Mollusca: Bivalva collected along the coast of Vietnam, with emphasis on regional differences and human health risk assessment Nguyen Phuc Cam Tu•Nguyen Ngoc Ha•Tetsuro Agusa• Tokutaka I
Trang 1O R I G I N A L A R T I C L E Environment
Trace elements in Anadara spp (Mollusca: Bivalva) collected
along the coast of Vietnam, with emphasis on regional differences
and human health risk assessment
Nguyen Phuc Cam Tu•Nguyen Ngoc Ha•Tetsuro Agusa•
Tokutaka Ikemoto•Bui Cach Tuyen• Shinsuke Tanabe•
Ichiro Takeuchi
Received: 23 March 2011 / Accepted: 30 August 2011 / Published online: 4 October 2011
Ó The Japanese Society of Fisheries Science 2011
Abstract This study measured concentrations of 21 trace
elements in whole soft tissue of the blood cockle Anadara
spp., which is a common food for local people, collected
along the coast of Vietnam Results showed that
concen-trations of As, Sr, Mo, Sn, and Pb in cockles collected from
Khanh Hoa Province in the Central Coastal Zone (CCZ)
had higher values than those from the other regions, while
cockles collected from the Mekong River Delta (MRD)
showed the highest concentrations of Hg Regional
differ-ences in trace element concentrations of the cockle may be
due to differences in human activities, i.e., shipyards in the
CCZ and agriculture in the MRD Trace element
concen-trations measured in the soft tissues of blood cockles
investigated here were within safe levels for human
con-sumption following criteria by the European Commission
(EC) and the United States Food and Drug Agency, but
several specimens had Cd levels exceeding the EC
guidelines of 1 lg/g wet weight The estimated target hazard quotients for trace elements via consuming bivalves were \1, indicating that the cumulative noncarcinogenic risk was completely insignificant However, the estimated target cancer risk values by assumed inorganic As con-centrations seem to implicate consumption of these cockles
as posing potential human health concerns
Keywords Blood cockle Anadara spp Cadmium Human health risk Trace elements Vietnam
Introduction
At present, nearly a quarter of Vietnam’s population lives
in the coastal provinces, and there is an increasing migra-tion into this region where there are many large cities (e.g., Hochiminh City) in addition to coastal economic and centralized industrial zones These activities have created increased pollution, most likely in hotspots such as the major estuaries and the coastline, which receive different kinds of wastes produced by inland industrial and popu-lation centers [1] The aquaculture industry in Vietnam has encountered serious issues in recent years, including poor water quality, disease outbreaks, and food safety problems
in products for export and local consumption, particularly from contaminated filter feeding bivalve mollusks [2] Besides the lyrate hard clam Meretrix lyrata, the blood cockle Anadara spp (Mollusca: Bivalva: Arcidae) are favored species of edible shellfish in Vietnam Among the blood cockle species, Anadara granosa is one of the most popular cultured species in brackish-water areas, particu-larly in southern Vietnam, whereas A nodifera is found more in the northern and central coast [2] These bivalves are cultured mostly on muddy tidal flats Cockles can also
N P C Tu T Ikemoto I Takeuchi (&)
Department of Life Environment Conservation,
Faculty of Agriculture, Ehime University,
Tarumi 3-5-7, Matsuyama, Ehime 790-8566, Japan
e-mail: takeuchi@agr.ehime-u.ac.jp
N N Ha T Agusa S Tanabe
Center for Marine Environmental Studies (CMES),
Ehime University, Bunkyo-cho 2-5, Matsuyama,
Ehime 790-8577, Japan
T Agusa
Department of Legal Medicine, Faculty of Medicine,
Shimane University, Enya 89-1, Izumo,
Shimane 693-8501, Japan
B C Tuyen
Research Institute for Biotechnology and Environment (RIBE),
Nong Lam University, Thu Duc District,
Hochiminh City, Vietnam
Fish Sci (2011) 77:1033–1043
DOI 10.1007/s12562-011-0410-3
Trang 2be cultured in nutrient-rich ponds and have a high capacity
for removing nutrient-derived primary production from
black tiger shrimp ponds between crops [2] Because
Anadara spp are filter feeding organisms, trace element
contaminants in the mudflats or shrimp pond beds tend to
accumulate in their tissues These cockles may act as the
main environmental sink of trace elements and therefore
may be an effective bioindicator of coastal pollution It is
well known that no single species of bivalve is present on
all coasts and, therefore, environmental monitoring
pro-grams often need to utilize multiple species Studies
comparing trace element profiles from several taxa taken at
