference spectra ranging from 70 to 95 per cent were used to match
polymers.
2.6. Quality control
The extraction of microplastics was done in a cleanroom where
workbenches were cleansed with distilled water before and after each
phase of the extraction procedure. The dissection of tissues was done in a
fume hood. During oyster removal, glass and metal items were utilized
whenever possible and were cleaned with distilled water before use.
Super-pure reagent-grade chemicals were used to prepare the extraction
solution. The prepared solution for digestion and density separation was
filtered through a 0.45 μm glass filter (CHEM-LAB- A55). Wearing of
synthetic clothing was limited throughout the entire process. All glass-
ware was covered with aluminum foil to prevent airborne contamination
from the working environment. Contamination controls consisted of a
sample-free KOH solution that was subjected to all the extraction pro-
cesses in the same conditions as the samples. Glass fiber filter was heated
in a muffle furnace for 3 h at 450 C to eliminate any contamination for
the filters.3
2.7. Human microplastic exposure via oyster consumption
Human health risk exposure to microplastics via the consumption of
contaminated oysters was determined using a simple parametric
approach. The first assessment was to estimate the weekly intake of MPs
items using the recommended shellfish consumption limit per week (50 g/
person/week) for Ghana reported by Agbekpornu (2021). The second
method was based on data from various countries regarding shellfish
consumption per capita per year: Ghana i.e., 2600 g/person/year
(Agbekpornu, 2021), France 672 g/person/year (AFSSA, CREDOC DGAC
2000), New Zealand 985.5 grams/person/year (Greening et al., 2003) and
USA 3066 g/person/year (OEHHA 2001). Human intake of microplastic
from oysters was computed by multiplying the total number of micro-
plastics in oysters from all four estuaries (i.e., the mean total number of
microplastics found in oyster tissues of 101 individuals) by the shellfish
consumption rate for the various countries (Barboza et al., 2020).
MP intake per week¼ The mean plastics (g/tissue) in all individuals analyzed
recommended shellfish intake per week (g)
Human MP intake per year per capita ¼ Mean microplastic (g/tissue) in all
oysters examined  consumption of shellfish per year per capita in selected
countries.
2.8. Statistical analysis
Statistical analyses for data generated were performed using IBM SPSS
Statistics v26 software. Microplastic abundance was estimated and re-
ported as the number of items per individual. Kruskal-Wallis/One Way
Analysis of Variance (One-Way ANOVA) was performed to test for differ-
ences in the number of MPs in oysters followed by post hoc Dunn's test for
multiple comparisons between the estuaries. Pearson correlation analysis
S. Addo et al. Heliyon 8 (2022) e12255
Table 2. Frequency of occurrence and mean abundance of microplastic in oysters
from estuaries in Ghana.
Description Densu Volta Nakwa Whin
Number of individual 30 30 30 30
oysters Examined
Number of individuals 30 28 15 17
containing plastic
MP frequency of 100 93 67 77
Occurrence (%)
MP Number 101 85 41 49
MP Abundance
Number of items per 3.4  1.0 2.8  1.1 1.4  1.3 1.6  1.2
individual in all examined oysters
Number of items per individual 3.4  1.0 3.0  0.8 2.1  1.1 2.1  0.9
in positive oysterswas performed to test the correlation between microplastic abundance and
oyster size. The level of significancewas set at p< 0.05, and average values
were expressed as mean  standard error of the mean (SE).
3. Results
3.1. Abundance of microplastics in oyster C. tulipa
According to the results obtained, no microplastics were detected in
blank samples. The absence of microplastic in the procedural blank
samples and filters is both an indication of the accuracy of the laboratory
tests and a confirmation of the precision and dependability of the
approach that was utilized in the process of recovering the microplastics.
The morphometric characteristics of the oysters and site descriptions of
the different estuaries where samples were collected are presented in
Table 1. The mean weight (g) of oysters was highest for Whin (10.60 
1.24) and lowest for the Volta estuaries (4.69  0.82). Meanwhile, shell
length ranked as follows: Whin > Densu > Nakwa > Volta (Table 1).
