Trace elements in anadara spp (mollusca bivalva) collected along the coast of vietnam, with emphasis on regional differences and human health risk assessment

Fish Sci (2011) 77:1033–1043 DOI 10.1007/s12562-011-0410-3 Environment ORIGINAL ARTICLE 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: 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 concentrations 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 differences 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 concentrations measured in the soft tissues of blood cockles investigated here were within safe levels for human consumption following criteria by the European Commission (EC) and the United States Food and Drug Agency, but several specimens had Cd levels exceeding the EC N P C Tu Á T Ikemoto Á 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 Á T Agusa Á 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 guidelines of 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 concentrations seem to implicate consumption of these cockles as posing potential human health concerns Keywords Blood cockle Á Anadara spp Á Cadmium Á Human health risk Á Trace elements Á Vietnam Introduction At present, nearly a quarter of Vietnam’s population lives in the coastal provinces, and there is an increasing migration 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 population 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, particularly 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 123 1034 be 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 programs 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 production 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) 123 Fish Sci (2011) 77:1033–1043 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 estuarine influence and feed on a mixture of detritus (or microorganisms attached to detritus) and benthic microalgae 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 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 Table to 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 determined using a cold vapor-atomic absorption spectrometer (AAS) (AA680, Shimadzu, Kyoto, Japan; Model HG-3000 cold vapor system, Sanso, Tsukuba, Japan) The concentrations 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:H2SO4: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 values 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) Fish Sci (2011) 77:1033–1043 1035 Fig Map of sampling locations for blood cockles Anadara spp For abbreviations, refer to Table Table Biometry of the blood cockle Anadara spp collected from the coast of Vietnam Species Region Location Anadara granosa SKEZ HCMC MRD Anadara nodifera CCZ Latitude Longitude Number Whole body wt (g)a Shell length (mm)a Water content (%)b Can Gio, Hochiminh City 10°23.2020 N 106°55.4460 E 15.5 ± 3.3 36.6 ± 2.3 85.2 6.84 BRVT Tan Thanh, Ba Ria Vung Tau 10°27.4130 N 107°05.4460 E 11.5 ± 0.8 34.0 ± 1.4 88.6 9.05 LA Can Giuoc, Long An 10°36.2160 N 106°40.2660 E 9.9 ± 0.5 31.5 ± 0.6 87.6 8.15 TG Go Cong Dong, Tien Giang 10°17.2770 N 106°46.4610 E 9.3 ± 0.3 29.8 ± 1.1 89.9 BT Binh Dai, Ben Tre 10°11.1170 N 106°41.3750 E 19.3 ± 1.3 37.1 ± 0.6 83.7 6.17 TV Duyen Hai, Tra Vinh 09°37.5850 N 106°29.5410 E 11.8 ± 2.5 32.1 ± 1.4 87.8 8.43 ST Vinh Chau, Soc Trang 09°19.6300 N 105°58.8670 E 12.8 ± 1.2 32.7 ± 1.2 85.6 6.98 BL Nha Mat, Bac Lieu 09°12.3390 N 105°44.3210 E Conversion factor (dry:wet)b 10.0 9.0 ± 0.5 30.7 ± 1.5 86.5 7.45 CM Ward Market, Ca Mau 09°10.376 N 105°08.5010 E 12.7 ± 1.5 34.0 ± 0.8 84.5 6.61 KG Rach Soi, Kien Giang 09°57.1580 N 105°07.1410 E 14.5 ± 1.5 34.4 ± 0.3 87.9 8.35 KH Nha Phu Bay, Khanh Hoa 12°20.5560 N 109°12.3360 E 14.1 ± 1.3 35.4 ± 0.5 84.0 6.62 a Mean and standard deviation b Mean Potential 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 probability of an individual developing cancer over a lifetime as 123 1036 a 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 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 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 provisional 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 Kolmogorov-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 123 Fish Sci (2011) 77:1033–1043 regional differences of trace element concentrations between blood cockles and hard clams, a two-independentsamples t test was used A p value of \0.05 indicated statistical significance Results Trace element concentrations Means and standard deviations of trace element concentrations of Anadara spp samples are shown in Table Concentration of Zn was the highest among the trace elements 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 (Table 2), 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 (Table 2) 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 concentration 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 relationship with shell length Results of