the same locations permit an assessment of the relative
bioavailabilities of trace elements to different species
[3, 4] Thus, the different species studied in this work
would be proposed as sentinel biomonitors to assess the
contamination status by trace element in the coastal zone
A number of studies on bivalve mollusks associated with
trace element pollution have been performed, but few
studies have been published related to Anadara spp [5 7]
According to our previous study, concentrations of trace
elements in hard clam Meretrix spp from the Vietnam
coast were typically high, particularly in samples collected
from the central coast, and estimation of cancer risk based
on As concentration indicated that hard clams pose a high
potential risk to local residents [8]
The objective of this study was to determine regional
differences in trace element concentrations of Anadara spp
collected along Vietnam’s coastal waters Furthermore, our
previously reported data on the hard clam Meretrix spp [8]
were compared with the present study in order to clearly
understand the contamination status of trace elements in
Vietnamese coastal environment The potential health risks
associated with consuming trace element levels in cockles
were also estimated
Materials and methods
Sample collection and preparation
Anadara spp were collected from extensive bivalve
pro-duction areas or were purchased from small stalls near
culture sites along the coast of Vietnam between 2003 and
2007 Anadara granosa was taken from Hochiminh City
(HCMC), Ba Ria Vung Tau (BRVT), Long An (LA), and
Tien Giang (TG) Provinces in the South Key Economic
Zone (SKEZ), and from Ben Tre (BT), Tra Vinh (TV), Soc
Trang (ST), Bac Lieu (BL), Ca Mau (CM), and Kien Giang
(KG) Provinces in the Mekong River Delta (MRD)
Anadara nodifera was sampled in Khanh Hoa (KH)
Province in the Central Coastal Zone (CCZ) (Fig 1) Both species are likely to be found on intertidal and marginally subtidal muddy substrates in areas where there is an estu-arine influence and feed on a mixture of detritus (or microorganisms attached to detritus) and benthic microal-gae from the sediment [9] Cockles were not purified because we were interested in estimating human health risks Samples were frozen in plastic bags and transported
to Ehime University, Japan, and maintained in a freezer below -20°C until dissection and trace element analysis could take place
Blood cockles from sampling sites (six individuals per site) were cleansed of mud by washing thoroughly with deionized water (Millipore, Milford, MA, USA) Cockles were measured for shell length and whole body weight, after which soft tissue was carefully removed using a clean stainless steel scalpel blade, then dried at 80°C for 12 h, and finally ground to a fine powder using a mortar and pestle in preparation for analysis Biometry and water content of cockles are shown in Table 1 Trace element concentrations
in blood cockle tissue were measured based on dry weight (wt) but were also converted to wet wt by use of the respective conversion factors given in Table1to allow for comparison with values from other studies and guidelines and to estimate potential health risk on a wet wt basis Trace element analyses
We used previously described methods for analyzing trace elements [8,10,11] Briefly, dried soft tissue was digested with concentrated nitric acid in a microwave system (Ethos
D, Milestone, Sorisole, BG, Italy) Mercury was deter-mined using a cold vapor-atomic absorption spectrometer (AAS) (AA680, Shimadzu, Kyoto, Japan; Model HG-3000 cold vapor system, Sanso, Tsukuba, Japan) The concen-trations of 19 trace elements (V, Cr, Mn, Co, Cu, Zn, Rb,
Sr, Mo, Ag, Cd, In, Sn, Sb, Cs, Ba, Tl, Pb, and Bi) were determined using an inductively coupled plasma-mass spectrometer (HP-4500, Hewlett-Packard, Avondale, PA, USA) with yttrium as an internal standard For As analysis, samples were digested with an acid mixture (HNO3:H
2-SO4:HClO4= 1:1:2) and determined using a hydride generation-AAS (HVG-1 hydride system, Shimadzu, Kyoto, Japan) Accuracies of the methods were assessed using a certified reference material DOLT-3 (National Research Council of Canada) in triplicate, and recovery of the elements ranged from 83 to 100% of the certified val-ues All data are expressed on a dry weight basis (lg/g dry wt) Detection limits for most trace elements were 0.001 lg/g dry wt, except for As, Sb, and Cs (0.01 lg/g dry wt), and Hg (0.05 lg/g dry wt)
Trang 3Potential human health risk assessments
Noncarcinogenic effects were evaluated by comparing the
