Bull Environ Contam Toxicol (2015) 94:749–755 DOI 10.1007/s00128-015-1534-4
Bioaccumulation of Heavy Metals in Oysters from the Southern Coast of Korea: Assessment of Potential Risk to Human Health Jong Soo Mok1 • Hyun Duk Yoo1 • Poong Ho Kim1 • Ho Dong Yoon1 • Young Cheol Park1 • Tae Seek Lee2 • Ji Young Kwon2 • Kwang Tae Son2 Hee Jung Lee2 • Kwang Soo Ha2 • Kil Bo Shim2 • Ji Hoe Kim2
•
Received: 15 September 2014 / Accepted: 24 March 2015 / Published online: 12 April 2015 Ó Springer Science+Business Media New York 2015
Abstract From 2009 to 2013, 80 oyster and 16 seawater samples were collected from the southern coast of Korea, including designated shellfish growing areas for export. The concentrations and bioaccumulation of heavy metals were determined, and a potential risk assessment was conducted to evaluate their hazards towards human consumption. The cadmium (Cd) concentration in oysters was the highest of three hazardous metals, including Cd, lead (Pb), and mercury (Hg), however, below the standards set by various countries. The metal bioaccumulation ratio in oysters was relatively high for zinc and Cd but low for Hg, Pb, arsenic, and chromium. The estimated dietary intakes of all heavy metals for oysters accounted for 0.02 %– 17.75 % of provisional tolerable daily intake. The hazard index for all samples was far\1.0, which indicates that the oysters do not pose an appreciable hazard to humans for the metal pollutants of study. Keywords Heavy metal Oyster Bioaccumulation Risk assessment Korea Molluscan shellfish are an important global food resource, but some heavy metals, including arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), and mercury (Hg), accumulated in the animals are harmful to humans, even at trace
& Jong Soo Mok [email protected] 1
Southeast Sea Fisheries Research Institute, National Fisheries Research & Development Institute, 397-68, Sanyang-iljuro, Sanyang-up, Tongyoung 650-943, Republic of Korea
2
Food Safety Research Division, National Fisheries Research & Development Institute, 216, Gijang-haeanro, Gijang-up, Gijang-gun, Busan 619-705, Republic of Korea
concentrations (EOS Ecology 2012). The metals accumulate in marine organisms from the aquatic environment, especially in various species of molluscan shellfish (Kobal et al. 2004; Mora et al. 2004; Borak and Hosgood 2007; Abdallah 2013; Mok et al. 2014a). To protect public health, authorities in various countries, such as Korea, the European Union (EU), China, Australia, and New Zealand, have established regulatory limits and monitoring programs for three hazardous metals, namely, Cd, Hg, and Pb [European Commission (EC) 2001, 2005; Food Standards Australia New Zealand (FSANZ) 2008; Li et al. 2013; Korea Ministry of Food and Drug Safety (KMFDS) 2014]. These heavy metal concentrations in shellfish must be monitored regularly to determine whether shellfish are safe to consume. According to Statistics Korea (2013), the country produced 303,278 tons of oysters in 2012. In particular, the Gyeongnam province, located at the south of Korea, produced the largest amount of oysters in Korea, accounting for about 87 % of oyster products produced in the country. The products are consumed domestically or exported mainly to the United States (US), Japan, and the EU (Mok et al. 2014a). The Korean government has established a memorandum of understanding with the US and EU to designate shellfish growing areas along the southern coast for export of shellfish that meet the standards set by these counties (Mok et al. 2014a). The Tongyeong region in Gyeongnam province has the designated shellfish growing areas for export, because it is an important oyster growing area in Korea. Therefore, heavy metal and other pollutants in Korean oysters from the southern coast are needed to assess shellfish quality both for Korean populations and to consumers in importing countries. In the present study, we determined the concentration and bioaccumulation of heavy metals in the oysters
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collected from the southern coast of Korea, including designated shellfish growing areas for export. The estimated dietary intake (EDI) of heavy metals via oyster consumption was compared to the provisional tolerable daily intake (PTDI) established by the Joint FAO/WHO Expert Committee on Food Additives (Joint FAO/WHO Expert Committee on Food Additives (JECFA) 1999, 2010a, b) and the U.S. Environmental Protection Agency (EPA 2013). In addition, an assessment of the potential risk of heavy metals in oysters was conducted using the target hazard quotient (THQ) and hazard index (HI).
Materials and Methods Oyster samples (Crassostrea gigas) were collected twice a year from 2009 to 2013 at the fixed monitoring stations along the southern coast of Korea (Fig. 1). The samples were collected at 2–3 m depths from a hanging rope culture. The samples of surface seawater were collected from the same fixed monitoring stations as oysters from 2012 to 2013. In the Tongyeong region, where the designated shellfish growing areas for export were located, 60 oyster samples were collected from six different stations, while 16 seawater samples were collected from five stations. In Jinhae Bay, 20 oyster samples were collected from stations 7 and 8. Oyster and seawater samples were chilled in coolers, and transported to the laboratory. Deionized water (DIW) was passed through a Milli-Q water purification system (Millipore, Billerica, MA, USA). Working standard solutions of Cd, Pb, As, Cr, nickel (Ni), copper (Cu), and zinc (Zn) were prepared by diluting 1000 mg/L standard solutions (Merck, Darmstadt, Germany) in DIW for the calibration. MESS-3, a marine sediment certified reference material (CRM), was purchased from the National Research Council of Canada
Fig. 1 Sampling locations along the southern coast of Korea
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(Ottawa, ON, Canada) and used as a calibration standard of combustion gold amalgamation method for Hg. The seawater samples were filtered through a vacuum filtration system and 0.4 lm membrane filters (Whatman, Maidstone, UK). The heavy metals, excluding Hg, in the seawater were extracted by a solvent extraction method using dithiocarbamate complexing agent, a di-isobutyl ketone (DIBK) organic phase, and Hg exchange back-extraction (Batterham and Parry 1996). Analysis was performed with an inductively coupled plasma mass spectrometer (ICP-MS; NexION 300D, PerkinElmer, Waltham, MA, USA). Hg in the filtered seawater, after adding hydroxylamine-HCl and stannous chloride (analytical grade, Merck), was determined using an automatic mercury analyzer (MERX, Brooks Rand, Seattle, WA, USA). The tissue samples were removed from shells and cleaned with DIW and homogenized. The homogenized tissues were freeze-dried with a vacuum freeze dryer (FDU-2100, EYELA, Tokyo, Japan) and then ground into powder for analysis. About 1.0 g powdered sample was placed in a 60-mL digestion vessel (Savillex, Eden Prairie, MN, USA), and after which 20 mL nitric acid (supra-pure grade, Merck) was added. The vessel was covered and left overnight at room temperature. The samples were digested with a heating digester (DigiPREP HP, SCP Science, Champlain, NY, USA). The digested samples were allowed to cool to room temperature, dissolved in 2 % nitric acid, filtered (glass wool), and their volumes were made up to 100 mL using 2 % nitric acid to analyze heavy metals, excluding Hg. All digested samples were analyzed in triplicate for Cd, Pb, As, Cr, Ni, Cu, and Zn using the ICPMS (NexION 300D, PerkinElmer). Approximately 0.1 g homogenized sample was supplied for the Hg analysis using a combustion gold amalgamation method with a direct mercury analyzer (DMA-80, Milestone, Milano, Italy).The heavy metal concentrations in oysters were expressed in micrograms per gram of wet weight sample. The quantitative recoveries of heavy metals in the oyster tissue CRM (n = 5) (NIST, Gaithersburg, MD) ranged from 91.1 % to 107.7 %, which are within the acceptable values recommended by AOAC International (2002). The detection limits of Cd, Pb, As, Cr, Ni, Cu, and Zn using the ICP-MS were 0.0012, 0.0038, 0.0067, 0.0103, 0.0033, 0.0039, and 0.0461 lg/kg, respectively. The detection limit of Hg using the mercury analyzer was 0.1481 lg/kg. Statistical evaluation was conducted using analysis of variance with the general linear model procedure (SAS version 9.2, SAS Institute, Cary, NC, USA). Duncan’s multiple-range test was applied to determine the significance of differences among the mean concentrations of heavy metals in the oyster samples.
