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RESEARCH ARTICLE
Metal accumulation in the marine bivalve, Marcia optima collected
from the coastal area of Phuket Bay, Thailand
Pensiri Akkajit
1,2,3,4
&Putri Fajriati
1
&Mongkolchai Assawadithalerd
5
Received: 26 May 2018 /Accepted: 16 October 2018
#Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
Metal contamination in seafood has raised public health concerns, especially for local residents who live in coastal areas. In this
study, the levels of cadmium (Cd), lead (Pb), mercury (Hg), and zinc (Zn) were determined in the marine bivalve, Marcia optima,
as well as in water, and sediment samples collected from the coastal area of Phuket Bay, Thailand. The results showed that metal
concentrations in sediments (4.05–7.14, 16.68–18.13, 164–213 mg kg
−1
for Cd, Pb, and Zn, respectively) and water samples
(0.16–0.44, 0.15–0.26, and 0.32–0.48 mg L
−1
for Cd, Pb, and Zn, respectively) were below the threshold effects concentration of
the sediment quality guidelines for adverse effects to occur and the marine water quality standards of Thailand. A human risk
assessment was performed and the results showed that the risks associated with M. optima consumption at Saphan Hin and
Paklok were negligible for most of the metals studied, with the maximum estimated daily intake value being observed for Zn
(0.00663 mg kg
−1
per day) at Saphan Hin. In addition, Cd, Zn, Pb, and Hg would be unlikely to pose a risk to human health with a
hazard quotient of less than 1, with only the bioaccumulation factor of Zn being detectable in both locations (0.034 and 0.026 at
Saphan Hin and Paklok, respectively). However, continuous monitoring is encouraged to prevent the risks associated with the
consumption of metal-contaminated seafood.
Keywords Marcia optima .Metals .Risk assessment .Phuket .Sediment
Introduction
Sediments can be used for monitoring metal contaminants
since they serve as a sink for pollutants in aquatic ecosystems
(Balcazar, 1999; Wolfa et al., 2001; Belgica et al., 2010;
Sekabira et al., 2010; Salah et al., 2012; Zhang et al., 2015).
However, the concentration of metal contaminants released to
the environment depends on physical and chemical factors
that may affect their behavior in the environment. Organisms
such as shellfish, especially bivalve species that live in sedi-
ments, can be used as a bio-indicator or bio-marker to monitor
the contamination level and the transfer of heavy metals in
coastal and/or estuarine regions (Azizi et al., 2018) due to
the ability of their bodies to bioaccumulate and magnify such
contaminants (Guéguen and Amiard, 2011). Bivalves are
widespread incoastal and estuarine regions and primarily feed
on organic detritus, phytoplankton, and zoobenthos, in which
sediments are rich. Bivalves are filter-feeding mollusks and
Responsible editor: Philippe Garrigues
*Pensiri Akkajit
pensiri.a@phuket.psu.ac.th
Putri Fajriati
putrifajriati@gmail.com
Mongkolchai Assawadithalerd
mongkolchai.a@gmail.com
1
Integrated Science and Technology Research Center (Applied
Chemistry/Environmental Management/Software Engineering),
Prince of Songkla University, Phuket Campus, Phuket 83120,
Thailand
2
Faculty of Technology and Environment, Prince of Songkla
University, Phuket Campus, Phuket 83120, Thailand
3
Research Program of Toxic Substance Management in the Mining
Industry, Center of Excellence on Hazardous Substance Management
(HSM), Bangkok 10330, Thailand
4
Research Unit of Site Remediation on Metals Management from
Industry and Mining (Site Rem), Chulalongkorn University,
Bangkok 10330, Thailand
5
Center of Excellence on Hazardous Substance Management (HSM),
Chulalongkorn University, Bangkok, Thailand
Environmental Science and Pollution Research
https://doi.org/10.1007/s11356-018-3488-7
can accumulate metal contaminants taken up directly through
their body tissues, which subsequently pass into the food-
chain (Lias et al., 2013) Thus, metal contaminants in sedi-
ments may be transferred to water and shellfish and threaten
the ecosystem and human health through shellfish
consumption.
Among the metal contaminants found in shellfish are Cd,
Pb, and Hg, which are non-essential elements and even in
trace amounts are toxic and damaging to human health
(Alina et al. 2012). Meanwhile Zn, which is an essential
metal, is also toxic although only in very high concentra-
tions (Silveira Fiori et al., 2018). Cd and Pb occur both
naturally such as rock weathering and through anthropo-
genic sources such as from traffic and metal mining opera-
tions. The non-essential element, Cd can cause toxic effects
in the kidneys and bones, while Pb causes metal neurotox-
icity in children and cardiovascular effects in adults (Loaiza
et al., 2018). Hg can occur naturally in the earth’scrustand
be released into the environment from volcanic activity or
the weathering of rocks. Anthropogenic sources of Hg in-
clude coal-fired power stations or other forms of coal burn-
ing, industrial processes, waste incinerators, and mining
operations (Munawer, 2018). There are various forms of
Hg including elemental (or metallic), inorganic, and organ-
ic (methylmercury or MeHg), which differ in their degree of
toxicity and their effects on the nervous, digestive, and im-
mune systems (World health organization (WHO), 2017).