trace element exposure level over a specified time period
with a reference dose (RfD), otherwise known as the target
hazard quotient (THQ) A THQ value of \1 indicates that
exposures are not likely to be associated with adverse noncarcinogenic effects The sum of all THQ values for multiple trace elements for a particular sampling site is represented by the hazard index (HI) [12] Likewise, target cancer risk (TR) was estimated as the incremental proba-bility of an individual developing cancer over a lifetime as
Fig 1 Map of sampling
locations for blood cockles
Anadara spp For abbreviations,
refer to Table 1
Table 1 Biometry of the blood cockle Anadara spp collected from the coast of Vietnam
Species Region Location Latitude Longitude Number Whole
body
wt (g)a
Shell length (mm)a
Water content (%)b
Conversion factor (dry:wet)b
Anadara
granosa
SKEZ HCMC Can Gio,
Hochiminh City
10°23.202 0 N 106°55.446 0 E 6 15.5 ± 3.3 36.6 ± 2.3 85.2 6.84 BRVT Tan Thanh, Ba
Ria Vung Tau
10°27.413 0 N 107°05.446 0 E 6 11.5 ± 0.8 34.0 ± 1.4 88.6 9.05
LA Can Giuoc,
Long An
10°36.216 0 N 106°40.266 0 E 6 9.9 ± 0.5 31.5 ± 0.6 87.6 8.15
TG Go Cong Dong,
Tien Giang
10°17.277 0 N 106°46.461 0 E 6 9.3 ± 0.3 29.8 ± 1.1 89.9 10.0 MRD BT Binh Dai, Ben Tre 10°11.117 0 N 106°41.375 0 E 6 19.3 ± 1.3 37.1 ± 0.6 83.7 6.17
TV Duyen Hai,
Tra Vinh
09°37.585 0 N 106°29.541 0 E 6 11.8 ± 2.5 32.1 ± 1.4 87.8 8.43
ST Vinh Chau,
Soc Trang
09°19.630 0 N 105°58.867 0 E 6 12.8 ± 1.2 32.7 ± 1.2 85.6 6.98
BL Nha Mat, Bac Lieu 09°12.339 0 N 105°44.321 0 E 6 9.0 ± 0.5 30.7 ± 1.5 86.5 7.45
CM Ward 7 Market,
Ca Mau
09°10.376 0 N 105°08.501 0 E 6 12.7 ± 1.5 34.0 ± 0.8 84.5 6.61
KG Rach Soi,
Kien Giang
09°57.158 0 N 105°07.141 0 E 6 14.5 ± 1.5 34.4 ± 0.3 87.9 8.35 Anadara
nodifera
CCZ KH Nha Phu Bay,
Khanh Hoa
12°20.556 0 N 109°12.336 0 E 6 14.1 ± 1.3 35.4 ± 0.5 84.0 6.62
a Mean and standard deviation
b Mean
Trang 4a result of exposures to potential carcinogen (i.e., inorganic
As in the present study) This risk was calculated using
average lifetime exposure values that were multiplied by
the oral slope factor for inorganic As [12] Estimation of
THQ and TR at each location followed the United State
Environmental Protection Agency (US EPA) Region 3
Risk-based Concentration (RBC) Table (US EPA Region
III website: http://www.epa.gov/reg3hwmd/risk/human/
pdf/NOVEMBER_2010_FISH.pdf; accessed 09 Dec 2010)
The methodology for estimating THQ and TR is described
in detail by Tu et al [8] RfDs were obtained from the RBC
table, except for Cr, Rb, In, Cs, Hg, Pb, and Bi Total Cr
was not available on the RBC table, the US EPA assumes
that the ratio of Cr(VI) to total Cr was 1:7 in fish tissue, and
offers the RfD for Cr(VI) Thus, we divided our total Cr
data by 7 to estimate the THQ for Cr Because most Hg in
shellfish tissue is present primarily as methyl mercury
(MeHg) [12], the conservative assumption was made that
total Hg is present as MeHg as recommended by the US
EPA [12] Lead was not listed on the RBC table; a
provi-sional tolerable weekly intake of 25 lg/kg body wt/week
(equal to 3.57 lg/kg body wt/day) was used [13] For
calculation of THQ and TR for inorganic As, we assumed
that inorganic As accounted for 10% of total As [14–16]
The bivalve consumption rate of 2.85 g/Vietnamese
person/day (FAO website: http://faostat.fao.org/site/368/
DesktopDefault.aspx?PageID=368#ancor; accessed 04 Jan
2011) was used for these estimations
Statistical analyses
One half of the value of the respective limit of detection
(LOD) was substituted for those values below the LOD and
used in statistical analysis and risk assessment Statistical
analyses were performed using the SPSS version 15 for
Windows (SPSS, Chicago, IL, USA) All data were tested
for goodness-of-fit to a normal distribution with
Kol-mogorov-Smirnov’s one sample test Because most of the
variables were not normally distributed, the data were
logarithmically transformed and subjected to parametric
statistics Pearson correlation analyses were performed for
shell length and trace element concentrations to determine
size effects in blood cockles Regional differences in trace
element concentrations in blood cockles were tested by
analysis of variance (ANOVA) or analysis of covariance
(ANCOVA) with shell length as the covariate wherever
practicable Prior to the use of ANCOVA, assumption of
equality (homogeneity) of regression slopes of dependent
(trace element concentration)-covariate (shell length)
relationships was tested by fitting a model containing
covariate-by-factor interaction If the homogeneity of