b
a
0.014 ± 0.003 (0.010-0.021)
0.600 ± 0.156
(0.397-0.951)
There is no significant difference (p \ 0.05)
Values are means ± standard deviations (range)
Mok et al. (2014a)
(0.005–0.019)
(0.267–0.930)
(0.005–0.010) 0.009 ± 0.003
(0.267–0.888)
0.591 ± 0.186
(0.005–0.010) 0.007 ± 0.001
(0.316–0.930) 0.500 ± 0.181
8 (10)
Total (80)
0.007 ± 0.002
0.563 ± 0.219
(0.007–0.014)
(0.326–0.820)
(0.005–0.018) 0.011 ± 0.002
(0.272–0.900)
0.510 ± 0.153
0.011 ± 0.004
(0.005–0.015)
(0.410–0.910)
0.549 ± 0.200
0.009 ± 0.003
(0.006–0.016)
0.647 ± 0.177
(0.419–0.910)
(0.005–0.014) 0.010 ± 0.003
(0.381–0.900)
0.704 ± 0.169
0.009 ± 0.002
(0.006–0.019)
0.615 ± 0.185
0.010 ± 0.004
0.637 ± 0.161
Hg
(0.357–0.910)
Cd
Heavy metal concentration (lg/g)a
7 (10)
Jinhae Bay (20)
6 (10)
5 (10)
4 (10)
3 (10)
2 (10)
Tongyeong (60) 1 (10)
Stations (no. of samples)
(0.018-0.201)
0.117 ± 0.066
–
(1.599–4.796)
2.690 ± 0.885
(0.055–0.312)
(1.620–3.955)
(0.064–0.190)
(1.790–4.563) 2.441 ± 0.926
2.727 ± 0.955
(1.599–3.000)
2.166 ± 0.467
(1.916–3.434)
2.585 ± 0.580
(1.886–4.271)
3.203 ± 0.880
(2.241–4.796)
3.448 ± 1.053
(1.663–4.292)
2.494 ± 0.884
(1.836–3.574)
2.454 ± 0.680
As
0.150 ± 0.062b
(0.060–0.212) 0.105 ± 0.040
0.112 ± 0.047
(0.067–0.240)
0.139 ± 0.054
(0.055–0.293)
0.154 ± 0.081
(0.115–0.289)
0.193 ± 0.060
(0.116–0.236)
0.173 ± 0.050
(0.110–0.239)
0.165 ± 0.044
(0.075–0.312)
0.162 ± 0.075
Pb
Table 1 Heavy metal concentrations in oysters collected from the southern coast of Korea
(0.087-0.431)
0.269 ± 0.096
(0.089–0.453)
0.215 ± 0.096
(0.094–0.354)
(0.140–0.378) 0.202 ± 0.091
0.228 ± 0.089
(0.091–0.340)
0.206 ± 0.098
(0.108–0.426)
0.222 ± 0.112
(0.089–0.333)
0.213 ± 0.087
(0.122–0.398)
0.240 ± 0.099
(0.090–0.398)
0.188 ± 0.103
(0.091–0.453)
0.224 ± 0.114
Cr
(0.069-0.225)
0.124 ± 0.043
(0.095–0.318)
0.153 ± 0.062b
(0.097–0.225)
(0.097–0.185) 0.144 ± 0.040
0.137 ± 0.032
(0.095–0.270)
0.150 ± 0.069
(0.098–0.275)
0.160 ± 0.074
(0.096–0.194)
0.140 ± 0.040
(0.101–0.313)
0.144 ± 0.067
(0.097–0.306)
0.165 ± 0.084
(0.098–0.318)
0.182 ± 0.076
Ni
(20.55-62.73)
34.45 ± 12.44
(17.23–55.68)
32.48 ± 11.10
(20.74–55.68)
(18.50–51.70) 35.35 ± 11.17
35.39 ± 9.43
(19.76–43.69)
28.05 ± 8.82
(20.41–53.73)
38.53 ± 10.72
(22.90–51.28)
40.06 ± 10.48
(18.05–54.70)
35.35 ± 13.06
(18.72–35.60)
24.32 ± 5.37
(17.23–36.03)
22.82 ± 5.86
Cu
(110.33-334.07)
180.29 ± 60.82
(90.68–274.11)
154.38 ± 46.84
(94.51–248.55)
(102.41–272.04) 146.71 ± 52.60
162.57 ± 52.01
(108.12–240.11)
159.07 ± 43.65
(90.76–231.08)
154.22 ± 45.18
(99.81–242.50)
156.29 ± 50.96
(100.09–274.11)
145.79 ± 51.25
(90.68–239.00)
151.78 ± 47.43
(95.46–240.58)
158.64 ± 45.70
Zn
Bull Environ Contam Toxicol (2015) 94:749–755 751
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752
Bull Environ Contam Toxicol (2015) 94:749–755
Table 2 Heavy metal concentrations in the seawater samples collected from the Tongyeong region in the southern coast of Korea Stations (no. of samples)
Heavy metal concentration (lg/L)a Cd
Hg
Pb
As
Cr
Cu
Zn
1 (3)
0.0019 ± 0.0003
0.0010 ± 0.0003
0.024 ± 0.009
0.303 ± 0.229
0.145 ± 0.027
0.633 ± 0.268
0.166 ± 0.013
(0.0016–0.0021)
(0.0007–0.0013)
(0.014–0.031)
(0.124–0.562)
(0.126–0.176)
(0.463–0.942)
(0.152–0.177)
0.0018 ± 0.0007
0.0018 ± 0.0010
0.025 ± 0.006
0.287 ± 0.179
0.174 ± 0.073
0.953 ± 0.188
0.266 ± 0.085
(0.0013–0.0026)
(0.0012–0.0030)
(0.018–0.031)
(0.148–0.489)
(0.100–0.246)
(0.771–1.146)
(0.170–0.332)
0.0020 ± 0.0007
0.0017 ± 0.0012
0.023 ± 0.008
0.292 ± 0.184
0.125 ± 0.025
0.603 ± 0.156
0.213 ± 0.076
(0.0013–0.0027)
(0.0007–0.0030)
(0.014–0.030)
(0.125–0.489)
(0.100–0.149)
(0.463–0.771)
(0.152–0.298)
5 (4)
0.0031 ± 0.0023 (0.0014–0.0063)
0.0021 ± 0.0014 (0.0005–0.0039)
0.044 ± 0.014 (0.026–0.059)
0.277 ± 0.205 (0.120–0.578)
0.168 ± 0.050 (0.109–0.231)
0.785 ± 0.392 (0.322–1.159)
0.269 ± 0.101 (0.145–0.378)
6 (3)
0.0014 ± 0.0002
0.0015 ± 0.0011
0.052 ± 0.026
0.384 ± 0.236
0.144 ± 0.043
0.412 ± 0.092
0.326 ± 0.247
(0.0012–0.0016)
(0.0005–0.0027)
(0.023–0.074)
(0.120–0.575)
(0.099–0.186)
(0.306–0.474)
(0.112–0.597)
0.0021 ± 0.0013b
0.0017 ± 0.0010b
0.034 ± 0.018
0.307 ± 0.182
0.152 ± 0.045
0.684 ± 0.288
0.249 ± 0.122
(0.0012–0.0063)
(0.0005–0.0039)
(0.014–0.074)
(0.120–0.578)
(0.099–0.246)
(0.306–1.159)
(0.112–0.597)
2 (3) 3 (3)
Total (16) a
Values are means ± standard deviations (range)
b
There is no significant difference (p \ 0.05)
Results and Discussion The selected metal concentrations in the oysters collected from eight fixed stations along the southern coast of Korea are shown in Table 1. The mean metal concentrations in oyster samples decreased in the order Zn (154.38 lg/g) [ Cu (32.48 lg/g) [ As (2.690 lg/g) [ Cd (0.591 lg/g) [ Cr (0.215 lg/g) [ Ni (0.153 lg/g) [ Pb (0.150 lg/g) [ Hg (0.009 lg/g. The differences of metal concentrations in oysters between Tongyeong region and Jinhae Bay and among stations were not significant. The mean concentrations of heavy metals in the oyster samples were similar to those collected from fish markets in Korea (Mok et al. 2014a). Some metals—Cd, Hg, Pb, As, and Cr—can harm humans, even in trace amounts (EOS Ecology 2012). The mean concentrations of As, which is the highest of the hazardous metals, at each oyster station ranged from 2.166 to 3.448 lg/g, with the highest found at station 3. The mean concentrations of Cd, which is the highest of the three hazardous metals (Cd, Pb, and Hg) with the regulatory limits set by Korea (KMFDS 2014), ranged from 0.267 to 0.930 lg/g. The mean Cd concentration in all oyster samples was 0.591 ± 0.186 lg/g, which is slightly less than the 0.640 lg/g for oysters reported by Sho et al. (2000), but above the 0.212 lg/g for oysters by Ham (2002) in Korea. According to Li et al. (2013), Cd concentrations in oyster (0.338 lg/g) were significantly higher (p \ 0.05) than those in both short-necked clam (0.133 lg/g) and razor clam (0.054 lg/g). Our previous results also indicate that the Cd concentrations in oyster (0.600 lg/g), which were the highest of the three hazardous