regional differences in trace element concentrations with statistical significance are shown in Fig Among analyzed trace elements, concentrations of As, Sr, Mo, Sn, and Pb in cockles from the CCZ and Hg concentrations in cockles collected from the MRD were significantly higher than those from the other regions Region SKEZ MRD Location V Cr Mn Co HCMC 0.19 ± 0.02 BRVT 0.52 ± 0.09 Cu 0.86 ± 0.40 15.9 ± 7.3 0.81 ± 0.14 1.5 ± 0.9 21.4 ± 6.3 1.3 ± 0.2 Zn As Rb Sr Mo Ag 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 7.26 ± 0.80 51.7 ± 2.8 12 ± 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 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 0.084 ± 0.034 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 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 ± 3.93 ± 0.45 40.7 ± 6.7 1.59 ± 0.64 0.24 ± 0.32 Region Location Cd In SKEZ MRD CCZ Sn Sb Cs Ba Hg Tl Pb Fish Sci (2011) 77:1033–1043 Table Trace element concentrations (mean ± standard deviation; lg/g dry wt) in the blood cockle Anadara spp collected from the coast of Vietnam Bi 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 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 0.047 ± 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 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 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 1037 123 1038 Fig 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 Fish Sci (2011) 77:1033–1043 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 (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 differences 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 concentration 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 elements 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 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 contribution of Cd to the HIs showed a high value for consumers 123 Fig 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) concentrations 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 from the MRD, particularly in ST (55%), while Co constituted the majority of the risk and contributed to nearly half of the total HIs for CM consumers The THQ for Fish Sci (2011) 77:1033–1043 1039 Fig Mean hazard indices (HIs) of individual trace elements from consuming blood cockle Anadara spp collected from different sites For abbreviations, refer to Table inorganic As had a larger percentage contribution 46% of HIs from KH in the CCZ Conversely, the target cancer risk estimates for inorganic As through consuming blood cockles from different locations along the coast of Vietnam were higher than 10-6 (range of 4.8 10-6 to 3.3 10-5) (Fig 5) The highest risk for inorganic As was 3.3 10-5 for 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 elements, 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 concentrations 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 Fig Mean estimated target cancer risks for assumed inorganic As through consuming blood cockle Anadara spp collected from different sites For abbreviations, refer to Table reported and were attributed primarily to increased metabolic 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 123 1040 concentrations 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/km2 and 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; accessed 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 concentrations 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 Macrobrachium rosenbergii and black tiger shrimp Penaeus monodon, and Cd in the hard clam Meretrix lyrata collected 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 123 Fish Sci (2011) 77:1033–1043 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 bottom in the intertidal zone and can be affected by freshwater, 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] Furthermore, 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 elsewhere 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 comparable 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 comparable 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 Fish Sci (2011) 77:1033–1043 1041 Table 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 Region Species Cr Cu Zn SKEZ, Vietnam Anadara granosa 1.4 7.25 80.2 MRD, Vietnam A granosa 0.85 8.05 94.8 CCZ, Vietnam A nodifera 0.85 6.90 96.6 Zhejiang, China Tegillarca granosaa 1.61 5.56 Juru, Malaysia A granosab 0.17 0.19 0.22 2.67 0.17 0.19 0.20 2.69 nd 6.3 6.89 Jejawi, Malaysia Perak, Malaysia Sabah, Malaysia A granosa A granosa As Cd Hg References 0.374 This study 7.7 5.07 5.1 7.43 0.10 0.474 This study 5.26 \0.05 2.71 This study 2.42 \0.05 0.060 [3] 0.89 1.33 0.11 [5] 0.87 1.36 0.12 [5] 1.8 4.74 [6] [31] [32] 26 64 96.0 0.08 Pb 6.1 0.630 Vietnamese guidelineb 2.0 0.5 1.5 EC guidelineb 1.0 0.5 1.5 [33] 1.7 [34] US FDA guidelineb 13 86 nd Not detected For region abbreviations, see Table a Synonym of A granosa b Based