Heavy Metal Monitoring Using Bivalved Shellfish from Zhejiang Coastal Waters, East China Sea

Transcription

1 Environ Monit Assess (2007) 129: DOI /s Heavy Metal Monitoring Using Bivalved Shellfish from Zhejiang Coastal Waters, East China Sea H. Huang & J. Y. Wu & J. H. Wu Received: 28 October 2005 / Accepted: 28 June 2006 / Published online: 21 October 2006 # Springer Science + Business Media B.V Abstract The interest of culturing bivalved shellfish (including mussels, clams, oysters etc.), has increased in recent years, but the consumption has been hampered both by high levels of heavy metals and toxic algae. The levels of heavy metals (Hg, Cd, Pb, Zn, Cu and As) were determined in soft tissues of different shellfish from Zhejiang coastal waters, East China Sea. The average concentrations of the heavy metals analyzed exhibited the following decreasing order: Zn > Cu > As > Cd > Pb > Hg. Comparison of heavy metals concentrations among species indicated that Bivalves clearly have significant potential as useful bioindicators; however, the results indicated that no one species is universally suitable, as is true of any organism used in these studies. The distribution of the metals was also investigated along the Zhejiang coast, which the results showed the mean concentration of Hg and Cd detected did not vary greatly and presented a similar spatial pattern at different sampling stations, the concentrations of Zn and Pb were highly variable at different sampling sites. The amounts of heavy metals in soft tissue of shellfish were also compared with those from the related species from other seas in China and world marine waters. The results suggested that the coastal area might be considered relatively unpolluted with heavy metals and the concentrations of metals in shellfish also below the seafood safety limits for human consumption. H. Huang (*) : J. H. Wu College of Marine Science & Technology, Shanghai Fisheries University, Shanghai , China hhuang@shfu.edu.cn H. Huang School of Environmental Science & Technology, Tongji University, Shanghai , China J. Y. Wu East China Sea Environment Monitoring Center, State Oceanic Administration, Shanghai , China J. Y. Wu Department of Environment, University of Massachusetts, Amherst, MA 01003, USA Keywords heavy metals. bivalved shellfish. bioindicator. maximum allowable concentration. Zhejiang coastal waters. East China Sea 1 Introduction There is considerable concern about the levels of heavy metals in ecosystems and their component organisms, particularly species at higher trophic levels. Concern is often high for aquatic systems that can accumulate contaminants rapidly through industrial and agricultural runoff because contaminants move quickly through aquatic systems. The concentrations of potentially toxic substances in sea water are extremely low

2 316 Environ Monit Assess (2007) 129: Table I Sampling sites and the number of species in each sampling site Site Site identification Shenjiamen County Xiangshan Port Shizhou City Taizhou Bay Leqing Bay Wenzhou Bay Number of species and vary considerably in space and time so that their determination is difficult and the obtained data are of doubtful practical interest (Phillips, 1977). However, bivalves are filter-feeders and thus obtain heavy elements not only from food and water but also from ingestion of inorganic particulate materials. Shellfish, especially bivalve mollusks, which are sedimentary, widespread and have a long life span, have been well established as bioindicators for monitoring the concentration of heavy metals in many areas of the world (Farrington, Goldberg, Risebrough, Martin, & Bowen, 1983; Giusti, 1999). The measurement of metal concentrations in biomonitors has been recognized as highly relevant in ecotoxicological terms because of the reflection of bioavailability in the ecosystem (Phillips & Rainbow, 1992). The hazardous impacts of such toxic and carcinogenic metals have driven the toxicologists_ attention to measure their concentrations in different foodstuffs. Concentrations of heavy metals in shellfish can also be a reasonable measurement for public health standards from animals_ health point of view (Albering, Moonen, Hoogeweff, & Kleinjans, 1999). In recent decades, the rapidly developing industrial and agricultural activities, municipal development have caused serious pollution problems in Zhejiang Province. Aquaculture is the most important industry in the littoral of Zhejiang Province. The seafood output of Zhejiang coastal waters ranks the top in China. In this article we present the levels of Mercury (Hg), Cadmium (Cd), Lead (Pb), Zinc (Zn), Copper (Cu) and Arsenic (As) in tissue of the different shellfish (Rititapes philippinarum, Sinonovacula constricta, Cyclina sinensis, Moerella iridescens, Tegillarca granaca) from Zhejiang coastal waters, East China Sea. The present study was also conducted to investigate whether the bivalve mollusks in Zhejiang coastal waters, East China Sea were contaminated with the heavy metals, thereby evaluating whether the shellfishes could be used for human consumption. 2 Materials and Methods Total 15 bivalve shellfish samples were collected approximately 50 cm below sea level during low tide Figure 1 Locations of the six sampling sites of Zhejiang coastal waters in East China Sea.