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metals, were higher than those (0.068 to 0.574 lg/g) in other bivalves, such as mussel, short-necked clam, bay scallop, comb pen shell, and ark shell (Mok et al. 2014a). All samples showed Cd concentrations within the regulatory limits (1.0–2.0 lg/g) set by the Codex Alimentarius Commission (2006) (2.0 lg/g) and other countries such as Korea (2.0 lg/g) (KMFDS 2014), Australia, New Zealand (both 2.0 lg/g) (FSANZ 2008), and the EU (1.0 lg/g) (EC 2001). The mean Hg concentrations of the samples at each station ranged from 0.007 to 0.010 lg/g, far lower than the limit (0.5 lg/g) in both Korea (KMFDS 2014) and the EU (EC 2005). The mean level (0.009 ± 0.003 lg/g) of Hg in all samples was about two- to three-fold lower than the levels for oysters reported in other Korean studies (Sho et al. 2000; Ham 2002). The mean Hg level was similar to the 0.007 lg/g for Chinese oysters (Li et al. 2013). The mean Pb level (0.150 ± 0.062 lg/g) in all samples was slightly lower than the levels (0.214 lg/g) for Korean oysters (Ham 2002) and the 0.209 lg/g for Chinese oysters (Li et al. 2013). The highest Pb concentration (0.312 lg/g) in oysters was about three- to six-fold below the limits (1.0–2.0 lg/g) set by various countries, e.g., 2.0 lg/g in Korea (KMFDS 2014), Australia, and New Zealand (FSANZ 2008), and 1.0 lg/g in the EU (EC 2001). The mean metal concentrations in seawater collected from Tongyeong region decreased, unlike those of oyster samples, in the order Cu (0.684 lg/L) [ As (0.307 lg/L) [ Zn (0.249 lg/L) [ Cr (0.152 lg/L) [ Pb (0.034 lg/L) [ Cd (0.0021 lg/L) [ Hg (0.0017 lg/L) (Table 2). The mean bioaccumulation factors of metals in all oyster
Bull Environ Contam Toxicol (2015) 94:749–755
Fig. 2 Bioaccumulation factor (a) of heavy metals in mussel, and target hazard quotients (THQs) and hazard index (HI) (b) for heavy metals via consumption of oyster in Korea. Scale bar represents one standard deviation. The bioaccumulation factor was calculated as the mean metal concentration in a gram of oyster (Table 1) divided by that in a milliliter of seawater (Table 2). THQs were represented according to the US Environmental Protection Agency (EPA) Human Health Risk Assessment approach (EPA 2013). The THQ was calculated using the equation THQ = (EF 9 ED 9 DI 9 HC)/ (RfD 9 BW 9 ET), where EF is the exposure frequency (350 days/ year); ED is the exposure duration (81 years), equivalent to the average lifetime in Korea (Statistics Korea 2013); DI is the average daily intake (0.0198 lg/kg/day) of oysters in Korea (KCDC 2011); HC is the heavy metal concentration in oysters (lg/g) shown in Table 1; RfD is the oral reference dose (lg/kg/day); BW is the average body weight (62.8 kg) of an adult in Korea (KCDC 2011); and ET is the average exposure time for non-carcinogens (ED 9 365 days/year). The RfDs of Hg, Pb, As, Cr, Ni, Cu, and Zn used the provisional tolerable daily intake shown in Table 3. RfD of Cd was set at 1.0 established by the EPA (2013). HI was calculated by summing the THQs of individual heavy metals
samples from surrounding seawater ranged from 1413- to 618,958-fold; the highest factor was found for Zn (Fig. 2a). The metals in oysters accumulated in the order Zn [ Cd [ Cu [ As [ Hg [ Pb [ Cr. The metal bioaccumulation factor in oysters was very high for Zn and Cd but relatively low for Hg, Pb, As, and Cr. We previously reported that the mean bioaccumulation factors of the same metals in the mussels collected from the southern coast of Korea ranged from 429- to 74,794-fold; the highest factor was found for Cd (Mok et al. 2014b). The metals in mussels, unlike oysters, accumulated in the order Cd [ As [ Hg [ Pb [ Zn [ Cu [ Cr; thus, the metal bioaccumulation was relatively high for Cd and As but low for Cr and Cu. The oysters accumulate 99.6. 40.2, 3.7 and 3.3-fold higher than the mussels for Cu, Zn, Cd, and Cr,
753
respectively, but the bioaccumulation factors of Hg, Pb, and As for the oysters were about four- to five-fold lower than the factors for mussels. The accumulation of heavy metals in marine organisms depends on both their uptake and elimination rates. Heavy metals are taken up through the organisms and concentrated at different levels in the body (Sivaperumal et al. 2007; Abdallah 2013). Present findings indicate that the oysters accumulate higher than the mussels for Cu, Zn, Cd, and Cr, however, lower than the mussels for Hg, Pb, and As. Therefore, it reveals that the animals accumulate different heavy metals and levels in the body from surrounding seawater. The EDIs of heavy metals represent the daily intake of heavy metals through the consumption of oysters for an adult. The EDI was compared to the PTDI proposed by the JECFA (1999, 2010a, b) and the EPA (2013). The PTDI values for Cd, Hg and Pb were established by the JECFA because of the risks of even trace concentrations of these metals to human health. As shown in Table 3, the EDI values of the hazardous metals (Cd, Hg, and Pb) for oysters were 1.2 9 10-2, 1.8 9 10-4, and 3.0 9 10-3 lg/kg/day, respectively, which account for only 0.03 %–1.41 % of the PTDI. The EDI values of the hazardous metals for oysters were higher than those (4.5 9 10-5–1.3 9 10-3 lg/kg/day) for mussels in Korea (Mok et al. 2014b). The EDIs of other metals (As, Cr, Ni, Cu, and Zn) were compared to the PTDI values based on the reference doses established by the EPA (2013). In the oysters, the EDI values of As, Cr, Ni, Cu, and Zn accounted for 17.75 %, 0.14 %, 0.02 %, 1.61 %, and 1.02 % of the PTDI, respectively. The EDI value for As was the highest of all tested metals, it is due to the relatively high As concentration (Table 1) and using the PTDI value of inorganic As (far more toxic than organic AS) for total As measured in oyster samples, including inorganic and organic AS. The THQ and HI were used to assess the potential risk to an adult of consuming heavy metals via oysters. The THQ was estimated by comparing the ingested amount of a heavy metal with a standard reference dose; the HI was the sum of the various THQs. The THQ and HI values proposed by the EPA are integrated risk indexes, and have been used widely for risk assessment of various contaminants in foods (Storelli 2008; Mok et al. 2014a). As shown in Fig. 2b, the mean THQ of the metals for oyster was low, ranging from 0.0001 to 0.1702; the highest THQ was found for As. The highest THQ of each metal in all species ranged from 0.0001 to 0.2262. The THQ for As was relatively high in all samples analyzed, but low for other metals. An HI exceeding 1.0 indicates that the contaminants are toxic and represent any hazard to human health (Abdallah 2013; Li et al. 2013). The mean and highest HI values were 0.2246 and 0.2987, respectively, well below 1.0.