One of the forms of most concern is MeHg and the total Hg
(THg) concentration in seafood is often used as a measure
of MeHg exposure (Kim et al., 2012). Finally, Zn is an
essential metal and relatively harmless as compared to other
metal contaminants. However, exposure to high doses has
toxic effects including Zn-induced copper deficiency, ab-
dominal pain, nausea and vomiting, lethargy, anemia, diz-
ziness, and gastrointestinal effects (World health organiza-
tion (WHO), 2017).
Phuket is the largest island in the south of Thailand. It was
formerly well known as a tin (Sn) mining area following the
discovery of Sn in Phuket in 1909. The Bang Yai canal is a
primary waterway which receives water from a reservoir up-
stream and flows through the former Sn mining area near
Phuket town and discharges into the sea in the Saphan Hin
area in Phuket Bay (Heednacram and Samitalampa, 2014).
Like most coastal areas, Saphan Hin is an important ecological
and economic area in the south-western part of Phuket.
However, there are anthropogenic activities such as a munic-
ipal solid waste incinerator and a boat parking area close to
Saphan Hin. The area is now becoming increasingly polluted
from both organic and inorganic contaminants discharged into
the canal and these can be considered as a potentially signif-
icant source of metal pollution and thus a potential threat to
people’s health (Akkajit and Suteersak, 2017; Suteerasak and
Bhongsuwan, 2008).
In Phuket, particularly in coastal areas, marine animals are
a common form of sustenance for local people and shellfish
are one of the commonly found seafoods that are harvested
and consumed regularly by local residents. The dominant
types of shellfish found in the Saphan Hin area are bivalves
although mussels, scallops, and clams can also be found there.
Marcia optima is a highly commercialized and economically
important bivalve consumed locally, both by local fishermen
and people living on the coast near Saphan Hin. M. optima is a
species of the Veneridae family with a life span of 3 years,
which is normally found in coastal areas with shallow sub-
tidal waters. Due to its abundance, largenumbers of M. optima
are consumed in Phuket. The shell grows to a maximum size
of 60.5 mm equilaterally, with a thick, solid, flattened, and
glossy surface (Powell and Cummins, 2018). Bearing in mind
that M. optima is sold commercially in local markets, the
measurement of levels of metal contaminants in the shellfish
tissues are a matter of public concern since shellfish consump-
tion is a significant pathway for human exposure to metal
contaminants. However, there has been no previous study of
metal contamination in commercial shellfish collected from
Bang Yai canal, Phuket nor of the risk of metal toxicity posed
by the consumption of those shellfish. Therefore, it was desir-
able to perform a risk assessment to evaluate the exposure of
local residents to toxic metals due to shellfish consumption.
The main objectives of this investigation were therefore (1) to
determine the concentrations of Cd, Hg, Pb, and Zn in the
bivalve, M. optima, found and harvested at Saphan Hin,
Phuket Bay and (2) to assess the risk to human health posed
by metal contaminants associated with shellfish consumption.
The findings of this study will enable the prioritization of
public health action and will provide base-line data for the
formulation of pollution control measures and the planning
of site management in this coastal area, especially for con-
sumers of M. optima.
Materials and methods
Study area
The Saphan Hin area at the outfall of the Bang Yai canal was
selected as the study area due to it is importance to local
residents. The northern and eastern parts of the area are
surrounded by mangrove forest and a public recreation park
while the southern and western parts accommodate a sports
complex, government authority offices, and residential areas.
Before the Bang Yai canal flows into Saphan Hin, it first flows
through a reservoir upstream at Kathu waterfall, then flows
through the former Sn mining area close to Phuket town, and
has its outfall in Phuket Bay. The area is affected by significant
sources of pollution that cause metal contaminants to accumu-
late in water and sediments. Three sampling points at Saphan
Environ Sci Pollut Res
Hin were selectedin this study as depicted in Fig. 1. Sediment,
shellfish, and water samples were collected on the same dates
in April (T1) and May (T2) in 2017. The Paklok area, which is
located on the east coast of Phuket province (longitude 8°00′
56.0″; latitude N 98°24′36.0″E) and is mainly occupied by
mangrove forest, was used as a background reference in order
to compare the associated risks presented by shellfish
consumption.