regression assumption was not rejected, ANCOVA was
applied to test differences between regions To compare
regional differences of trace element concentrations between blood cockles and hard clams, a two-independent-samples t test was used A p value of \0.05 indicated statistical significance
Results Trace element concentrations Means and standard deviations of trace element concen-trations of Anadara spp samples are shown in Table2 Concentration of Zn was the highest among the trace ele-ments analyzed, followed by Mn, Sr, As, Cu, Cd, and Rb The mean concentrations of Zn and Mn in Anadara spp ranged from 51.3 to 113 lg/g and from 11.3 to 63.9 lg/g (Table2), respectively Moreover, the mean concentrations
of Cd and As were present at relatively high levels in the tissues of blood cockles, ranging from 2.15 to 9.61 lg/g, and from 3.5 to 26 lg/g, respectively (Table2) Similar mean concentrations of Cu (ranged from 5.37 to 9.89 lg/g),
Rb (ranged from 2.57 to 4.52 lg/g), and Sr (ranged from 21.0 to 40.7 lg/g) were observed in blood cockles from the sampling locations (Table 2) The lowest concentra-tion in cockle tissues was In (ranged from 0.001 to 0.005 lg/g)
For all the blood cockles analyzed, concentrations of Cr (Pearson correlation, r = -0.28, p \ 0.05), Mn (r = -0.53,
p \0.001), Co (r = -0.47, p \ 0.001), Cu (r = -0.30,
p \0.05), Sr (r = -0.31, p \ 0.05), Cd (r = -0.27, p \ 0.05), Sb (r = -0.41, p \ 0.001), Ba (r = -0.52,
p \0.001), and Hg (r = -0.34, p \ 0.01) were negatively correlated with shell length, whereas no correlations were found between concentrations of the others and shell length (p [ 0.05)
Regional differences in trace element concentrations For regional comparisons, the cockle sampling sites were pooled into three regions: SKEZ, MRD, and CCZ Because
of the significant correlations between shell length and tissue concentration of Cr, Mn, Co, Cu, Sr, Cd, Sb, Ba, and
Hg, a comparison among regions was conducted using ANCOVA with shell length as the covariate In contrast, ANOVA was used for assessment of variations between regions for trace elements that had no significant relation-ship with shell length
Results of regional differences in trace element con-centrations with statistical significance are shown in Fig.2 Among analyzed trace elements, concentrations of As, Sr,
Mo, Sn, and Pb in cockles from the CCZ and Hg con-centrations in cockles collected from the MRD were sig-nificantly higher than those from the other regions
Trang 5Table 2 Trace element concentrations (mean ± standard deviation; lg/g dry wt) in the blood cockle Anadara spp collected from the coast of Vietnam
SKEZ HCMC 0.19 ± 0.02 0.86 ± 0.40 15.9 ± 7.3 0.81 ± 0.14 6.83 ± 1.08 82.5 ± 10.3 5.6 ± 0.6 3.32 ± 0.21 24.3 ± 1.9 0.664 ± 0.094 0.73 ± 0.44
BRVT 0.52 ± 0.09 1.5 ± 0.9 21.4 ± 6.3 1.3 ± 0.2 7.26 ± 0.80 51.7 ± 2.8 12 ± 1 3.61 ± 0.61 38.3 ± 12.0 0.591 ± 0.077 0.051 ± 0.013
LA 0.81 ± 0.22 1.1 ± 0.3 63.9 ± 31.9 2.1 ± 0.3 5.37 ± 0.34 73.3 ± 7.3 5.4 ± 1.0 4.39 ± 0.36 31.8 ± 2.6 0.512 ± 0.079 0.087 ± 0.107
TG 0.48 ± 0.32 2.1 ± 1.1 36.8 ± 11.6 1.7 ± 0.2 9.55 ± 1.57 113 ± 10 8.2 ± 0.2 4.43 ± 0.66 35.2 ± 14.7 0.725 ± 0.050 1.4 ± 1.1 MRD BT 0.44 ± 0.05 0.58 ± 0.10 29.1 ± 6.6 1.2 ± 0.1 6.87 ± 1.49 90.1 ± 16.4 3.5 ± 0.4 3.78 ± 0.36 21.0 ± 4.0 0.534 ± 0.052 0.19 ± 0.11
TV 0.43 ± 0.08 0.51 ± 0.03 30.3 ± 3.9 2.6 ± 0.8 8.96 ± 1.06 86.1 ± 14.3 4.9 ± 0.5 2.57 ± 0.28 29.1 ± 4.2 0.541 ± 0.054 0.11 ± 0.08
ST 1.0 ± 1.6 1.3 ± 1.4 26.3 ± 13.0 1.1 ± 0.3 7.90 ± 0.30 81.7 ± 9.5 4.8 ± 0.5 3.65 ± 2.23 35.9 ± 5.4 0.621 ± 0.052 0.084 ± 0.034
BL 0.41 ± 0.16 0.84 ± 0.26 56.5 ± 27.2 1.4 ± 0.3 9.89 ± 2.52 107 ± 10 7.0 ± 0.4 4.00 ± 0.34 30.7 ± 2.9 0.701 ± 0.087 0.99 ± 0.47
CM 0.73 ± 0.30 0.78 ± 0.33 33.1 ± 6.4 1.6 ± 0.5 5.97 ± 0.42 92.8 ± 20.2 3.7 ± 0.8 4.52 ± 0.63 21.8 ± 3.9 0.465 ± 0.053 0.085 ± 0.139
KG 0.43 ± 0.27 1.1 ± 0.3 27.5 ± 11.9 1.4 ± 0.4 8.73 ± 2.54 111 ± 11 7.0 ± 1.6 4.31 ± 0.48 26.0 ± 3.6 0.623 ± 0.044 0.64 ± 0.36 CCZ KH 0.62 ± 0.21 0.85 ± 0.31 11.3 ± 3.8 0.77 ± 0.16 6.90 ± 1.34 96.6 ± 5.5 26 ± 5 3.93 ± 0.45 40.7 ± 6.7 1.59 ± 0.64 0.24 ± 0.32
SKEZ HCMC 3.83 ± 0.26 0.003 ± 0.001 0.067 ± 0.010 0.02 ± 0.00 0.01 ± 0.00 0.72 ± 0.29 \ 0.05 0.004 ± 0.001 0.153 ± 0.019 0.011 ± 0.001
BRVT 2.68 ± 0.70 0.005 ± 0.002 0.068 ± 0.014 0.02 ± 0.00 0.03 ± 0.01 0.76 ± 0.31 \ 0.05 0.007 ± 0.002 0.208 ± 0.050 0.018 ± 0.003
LA 5.57 ± 1.15 0.005 ± 0.006 0.064 ± 0.025 0.02 ± 0.01 0.09 ± 0.03 3.0 ± 1.0 0.13 ± 0.04 0.012 ± 0.008 0.625 ± 0.139 0.118 ± 0.028