A total of 276 particles were extracted from the tissues of 120 C.
tulipa, from four estuaries along the Gulf of Guinea with an average of
2.30  1.40 MP items per individual. Of these samples, 101 out of 120
individuals examined (c. 84%) had ingested at least one MP particle. All
oysters collected from various estuaries exhibited a distribution profile of
microplastics that generally showed a decreasing concentration with
distance from metropolitan centers. For instance, a significantly higher
abundance of microplastics was observed in samples from Densu (3.4 
1.0 items/individual) and Volta (2.8  1.1 items/individual) estuaries
near metropolitan areas of Greater Accra, whereas estuaries located near
rural settlements contained fewer microplastics, i.e., Nakwa (1.4  1.3
items/individual) and Whin (1.6  1.2 items/individual) (p < 0.01).
The percentage of MP occurrence for each estuary is presented in
Table 2, where oysters from the Densu delta and the Volta recorded the
highest percentage of individuals with MP's (100% and 93% respec-
tively), while the lowest recorded was at the Nakwa estuary (67%). The
abundance of MPs ranged from 1 to 5 items per individual, with the
highest abundance recorded from the Densu delta (n ¼ 101) and the
lowest recorded at the Nakwa estuary (n ¼ 41). Analysis of variance
(ANOVA) showed significant differences between microplastic abun-
dance and locations. This significant variation according to the post hoc
Dunn test existed between Densu and Nakwa (p < 0.01), and Densu and
Whin (p< 0.01). Volta and Nakwa (p< 0.01), Volta andWhin (p< 0.01).
Densu and Volta were significantly different from Whin and Nakwa.
When samples were examined based on wet weight, oysters collected
from the Volta estuary exhibited the highest MP abundance, with an
average of 1.64 0.63 items per gram tissue, while the lowest abundance
was recorded in the Whin estuary with 0.29  0.14 items per gram tissue
(Figure 2b). Meanwhile, a weak correlation was observed between the
abundance of microplastic and oyster size from the different locations.
Nakwa (r ¼ 0.084, p ¼ 0.766) Whin (r ¼ 0.338, p ¼ 0.178) Volta (r ¼
-0.157, p ¼ 0.533) Densu (r ¼ 0.011, p ¼ 0.965).3.2. Characteristics of microplastics in C. tulipa
3.2.1. Shape
The proportion of different shapes of microplastics in the sampled
specimen is presented in Figure 3a and categorized as: fibers, fragments,Table 1. Morphometry of oysters and site description of estuaries.
Location Average Shell Average Site
length (cm) Weight (g) Description
Densu 7.20  1.83 5.45  1.54 Urban
Volta 4.69  0.82 2.12  0.75 Urban
Nakwa 7.01  0.85 3.58  0.84 Rural
Whin 10.60  1.24 10.21  1.41 Peri-urban
4
and films. Fibers and fragments were found in samples from all studied
sites whereas no film was recorded in samples from the Whin estuary.
Fiber was the most predominant shape in oysters and accounted for
approximately 69% of microplastics identified, while fragments and
films recorded 27% and 4%, respectively at the different studied sites.
Oysters from Whin (77%) and Densu (70%) recorded the highest per-
centage of fiber occurrence, while the lowest recorded was Nakwa (64%)
(Figure 3a).
3.2.2. Size and colour
The length of MPs ranged from 33 μm to 4870 μm, with <1000 μm
being the most common size observed and accounting for more than 90%
of all categories (Figure 3b). Specifically, as illustrated in Figure 3b, the
proportion of the various sizes for all sampling sites was as follows:
33–50 μm (5.42%), 50–100 μm (24.63%), 100–500 μm (46.80%),
500–1000 μm (13.30%), 1000–3000 μm (6.90%), 3000–5000 μm
(2.96%). The results showed that 100% of the extracted MPs were within
the defined MP size range (1 μm–5 mm). Microplastics in oysters were in
multiple colours, mainly white, green, yellow, blue, black, and red
(Figure 3c). Black was the most dominant colour, which accounted for
55% of the total number of microplastics observed. The proportion of
deep colours (black, red, and blue) was 68% significantly higher than
24% of light colours (white, yellow, and green) (p < 0.05).