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Table 3 Estimated dietary intakes (EDIs) of heavy metals via the consumption of oysters collected from the southern coast of Korea Heavy metal
EDIs (lg/kg/day)a PTDI values (lg/kg/day)
b
Cd
Hg
Pb
As
Cr
Ni
Cu
Zn
1.2 9 10-2
1.8 9 10-4
3.0 9 10-3
5.3 9 10-2
4.3 9 10-3
3.0 9 10-3
6.4 9 10-1
3.1 9 100
0.83
0.57
3.57
0.3
3.0
20
40
300
a The EDI value for an adult was calculated using the equation EDI = (HC 9 DI)/BW, where HC is the mean heavy metal concentration in oysters shown in Table 1, DI and BW are the average daily intake (0.0198 lg/kg/day) of oysters and the average body weight (62.8 kg) of an adult human in Korea (KCDC 2011) b
The provisional tolerable daily intake (PTDI) values of Hg, Pb, and Cd were based on the provisional tolerable weekly intake (PTWI) data for Hg and Pb, and provisional tolerable monthly intake data for Cd from the Joint FAO/WHO Expert Committee on Food Additives (JECFA 1999, 2010a, b), in which the PTWI value of inorganic Hg was used for total Hg. The PTDI values of other metals, such as As (assuming that total As is inorganic As), Cr (assuming that total Cr is Cr[VI]), Ni (assuming that all Ni is Ni soluble salts), Cu, and Zn (assuming that all Zn is Zn and compounds), were based on the oral reference doses established by the U.S. Environmental Protection Agency (2013)
This is the first report of concentrations and risk assessment of heavy metals in oysters in the designated shellfish growing areas for export in Korea. The oysters, which are produced from the designated shellfish growing areas, are consumed domestically or exported mainly to the United States (US), Japan, and the EU (Mok et al. 2014a). The heavy metal concentrations in the oysters are considered to be important information both in Korea and in importing countries. Therefore, a monitoring program of the metals for the oysters in the designated shellfish growing areas should be operated regularly at the appropriate frequency. In conclusion, the Cd concentration was the highest of the three hazardous metals (Cd, Pb, and Hg); however, the concentrations of the harmful metals in all samples were within the regulatory limits set by Korea and other countries. The metal bioaccumulation ratio in oysters was relatively high for Zn and Cd but low for Hg, Pb, As, and Cr. The EDIs of each metal tested for oysters ranged from 0.02 % to 17.75 % of the PTDI values; the highest value was measured for As. The HI for all oysters was far\1.0, which indicates that the intake of metals via consumption of this animal does not represent an appreciable hazard to humans. Acknowledgments This work was supported by a grant from the National Fisheries Research and Development Institute of Korea (RP2015-FS-001).
References Abdallah MAM (2013) Bioaccumulation of heavy metals in mollusca species and assessment of potential risks to human health. Bull Environ Contam Toxicol 90:552–557 AOAC International (2002) AOAC guidelines for single laboratory validation of chemical methods for dietary supplements and botanicals. AOAC, Gaithersburg Batterham GJ, Parry DL (1996) Improved dithiocarbamate/oxine solvent extraction method for the preconcentration of trace metals from seawater using metal exchange back-extraction. Mar Chem 55:381–388
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Borak J, Hosgood HD (2007) Seafood arsenic: implications for human risk assessment. Regul Toxicol Pharmacol 47:204–212 Codex Alimentarius Commission (2006) Report of the 29th session of Codex Alimentarius Commission. ALINORM 06/29/41. Codex Alimentarius Commission, Geneva EC (European Commission) (2005) Commission Regulation (EC) No. 78/2005 of 19 Jan 2005 amending Regulation (EC) No. 466/2001 as regards heavy metals. http://eur-lex.europa.eu/ LexUriServ/LexUriServ.do?uri=OJ:L:2005:016:0043:0045:EN: PDF. Accessed 26 Aug 2013 EOS Ecology (2012) Heavy metals in fish and shellfish. EOS Ecology, Christchurch EPA (U.S. Environmental Protection Agency) (2013) Human health risk assessment. http://www.epa.gov/reg3hwmd/risk/human/ index.htm. Accessed 6 Aug 2013 European Commission (EC) (2001) Commission Regulation (EC) No. 466/2001 of 8 March 2001 setting maximum levels for certain contaminants in foodstuffs. http://eur-lex.europa.eu/LexUriServ/ LexUriServ.do?uri=OJ:L:2001:077:0001:0013:EN:PDF. Accessed 26 August 2013 FSANZ (Food Standards Australia New Zealand) (2008) Australia New Zealand food standards code (incorporating amendments up to and including amendment 97). Anstat Pty Ltd., Melbourne Ham HJ (2002) Distribution of hazardous heavy metals (Hg, Cd and Pb) in fishery products, sold at Garak wholesale markets in Seoul. J Food Hyg Safety 17:146–151 Joint FAO/WHO Expert Committee on Food Additives (JECFA) (1999) Summary and conclusions of the 53rd meeting of the Joint FAO/WHO Expert Committee on Food Additives (JECFA). JECFA/53/SC. JECFA, Rome Joint FAO/WHO Expert Committee on Food Additives (JECFA) (2010a) Summary and conclusions of the 72nd meeting of the Joint FAO/WHO Expert Committee on Food Additives (JECFA). JECFA/72/SC. JECFA, Rome Joint FAO/WHO Expert Committee on Food Additives (JECFA) (2010b) Summary and conclusions of the 73nd meeting of the Joint FAO/WHO Expert Committee on Food Additives (JECFA). JECFA/73/SC. JECFA, Geneva KCDC (Korea Centers for Disease Control and Prevention) (2011) Korea health statistics 2010: The fifth Korea national health and nutrition examination survey. KCDC, Cheongju KMFDS (Korea Ministry of Food and Drug Safety) (2014) Korea food code. http://fse.foodnara.go.kr/residue/RS/jsp/menu_02_ 01_01.jsp. Accessed 21 June 2014 Kobal AB, Horvat M, Prezelj M, Brisˇki AS, Krsnik M, Dizdarevicˇ T, Mazej D, Falnoga I, Stibilj V, Arnericˇ N, Kobal D, Osredkar J (2004) The impact of long-term past exposure to elemental