TG 8.19 ± 1.23 0.002 ± 0.000 0.028 ± 0.008 0.04 ± 0.01 0.05 ± 0.04 2.8 ± 1.6 0.13 ± 0.05 0.006 ± 0.003 0.509 ± 0.144 0.026 ± 0.002 MRD BT 8.97 ± 0.78 0.001 ± 0.000 0.029 ± 0.013 0.02 ± 0.00 0.02 ± 0.00 1.4 ± 0.3 0.12 ± 0.04 0.006 ± 0.002 0.227 ± 0.034 0.024 ± 0.005
TV 9.06 ± 1.00 0.002 ± 0.000 0.047 ± 0.020 0.03 ± 0.00 0.01 ± 0.01 1.9 ± 0.6 0.11 ± 0.02 0.003 ± 0.001 0.401 ± 0.077 0.047 ± 0.005
ST 9.61 ± 1.63 0.003 ± 0.004 0.073 ± 0.050 0.04 ± 0.02 0.10 ± 0.19 4.4 ± 5.2 0.09 ± 0.01 0.009 ± 0.015 0.763 ± 0.501 0.021 ± 0.010
BL 7.12 ± 0.85 0.002 ± 0.001 0.033 ± 0.006 0.03 ± 0.01 0.03 ± 0.02 2.3 ± 0.6 0.11 ± 0.02 0.006 ± 0.002 0.422 ± 0.103 0.023 ± 0.002
CM 2.15 ± 0.60 0.003 ± 0.001 0.033 ± 0.009 0.02 ± 0.01 0.06 ± 0.04 1.4 ± 0.8 0.08 ± 0.04 0.005 ± 0.002 0.530 ± 0.230 0.064 ± 0.046
KG 7.67 ± 1.52 0.001 ± 0.000 0.219 ± 0.535 0.02 ± 0.01 0.04 ± 0.03 2.0 ± 1.1 0.11 ± 0.05 0.004 ± 0.002 0.500 ± 0.166 0.029 ± 0.011 CCZ KH 5.26 ± 1.91 0.004 ± 0.002 0.568 ± 0.471 0.02 ± 0.01 0.02 ± 0.01 0.80 ± 0.50 \ 0.05 0.005 ± 0.002 2.71 ± 0.73 0.055 ± 0.012
Trang 6(ANOVA or ANCOVA, p \ 0.05) Concentrations of Mn
and Co in the CCZ cockles, Zn in the SKEZ cockles, and In
in the MRD cockles were the lowest among regions
(p \ 0.05) Chromium levels in the SKEZ blood cockles
were greater than those in the MRD animals (p \ 0.001),
though neither zone was significantly different from the
CCZ measurement (p [ 0.05) Cadmium concentrations in
the SKEZ cockles were lower than those from the MRD
animals (p \ 0.01), but there were no significant
differ-ences between Cd values in cockles from the SKEZ and
CCZ, or between those values from the MRD and CCZ
(p [ 0.05) Barium concentration in the MRD cockles was
higher than those from the CCZ (p \ 0.05), but there were
no significant differences in Ba concentration between the
SKEZ and the other two regions (p [ 0.05) The
concen-tration of V, Cu, Rb, Ag, Sb, Cs, Tl, and Bi did not differ
significantly among regions (p [ 0.05)
In comparison with our previous results for trace
ele-ments in hard clam Meretrix spp [8], concentrations of Cr,
Mn, Cu, Mo, Ag, Cd, Sb, Hg, Pb, and Bi in the SKEZ
cockles, Mn, Zn, Mo, Ag, Cd, Sb, Hg, Pb, and Bi in the
MRD cockles, and As, Cd, Pb, and Bi in the CCZ cockles
were higher (two-independent-samples t test, p \ 0.05;
Fig.3) In contrast, concentrations of Co, Sr, and Cs in the
SKEZ clams, Co, As, Sr, In, Cs, Ba, and Tl in the MRD
clams, and V, Co, Cu, Rb, Sr, Mo, Cs, Ba, and Tl in the
CCZ clams were elevated (p \ 0.05; Fig.3)
Estimation of potential human health risk
As shown in Fig.4 and represented by the THQ and HIs,
the noncarcinogenic risks associated with the consumption
of blood cockle were \1 Considering the composition of
the relative contribution to THQ by trace elements, the
highest risk contribution of trace elements for consumers is
from Cd (range of 20–55%), followed by Co (range of
14–49%) and inorganic As (range of 7–46%) The
contri-bution of Cd to the HIs showed a high value for consumers
from the MRD, particularly in ST (55%), while Co con-stituted the majority of the risk and contributed to nearly half of the total HIs for CM consumers The THQ for
Fig 2 Regional differences in trace element concentrations in blood
cockle Anadara spp All trace elements with significantly different
(p \ 0.05) concentrations between regions are represented in this
figure Data represent the mean and standard deviation of the trace element concentrations (log transformed) *p \ 0.05, **p \ 0.01, and
***p \ 0.001 For abbreviations, refer to Table 1
Fig 3 Species-specific differences in trace element concentrations between blood cockle Anadara spp and hard clam Meretrix spp [ 8 ] Selected trace elements with significantly different (p \ 0.05) con-centrations between two species in all three regions are represented in this figure Data represent the mean and standard deviation of the trace element concentrations (log transformed) *p \ 0.05,
**p \ 0.01, and ***p \ 0.001 For abbreviations, refer to Table 1
Trang 7inorganic As had a larger percentage contribution 46% of
HIs from KH in the CCZ
Conversely, the target cancer risk estimates for
inor-ganic As through consuming blood cockles from different
locations along the coast of Vietnam were higher than 10-6
(range of 4.8 9 10-6to 3.3 9 10-5) (Fig.5) The highest
risk for inorganic As was 3.3 9 10-5for consumption of
cockles by KH residents in the CCZ
Discussion
Trace element concentrations in blood cockle
Bivalves are often used as a measure of contamination in
estuarine waters because they usually accumulate high
concentrations of trace elements [17] Among trace
ele-ments, Zn is an essential element that is present in all