Shellfish and sediment sampling and preparation
Triplicate samples of the water, surface sediments, and bi-
valves were collected on the same sampling dates from all
the sites. The water samples were taken near the surface (20-
cm below the water table) and put into 0.5-L plastic bottles,
then acidified with HNO
3
for preservation, before being
transported to the laboratory. The chemical properties were
determined in the field using field-moist samples (Gleason
et al., 2003) for both the water and sediment samples, included
their temperature, pH (1:2 soil/water suspensions) (Gleason
et al., 2003) and oxidation-reduction potential (ORP) (WD-
35618-32, Oakton, USA) (Gleason et al., 2003), electrical
conductivity (EC) (EC-3, HM, USA), dissolved oxygen
(DO) (WA2017SD, Lutron, Taiwan) and total dissolved solid
(TDS). In the laboratory, the water samples were filtered
through GF/C filters (Whatman, UK). For the sediments, sur-
face sediments (5–10-cm depth) were collected using a plastic
tube sediment sampler and were placed in plastic zip-lock
bags and kept chilled in an insulated container throughout
the transportation to the laboratory. The sediment samples
were then air-dried at 60 °C for 48 h or until a constant weight
was achieved, then sieved through a no. 230 nylon sieve (pore
size < 63 μm).
The marine bivalve, M. optima which are abundant and are
mostly consumed by the local people in the Saphan Hin area,
were used in this study to assess the risks to human health.
Bivalve samples were collected each month with the help of a
fisherman. Two kilograms of bivalve specimens were collect-
ed manually from the surface to a depth of 0.5 m and placed in
plastic bags which were chilled before being transported to the
laboratory at Prince of Songkla University, Phuket campus for
further processing and analysis. All the shellfish samples were
rinsed several times with tap water followed by deionized
water in order to remove any particles attached at the time of
collection. Then approximately 20 individuals of M. optima
with similar shell lengths (approximately 4 cm) were selected,
individually numbered, and weighed using scales. The mean
shell length was 4.71 ± 0.31 cm. The soft tissue of the shellfish
was then removed from the shells with a plastic knife and put
onto an aluminum foil tray and oven dried at 60 °C until a
constant weight was achieved. The weight of the dried tissues
was recorded and the moisture content (%) was calculated.
Then, the samples were ground and homogenized using a
porcelain mortar, sieved, and stored for the determination of
the concentrations of metals.
Metal analysis
Metal contaminant digestion for the water, sediment, and
shellfish samples followed a modified US EPA 3052 method
(1996). A composite sample of M. optima of the same size
was used for the analysis. A weight of about 0.5 g of sediment
and 1.0 g of M. optima samples were added to 3 ml of con-
centrated nitric acid (69% HNO3) and 9 ml hydrochloric acid
(37% HCl) and placed in an iPrep vessel. All the metals were
determined by inductively coupled-plasma optical emission
spectrometer (ICP-OES) using an Optima 8000 spectrometer
(Perkin Elmer Instruments). The analytical method used for
the metal determination was checked by using certified refer-
ence material (Fish Muscle European Reference Material,
ERM BB422) for shellfish and marine sediment certified ref-
erence material (MESS-4 National Research Council, Canada,
2016) for the sediments. All the samples and reference mate-
rials were run in triplicate for the total digestion (US EPA
Method 3052). The results of the MESS-4 (Pb 20.75 ± 0.63
and Zn 139.87 ± 3.83 mg kg
−1
) and ERM BB422 (Cd 0.0089
± 0.63, Hg 0.69 ± 0.13 and Zn 14.7 ± 1.9 mg kg
−1
)obtainedin
this study showed acceptable ranges within the certified
values (Pb 21.5 and Zn 147 mg kg
−1
for MESS-4; and Cd
0.0075, Hg 0.601 and Zn 16 mg kg
−1
for ERM BB422, re-
spectively). The method detection limits for Cd, Pb, Hg, and
Zn were 0.02 mg kg
−1
, 0.01 mg kg
−1
, 3.83 μgkg
−1
,and
0.02 mg kg
−1
, respectively. The wavelengths used were Pb:
220.353, Cd: 228.802, and Hg: 253.652.
Human health risk assessment
A human health risk assessment was conducted to determine
the potential health risk to local residents who consume shell-
fish from the Saphan Hin area, due to exposure to toxic metal
contaminants emanating from the former Sn mining and other
anthropogenic sources. The assessment was based on the es-
timated daily intake (EDI), hazard quotient (HQ), and bioac-
cumulation factor (BF) of the metal contaminants. The EDI of
shellfish by local residents was based on the metal concentra-
tions in shellfish tissue and the average daily shellfish con-
sumption rate. A questionnaire was used as the research in-
strument to collect data for the site-specific parameters for the
risk assessment. It was divided into two parts; (1) demograph-
ic information and (2) M. optima consumption. The target
population of this survey consisted of local residents from
the Saphan Hin area of Phuket province, Thailand. The survey
was based on both multiple-choice and open response items.
The age, gender, body weight, and occupations of the respon-
dent family members were established as well as whether any
of them were pregnant. The respondents were also asked
Environ Sci Pollut Res
whether they consume shellfish, and if so, the frequency of
consumption and the quantity per meal. A picture of the shell-
fish, M. optima, was also shown to the respondents in order to
obtain information about serving sizes. The size of the sample
used in this study was calculated according to the Taro
Yamane formula (Yamane, 1967) at a 95% confidence level
as per the following equation;
n¼N
1þNe2ð1Þ
where nis the sample size, Nis the population size based on
the number of residents estimated for the Muang district,
Phuket province (Department of Provincial Administration,
Official Statistics Registration Systems, 2010), and eis the
level of precision required (p< 0.05). The survey thus includ-
ed 100 participants (46 males and 54 females) of whom the
largest group was aged between 20 and 29 years old (37%).