Bull Environ Contam Toxicol (2015) 94:749–755 mercury on antioxidative capacity and lipid peroxidation in mercury miners. J Trace Elem Med Biol 17:261–274 Li J, Huang ZY, Hu Y, Yang H (2013) Potential risk assessment of heavy metals by consuming shellfish collected from Xiamen. China Environ Sci Pollut Res 20:2937–2947 Mok JS, Kwon JY, Son KT, Choi WS, Kang SR, Ha NY, Jo MR, Kim JH (2014a) Contents and risk assessment of heavy metals in marine invertebrates from Korean coastal fish markets. J Food Prot 77:1022–1030 Mok JS, Yoo HD, Kim PH, Yoon HD, Park YC, Lee TS, Kwon JY, Son KT, Lee HJ, Ha KS, Shim KB, Jo MR, Kim JH (2014b) Bioaccumulation of heavy metals in mussels in the Changseon area, Korea, and assessment of potential risk to human health. Fish Aquat Sci 17:1–6 Mora S, Scott WF, Eric W, Sabine A (2004) Distribution of heavy metals in marine bivalves, fish and coastal sediments in the gulf and gulf of Oman. Mar Pollut Bull 49:410–424
755 Sho YS, Kim JS, Chung SY, Kim MH, Hong MK (2000) Trace metal contents in fishes and shellfishes and their safety evaluation. J Korean Soc Food Sci Nutr 29:549–554 Sivaperumal P, Sankar TV, Viswanathan Nair PG (2007) Heavy metal concentrations in fish, shellfish and fish products from internal markets of India vis-a-vis international standards. Food Chem 102:612–620 Statistics Korea (2013) Korean statistical information service (KOSIS). http://kosis.kr/index/index.jsp. Accessed 22 Aug 2013 Storelli MM (2008) Potential human health risks from metals (Hg, Cd, and Pb) and polychlorinated biphenyls (PCBs) via seafood consumption: estimation of target hazard quotients (THQs) and toxic equivalents (TEQs). Food Chem Toxicol 46:2782–2788
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Bioaccumulation of Heavy Metals in Oysters from the Southern Coast of Korea: Assessment of Potential Risk to Human Health Jong Soo Mok1 • Hyun Duk Yoo1 • Poong Ho Kim1 • Ho Dong Yoon1 • Young Cheol Park1 • Tae Seek Lee2 • Ji Young Kwon2 • Kwang Tae Son2 Hee Jung Lee2 • Kwang Soo Ha2 • Kil Bo Shim2 • Ji Hoe Kim2
•
Received: 15 September 2014 / Accepted: 24 March 2015 / Published online: 12 April 2015 Ó Springer Science+Business Media New York 2015
Abstract From 2009 to 2013, 80 oyster and 16 seawater samples were collected from the southern coast of Korea, including designated shellfish growing areas for export. The concentrations and bioaccumulation of heavy metals were determined, and a potential risk assessment was conducted to evaluate their hazards towards human consumption. The cadmium (Cd) concentration in oysters was the highest of three hazardous metals, including Cd, lead (Pb), and mercury (Hg), however, below the standards set by various countries. The metal bioaccumulation ratio in oysters was relatively high for zinc and Cd but low for Hg, Pb, arsenic, and chromium. The estimated dietary intakes of all heavy metals for oysters accounted for 0.02 %– 17.75 % of provisional tolerable daily intake. The hazard index for all samples was far\1.0, which indicates that the oysters do not pose an appreciable hazard to humans for the metal pollutants of study. Keywords Heavy metal Oyster Bioaccumulation Risk assessment Korea Molluscan shellfish are an important global food resource, but some heavy metals, including arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), and mercury (Hg), accumulated in the animals are harmful to humans, even at trace
& Jong Soo Mok [email protected] 1
Southeast Sea Fisheries Research Institute, National Fisheries Research & Development Institute, 397-68, Sanyang-iljuro, Sanyang-up, Tongyoung 650-943, Republic of Korea
2
Food Safety Research Division, National Fisheries Research & Development Institute, 216, Gijang-haeanro, Gijang-up, Gijang-gun, Busan 619-705, Republic of Korea
concentrations (EOS Ecology 2012). The metals accumulate in marine organisms from the aquatic environment, especially in various species of molluscan shellfish (Kobal et al. 2004; Mora et al. 2004; Borak and Hosgood 2007; Abdallah 2013; Mok et al. 2014a). To protect public health, authorities in various countries, such as Korea, the European Union (EU), China, Australia, and New Zealand, have established regulatory limits and monitoring programs for three hazardous metals, namely, Cd, Hg, and Pb [European Commission (EC) 2001, 2005; Food Standards Australia New Zealand (FSANZ) 2008; Li et al. 2013; Korea Ministry of Food and Drug Safety (KMFDS) 2014]. These heavy metal concentrations in shellfish must be monitored regularly to determine whether shellfish are safe to consume. According to Statistics Korea (2013), the country produced 303,278 tons of oysters in 2012. In particular, the Gyeongnam province, located at the south of Korea, produced the largest amount of oysters in Korea, accounting for about 87 % of oyster products produced in the country. The products are consumed domestically or exported mainly to the United States (US), Japan, and the EU (Mok et al. 2014a). The Korean government has established a memorandum of understanding with the US and EU to designate shellfish growing areas along the southern coast for export of shellfish that meet the standards set by these counties (Mok et al. 2014a). The Tongyeong region in Gyeongnam province has the designated shellfish growing areas for export, because it is an important oyster growing area in Korea. Therefore, heavy metal and other pollutants in Korean oysters from the southern coast are needed to assess shellfish quality both for Korean populations and to consumers in importing countries. In the present study, we determined the concentration and bioaccumulation of heavy metals in the oysters
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750
collected from the southern coast of Korea, including designated shellfish growing areas for export. The estimated dietary intake (EDI) of heavy metals via oyster consumption was compared to the provisional tolerable daily intake (PTDI) established by the Joint FAO/WHO Expert Committee on Food Additives (Joint FAO/WHO Expert Committee on Food Additives (JECFA) 1999, 2010a, b) and the U.S. Environmental Protection Agency (EPA 2013). In addition, an assessment of the potential risk of heavy metals in oysters was conducted using the target hazard quotient (THQ) and hazard index (HI).