3 Environ Monit Assess (2007) 129: Table II Results of analysis of standard reference materials (2g/g dry weight) Metals Hg Zn Cu Cd Pb As Certified values T T T T T T 0.79 Observed values T T T T T T 0.43 Recovery (%) in August 2002 from six sites along the coastal area of Zhejiang Province, China. The sampling sites and sampling species were illustrated in Table I and Figure 1. The bivalves selected were dominant, commercially important species consumed by people living in the study area and environs. Sufficiently large numbers of individuals were collected at each site to provide good representatives of the species. The collected bivalve mollusks samples were cleaned with deionised water and stored in plastic bags at j20-c until analysis. Upon analysis, the bivalves were allowed to thaw at room temperature and soft parts were carefully dissected after shucked with stainless steel instruments. Soft tissues were dissected, cleaned, rinsed, dried with paper and freeze dried with a lyophilizer at j80-c for 48 h after measuring the fresh weight. Fresh soft tissues of each individual were also measured to the nearest 0.1 mg. For each sampling site, a composite sample for each species was prepared by homogenizing the selected in a mixer for metal analysis. Metal analysis was performed following the method described in Belinsky, Kuhnlein, Yeboah, Pennt, and Chan (1996). Approximately 0.5 g the freeze-dried soft tissue homogenate was weighed into acid-washed 50 ml boiling tubes (two replicates per sample), and 8 ml of 70% nitric acid (Fisher Scientific, Trace Metal Grade) were added to each tube. Tubes were covered with glass condensers and the samples were predigested at room temperature overnight. Digestion was continued for 8 h at 120-C. Digests were cooled to room temperature and made to 25 ml with distilled and deionised water. The final concentration of nitric acid in the digest was about 22% w/v. Total concentrations of heavy metals in acid digests were determined by atomic absorption spectrophotometry (AAS). Zn was determined by AAS on the flame mode; Cu, Cd, Pb and As were determined by graphite-furnace AAS; Hg was analyzed by the cold Table III Trace element concentrations (range and overall means T SD) in whole soft parts of different shellfish species from six stations along Zhejiang coastline, East China Sea (2g/g, wet wt), August 2002 Species Site Hg Zn Cu Cd Pb As Rititapes philippinarum Sinonovacula constricta Cyclina sinensis Moerella iridescens Tegillarca granosa Range Average TS.D

4 318 Environ Monit Assess (2007) 129: Figure 2 Comparison of heavy metal (Hg * 100, Cd * 10, Cu, As * 10, Zn and Pb * 100) concentration (mg/g) between species from Zhejiang coastal waters, East China Sea Rititapes philippinarun Sinonovacula constricta Cyclina sinensis Moerella iridescens Tegillarca ggranosa Cd*10 Hg*100 Pb*100 Zn As*10 Cu vapor generation AAS (10% w/v stannous chloride in 20% v/v HCl is used as reducing reagent). Although we recognize As is metalloid, it was referred as Bmetal^ throughout the text. The analytical methodologies used in this study were confirmed for accuracy by a certified standard reference material (Standard oyster Tissue 1566a) obtained from the U.S. Department of Commerce, Figure 3 Trend of distribution of heavy metal (Hg * 100, Zn, Cu, Cd * 10, Pb * 100 and As * 10) concentration (mg/g) in bivalved shellfish from Zhejiang coastal waters, East China Sea. 15 Hg*100 Zn Cu Cd*10 Pb*100 As*10 Concentration ( µg/g, wet wt) Sampling Sites Number