Their educational qualifications were mainly bachelor’sde-
grees (37%) and diplomas (34%). The major occupational
groups were comprised of those self-employed in private
companies (27%) and employees (23%). Based on the an-
swers to the questionnaire, the daily average number of shell-
fish consumed was 14.31 and applying the average fresh
weight (g) of the shellfish recorded (4.119 g fresh weight),
the ingestion rate (IR) was calculated to be 58.94 g per day,
and this number was used throughout this study for the pur-
poses of the risk assessment.
Fig. 1 Sampling locations for marine bivalves (Marcia optima), water, and sediment samples
Environ Sci Pollut Res
The EDI (mg kg
−1
per day) was calculated by Eq. (2)fol-
lowing Phuong et al. (2015); where C
metal
is the concentration
of metal in the shellfish (mg kg
−1
on a fresh weight basis);
W
food
is the daily average consumption of shellfish (4.119 g
fresh weight); and BW is the body weight of local residents
(64.5 kg). The W
food
and BW were obtained from the answers
to the questionnaire.
EDI ¼Cmetal Wfood
BW ð2Þ
In addition, a hazard quotient (HQ) was used to estimate
the risk for non-carcinogenic metal contaminants which was
calculated as the ratio of the EDI to the reference dose (RfD)
(Eq. (3)).
HQ ¼EDI
RfD ð3Þ
where EDI is the intake of metal contaminants through the
consumption of shellfish (from Eq. (2)); RfD is the reference
dose (Cd: 1.0 × 10
−3
mg kg
−1
per day, Hg: 3.0 × 10
−4
mg kg
−1
per day, Pb: 4.0 × 10
−3
mg kg
−1
per day, and Zn: 3.0 ×
10
−1
mg kg
−1
per day) (Nriagu, 2007). Furthermore, the BF
can be used to describe how much of the metal contaminants
in the environment are transferred to shellfish tissues. The
calculation is given in the following equation as reported by
Beltran-Pedreros et al. (2011).
BF ¼Cshellfish
Csediment
ð4Þ
where C
shellfish
is the metal contaminant concentration in
the shellfish tissue samples (mg kg
−1
)andC
sediment
is the
metal contaminant concentration in the sediment samples
(mg kg
−1
).
Results and discussion
Chemical properties of water and sediment samples
The chemical properties of the water and sediment samples
are presented in Table 1. According to the results, the water
samples at Saphan Hin showed a neutral to very slightly alka-
line pH value with a range of 7.0 and 7.2. The water temper-
ature ranged from 29.2 °C to 29.7 °C during the time of sam-
pling and no significant differences were found between the
sampling periods (ANOVA, p> 0.05). The DO is the amount
of oxygen dissolved in water. The low DO might cause pol-
lution problems for aquatic life, such as impaired fish devel-
opment and maturation or increased fish mortality (Popa et al.,
2012). In this study, the DO at T2 met Thailand’s sea water
quality standards (Pollution Control Department, Ministry of
Natural Resources and Environment, 2006)andwasgreater
than 4 mg L
−1
, while at T1 it was lower than the regulation
amount (3.8 mg L
−1
). The amount of DO required by aquatic
life has been reported to vary, with creatures such as crabs,
oysters, and worms needing only minimal amounts of oxygen
(1–6mgL
−1
), while shallow water fish need higher levels of
4–15 mg L
−1
(Fundamentals of Environmental
Measurements, 2016).
In addition, the total dissolved solids (TDS) in the water
samples was determined, which ranged from 16.7 to
25.0 mg L
−1
, which is lower than the limit given by the
FAO for irrigation water (Ayers and Westcot, 1994). The con-
centration of TDS in water samples is determined by the ge-
ology of the drainage, atmospheric precipitation, and
evaporation-precipitation (Weber-Scannell and Duffy, 2007).
A high TDS value can increase salinity and be toxic to aquatic
life and thus limit biodiversity by excluding less-tolerant spe-
cies and causing acute or chronic effects at specific life stages
(Tawati et al., 2018).
The EC of the water samples ranged from 160 to 430
(mS cm
−1
). The EC values varied between T1 and T2, and
were below the limit set by the World Health Organization
(WHO) (750 μScm
−1
) and the FAO (3000 μScm
−1
)for
irrigation. The EC values of the water samples in this study
were similar to the result reported by Tawati et al. (2018)who
found that the EC values of water samples collected from the
Sumber Maron River, Malang, Indonesia were from 243 to
270 μmcm
−1
.