organisms, and concentrations of Zn in tissues of several
bivalve species including scallops, clams, oysters, and
mussels are on the order of 100–1,000 lg/g, with little
variation among species [17] Zinc is not limiting to normal
molluscan life processes in the marine environment and
filter-feeding mollusks accumulated the highest
concen-trations of Zn in soft tissues [17] In the present study, the
mean concentrations of Zn in blood cockle differed slightly
among the sampling sites These results showed that blood
cockle could regulate its soft tissue levels of Zn Phillips
and Rainbow [4] reported that several bivalve species are
known to possess this ability
In several studies, trends of decreasing trace element
concentrations with increasing shell length have been
reported and were attributed primarily to increased meta-bolic rates in smaller organisms, which corresponded to a so-called growth dilution effect [8, 18–21] Boyden [18] reported similar size-concentration relationships for Cu,
Zn, and Pb in the limpet Patella vulgate collected from Portishead, Severn Estuary Joiris and Azokwu [20] observed the same results with Cd and Pb in the West African bloody cockle Anadara (Senilia) selinis collected from Bonny River estuary in the Niger Delta area of Nigeria In a previous study of hard clams from Vietnam [8], we also found an inverse relationship of decreasing
Fig 4 Mean hazard indices
(HIs) of individual trace
elements from consuming blood
cockle Anadara spp collected
from different sites For
abbreviations, refer to Table 1
Fig 5 Mean estimated target cancer risks for assumed inorganic As through consuming blood cockle Anadara spp collected from different sites For abbreviations, refer to Table 1
Trang 8concentrations of Zn, As, Mo, Sn, and Bi with increasing
shell size
Regional differences in trace element concentrations
The estimated human population density of Khanh Hoa
Province (CCZ) is 220/km2, in contrast with 510/km2and
428/km2 for the SKEZ and MRD, respectively (General
Statistics Office of Vietnam website:http://www.gso.gov
vn/default.aspx?tabid=387&idmid=3&ItemID=9865;
acce-ssed 21 Dec 2010), indicating that human activities in the
CCZ are lower than in the others However, the blood
cockles in the CCZ showed the highest mean
concentra-tions of As (26 lg/g), Sr (40.7 lg/g), Mo (1.59 lg/g), Sn
(0.568 lg/g), and Pb (2.71 lg/g) We observed similar
results in a previous study in which concentrations of As,
Mo, Sn, and Pb were highest in hard clam Meretrix spp
collected from the CCZ [8] These results suggest that
some point sources of trace element contamination are
present in the CCZ, in spite of the relatively lower human
activity Contaminants likely originated from industrial
waste from large shipyards near the sampling site As
compared to a more distant site, elevated levels of Cr, Cu,
Zn, Cd, and Pb were reported in water, sediment, and the
oyster Saccostrea cucullata collected from the vicinity of a
shipyard in Khanh Hoa Province [22] The shipyard used
copper slag as a blasting abrasive for the removal of rust,
paint chips, and marine deposits on the surfaces of ship
hulls The slag contained high levels of Cr (336 lg/g), Cu
(8,549 lg/g), Zn (7,275 lg/g), and Pb (113 lg/g) [22] In
fact, the CCZ was reported as one of the hot spots for trace
element contamination in Vietnam [1]
In contrast, concentrations of Hg were found to be the
highest in the MRD cockles Moreover, accumulated Cd
concentrations were greater in blood cockles from this
region, particularly sampling sites close to the mouth of the
Mekong River such as TV (9.06 lg/g) and ST (9.61 lg/g),
when compared with those in cockles collected from the
other sites Our previous studies also reported relatively
high levels of Cd and Hg in the giant river prawn
Mac-robrachium rosenbergii and black tiger shrimp Penaeus
monodon, and Cd in the hard clam Meretrix lyrata
col-lected from the MRD [8,10,11], suggesting that sources of
Hg and Cd contamination in the MRD may be agricultural
use of mineral fertilizers As stated by the Agency for
Toxic Substances and Disease Registry (ATSDR), Hg is
released to cultivated soils through the direct application of
inorganic and organic fertilizers (e.g., sewage sludge and
compost), lime, and fungicides containing Hg (ATSDR
toxicological profile for mercury website: http://www
atsdr.cdc.gov/ToxProfiles/tp46.pdf; accessed 25 May
2011) Furthermore, because of intensive crop cultivation
on alluvial soils, some soils in the MRD receive large
