| Ningbo City is located in the southeast coastal areas of China with a total lengh of 1594.4 km, including continental coastline about 835.80 km and island coastline about 758.60 km. Ningbo's gulf coastline is from the Hangzhou Bay to the Sanmen Bay, which consists of eight counties including Yuyao, Cixi, Zhenhai, Yinzhou, Beilun, Fenghua, Ninghai and Xiangshan. In the past twenty years,with the rapid economic development of Changjiang Delta area, the coastal environment was increasingly influenced by land-based pollutants, mariculture and marine transportation, etc. The marine environmental quality in this area is worsening over years, especially the increasing total drainage pollutants of heavy metal. Heavy metal is a nondegradable pollutant, which could cause teratogenic, carcinogenic, and lethal danger to marine life. Furthermore, it can be accumulated in marine life, and be passed along the food chain to further enlarge, and even endanger human health. Since 1950s, heavy metal contamination events happened in Japan and Europe successively, which caused scientists and government leaders all over the world to put great attention. Therefore, it is great important to prevent seafood from the contaminations of heavy metals.In this paper, the distribution of heavy metal residues were identified through the analysis of heavy metal residues in economic seashell collected from coastal areas of Ningbo City. This study also discussed the safety standard of economic seashell referred to the domestic and foreign standards and the actual situation of the ecological environment in Ningbo City to preliminarily classified the food safety standard of seashell in this area.In November 2007 and May 2008, 42 economic seashell samples (such as Ostreidae sp, Sinonovacula constricta, Ratitapes philippinarun, and Scapharca subcrenata) were colleted from 19 stations in Ningbo sea area with fixed-point methods. The heavy metal content of Pb, Cd, Cr, Cu, Zn, Hg, and As.were detected.The results of six sea areas showed that Fenghua was the cleanest sea area, then Zhenhai, Xiangshan, Beilun, Cixi, finally Beilun. The residues of Pb and Cd content in Sinonovacula constricta from Cixi was much higher than others, while Cu and Zn in Oyster from Ninghai was the highest, and Sinonovacula constricta from Xiangshan and Ninghai was higher in Cr content than others. Zn, Cu, Pb and Cr were mainly detected in Oyster, while Cd detected in Oyster and Scapharca subcrenata. The concentration of Hg was almost at the same lever in all the tested seashell and As in Ratitapes philippinarun was lower. The residues of Cu, Zn and Hg in Oyster from Ningbo coastal area were less than others. The concentration of Cd in Scapharca subcrenata was lower than the coastal areas of the Yellow Sea, the Bohai Bay as well as the northern part of the Yangtse Rive.The concentration of Cd in Oyster was lower than the coastal areas of Guangdong and so on, and was close to Rushan Bay and American coastal areas. Furthermore, the concentration of Cr, As and Pb was at the same level as overseas and domestic areas. In a word, the residue of heavy metal in economical shellfish from Ningbo sea areas was the same as overseas and domestic areas. So it can be concluded that Ningbo sea areas were not polluted seriously. The concentrations of heavy metal in economical shellfish showed that the shellfish was healthy food, and only 7.14% of Ostreidae sp.and Sinonovacula constricta was risky shellfish.Ocean environment is one of the most important part in the global life supporting system, and its environmental quality and ecology status is the premise of persistent utilization and resource exploitation. The biological index is important in oceanic environment measurement and quality estimation. Bothos(Bivalves) can show the pollution degree of sediment and water quality for their little activity and region representation, which suggested they play a significant role in ocean pollution as biological index. |
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