For the sediment samples, the pH values ranged from near
neutral to slightly alkaline (7.1–8.1) with minor fluctuations
among the different sampling points (Table 1). It was found
that the pH values in this study exhibited a similar trend to
those in a previous study conducted in the Saphan Hin area
(pH 6.8–8.3 and 6.9–8.1; Akkajit and Suteersak, 2017).
Higher pH values can promote adsorption and precipitation,
resulting in a decrease of metal contaminant mobility, whereas
low pH values are associated with the release of metal con-
taminants (Violante et al., 2010). Changes in the oxidation
state of the metals in the sediment can affect metal mobility
and solubility in the environment (Lee, 2006). In this study,
the ORP of the sediments ranged from 204.2 to −71.28 mV,
which indicated the reduced condition of the sediment. It has
been reported that the mobility of metals increases in the low
oxidation stage (Eh < 100 mV) and as sediments become an-
aerobic, the redox potential decreases and eventually trans-
forms to the more soluble reduced form of metals (Kabata-
Pendias and Pendias, 2001). The EC values in the sediment
samples obtained in this study (366–732 mS cm
−1
) were lower
than the standard EC value of salt-affected sediment in
Thailand, of higher than 2000 μS/cm (Arunin and
Pongwichian, 2015).
Environ Sci Pollut Res
Metal concentrations
Metal concentrations in water and sediment samples
The metal contaminant levels in the water and sediment sam-
ples in this study are presented in Table 2. According to the
results, the water samples taken from the Bang Yai canal at
Saphan Hin showed high concentration levels of Cd, Pb, and
Zn (0.16–0.44 mg L
−1
,0.15–0.29 mg L
−1
and 0.20–
0.48 mg L
−1
, respectively). However, the highest Cd and Pb
concentrations (0.44 mg L
−1
and 0.26 mg L
−1
, respectively)
were observed in water samples from Paklok. It was found
that all the metal concentrations in the water exceeded the
marine water quality standards of Thailand for recreational
activities regulated by the Pollution Control Department
(2006) (Table 2) and were higher than those found by
Kingsawat and Roachanakanan’s(2011) study of the Pradu
canal, Samut Songkhram province, Thailand, which found Cd
concentrations in water samples of 0.10 to 1.31 μgL
−1
.
Statistical analysis revealed that the sampling period did not
have an influence on the metal concentration levels (p<0.05).
The run-off flowing into the Bang Yai canal causes high metal
contaminant levels in the water, and it is suggested that the
local government and relevant agencies should regularly mon-
itor the contamination level and take action to prevent or re-
duce the hazardous impacts of metals on the environment.
All the metals studied were detected in the sediment sam-
ples collected from both Saphan Hin and Paklok. The metal
concentrations in the sediments were higher than those in the
water samples (Table 2) since metal contamination in water is
subject to seasonal variations (Rzymski et al., 2014). In this
study, the metal concentrations in the water samples exhibited
the following decreasing order: Zn > Cd > Pb, while the con-
centration of metal contaminants in the sediments showed the
following trend: Zn > Pb > Cd. The flow of the Bang Yai canal
is toward Saphan Hin with its outfall in Phuket Bay and this
can stimulate high rates of metal deposition and bioaccumu-
lation of the metals in these areas. The results show that the
sediments collected from the Bang Yai canal at Saphan Hin
contained similar levels of metals to those found at Paklok
(Table 2). This finding supports the previous work of
Akkajit and Suteersak (2017) which determined that metal
accumulation in sediment cores at Saphan Hin showed similar
Pb and Zn concentration ranges (6.33–36.52 mg Pb kg
−1
and
21.63–73.59 mg Zn kg
−1
). The highest Pb and Zn concentra-
tions (18.13 mg kg
−1
and 213 mg kg
−1
, respectively) were
observed in sediment samples from Saphan Hin at T1.
However, the levels of Pb found were below the threshold
effects concentration (TEC) of the sediment quality guidelines
for adverse effects to occur (35.8 mg kg
−1
) (Helen et al.,
2016).