3.3. Polymer composition of microplastic
Eighty random subsamples of MPs (29 % of the total MPs identified)
were selected for FTIR analysis, and 92% of them were found to be
synthetic polymers correspondingly. The remaining 8% came from nat-
ural sources, principally consisting of fibers of 6% cotton and 2% cellu-
lose Figure 4. Among the synthetic polymers identified, the distribution
was ranked as polyethylene (36%), polypropylene (22%), polyamide
(16%), polystyrene (12%), cellophane (7%) and polyester (7%). Poly-
ethylene, polypropylene, polystyrene, and polyamide were found to be
the most abundant polymers in C. tulipa tissues throughout all four es-
tuaries, and together they accounted for 86% of all MPs polymers
examined. Other polymers identified were cellophane (CP), cotton and
cellulose. See photographs of spectra pecks from FTIR analysis (Figure 4).
3.4. Human microplastic intake
Microplastics are inadvertently consumed by humans through the
consumption of food derived from a wide variety of sources, and bivalves
are not an exception. The study preliminary investigated the weekly and
annual oyster consumption for adult populations in Ghana and other
regions of the world. In Ghana, the estimated weekly intake for adults
ranged from 14.0 to 82.0 MP items per week and 754 to 4160 items per
capita per year (Table 3). Based on this backdrop as per their consump-
tion, persons based in the USA, France and New Zealand exposures
S. Addo et al. Heliyon 8 (2022) e12255
Figure 2. Boxplot showing the range in abundance of MPs extracted from C. tulipa at each estuary computed based on (a) items per individual, (b) items per gram
tissue (n ¼ 30; N ¼ 120). Boxes represent the first and third quartile, middle bar, the median and error bar maximum and minimum valves.ranged from (17–94), (1.2–20.8) and (5.5–30.4) for weekly intakes and
(889.4–4906), (195–1075) and (286–1577) annually.
4. Discussion
The study revealed high variability in the spatial distribution and
abundance of MP in oysters from the coastal waters of Ghana. The het-
erogeneous distribution pattern for MP abundance may be due to the
unique anthropogenic pressures experienced by each sampled site, the
proximity to human settlements, and other commercial activities. For
instance, microplastics from urban estuaries were higher than those from
rural estuaries, indicating that wastewater from urban cities might be the
main source and retention of microplastics. Such observation was made5
elsewhere by Pappoe et al. (2022); Joyce et al., 2022; Li et al. (2018),
where anthropogenic factors from cities played a significant role in
microplastic abundance and distribution. The Densu estuary is a marine
protected area due to its ecological significance but recorded the highest
mean abundance of MPs (Table 2). This could be attributable to the
recent encroachment and expansion activities within its buffer zone,
which have led to the construction of large-scale commercial activities
such as the establishment of industries, hotels, and residential facilities
that discharge their waste straight into the estuary. The worse of these is
the establishment of the Oblogo dump site within proximity of the water
banks coupled with other unauthorized dump sites created by commu-
nities dotted along the estuary which serve as key sources of plastic
pollution for the Densu river (Osei et al., 2011; Nyame et al., 2012).
S. Addo et al. Heliyon 8 (2022) e12255
Figure 3. Morphological characteristics of MPs in C. tulipa, (a) shapes, (b) sizes, (c) colour.Microplastic abundance from densely populated and industrialized set-
tlements is projected to be higher than that from rural settlements
characterized by minimal human activities. Therefore, it is not surprising
that oysters from the Densu and Volta estuaries, located in the Greater6
Accra Region, Ghana's most populous region recorded more microplastic
abundance.
The average abundance of MPs in the current study was 2.5  1.3
items/individual. When compared with shellfish from other regions of
S. Addo et al. Heliyon 8 (2022) e12255
Figure 4. FTIR spectra of common MPs in Oyster. (A) Polyamide (PA), (B) Polyethylene (PE), (C) Polypropylene (PP), and (D) Polystyrene (PS).the world, the MP abundance in the oysters (Crassostrea tulipa) was
higher than that in Crassostrea gigas from France (Phuong et al., 2018),
USA (Martinelli et al., 2020) and South Korea (Cho et al., 2019), as well7
asMytilus edulis from Belgium (Mathalon and Hill, 2014). The abundance
of microplastics found in this study is consistent with those reported in
Perna canaliculus from New Zealand (Webb et al., 2019) andMytilus edulis
S. Addo et al. Heliyon 8 (2022) e12255
Table 3. Estimated weekly and annual intake of microplastic for adult
populations.