Materials and Methods Oyster samples (Crassostrea gigas) were collected twice a year from 2009 to 2013 at the fixed monitoring stations along the southern coast of Korea (Fig. 1). The samples were collected at 2–3 m depths from a hanging rope culture. The samples of surface seawater were collected from the same fixed monitoring stations as oysters from 2012 to 2013. In the Tongyeong region, where the designated shellfish growing areas for export were located, 60 oyster samples were collected from six different stations, while 16 seawater samples were collected from five stations. In Jinhae Bay, 20 oyster samples were collected from stations 7 and 8. Oyster and seawater samples were chilled in coolers, and transported to the laboratory. Deionized water (DIW) was passed through a Milli-Q water purification system (Millipore, Billerica, MA, USA). Working standard solutions of Cd, Pb, As, Cr, nickel (Ni), copper (Cu), and zinc (Zn) were prepared by diluting 1000 mg/L standard solutions (Merck, Darmstadt, Germany) in DIW for the calibration. MESS-3, a marine sediment certified reference material (CRM), was purchased from the National Research Council of Canada
Fig. 1 Sampling locations along the southern coast of Korea
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Bull Environ Contam Toxicol (2015) 94:749–755
(Ottawa, ON, Canada) and used as a calibration standard of combustion gold amalgamation method for Hg. The seawater samples were filtered through a vacuum filtration system and 0.4 lm membrane filters (Whatman, Maidstone, UK). The heavy metals, excluding Hg, in the seawater were extracted by a solvent extraction method using dithiocarbamate complexing agent, a di-isobutyl ketone (DIBK) organic phase, and Hg exchange back-extraction (Batterham and Parry 1996). Analysis was performed with an inductively coupled plasma mass spectrometer (ICP-MS; NexION 300D, PerkinElmer, Waltham, MA, USA). Hg in the filtered seawater, after adding hydroxylamine-HCl and stannous chloride (analytical grade, Merck), was determined using an automatic mercury analyzer (MERX, Brooks Rand, Seattle, WA, USA). The tissue samples were removed from shells and cleaned with DIW and homogenized. The homogenized tissues were freeze-dried with a vacuum freeze dryer (FDU-2100, EYELA, Tokyo, Japan) and then ground into powder for analysis. About 1.0 g powdered sample was placed in a 60-mL digestion vessel (Savillex, Eden Prairie, MN, USA), and after which 20 mL nitric acid (supra-pure grade, Merck) was added. The vessel was covered and left overnight at room temperature. The samples were digested with a heating digester (DigiPREP HP, SCP Science, Champlain, NY, USA). The digested samples were allowed to cool to room temperature, dissolved in 2 % nitric acid, filtered (glass wool), and their volumes were made up to 100 mL using 2 % nitric acid to analyze heavy metals, excluding Hg. All digested samples were analyzed in triplicate for Cd, Pb, As, Cr, Ni, Cu, and Zn using the ICPMS (NexION 300D, PerkinElmer). Approximately 0.1 g homogenized sample was supplied for the Hg analysis using a combustion gold amalgamation method with a direct mercury analyzer (DMA-80, Milestone, Milano, Italy).The heavy metal concentrations in oysters were expressed in micrograms per gram of wet weight sample. The quantitative recoveries of heavy metals in the oyster tissue CRM (n = 5) (NIST, Gaithersburg, MD) ranged from 91.1 % to 107.7 %, which are within the acceptable values recommended by AOAC International (2002). The detection limits of Cd, Pb, As, Cr, Ni, Cu, and Zn using the ICP-MS were 0.0012, 0.0038, 0.0067, 0.0103, 0.0033, 0.0039, and 0.0461 lg/kg, respectively. The detection limit of Hg using the mercury analyzer was 0.1481 lg/kg. Statistical evaluation was conducted using analysis of variance with the general linear model procedure (SAS version 9.2, SAS Institute, Cary, NC, USA). Duncan’s multiple-range test was applied to determine the significance of differences among the mean concentrations of heavy metals in the oyster samples.
b
a
0.014 ± 0.003 (0.010-0.021)
0.600 ± 0.156
(0.397-0.951)
There is no significant difference (p \ 0.05)
Values are means ± standard deviations (range)
Mok et al. (2014a)
(0.005–0.019)
(0.267–0.930)
(0.005–0.010) 0.009 ± 0.003
(0.267–0.888)
0.591 ± 0.186
(0.005–0.010) 0.007 ± 0.001
(0.316–0.930) 0.500 ± 0.181
8 (10)
Total (80)
0.007 ± 0.002
0.563 ± 0.219
(0.007–0.014)
(0.326–0.820)
(0.005–0.018) 0.011 ± 0.002
(0.272–0.900)
0.510 ± 0.153
0.011 ± 0.004
(0.005–0.015)
(0.410–0.910)
0.549 ± 0.200
0.009 ± 0.003
(0.006–0.016)
0.647 ± 0.177
(0.419–0.910)
(0.005–0.014) 0.010 ± 0.003
(0.381–0.900)
0.704 ± 0.169
0.009 ± 0.002
(0.006–0.019)
0.615 ± 0.185
0.010 ± 0.004
0.637 ± 0.161
Hg
(0.357–0.910)
Cd
Heavy metal concentration (lg/g)a
7 (10)
Jinhae Bay (20)
6 (10)
5 (10)
4 (10)
3 (10)
2 (10)
Tongyeong (60) 1 (10)
Stations (no. of samples)
(0.018-0.201)
0.117 ± 0.066
–
(1.599–4.796)
2.690 ± 0.885
(0.055–0.312)
(1.620–3.955)
(0.064–0.190)
(1.790–4.563) 2.441 ± 0.926
2.727 ± 0.955
(1.599–3.000)
2.166 ± 0.467
(1.916–3.434)
2.585 ± 0.580
(1.886–4.271)
3.203 ± 0.880
(2.241–4.796)
3.448 ± 1.053
(1.663–4.292)
2.494 ± 0.884
(1.836–3.574)
2.454 ± 0.680
As
0.150 ± 0.062b
(0.060–0.212) 0.105 ± 0.040
0.112 ± 0.047
(0.067–0.240)
0.139 ± 0.054
(0.055–0.293)
0.154 ± 0.081
(0.115–0.289)
0.193 ± 0.060
(0.116–0.236)
0.173 ± 0.050
(0.110–0.239)
0.165 ± 0.044
(0.075–0.312)
0.162 ± 0.075
Pb
Table 1 Heavy metal concentrations in oysters collected from the southern coast of Korea
(0.087-0.431)
0.269 ± 0.096
(0.089–0.453)
0.215 ± 0.096
(0.094–0.354)
(0.140–0.378) 0.202 ± 0.091
0.228 ± 0.089
(0.091–0.340)
0.206 ± 0.098
(0.108–0.426)
0.222 ± 0.112
(0.089–0.333)
0.213 ± 0.087
(0.122–0.398)
0.240 ± 0.099
(0.090–0.398)
0.188 ± 0.103
(0.091–0.453)
0.224 ± 0.114
Cr
(0.069-0.225)
0.124 ± 0.043
(0.095–0.318)
0.153 ± 0.062b
(0.097–0.225)
(0.097–0.185) 0.144 ± 0.040
0.137 ± 0.032
(0.095–0.270)
0.150 ± 0.069
(0.098–0.275)
0.160 ± 0.074
(0.096–0.194)
0.140 ± 0.040
(0.101–0.313)
0.144 ± 0.067
(0.097–0.306)
0.165 ± 0.084
(0.098–0.318)
0.182 ± 0.076
Ni
(20.55-62.73)
34.45 ± 12.44
(17.23–55.68)
32.48 ± 11.10
(20.74–55.68)
(18.50–51.70) 35.35 ± 11.17
35.39 ± 9.43
(19.76–43.69)
28.05 ± 8.82
(20.41–53.73)
38.53 ± 10.72
(22.90–51.28)
40.06 ± 10.48
(18.05–54.70)
35.35 ± 13.06
(18.72–35.60)
24.32 ± 5.37
(17.23–36.03)
22.82 ± 5.86
Cu
(110.33-334.07)
180.29 ± 60.82
(90.68–274.11)
154.38 ± 46.84
(94.51–248.55)
(102.41–272.04) 146.71 ± 52.60
162.57 ± 52.01
(108.12–240.11)
159.07 ± 43.65
(90.76–231.08)
154.22 ± 45.18