Several factors affect the transport, distribution, and fate of
metals as non-point source pollutants. In the area studied, the
proximity of crowded residential areas, and agricultural areas,
the storage of municipal waste for incineration, and the con-
sequent production of fly ash and bottom ash are partly re-
sponsible for the high levels of Cd and Zn in both the sea
water and sediment. These sources combine with the effects
of run-off and high average rainfall to spread metals into the
coastal waters, and this is aggravated by the fact that the area
studied is located on a flood plain where many anthropogenic
activities lead to the accumulation and adsorption of metal
contaminants in high-pH sediments with a high organic matter
content. Based on the results of this study, the water and
Table 1 The chemical properties of the water and sediment samples
Time Water samples
pH ORP (mV) EC (mS cm
1
)DO(mgL
−1
) TDS (mg L
−1
)
T1 7.0 ± 0.00 34.5 ± 0.04 323 ± 0.06 3.58 ± 0.00 17.2 ± 0.04
7.0 ± 0.02 27.1 ± 0.05 430 ± 0.09 3.60 ± 0.02 17.6 ± 0.06
7.0 ± 0.02 36.8 ± 0.07 401 ± 0.05 4.13 ± 0.04 16.7 ± 0.03
T2 7.3 ± 0.02 165 ± 0.08 248 ± 0.04 5.69 ± 0.03 25.0± 0.07
7.2 ± 0.07 160 ± 0.08 160 ± 0.04 5.93 ± 0.03 22.6± 0.03
7.1 ± 0.01 161 ± 0.05 161 ± 0.06 5.90 ± 0.01 22.2± 0.07
Sediment samples
T1 7.1 ± 0.02 −138.9 ± 0.04 424 ± 0.00 ––
7.6 ± 0.11 −121.5 ± 0.04 366 ± 0.02 ––
8.1 ± 0.08 −204.2 ± 0.05 435 ± 0.01 ––
T2 8.0 ± 0.05 −71.3±0.06 732±0.02 ––
7.3 ± 0.07 −174.5 ± 0.05 731 ± 0.00 ––
7.6 ± 0.01 −198.4 ± 0.05 688 ± 0.05 ––
Data presented as mean ± SD
Environ Sci Pollut Res
sediment samples constitute a significant source of metal con-
taminants and this should be called for concern about the
effects on the local ecosystem.
Metal concentrations in shellf ish samples
Metal bioavailability is an important factor determining metal
toxicity as it is the metal fraction that is available for incorpo-
ration into an organism (Väänänen et al. 2018). It is well
known that metal bioavailability is a function of physico-
chemical factors of both water and sediments including the
water pH, the redox potential, temperature, hardness, and total
organic content (Akkajit and Tongcumpou, 2010; Rzymski
et al., 2014). Pollution from upstream in the Bang Yai canal
can have a great impact on the water and sediment qualities
downstream and can contribute to the contamination of the
aquatic environment and its biota, including bivalves and ma-
rine fish. Therefore, the bivalve, M. optima, was used in this
study as an indicator to determine the overall environmental
status of the area.
From the results obtained, while metal contaminants were
detected in the M. optima samples, those of Pb and Cd were
below the detection limit of the instrument (Table 3). Cd and
Pb contaminants found in water and sediment samples can be
defined as from non-point source and the leaching of metal
contaminants through run-off may significantly increase metal
concentrations. However, the low metal contents in the shell-
fish samples were observed and the magnitude of metals con-
centrations found in this order; sediment > water > biota
which corresponding to the results of Weber et al. (2013).
Mangrove forests at the study sites with high organic matter
in soil and sediment may cause metal-organic matter
interactions and lower metal bioavailable fraction in water
and bivalve. Sharif et al. (2016) reported that the shellfish
have different trends of bioaccumulation as there are many
factors that could affect the bioaccumulation rate such as eat-
ing habits, anatomical difference, physiological difference,
and metabolism reactions.
Among the metal contaminants of interest, a more elevated
Zn level was observed in M. optima as compared to other
metals. Zn is essential for plant, animal, and human growth
Table 3 Metal concentrations in Marcia optima (mg kg
−1
) collected from Saphan Hin, Phuket
Metal concentration (± SD)
Pb (mg kg
−1
)Cd(mgkg
−1
)Zn(mgkg
−1
)Hg(μgkg
−1
)
May (T1) ND ND 7.25 ± 0.13 26.68 ± 2.37
June (T2) ND ND 7.99 ± 0.10 11.22 ± 0.93
July (T3) < 0.45 0.10 ± 0.00 8.12 ± 0.07 ND
Ministry of Public Health, Thailand (MPHT, 1986) < 1 mg kg
−1
NA < 100 mg kg
−1
<0.5 mgkg
−1
Food and Drug Administration of the United States (USFDA, 1990) 11.50 25.0 –NA
Data presented as mean ± SD
NA, not available; ND, not detectable (limit of detection of Cd, Pb, and Hg are 0.02 mg kg
−1
,0.01mgkg
−1
, and 3.83 μgkg
−1
, respectively
Table 2 Metal concentrations in sediment (mg kg
−1
) and water (mg L
−1
)samples
Sampling sites Metal concentration in sediment
(mg kg
−1
)
Metal concentration in water
(mg L
−1
)
Cd Pb Zn Cd Pb Zn
T1 4.05 ± 0.02 18.13 ± 0.26 213 ± 1.01 0.16 ± 0.02 0.15 ± 0.09 0.48 ± 0.01
T2 5.01 ± 0.38 16.89 ± 0.29 164 ± 1.00 0.25 ± 0.00 0.20 ± 0.02 0.32 ± 0.01
Paklok 7.14 ± 0.31 16.68 ± 0.41 169 ± 0.80 0.44 ± 0.02 0.26 ± 0.03 0.36 ± 0.09
Range 4.05–7.14 16.68–18.13 164–213 0.16–0.44 0.15–0.26 0.32–0.48
Standards
a
0.99 mg kg
−1a
35.8 mg kg
−1a