amounts of fertilizer, particularly phosphates containing Cd levels ranging from 0.02 to 2.76 mg/kg [23] In addition, the high accumulation of Cd in the MRD cockles may be due to Cd bioavailability in the low salinity environment
As mentioned above, salinity is a natural factor influencing metal uptake, and it is well known that there is an increased net uptake of Cd by bivalves at low salinities [19,24–26] According to Debenay and Luan [27], HCMC and its surroundings were the most affected by marine waters, whereas TV and its vicinity were exposed to the strongest freshwater influence
The species-specific variations between blood cockle and hard clam could be due to differences in their habitats and feeding habits Blood cockles live on the muddy bot-tom in the intertidal zone and can be affected by fresh-water, whereas hard clams occur in sand and/or muddy sand flats in large estuarine areas with greater marine influence [2, 28] Several studies have been conducted to evaluate the influence of salinity or sediment type on trace element uptake in bivalve species Sarkar et al [29] reported that a high organic carbon value together with high clay concentration in sediment enhances elevated concentration of Cd, Zn, and Hg by cockle Anadara granosa from Jharkhali (India) Moreover, most studies suggest an increased net uptake of Hg, Pb, and in particular
Cd by bivalves at lower salinities [19, 24, 25] Further-more, the assimilation efficiencies of Ag and Cd in bivalves were higher from organic-rich sediments than those from organic-poor sediments [30]
Comparison with published data and the guidelines Our data were compared with measurements made else-where in Asia (Table 3) Chromium concentrations in cockles from Vietnam were found to be similar to or higher than those reported from Juru and Jejawi, Malaysia [5] This study shows that the average concentrations of Cu, Zn, and
Cd in Anadara spp collected from Vietnam were compa-rable to or higher than those in this species from Perak and Sabah, Malaysia, and from Zhejiang, China, but exceeded the mean Cu, Zn, and Cd in cockles from Juru and Jejawi, Malaysia [3,5,7] Arsenic concentrations in Anadara spp found in the SKEZ and MRD were similar to those in cockles from Juru and Jejawi, Malaysia [5] However, As levels in this species obtained from the CCZ were higher than those in cockles from Juru and Jejawi, Malaysia [5] Comparing the mean Pb concentrations in cockles found in this work from the SKEZ and MRD with those from other countries shows that the levels from Vietnam were com-parable to those in cockles from Juru and Jejawi, Malaysia, and from Zhejiang, China, yet lower than those in cockles from Perak and Sabah, Malaysia [3,5,7,31] However, Pb levels in this species obtained from the CCZ were higher
Trang 9than those in cockles from Juru and Jejawi, Malaysia, and
from Zhejiang, China, which were comparable to those of
cockles from Perak and Sabah, Malaysia [3,5,7,31] The
concentrations of Hg reported in this work were lower than
those in blood cockles studied previously [3,5]
The concentrations of most trace elements in Anadara
spp were below the reference values for human
con-sumption set by the European Commission (EC), the US
Food and Drug Agency (US FDA), and the Vietnamese
Ministry of Agriculture and Rural Development (MARD)
[32–34] However, over 30% (21/66) of cockle samples
had Cd levels exceeding the EC guideline of 1 lg/g wet wt
(Fig.6) In particular, most specimens from BT, TV, and
ST were above the EC limit (Fig.6) Recently, the
sanitation monitoring program for the bivalve mollusk
production area in 2010 conducted by the National
Agro-Forestry-Fisheries Quality Assurance Department, MARD
also found Cd concentrations in BT cockle ranging from
1.7 to 2.1 lg/g wet wt [35], exceeding the current
Viet-namese safety guideline of 2 lg/g wet wt for bivalve
mollusks as set by the MARD [32] Therefore, to wholly
meet the European Union (EU) requirements for an
EU-approved better management production area, the authority
recommends that these aquaculture areas open for
har-vesting under the condition that the bivalves go through
purification (relaying) before consumption and proposes a
sampling frequency of once per week when harvesting is
being done [35]
Estimation of human health risks
In the present study, there were no estimated THQs and HIs
for all trace elements [1, suggesting that non-cancer health
effects from consuming blood cockles were insignificant
Concerning the relative contribution of each trace element
to THQs, the potential health risks of Cd were highest in comparison to other trace elements investigated Because