on wet wt than 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 consumption 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 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 AgroForestry-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 Vietnamese safety guideline of lg/g wet wt for bivalve mollusks as set by the MARD [32] Therefore, to wholly meet the European Union (EU) requirements for an EUapproved better management production area, the authority recommends that these aquaculture areas open for harvesting 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 Fig 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 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 123 1042 cadmium website: http://www.atsdr.cdc.gov/ToxProfiles/ tp5.pdf; accessed 25 May 2011) Using the US EPA RfD of lg/kg/day for estimating noncarcinogenic risk associated 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 lg/kg/day limits Satarug et al [37] believed that the recommended Cd intake of 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 exposure in the normal diet and exposure that could produce deleterious effects, particularly in persons consuming bivalves on a regular basis Cadmium toxicity via consuming 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 estimate 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 consumption 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 concentration and speciation of As in bivalves and the biogeochemical 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 concentrations in blood cockles Anadara spp among regions may be explained by differences in human activities, i.e., shipyards 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 programs should be developed and implemented to ensure that bivalves are grown from areas with acceptable levels of chemical pollution 123 Fish Sci (2011) 77:1033–1043 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 Promotion of Science (No 2109237 to NPCT, and No 207871 to TA) are also acknowledged References MONRE (Vietnamese Ministry of Natural Resources and Environment) (2004) Country report on land based pollution in Vietnam 2004 MONRE, Hanoi MOFI (Vietnamese Ministry of Fisheries) (2006) Guidelines for environmental management of aquaculture investments in Vietnam MOFI, Hanoi Huang H, Wu JY, Wu JH (2007) Heavy metal monitoring using bivalved shellfish from Zhejiang Coastal Waters, East China Sea Environ Monit Assess 129:315–320 Phillips DJH, Rainbow PS (1988) Barnacles and mussels as biomonitors of trace elements: a comparative study Mar Ecol Prog Ser 49:83–93 Alkarkhi AFM, Ismail N, Easa AM (2008) Assessment of arsenic and heavy metal contents in cockles (Anadara granosa) using multivariate statistical techniques J Hazard Mater 150:783–789 Mat I (1994) Arsenic and trace metals in commercially important bivalves, Anadara granosa and Paphia undulata Bull Environ Contam Toxicol 52:833–839 Mat I, Maah MJ, Johari A (1994) Trace metals in sediments and potential availability to Anadara granosa Arch Environ Contam Toxicol 27:54–59 Tu NPC, Ha NN, Agusa T, Ikemoto T, Tuyen BC, Tanabe S, Takeuchi I (2010) Concentrations of trace elements in Meretrix spp (Mollusca: Bivalva) along the coasts of Vietnam Fish Sci 76:677–686 Broom MJ (1985) The biology and culture of marine bivalve molluscs of the genus Anadara International Center for Living Aquatic Resources Management, Manila 10 Tu NPC, Ha NN, Ikemoto T, Tuyen BC, Tanabe S, Takeuchi I (2008) Bioaccumulation and distribution of trace elements in tissues of giant river prawn Macrobrachium rosenbergii (Decapoda: Palaemonidae) from South Vietnam Fish Sci 74:109–119 11 Tu NPC, Ha NN, Ikemoto T, Tuyen BC, Tanabe S, Takeuchi I (2008) Regional variations in trace element concentrations in tissues of black tiger shrimp Penaeus monodon (Decapoda: Penaeidae) from South Vietnam Mar Pollut Bull 57:858–866 12 US EPA (United States Environmental Protection Agency) (2000) Guidance for assessing chemical contaminant data for use in fish advisories, volume II Risk assessment and fish consumption limits US EPA, Washington, DC 13 EC (European Commission) (2004) Report from Task 3.2.11: assessment of the dietary exposure to arsenic, cadmium, lead and mercury of the population of the EU Member States EC, Brussels 14 Han BC, Jeng WL, Chen RY, Fang GT, Hung TC, Tseng RJ (1998) Estimation of target hazard quotients and potential health risks for metals by consumption of seafood in Taiwan Arch Environ Contam Toxicol 35:711–720 15 Han BC, Jeng WL, Hung TC, Ling YC, Shieh MJ, Chien LC (2000) Estimation of metal and organochlorine pesticide Fish Sci (2011) 77:1033–1043 16 17 18 19 20 21 22 23 24 25 26 27 28 29 exposures and potential health threat by consumption of oysters in Taiwan Environ Pollut 109:147–156 MacIntosh DL, Spengler JD, Ozkaynak H, Tsai L, Ryan PB (1996) Dietary exposures to selected metals