Exposure Ghana USA France New Zealand
Weekly intake
Oyster consumption/ 50 59 13 19
week (g)
MPs ranges 14.5–80 17–94.4 1.2–20.8 5.51–30.4
Mean MP intake (item/ 50 59 13 19
week)
Annual intake
Oyster consumption/ 2,600 3066 672 985.5
capita/year (kg)
MPs ranges 754–4160 889.4–4906 195–1075 286–1577
Mean MP intake (item/ 2,600 3066 672 985.5
capita/year)from Scotland (Courtene-jones et al., 2017). However, our results are
lower than those found in Crassostrea gigas from China (Teng et al.,
2019),Magallana bilineatan from India (Petterson et al. 2019), Crassostrea
gigas from Canada (Murphy, 2018) and Crassostrea viginica from USA
(Waite et al., 2018) (Table 4). The variations in MP abundance could be
attributed to the extent of plastic contamination of oyster habitats,
pollution status and exposure levels of the different geographical areas.
Besides, pollution status variability due to locations, and methodological
techniques used could also be sources of heterogeneity and variability in
the results found in literature.
The size of microplastics has been found to have a direct association
with the frequency of ingestion in bivalves. Smaller-sized MP fractions
are more likely to absorb environmental pollutants which may expose
human susceptibility to environmental contaminants via shellfish con-
sumption According to the findings of a review study conducted by Fu
et al. (2020), it was found that out of 24 publications that were investi-
gated, more than 70% of authors had reported that the dominant
microplastic size was less than 1000 μm in aquatic organisms. These
findings are comparable to our studies, where approximately 85% of
microplastic was discovered in the size range of 50 μm–1000 μm. There isTable 4. Microplastic abundance is shellfish from different parts of the world.
Country Species Analytical Microplastics Abundanc
Method
Ghana Crassostrea tulipa KOH/ZnCl2 2.5  1.3 Item/individu
China Saccostrea cucullata KOH 1.7–7.0 Item/individua
Greece Mytilus galloprovincialis H2O2 0.9  0.2
China Scapharca subcrenata H2O2/NaCl 10.5 Item/gram
China Crassostrea gigas KOH/H2O2 2.93 Item/individual
India Magallana bilineata KOH/NaI 6.9  3.8
Belgium Mytilus edulis NHO3: HCl 0.35 Item/gram
Belgium Mytilus edulis HNO3 0.2  0.3
Italy Mytilus galloprovincialis H2O2 3.6–12.4 Item/individu
New Zealand Perna canaliculus HNO3 0–1.5
USA Siliqua patula KOH/NaCl 8.8  0.4
United Kingdom Mytilus edulis H2O2/NaCl 1.1–6.4
France Crassostrea gigas KOH/NaCl 0.60  0.56
Scotland Mytilus edulis Enzyme: trypsin 1.05–4.44 Item/gram
Italy Mytilus galloprovincialis HNO3: HCl 0.11  0.12
USA Crassostrea gigas H2O2 0.69–3.00
USA Crassostrea viginica KOH 3.84  3.39 Item/gram
Canada Crassostrea gigas HNO3 39  27 Item/individua
Canada Crassostrea gigas KOH 0.22  0.22 Item/indiv
South Korea Crassostrea gigas KOH 0.97  0.74 Item/indiv
8
documented evidence that MPs smaller than 20 μm could infiltrate and
translocate in the tissues of most marine biota (Hale et al., 2020). Other
scientific studies argue that particles of sizes less than 150 μm are ex-
pected to be able to pass the human gut barrier and cause adverse effects
on sensitive organs. (Chain, 2016). In recent studies, different MP size
ranges have been found in human samples. In human placenta samples,
for example, MPs identified range in size from 20.3 to 307.3 um, with the
20–100 um size class accounting for 82% of the total MPs detected (Zhu
et al., 2022). Amato-Lourenço et al. (2021) reported a size range of
8.12–16.8 μmMP in human lungs, whereas microplastic ranging between
44–210 μm have been found in human sputum (Huang et al., 2022).