5 Environ Monit Assess (2007) 129: Table IV Comparison of heavy metals concentrations (2g/g, wet wt) in soft tissue of shellfish from Zhejiang coastal waters, other seas in China and world marine waters Location Hg Zn Cu Cd Pb As Source Zhejiang Coast, China This study Bohai Sea and Huanghai He, 1996 Sea, China Hong Kong Coast Blackmore, 1998 Bergen Harbor, Norway Andersen, Maage, and Johannessen, 1996 Mediterranean Sea, Egypt El-Sikaily et al., 2004 Red Sea, Egypt El-Sikaily et al., 2004 National Bureau of Standards, Gaithersburg, Maryland). Two sample blanks were analyzed together with each sample batch. Concentrations of metals in blanks were below detection limits in all analyses. Each standard and sample was measured in duplicate and the sample was re-analyzed if the relative standard deviation (SD) of the two measurements was higher than 10%. These values were evaluated by comparing the results obtained for the reference material, Oyster 1566a, with its certified values (Table II). Results of metal concentrations always fell within 10% SD of certified values; recoveries of spiked samples were 90% or better, which confirmed the validity of the method used. 3 Results and Discussion Tissue metal concentration (2g/g wet weight) of five species of shellfish collected from Zhejiang coastal waters are presented in Table III. Figure 2 illustrated the average metal concentration in different mollusks from all sampling stations. The pattern of heavy metals occurrence in soft tissues of different shellfish samples in order of decreasing contents, were Zn > Cu > As > Cd > Pb > Hg. The Zn concentration was the dominant metal among all the studied metals. Accumulation of Hg in collected bivalve mollusks samples was ranged from to mg/g with average value T g/g wet weight. No significant difference was record between the five species. The average concentration of Hg was the highest in specimens of Rititapes philippinarum, reached g/g. Accumulation of Cd in collected mollusks samples showed concentrations ranged from to g/g with average value 0.12 T g/g wet weight. The concentration of Cd was significantly different species. Accumulation of Cu and As in collected mollusks samples were ranged from 1.31 to g/g with average value 3.06 T g/g, and to g/g with average value T g/g wet weight, respectively. Zn contents recorded in the collected mollusks samples varied between 3.34 and g/g with average value 8.98 T g/g wet weight. The concentration of Pb as determined in the mollusks were varied between and g/g with average value T g/g wet weight. From Figure 2, Rititapes philippinarum and Sinonovacula constricta showed an ability to concentrate Hg to some degree in soft edible tissues. Tegillarca granosa and Scapharca subcrenata had greater aptitude for bioaccumulation of Cd. Mytilus edulis, Sinonovacula constricta and Cyclina sinensis had greater ability for accumulation of Pb. Mytilus edulis and Sinonovacula constricta manifested the most Table V Maximum allowable concentration (MAC) of heavy metals (mg/g, wet wt) in seafood bivalve shellfish (Zhang, Jin, & Zhou, 2004) Country or area Hg As Cd Pb CAC standard China Australia 0.5, , Canada Hong Kong, China USA 1.0 New Zealand 0.5 Japan 0.4 not available in seafood safety standard.

6 320 Environ Monit Assess (2007) 129: bioaccumulation capacity of Zn; Sinonovacula constricta and Mytilus edulis had stronger ability for bioaccumulation of Cu; Sinonovacula constricta manifested the most bioaccumulation capacity of As. These species had the potential of being used as biomonitors of heavy metals in coastal waters. The use of mollusks as bioindicators turned out to be very valuable for the study of a coastal area with fairly significant basal contamination levels. However, no one species is universally suitable, as is true of any organism used in these studies. It is recommended to use several species representing different trophic levels in combination with chemical and hydrologic measurements when an effective biomonitoring approach is designed. It is essential that any biomonitoring plan be specific to the needs of the particular site so that all avenues of potential concern can be reliably observed. A trend was obtained in the assessment of metals distribution of bivalve mollusks in all six studied sites (Figure 3). Trend showed the mean concentration of Hg and Cd detected in the soft tissues did not vary greatly and presented a similar spatial pattern at different sampling stations, reached the highest level at Site 2 (Xiangshan Port). Concentration of Cu was a bit higher at Site 4 (Taizhou Bay), which was twice as Site 6 (Wenzhou Bay). The amount of As was not remarkably different, slightly higher in Site 1 (Shenjiamen County). The concentrations of Zn and Pb were highly variable at different sampling sites. The concentration of Zn reached 14.2 mg/g at site 2 (Xiangshan Port) and that was significantly higher than in site 1 (Shenjiamen County, 6.46 mg/g). The concentration of Pb have accumulated mg/g at Site 5 (Leqing Bay), much higher than 5.1 mg/g at Site 2 (Xiangshan Port). The amounts of heavy metals in soft tissue of shellfish were compared with those from the related species from other seas in China and world marine waters. From Table IV, except for Cu level slightly higher than from Bergen Harbor, the concentrations of heavy metal in soft tissue of shellfish from Zhejiang coast were relatively low, therefore the coastal waters was still clean. Concentrations of Hg, Cd, Pb and As reported in our study appeared to be below the limits for human consumption in seafood bivalve shellfish, but care must be taken considering the most coastal people regularly consume large quantities of seafood (Table V). A systematic and in-depth research still needs to be conducted to further understand the distributions and accumulation characteristics of potentially toxic trace metal concentrations in different marine organisms from this region. Acknowledgments This study was supported by Shanghai Education Committee Scientific Research Project (05-232) and the Opening Fund of the Key Laboratory of Yangtze Aquatic Environment (Tongji University) Ministry of Education (YRWEF06005). We thank the numerous technicians from East China Sea Environment Monitoring Center, State Oceanic Administration for their participation in field sampling campaign. References Albering, H. J., Moonen, E. J. C., Hoogeweff, J. A., & Kleinjans, J. C. S. (1999). Human health risk assessment in relation to environmental pollution of two artificial freshwater lakes in The Netherlands. Environmental Health Perspectives, 107, Andersen, V., Maage, A., & Johannessen, J. (1996). Heavy metals in Blue Mussels (Mytilus edulis) in the Bergen Harbor Area, western Norway. Bulletin of Environmental Contamination and Toxicology, 57, Belinsky, D. L., Kuhnlein, H. V., Yeboah, F., Pennt, A. F., & Chan, H. M. (1996). Composition of fish consumed by the James Bay Cree. 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