| The paper takes several familiar macrobenthos along Changjiang coastal flat as our research object. We mainly study the heavy metal's concentration and space-time distribution of Cu, Zn, Pb, Cr, Ni in macrobenthos. The mechanism of macrobenthos assimilating heavy metals and the effect of biologic and abiological factors to the enrichment content of heavy metals are discussed. At the basis of synthesizing correlative fields we evaluate the entironment quality in Changjing coastal flat. Combining with acute toxicity test, we estimate the maximal environment capability of organism in Changjiang coastal flat. Accordingly we can offer foundation for establishing environmental permit standard. The primary results as follows.1 The heavy metals' enrichment content of benthos shows definite seasonal difference. In summer, the enrichment content of Bullacta exarata, Corbicula fluminea, Sesarma dehaani and Ilyoplax deschampsi is correspondingly higher than spring and autumn.2 The enrichment content of benthos to heavy metals exist regional difference. The content of the same benthos is diverse in different site. Using Metal Pollution Index to appraise the heavy metals' holistic circs , we find the heavy metals' enrichment content of Corbicula fluminea in LH and LC is higher than XP, GL and CD. At the same time we also appraise the holistic circs of Sesarma dehaani. We find that the heavy metals' enrichment content in DGG, BL and LG is the most highest and corresponding content in QY is the lowest.3 The cumulation of mollusk to heavy metals has segmental difference. In our experiment it shows that most heavy metals in mollusk concentrate on flesh, only a few in shell.4 Benthos' size and cumulation faculty can affect the accumulation. In our experiment it shows that the bigger Sesarma dehaani can cumulate much Cu, Zn, Pb, Cr than the little ones in CD and QL which have low Metal Pollution Index. While in the place of DGG which has high Metal Pollution Index, it is the little ones that can cumulate much heavy metals. Different kinds of benthos have dissimilar cumulation faculty to heavy metals, such as Bullacta exarata is the strongest one for cumulating Cu, Corbicula fluminea is for cumulating Zn and the two kinds of benthos also have strong cumulation faculty for Pb and Cr.5 Some abiological factors such as water temperature, salinity, surface sediment granularity and organic matter content, heavy metals content in sediment and suspended particle, mutual action of heavy metals etc have definite effects on heavy metals' cumulation content of benthos. It shows that higher temperature conduces to assimilating Cu, Zn, Cr and Ni by Bullacta exarata, Corbicula fluminea, Sesarmadehaani and Ilyoplax deschampsi. In autumn the Cu and Zn content in Corbicula fluminea shows positive correlation with salinity and the Pb content in Sesarma dehaani shows negative correlation with salinity. In spring the Zn content in Sesarma dehaani shows negative correlation with salinity. The Cu content in Corbicula fluminea shows marked positive correlation with surface sediment granularity. It means that thick granularity can conduce to cumulating Cu by Corbicula fluminea. The Zn and Pb content in Corbicula fluminea shows definite correlation with organic matter content in sediment in that Zn content shows definite correlation and Pb shows negative correlation. The Cu and Zn content in Corbicula fluminea is higher than that of corresponding sediment and suspended particle. It indicates that Corbicula fluminea adapts to acting as the Cu and Zn referent in Changjiang coastal flat. Sesarma dehaani adapts to acting as the Cu referent. The heavy metals in benthos have mutual action with each other. It is manifested that Cu-Cr, Cu-Ni, Zn-Cr, Zn-Ni, Cr-Ni shows positive correlation and Zn-Pb shows negative correlation for Corbicula fluminea and Zn-Ni and Pb-Cr shows positive correlation for Sesarma dehaani.6 By 24h acute toxicity test for Bullacta exarata we can calculate the follows. Firstly, LC50for Cu is 0.25g/L and LDioo is 0.41g/L...
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