Comparing these reported sizes in human studies with our findings, we
contend that approximately 30% of the microplastics found in the oysters
have the potential to pass through human gut barriers when ingested and
be translocated to other human organ tissues.
In terms of MP shape, fibers and fragments were the most prevalent
microplastics in this study due to their abundance and extensive distri-
bution in the estuarine environment as they have been identified as the
most common microplastic in lakes, rivers, estuaries, the ocean, and
wastewater treatment plant effluents (Salvador Cesa et al., 2017). Due to
their abundant presence in waterbodies, they are more likely to be
ingested by invertebrates such as oysters, mussels, shrimps and echino-
derms (Baechler et al., 2020; Hermabessiere et al., 2019; Mohsen et al.,
2019; Patterson et al., 2019; Li et al., 2015; Vandermeersch et al., 2015)
which could impair their feeding behaviour and disrupt their energy
budget (Lusher et al., 2013). The sources of these fibers in aquatic en-
vironments have been linked to the growing textile manufacturing and
hospitality industries along major rivers and lakes that discharge directly
into them (Joshy et al., 2022; Browne et al., 2013). However, it is
important to note that all the sampled locations in this study are active
fishing sites where the loss of synthetic fishing gears (i.e., nets, ropes, and
lines) could contribute to fibrous pollution.
The prevalence of black-coloured microplastics may be ascribed to
the indiscriminate littering and disposal of polyethylene carrier bags
commonly used for shopping in Ghana. Similar results were obtained by
Adika et al. (2020) who observed the dominance of black colour among
several colours identified as dark coloured microplastics may not be onlye Common Dominant Dominant Reference
size (um) shape polymer
al 100–500 Fiber Polyethylene This Work
l 20–50 Fiber Polyethylene Li et al., (2018)
terephthalate
100–500 Fragment polyethylene Digka et al., (2018)
5–250 Fiber Polyethylene Li et al., (2015)
>500 Fiber Cellophane Teng et al., (2019)
250–500 Fiber Polyethylene Petterson et al. 2019
1000–1500 Fiber N/A De Witte et al., (2014)
20–90 N/A N/A Cauwenberghe et al., 2015
al 1700–1900 Fiber N/A Renzi et al., (2018)
100–200 Fragment Polyethylene Webb et al. (2019)
500–1000 Fiber Polyethylene Baechler et al. (2020)
terephthalate
5–250 Fiber Polyester Li et al. (2018)
50–100 Fragment Polypropylene Phuong et al. (2018)
1200 Fiber Polyamide Courtene-jones et al., 2017
N/A Fragment N/A Vandermeersch et al., 2015
20–1300 Fiber Polyethylene Martinelli et al., (2020)
N/A Fiber Polyethylene Waite et al., (2018)
l <530 Fiber Polystyrene Murphy 2018
idual 10–5000 Fiber N/A Covernton and Id (2019)
idual 100–200 Fragment Polyethylene Cho et al. (2019)
S. Addo et al. Heliyon 8 (2022) e12255visible to the oysters but be more prevalent to be ingested due to simi-
larities to prey items and hence more likely to be detected in the oysters
as previously observed in experimental studies on fish species (Xiong
et al., 2019; Ory et al., 2018).
The polymer types identified in the current studies (polyethylene,
polypropylene, polyamide and polystyrene) are principal components of
most fishing gears such as ropes, nets, and floats (Pappoe et al., 2022).
These fibers may have been accessible to the organisms either because of
wear and tear while the fishing gear was being used or possibly as a result
of the dangers posed by abandoned, lost or discarded fishing gear, which
does not appear to attract the attention of waste managers. Aside its use
in the fishing industries, polyethylene and polypropylene are principal
components of food packaging, plastic containers and the production of
textiles (Joshy et al., 2022; Gedik and Eryaşar, 2020).