and pesticides Environ Health Perspect 104:202–209 Eisler R (1981) Trace metal concentrations in marine organisms Pergamon, New York Boyden CR (1974) Trace element content and body size in molluscs Nature 251:311–314 Phillips DJH (1976) The common mussel Mytilus edulis as an indicator of pollution by zinc, cadmium, lead and copper I Effects of environmental variables on uptake of metals Mar Biol 38:59–69 Joiris CR, Azokwu MI (1999) Heavy metals in the bivalve Anadara (Senilia) senilis from Nigeria Mar Pollut Bull 38:618–622 Riget F, Johansen P, Asmund G (1996) Influence of length on element concentrations in blue mussels (Mytilus edulis) Mar Pollut Bull 32:745–751 Vinh LT (2006) Impact assessment of heavy metal discharges from the Hyundai-Vinashin shipyard on the southwest part of Van Phong Bay, Vietnam In: Proceedings of the workshop on finalization of the projects VS/RDE/02: management tools of coastal environment for sustainable development, Nha Trang, Vietnam, 5–7 May 2006 Hung NN, Ve NB, Buresh RJ, Bayley M, Watanabe T (2005) Sustainability of paddy soil fertility in Vietnam In: Rice is life: scientific perspectives for the 21st century Proceedings of the World Rice Research Conference, Tokyo and Tsukuba, Japan, 4–7 November 2005 Denton GRW, Burdon-Jones C (1981) Influence of temperature and salinity on the uptake, distribution and depuration of mercury, cadmium and lead by the black-lip oyster Saccostrea echinata Mar Biol 64:317–326 Jackim E, Morrison G, Steele R (1977) Effects of environmental factors on radiocadmium uptake by four species of marine bivalves Mar Biol 40:303–308 Rainbow PS (1985) The biology of heavy metals in the sea Int J Environ Stud 25:195–211 Debenay JP, Luan BT (2006) Foraminiferal assemblages and the confinement index as tools for assessment of saline intrusion and human impact in the Mekong Delta and neighbouring areas (Vietnam) Rev Micropaleontol 49:74–85 Carpenter KE, Niem VH (eds) (1998) FAO species identification guide for fishery purposes The living marine resources of the Western Central Pacific Seaweeds, corals, bivalves and gastropods, vol FAO, Rome, pp 1–686 Sarkar SK, Cabral H, Chatterjee M, Cardoso I, Bhattacharya AK, Satpathy KK, Alam MA (2008) Biomonitoring of heavy metals 1043 30 31 32 33 34 35 36 37 38 39 40 41 using the bivalve molluscs in Sunderban mangrove wetland, northeast coast of Bay of Bengal (India): possible risks to human health Clean Soil Air Water 36:187–194 Griscom SB, Fisher NS, Luoma SN (2000) Geochemical influences on assimilation of sediment-bound metals in clams and mussels Environ Sci Technol 34:91–99 Abdullah MH, Sidi J, Aris AZ (2007) Heavy metals (Cd, Cu, Cr, Pb and Zn) in Meretrix meretrix Roding, water and sediments from estuaries in Sabah, North Borneo Int J Environ Sci Educ 2:69–74 MARD (Vietnamese Ministry of Agriculture and Rural Development) (2010) Promulgating the lists of food safety criteria and maximum levels thereof in certain domestically-produced or imported foodstuffs of animal origin under the management of the Ministry of Agriculture and Rural Development (No 29/2010/TT-BNNPTNT) MARD, Hanoi EC (European Commission) (2006) Setting maximum levels for certain contaminants in foodstuffs Commission regulation (EC) No 1881/2006 Off J Eur Union 364:5–24 National Shellfish Sanitation Program (2009) Guide for the control of molluscan shellfish 2007 revision US Department of Health and Human Services, Food and Drug Administration, Center for Food Safety and Applied Nutrition National Shellfish Sanitation Program, Washington DC NAFIQAD (National Agro-Forestry-Fisheries Quality Assurance Department) (2010) Report on results of harvesting status and post-harvest treatment June 2010 NAFIQAD, Hanoi (in Vietnamese) Satarug S, Moore MR (2004) Adverse health effects of chronic exposure to low-level cadmium in foodstuffs and cigarette smoke Environ Health Perspect 112:1099–1103 Satarug S, Haswell-Elkins MR, Moore MR (2000) Safe levels of cadmium intake to prevent renal toxicity in human subjects Br J Nutr 84:791–802 Widmeyer J, Bendell-Young L (2008) Heavy metal levels in suspended sediments, Crassostrea gigas, and the risk to humans Arch Environ Contam Toxicol 55:442–450 Cheng WWL, Gobas FAPC (2007) Assessment of human health risks of consumption of cadmium contaminated cultured oysters Hum Ecol Risk Assess 13:370–382 Liu C-W, Liang C-P, Huang FM, Hsueh Y-M (2006) Assessing the human health risks from exposure of inorganic arsenic through oyster (Crassostrea gigas) consumption in Taiwan Sci Total Environ 361:57–66 Peshut PJ, Morrison RJ, Brooks BA (2008) Arsenic speciation in marine fish and shellfish from American Samoa Chemosphere 71:484–492 123 ... 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... 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... decreasing 123 1040 concentrations 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