121 mg kg
−1b
<5 μgL
−1b
<8.5 μgL
−1b
<50 μgL
−1
Data presented as mean ± SD
a
Threshold effects concentration (TEC) of the sediment quality guidelines
b
Marine water quality standards of Thailand (Class 4 Recreation), Pollution Control Department, Ministry of Natural Resources and Environment
Marine water quality standards (2006)
Source: Helen et al. (2016)
Environ Sci Pollut Res
and can be found in varying concentrations in sediments,
plants, and animals (Alloway, 1990); however, Zn can be tox-
ic to aquatic biota at elevated concentrations. It has been re-
ported that Zn concentrations in marine organisms can be
found at substantially higher levels as compared to other
metals, and Olmedo et al. (2013) found that Zn had the highest
concentration of any metal in fresh mackerel (8.09 mg kg
−1
),
cuttlefish (7.76 mg kg
−1
), anchovy (7.04 mg kg
−1
), clam
(6.30 mg kg
−1
), and shrimp (6.28 mg kg
−1
) obtained from
Andalusia, southern Spain. Lias et al. (2013)alsoreportedthat
the concentration of Zn was the highest of any metal in sedi-
ments and the tissue of Marcia Marmorata sp. collected from
the coastal area of Kuala Perlis, Malaysia (121.0 mg kg
−1
and
93.1 mg kg
−1
, respectively). However, Chaiyarat et al. (2013)
found that Zn was at the lowest level of metal contaminants in
mangrove crabs (Sesarma mederi) from the mangroves of the
Chao-Phraya, Tha-Chin, and Mae-Klong rivers in central
Thailand (Cd > Cu > Pb > Zn). The metal concentrations in
edible marine organisms in other parts of Thailand have been
widely studied; for example, in the coastal area of
Chachoengsao province, Cd, Pb, Hg, and Zn in A. granosa
samples did not exceed the food compliance limits set by the
Ministry of Public Health, Thailand (Worakhunpiset, 2018).
Rzymski et al. (2014) reported that metal concentrations in
bivalves generally followed the level of contamination of their
environment, in particular the sediment. By reference to the
metal concentration levels (Cd, Hg, Pb, and Zn) specified by
the Ministryof Public Health, Thailand (MPHT, 1986) and the
Food and Drug Administration of the United States (USFDA,
1990), it was found that the metal accumulations in M. optima
were below those standards and were also lower than those
reported in other studies (Phuong et al., 2015;Sharifetal.,
2016). This would suggest that the consumption of M. optima
collected from Saphan Hin by the local residents can be con-
sidered to be safe. However, continuous monitoring is to be
encouraged in order to prevent any risk associated with the
consumption of metal-contaminated seafood reaching danger-
ous levels.
Human health risk assessment
In the risk assessment conducted in this study, the health risk
due to metal contaminants in shellfish was determined for
local residents. Based on the average number of shellfish con-
sumed determined from the questionnaire and the average wet
weight (g) of the shellfish recorded, the IR was found to be
58.94 g per day. Moreover, the average BW of the local resi-
dents was 64.5 kg and these quantities were used to calculate
the EDI in milligrams of metal per kilogram of body weight
per day, as shown in Table 4.
The potential health risk from Cd and Pb was lowest due to
the very low concentrations found in shellfish. According to
the results, it can be seen that the Pb levels both in Saphan Hin
and Paklok found in this study presented no risk to human
health (Table 4). However, the EDIs based on the findings at
Saphan Hin of Hg and Zn (0.000024 μgkg
−1
per day and
0.00663 mg kg
−1
per day, respectively) through M. optima
consumption could present a potential risk to human health
as did those for Cd and Zn at Paklok (0.000137 mg kg
−1
per
day and 0.00409 mg kg
−1
per day, respectively).
The FAO and WHO Joint Expert Committee on Food
Additives (JECFA, 1993) set levels for the tolerable intake
of heavy metals in their Provisional Tolerable Weekly Intake
(PTWI) which represents the maximum amount of a contam-
inants to which a person should be exposed per week over a
lifetime without incurring an unacceptable risk to their health
(Peycheva et al., 2016). According to the FAO/WHO, the
intake estimates expressed per unit body weight per week
forCd,MeHg,Pb,andZnare7μgkg
−1
,1.6μgkg
−1
,
25 μgkg
−1
,and7mgkg
−1
, respectively (Renieri et al.,
2014). It can be seen that the EDI levels of the metals studied
were considerably below the PTWI, indicating that M. optima
from Saphan Hin and Paklok cannot be considered to consti-
tute a risk to human health. As reported by Sharif et al. (2016),
the EDI of Cd and Pb in other seafood such as clam (Meretrix
spp.), scallop (Amusium pleuronectes), and conch (Strombus
canabrium) are higher than those in the present study (0.02–
1.58 and 0.10–0.25 μgkg
−1
per day for Cd and Pb, respec-
tively). The bivalve clam, Marcia hiantina, sampled at Nha
Trang Bay in Vietnam also showed higher EDI values for Cd
(0.038 μgkg
−1
per day) and Zn (3.380 μgkg
−1
per day)
(Phuong et al., 2015).