(99.81–242.50)
156.29 ± 50.96
(100.09–274.11)
145.79 ± 51.25
(90.68–239.00)
151.78 ± 47.43
(95.46–240.58)
158.64 ± 45.70
Zn
Bull Environ Contam Toxicol (2015) 94:749–755 751
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752
Bull Environ Contam Toxicol (2015) 94:749–755
Table 2 Heavy metal concentrations in the seawater samples collected from the Tongyeong region in the southern coast of Korea Stations (no. of samples)
Heavy metal concentration (lg/L)a Cd
Hg
Pb
As
Cr
Cu
Zn
1 (3)
0.0019 ± 0.0003
0.0010 ± 0.0003
0.024 ± 0.009
0.303 ± 0.229
0.145 ± 0.027
0.633 ± 0.268
0.166 ± 0.013
(0.0016–0.0021)
(0.0007–0.0013)
(0.014–0.031)
(0.124–0.562)
(0.126–0.176)
(0.463–0.942)
(0.152–0.177)
0.0018 ± 0.0007
0.0018 ± 0.0010
0.025 ± 0.006
0.287 ± 0.179
0.174 ± 0.073
0.953 ± 0.188
0.266 ± 0.085
(0.0013–0.0026)
(0.0012–0.0030)
(0.018–0.031)
(0.148–0.489)
(0.100–0.246)
(0.771–1.146)
(0.170–0.332)
0.0020 ± 0.0007
0.0017 ± 0.0012
0.023 ± 0.008
0.292 ± 0.184
0.125 ± 0.025
0.603 ± 0.156
0.213 ± 0.076
(0.0013–0.0027)
(0.0007–0.0030)
(0.014–0.030)
(0.125–0.489)
(0.100–0.149)
(0.463–0.771)
(0.152–0.298)
5 (4)
0.0031 ± 0.0023 (0.0014–0.0063)
0.0021 ± 0.0014 (0.0005–0.0039)
0.044 ± 0.014 (0.026–0.059)
0.277 ± 0.205 (0.120–0.578)
0.168 ± 0.050 (0.109–0.231)
0.785 ± 0.392 (0.322–1.159)
0.269 ± 0.101 (0.145–0.378)
6 (3)
0.0014 ± 0.0002
0.0015 ± 0.0011
0.052 ± 0.026
0.384 ± 0.236
0.144 ± 0.043
0.412 ± 0.092
0.326 ± 0.247
(0.0012–0.0016)
(0.0005–0.0027)
(0.023–0.074)
(0.120–0.575)
(0.099–0.186)
(0.306–0.474)
(0.112–0.597)
0.0021 ± 0.0013b
0.0017 ± 0.0010b
0.034 ± 0.018
0.307 ± 0.182
0.152 ± 0.045
0.684 ± 0.288
0.249 ± 0.122
(0.0012–0.0063)
(0.0005–0.0039)
(0.014–0.074)
(0.120–0.578)
(0.099–0.246)
(0.306–1.159)
(0.112–0.597)
2 (3) 3 (3)
Total (16) a
Values are means ± standard deviations (range)
b
There is no significant difference (p \ 0.05)
Results and Discussion The selected metal concentrations in the oysters collected from eight fixed stations along the southern coast of Korea are shown in Table 1. The mean metal concentrations in oyster samples decreased in the order Zn (154.38 lg/g) [ Cu (32.48 lg/g) [ As (2.690 lg/g) [ Cd (0.591 lg/g) [ Cr (0.215 lg/g) [ Ni (0.153 lg/g) [ Pb (0.150 lg/g) [ Hg (0.009 lg/g. The differences of metal concentrations in oysters between Tongyeong region and Jinhae Bay and among stations were not significant. The mean concentrations of heavy metals in the oyster samples were similar to those collected from fish markets in Korea (Mok et al. 2014a). Some metals—Cd, Hg, Pb, As, and Cr—can harm humans, even in trace amounts (EOS Ecology 2012). The mean concentrations of As, which is the highest of the hazardous metals, at each oyster station ranged from 2.166 to 3.448 lg/g, with the highest found at station 3. The mean concentrations of Cd, which is the highest of the three hazardous metals (Cd, Pb, and Hg) with the regulatory limits set by Korea (KMFDS 2014), ranged from 0.267 to 0.930 lg/g. The mean Cd concentration in all oyster samples was 0.591 ± 0.186 lg/g, which is slightly less than the 0.640 lg/g for oysters reported by Sho et al. (2000), but above the 0.212 lg/g for oysters by Ham (2002) in Korea. According to Li et al. (2013), Cd concentrations in oyster (0.338 lg/g) were significantly higher (p \ 0.05) than those in both short-necked clam (0.133 lg/g) and razor clam (0.054 lg/g). Our previous results also indicate that the Cd concentrations in oyster (0.600 lg/g), which were the highest of the three hazardous
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metals, were higher than those (0.068 to 0.574 lg/g) in other bivalves, such as mussel, short-necked clam, bay scallop, comb pen shell, and ark shell (Mok et al. 2014a). All samples showed Cd concentrations within the regulatory limits (1.0–2.0 lg/g) set by the Codex Alimentarius Commission (2006) (2.0 lg/g) and other countries such as Korea (2.0 lg/g) (KMFDS 2014), Australia, New Zealand (both 2.0 lg/g) (FSANZ 2008), and the EU (1.0 lg/g) (EC 2001). The mean Hg concentrations of the samples at each station ranged from 0.007 to 0.010 lg/g, far lower than the limit (0.5 lg/g) in both Korea (KMFDS 2014) and the EU (EC 2005). The mean level (0.009 ± 0.003 lg/g) of Hg in all samples was about two- to three-fold lower than the levels for oysters reported in other Korean studies (Sho et al. 2000; Ham 2002). The mean Hg level was similar to the 0.007 lg/g for Chinese oysters (Li et al. 2013). The mean Pb level (0.150 ± 0.062 lg/g) in all samples was slightly lower than the levels (0.214 lg/g) for Korean oysters (Ham 2002) and the 0.209 lg/g for Chinese oysters (Li et al. 2013). The highest Pb concentration (0.312 lg/g) in oysters was about three- to six-fold below the limits (1.0–2.0 lg/g) set by various countries, e.g., 2.0 lg/g in Korea (KMFDS 2014), Australia, and New Zealand (FSANZ 2008), and 1.0 lg/g in the EU (EC 2001). The mean metal concentrations in seawater collected from Tongyeong region decreased, unlike those of oyster samples, in the order Cu (0.684 lg/L) [ As (0.307 lg/L) [ Zn (0.249 lg/L) [ Cr (0.152 lg/L) [ Pb (0.034 lg/L) [ Cd (0.0021 lg/L) [ Hg (0.0017 lg/L) (Table 2). The mean bioaccumulation factors of metals in all oyster
Bull Environ Contam Toxicol (2015) 94:749–755
Fig. 2 Bioaccumulation factor (a) of heavy metals in mussel, and target hazard quotients (THQs) and hazard index (HI) (b) for heavy metals via consumption of oyster in Korea. Scale bar represents one standard deviation. The bioaccumulation factor was calculated as the mean metal concentration in a gram of oyster (Table 1) divided by that in a milliliter of seawater (Table 2). THQs were represented according to the US Environmental Protection Agency (EPA) Human Health Risk Assessment approach (EPA 2013). The THQ was calculated using the equation THQ = (EF 9 ED 9 DI 9 HC)/ (RfD 9 BW 9 ET), where EF is the exposure frequency (350 days/ year); ED is the exposure duration (81 years), equivalent to the average lifetime in Korea (Statistics Korea 2013); DI is the average daily intake (0.0198 lg/kg/day) of oysters in Korea (KCDC 2011); HC is the heavy metal concentration in oysters (lg/g) shown in Table 1; RfD is the oral reference dose (lg/kg/day); BW is the average body weight (62.8 kg) of an adult in Korea (KCDC 2011); and ET is the average exposure time for non-carcinogens (ED 9 365 days/year). The RfDs of Hg, Pb, As, Cr, Ni, Cu, and Zn used the provisional tolerable daily intake shown in Table 3. RfD of Cd was set at 1.0 established by the EPA (2013). HI was calculated by summing the THQs of individual heavy metals