The presence of microplastics in the oysters does not only mirror the
contamination status of these estuaries in Ghana but also presents a
public health challenge to consumers, and hence research on human
health effects of microplastics is vital. Although the subtle effect of plastic
ingestion on humans is not well understood, there is documented evi-
dence of physical damage to sensitive organs via plastic ingestion (Li
et al., 2018). The exposure assessment in this present study indicates that
Ghanaian consumers may be exposed to as high as 80 microplastics per
week and 4,160microplastic particles per year (Table 3). Considering the
probability of exposure in other regions of the world, estimated annual
ingestion rates were highest for the USA followed by New Zealand and
France corresponding to the dietary oyster intake rate (Table 3).
Although not a common practice for bivalve consumption, in areas where
attempts are made to remove the digestive tract, exposures could be
minimized.
Based on the average MP item per gram tissue (1.0 g/tissue), the
estimated mean human intake of microplastics for the general population
consuming 50 g of the assessed species was 50 MP items/week or 2,600
MP items/year, corresponding to 1.0 MP item/g/week and 52 MP item/
g/year. These figures are many folds higher than those previously esti-
mated for humans consuming oysters from South Korea, namely 0.412
MP items/week and 21.4 MP items/year, corresponding to 0.071 MP
items/g/week and 3.70 MP items/g/year (Cho et al., 2019) and Cras-
sostrea gigas from France namely 21 MP items/week or 1,136 MP
items/year, corresponding to 0.45 MP items/g/week and 28.5 MP
items/g/year (Van Cauwenberghe & Janssen, 2014).
Our findings suggest that the annual dietary exposure for Ghanaian
shellfish consumers might be one order of magnitude higher. Despite the
high level of human exposure with reference to this study, uncertainties
remain; it is unknown if the ingested dose equals the absorbed dose or
whether cooking significantly affects plastic toxicity. Although the study
provides baseline data on the occurrence and abundance of microplastics
in shellfish from the coastal waters of Ghana, we acknowledge that the
sample size is relatively small and so it is recommended that further
studies are undertaken on a wider scope.
5. Conclusion
This study provides baseline data on microplastics in oysters from the
coastal waters of Ghana. Oysters and other species of bivalves are clas-
sified globally as good indicators of pollutants and this study has
confirmed that the oysters may be considered in future studies as a po-
tential candidate for plastic polymer monitoring in West Africa where
they predominate. Microplastic abundance was high in oysters from
populated communities due to intensive anthropogenic activities. The
high prevalence of microfibers in oyster samples suggests improper
disposal or mismanagement of effluent into water bodies. Our findings
further indicate that microplastic abundance in oysters does not depend
on the size of the organism but rather on the time and frequency of
exposure. The estimated microplastic intake per capita per year for
Ghana revealed that exposure to microplastics from shellfish consump-
tion may be significantly higher in countries with high oyster9
consumption rates. However, the toxic effect of microplastics on human
health is not well understood. Therefore, further studies are needed to
highlight the toxicity of plastic exposure to human health.
Declarations
Author contribution statement
Samuel Addo: Conceived and designed the experiments; Contributed
reagents, materials, analysis tools or data; Wrote the paper.
Charles Mario Boateng; Harriet Danso - Abbeam: Analyzed and
interpreted the data; Wrote the paper.
Rhode lims Diyie: Conceived and designed the experiments; Analyzed
and interpreted the data.
Collins Prah Duodu: Performed the experiments; Analyzed and
interpreted the data; Wrote the paper.
Kofi Ferni Anyan: Performed the experiments; Analyzed and inter-
preted the data.
Ernestina Abbew Williams; Akosua Ohemaa Amakye: Performed the
experiments.
Obed Asamoah; Elvis Nyarko: Analyzed and interpreted the data.Funding statement
This research did not receive any specific grant from funding agencies
in the public, commercial, or not-for-profit sectors.Data availability statement
Data will be made available on request.Declaration of interest’s statement
The authors declare no conflict of interest.Additional information
No additional information is available for this paper.
Acknowledgements
The authors would like to express their profound gratitude to the
entire staff of the Marine and Fisheries science department for the sup-
port and usage of laboratory facilities. Special appreciation to Mr Dus-
mond Maccarthy, Mr Samuel Tawia and Miss Vera Mensah for their
assistance in sample collection and preparation. We also acknowledge
the involvement of Mr Samuel Attuah from the Department of chemistry
during polymer identification analysis.
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