To assess the health risks, the HQ was calculated based on
the ratio of the potential exposure to metal contaminants to the
level at which no adverse effects are expected (Liang et al.,
2017). An HQ ≤1 indicates no significant risk; 1 < HQ < 9.9
indicates a low risk; 10 < HQ < 19.9 indicates a moderate risk;
20 < HQ < 99 indicates a high risk, and an HQ ≥100 indicates
a serious level of risk. Based on the calculation of the HQ in
M. optima, all the metals studied had HQ values below 1,
indicating that the intake of these metals from M. optima
would be unlikely to cause adverse health effects and pose
no risk to human health. The highest risk for human health
at Saphan Hin and Paklok in terms of HQ can be ranked as Hg
> Zn > Cd = Pb and Cd > Zn > Pb = Hg, respectively. This
result is similar to that of other studies which have found HQs
of less than 1 (Sharif et al., 2016; Janadeleh and Jahangiri,
2016).
Metal uptake from sediments can be considered as an im-
portant pathway for food-chain transfer. The BF, representing
the ratio of metal concentration in the shellfish (mg kg
−1
)to
the concentration of metal in the sediments (mg kg
−1
), was
calculated for Cd, Zn, and Pb to estimate their accumulation
behavior (Table 4) and this can be used to describe how much
of the metal contaminants in the sediments are transferred to
the shellfish tissues. If the BF is greater than 1, then the
Environ Sci Pollut Res
shellfish samples can be regarded as accumulators; a BF of 1
indicates no influence and if the BF is less than 1, then the
shellfish samples can be regarded as being excluders (Sophia
and Milton, 2017). According to the results, the BFs of all the
metals in M. optima at both Saphan Hin and Paklok showed
that only the BF
Zn
(0.034 and 0.026, respectively) was detect-
able, while those of the other metals were negligible due to
their very low concentrations in both the sediments and shell-
fish. However, since Zn plays a physiological role in growth,
high transfer of this metal is to be expected.
Unfortunately, it was found that the risk posed by Cd to
human health from the consumption of shellfish harvested at
Paklok was appreciable as the BF of Cd was 10 orders of
magnitude higher than that of Zn (BF
Cd
=0.21 and BF
Zn
=
0.026). Cd can be found in the Earth’s crust and commonly
co-exists with Zn ore (Akkajit and Tongcumpou, 2010). The
rate of bioaccumulation of metal contaminants in organisms
depends on the ability of the organisms to absorb or digest the
metals. Many factors, including the lipid contents in the tis-
sues, the age, the feeding mechanism, and/or feeding habits of
an organism can influence metal accumulation in shellfish
(Onojake et al., 2015). A higher Cd accumulation in shellfish
as compared to other metals was reported by Li et al. (2015)
and this probably relates to a form of Cd that exists as a
soluble phase in the aquatic environment and can therefore
be easily be taken up by organisms (Li et al.).
Conclusions
In conclusion, the water samples collected along the Bang Yai
canal at Saphan Hin, Phuket which are affected by the effluent
from old Sn mining ponds showed that the metal concentra-
tions (mg L
−1
) exhibited the following decreasing order, Zn >
Cd > Pb, while the concentration of metal contaminants in the
sediments (mg kg
−1
) showed the trend, Zn > Pb > Cd.
However, these levels do not exceed the TEC of the sediment
quality guidelines for adverse effects to occur and the marine
water quality standards of Thailand set by the Pollution
Control Department (2006). Based on the metal concentra-
tions and risk indices, Pb was the metal which posed the least
risk to human health while Zn was the only metal substantially
detected in both areas studied (EDI = 0.00663 and
0.00409 mg kg
−1
per day, HQ = 0.0221 and 0.0136, BF =
0.034 and 0.026 at Saphan Hin and Paklok, respectively).
Based on the HQ and BF values, Cd, Zn, Pb, and Hg would
be unlikely to pose a risk to human health risk particularly as
none exceeded the HQ threshold of 1 (HQ< 1) and there were
very low metal concentrations found in both the sediment and
shellfish. However, governmental agencies and local authori-
ties shouldcontinue monitoring the pollution level in the Bang
Yai canal and Phuket Bay to ensure food safety and should
also promote public education regarding the issue of heavy
metal contamination.
Acknowledgements The authors thank the Office of the Higher
Education Commission (OHEC) and the S&T Postgraduate Education
and Research Development Office (PERDO) for financial support of
the Research Program and thank the Ratchadaphiseksomphot
Endowment Fund, Chulalongkorn University for the Research Unit. We
would like to express our sincere thanks to the Environmental Research
Institute (ERIC) and the Center of Excellence on Hazardous Substance
Management (HSM), Chulalongkorn University for their invaluable sup-
port in terms of facilities and scientific equipment. Special thanks to the
Faculty of Technology and Environment, Prince of Songkla University,
Phuket Campus for partial financial support.
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