Cd is a cumulative toxin and has a very long half-life (from several months up to several years) in the body, exposure
of children to even low amounts may have long-term adverse consequences The exposure to Cd is associated with renal dysfunction, increased calciuria, osteoporosis, and a risk of fractures (ATSDR toxicological profile for
Table 3 Comparison of mean concentrations of trace elements (lg/g dry wt) in the blood cockle Anadara spp with those from other Asian countries and human consumption guidelines
SKEZ, Vietnam Anadara granosa 1.4 7.25 80.2 7.7 5.07 0.08 0.374 This study
Zhejiang, China Tegillarca granosaa 1.61 5.56 2.42 \ 0.05 0.060 [ 3 ] Juru, Malaysia A granosab 0.17 0.19 0.22 2.67 0.89 1.33 0.11 [ 5 ]
nd Not detected For region abbreviations, see Table 1
a Synonym of A granosa
b Based on wet wt
Fig 6 Comparison of Cd concentrations (lg/g wet wt) in blood cockle Anadara spp with European Commission (EC) guidelines for human consumption [ 33 ] For abbreviations, refer to Table 1
Trang 10cadmium website: http://www.atsdr.cdc.gov/ToxProfiles/
tp5.pdf; accessed 25 May 2011) Using the US EPA RfD
of 1 lg/kg/day for estimating noncarcinogenic risk
asso-ciated with Cd, our results indicate that the consumption of
cockles at the current rate was not harmful to consumers
Yet, Satarug and Moore [36] reported that Cd-linked bone
and kidney toxicities have been observed in people whose
dietary Cd intakes were well within 1 lg/kg/day limits
Satarug et al [37] believed that the recommended Cd
intake of 1 lg/kg/day was shown to be too high to ensure
that renal dysfunction does not occur as a result of dietary
Cd intake As stated by Widmeyer and Bendell-Young
[38], there is little to no safety margin between Cd
expo-sure in the normal diet and expoexpo-sure that could produce
deleterious effects, particularly in persons consuming
bivalves on a regular basis Cadmium toxicity via
con-suming bivalves should be considered, particularly for high
risk groups, including women with low iron stores, people
with renal impairment, smokers, children, and indigenous
people as suggested by Cheng and Gobas [39]
On the other hand, the TR values of inorganic As due to
consumption of this cockle indicated that human health risk
might be of concern However, caution must be taken
because this estimation of risk was based on the assumptions
of the ratio of inorganic As to total As due to the lack of
information on the contamination status of As compounds in
Vietnamese bivalves The assumption of 10% inorganic As
from the total As concentration has often been used to
esti-mate health risk [14–16] However, use of this ratio may have
overestimated the true risk levels for As exposure For
example, in two studies from the same location for
con-sumption of oyster Crassostrea gigas in Taiwan, Liu et al
[40] measured the inorganic As fraction in oysters at 1.64%
of total As, and estimated TR nearly 10 times less than Han
et al [14] who assumed 10% as inorganic As in this oyster
[41] Clearly, more studies are needed regarding the
con-centration and speciation of As in bivalves and the
biogeo-chemical cycling of As in aquatic environments of Vietnam
Based on the results of this study, it may be concluded
that the significant differences in trace element
concen-trations in blood cockles Anadara spp among regions may
be explained by differences in human activities, i.e.,
ship-yards in the CCZ and agriculture in the MRD It can also be
concluded that levels of Cd and As in blood cockles in
Vietnam may be a public health concern Further research
on understanding the distribution and accumulation profiles
of potential toxic trace elements in different marine
organisms from these regions is clearly warranted Also, it
is essential that ongoing environmental monitoring
pro-grams should be developed and implemented to ensure that
bivalves are grown from areas with acceptable levels of
chemical pollution
Acknowledgments We express our sincere thanks to Dr Todd Miller, Center for Marine Environmental Studies (CMES), Ehime University, for critical review of the manuscript This study was partially supported by a grant from the Research Revolution 2002 (RR2002) of the Project for Sustainable Coexistence of Humans, Nature, and the Earth (FY2002) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan, and Global COE Program from MEXT The Grants-in-Aid for Scientific Research for Postdoctoral Fellows by the Japan Society for the Pro-motion of Science (No 2109237 to NPCT, and No 207871 to TA) are also acknowledged.
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