samples from surrounding seawater ranged from 1413- to 618,958-fold; the highest factor was found for Zn (Fig. 2a). The metals in oysters accumulated in the order Zn [ Cd [ Cu [ As [ Hg [ Pb [ Cr. The metal bioaccumulation factor in oysters was very high for Zn and Cd but relatively low for Hg, Pb, As, and Cr. We previously reported that the mean bioaccumulation factors of the same metals in the mussels collected from the southern coast of Korea ranged from 429- to 74,794-fold; the highest factor was found for Cd (Mok et al. 2014b). The metals in mussels, unlike oysters, accumulated in the order Cd [ As [ Hg [ Pb [ Zn [ Cu [ Cr; thus, the metal bioaccumulation was relatively high for Cd and As but low for Cr and Cu. The oysters accumulate 99.6. 40.2, 3.7 and 3.3-fold higher than the mussels for Cu, Zn, Cd, and Cr,
753
respectively, but the bioaccumulation factors of Hg, Pb, and As for the oysters were about four- to five-fold lower than the factors for mussels. The accumulation of heavy metals in marine organisms depends on both their uptake and elimination rates. Heavy metals are taken up through the organisms and concentrated at different levels in the body (Sivaperumal et al. 2007; Abdallah 2013). Present findings indicate that the oysters accumulate higher than the mussels for Cu, Zn, Cd, and Cr, however, lower than the mussels for Hg, Pb, and As. Therefore, it reveals that the animals accumulate different heavy metals and levels in the body from surrounding seawater. The EDIs of heavy metals represent the daily intake of heavy metals through the consumption of oysters for an adult. The EDI was compared to the PTDI proposed by the JECFA (1999, 2010a, b) and the EPA (2013). The PTDI values for Cd, Hg and Pb were established by the JECFA because of the risks of even trace concentrations of these metals to human health. As shown in Table 3, the EDI values of the hazardous metals (Cd, Hg, and Pb) for oysters were 1.2 9 10-2, 1.8 9 10-4, and 3.0 9 10-3 lg/kg/day, respectively, which account for only 0.03 %–1.41 % of the PTDI. The EDI values of the hazardous metals for oysters were higher than those (4.5 9 10-5–1.3 9 10-3 lg/kg/day) for mussels in Korea (Mok et al. 2014b). The EDIs of other metals (As, Cr, Ni, Cu, and Zn) were compared to the PTDI values based on the reference doses established by the EPA (2013). In the oysters, the EDI values of As, Cr, Ni, Cu, and Zn accounted for 17.75 %, 0.14 %, 0.02 %, 1.61 %, and 1.02 % of the PTDI, respectively. The EDI value for As was the highest of all tested metals, it is due to the relatively high As concentration (Table 1) and using the PTDI value of inorganic As (far more toxic than organic AS) for total As measured in oyster samples, including inorganic and organic AS. The THQ and HI were used to assess the potential risk to an adult of consuming heavy metals via oysters. The THQ was estimated by comparing the ingested amount of a heavy metal with a standard reference dose; the HI was the sum of the various THQs. The THQ and HI values proposed by the EPA are integrated risk indexes, and have been used widely for risk assessment of various contaminants in foods (Storelli 2008; Mok et al. 2014a). As shown in Fig. 2b, the mean THQ of the metals for oyster was low, ranging from 0.0001 to 0.1702; the highest THQ was found for As. The highest THQ of each metal in all species ranged from 0.0001 to 0.2262. The THQ for As was relatively high in all samples analyzed, but low for other metals. An HI exceeding 1.0 indicates that the contaminants are toxic and represent any hazard to human health (Abdallah 2013; Li et al. 2013). The mean and highest HI values were 0.2246 and 0.2987, respectively, well below 1.0.
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Table 3 Estimated dietary intakes (EDIs) of heavy metals via the consumption of oysters collected from the southern coast of Korea Heavy metal
EDIs (lg/kg/day)a PTDI values (lg/kg/day)
b
Cd
Hg
Pb
As
Cr
Ni
Cu
Zn
1.2 9 10-2
1.8 9 10-4
3.0 9 10-3
5.3 9 10-2
4.3 9 10-3
3.0 9 10-3
6.4 9 10-1
3.1 9 100
0.83
0.57
3.57
0.3
3.0
20
40
300
a The EDI value for an adult was calculated using the equation EDI = (HC 9 DI)/BW, where HC is the mean heavy metal concentration in oysters shown in Table 1, DI and BW are the average daily intake (0.0198 lg/kg/day) of oysters and the average body weight (62.8 kg) of an adult human in Korea (KCDC 2011) b
The provisional tolerable daily intake (PTDI) values of Hg, Pb, and Cd were based on the provisional tolerable weekly intake (PTWI) data for Hg and Pb, and provisional tolerable monthly intake data for Cd from the Joint FAO/WHO Expert Committee on Food Additives (JECFA 1999, 2010a, b), in which the PTWI value of inorganic Hg was used for total Hg. The PTDI values of other metals, such as As (assuming that total As is inorganic As), Cr (assuming that total Cr is Cr[VI]), Ni (assuming that all Ni is Ni soluble salts), Cu, and Zn (assuming that all Zn is Zn and compounds), were based on the oral reference doses established by the U.S. Environmental Protection Agency (2013)
This is the first report of concentrations and risk assessment of heavy metals in oysters in the designated shellfish growing areas for export in Korea. The oysters, which are produced from the designated shellfish growing areas, are consumed domestically or exported mainly to the United States (US), Japan, and the EU (Mok et al. 2014a). The heavy metal concentrations in the oysters are considered to be important information both in Korea and in importing countries. Therefore, a monitoring program of the metals for the oysters in the designated shellfish growing areas should be operated regularly at the appropriate frequency. In conclusion, the Cd concentration was the highest of the three hazardous metals (Cd, Pb, and Hg); however, the concentrations of the harmful metals in all samples were within the regulatory limits set by Korea and other countries. The metal bioaccumulation ratio in oysters was relatively high for Zn and Cd but low for Hg, Pb, As, and Cr. The EDIs of each metal tested for oysters ranged from 0.02 % to 17.75 % of the PTDI values; the highest value was measured for As. The HI for all oysters was far\1.0, which indicates that the intake of metals via consumption of this animal does not represent an appreciable hazard to humans. Acknowledgments This work was supported by a grant from the National Fisheries Research and Development Institute of Korea (RP2015-FS-001).
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