Studies on the Variation of Heavy Metal Concentrations in Bivalve

• Main Authors: Wen-Der Chen, 陳文德
• Other Authors: none
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/64310362968940233507

碩士 === 大仁科技大學 === 環境管理研究所 === 95 === Bivalves are widely used as bioindicators of heavy metal pollution in coastal areas because they are known to concentrate metal elements, providing a time-integrated indication of environmental contamination. Ta-Peng Bay Lagoon is a shallow, productive, coastal lagoon, located at the south-southwestern coast of Taiwan. It has plentiful biological resources such as fishes, crabs and bivalves. The lagoon receives sewage discharged from near fisheries, domestic and agricultural wastewater. Some heavy metals had contaminated the water quality of lagoon and were concentrated in the soft tissues of bivalve mollusks. After green oyster incident occurred in 1986, the potential risk of human consumption has been brought up to public attention. The aim of this study was to go further into the basic knowledge needed before using clam Katelysia hiantina as bioindicator, on one hand by analyzing possible seasonal variations in the concentrations of different metals in the soft tissues of bivalve mollusks, and on the other by establishing the background levels of the metals in these bivalve mollusks and appreciated for human consumption in the study area. The results reported here provide valuable information on heavy metal pollution in mariculture zone, Ta-Peng Bay Lagoon and importer. We also studied the correlations among metal contents in different species and season series. In this article, four easily obtained and abundant bivalve mollusks, including Anadara antiquate, Katelysia hiantina, Perna viridis and Anomalocardia squamosa were collected from Ta-Peng Bay Lagoon. Furthermore, the species Sanguinolaria diphos from mariculture zone and the species Paphia undulata from importer were also collected and analyzed in this study. All samples were analysed for six elements by AAS, and statistical analyses were performed with SPSS. The correlation analysis and ANOVA were used to extract information from the chemical analysis in order to find the relationships among these heavy metals. Tukey HSD Procedure was used to identify specific differences among the studied groups. The results show that Cd presents the lowest mean concentration in six species and the concentrations of Cu and Zn were considerably higher than other elements in the soft tissue of bivalves, Zn especially. In contrast to previous research, it is common to find higher concentrations of Zn and Cu in the soft tissue of bivalves. Furthermore, we found that viscera surpass muscles much in the concentrations of metal elements. It means that the viscrea of mussels had considerable high ability to accumulate heavy metals. Seasonal variation in the different metals followed a similar pattern in bivalves and appeared to be caused by dilution effect in the period of maximal growth rate; but concentrated in the periods of slow growth rate. Compare with Usero (2005) that spatial differences in the metal concentrations indicated by a low MPI (3.4~3.8) of unpolluted area and a high value (6.8~7.8) of polluted area. It shows that Ta-Peng Bay Lagoon is not contaminated by heavy metals. There is a significant correlation for concentration of Cd in organism. This can be explained that different organisms have different levels of Cd concentration. There is a significant negative relationship (p＜0.01) between two metal elements (Pb and Ni) and season; negative relationship (p＜0.05) between Cr and season. This showed that concentrations of Pb, Ni and Cr were decreased with season series. We found that all organisms had mean values below the WHO’s legal limits, but deserved to be mentioned was that near 33.3 ％ specimens of A. antiquate in Cd concentration in winter (12/2005) were over WHO’s legal limit (0.5 μg/g), get up to 0.79 μg/g. In regard to this result more extensive investigation should be done to confirm this result in further. In this study, indicator organisms should be good accumulators of heavy metals and their tissue concentrations must reflect metal contaminations. The K. hiantina would be playing the role for its sensitive variation in Cd concentration. Even then, a continuous examination of metal concentrations of venerid K. hiantina would strengthen this proposition in future.