| "Mussel Watch" is a very applicable approach to monitor the spatial and temporal changes in heavy matals using marine bivalve mussels as bio-indictor species, and has been applied to many marine or coast monitoring programs worldwide. However, few studies are available on corresponding pollution monitoring with freshwater bivalves so far. In the prersent study, common freshwater bivalve mussels were used as the sentinel organisms and investigated for the first time on the residual content and distribution of heavy metal and metalloid elements (e.g., Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Ag, Cd, Pb, Hg) in Swan mussels Anodonta woodiana collected from separate water areas (e.g., Huzhou, Dapu, Xueyan, Manshan, Wulihu) around the Taihu Lake, and triangle shell mussels Hyriopsis cumingii from an aquicultural ponds in Gongan Country and in the Tongzhuanghe River, a natural waterbody, in the Three-Gorges Reservoir Region, respectively, for assessment and evaluation of the contamination status of the heavy metals and metalloids. The aim of this study was to further evaluate the feasibility to establish the "Freshwater Mussel Watch" system for inland fishery environments, and at the same time, to establish an innovative "standardized freshwater mussel" population by artificial propagation techniques, which will be transplanted to the typical fishery waters.The main results from the study are as follows:1. Bioaccumulation of heavy metal and metalloid elements in A. woodiana from the Taihu Lake of China:Data are presented for13trace metals (Cr, Mn,Fe, Co, Ni, Cu, Zn, As, Se, Mo, Ag, Cd, and Pb) in38bivalve mussels A. woodiana from four separate sites (Huzhou, Dapu, Sansandao, and Manshan) around the Taihu Lake of China. All elemental concentrations generally ranked in decreasing order, Mn>Fe>Zn>As≈Cu≈Cd≈Se>Pb>Mo≈Ag, except that Cr, Co,and Ni were not detected. A. woodiana was able to bioaccumulate essential Mn and toxic Cd to the extremely high level of19240and53mg/kg dry weight, respectively. Geographical differences in the concentrations of trace elements were usually significant between sampling sites except for As and Pb, and the mussels from Sanshandao site had mostly accumulated or were contaminated with essential and toxic elements.The residue level of Cd in A. woodiana from the Sanshandao and Manshan sites appeared to be even higher than those of the essential elements Cu and Se, and exceeded the corresponding maximum residue limits of China.2. Residues of mercury in the bivalve mussels A. woodiana from the Wulihu area of the Taihu Lake of China:Residues of mercury (Hg) in the soft tissues of eighteen A. woodiana and sediment samples collected from Wulihu area of the Taihu(the most polluted area in the lake) were analyzed by a NIC Automatic Mercury Analyzer/MA-2000. The residual Hg levels of the mussels were detected and ranged0.000～0.011mg·kg-1dry weight with an average of0.005mg·kg-1dry weight. The Hg detection rate for the mussels was83%.Those of the sediment samples ranged0.063～0.227mg·kg-1dry weight with an average of0.135mg·kg-1dry weight. Hg levels of the mussels and sediments were significantly lower than the corresponding national standards for limit of Hg in foods (GB2762-1994and NY5073-2001), and sludges (GB4284-1984) or soils (GB15618-1995), respectively. Additionally, the Hg index of geoaccumulation (Igeo) in the sediments was only-1.96. The residual Hg situations of both mussels and sediments suggested the same tendency that Hg contamination now in the Wulihu area is very low. This phenomenon should be caused by recent ecological silt dredging in whole Wulihu water area. Significant geographic difference was only documented in the sediment Hg levels.3. Mercury residues in tissues of bivalve mussels A. woodiana from Taihu Lake of China:Residues of Hg were analyzed by an NIC Automatic Mercury Analyzer MA-2000in soft tissues of A. a woodiana collected from Taihu Lake at Sanshandao of Wuxi, Xueyan of Changzhou, Dapu of Yixing, Huzhou of Zhejiang and Huazhuang of Wuxi during the years of2003-04. Mercury residues were evidently found in tissues of all swan mussels. Statistically significant diference existed among various sampling sites. Detected residual Hg levels in the mussel tissues were in the range0.002to0.293mg/kg with an average of0.093mg/kg by dry weight, and were consistent with that in the sediment of respective nearby waters. The research result has further proved that it is adaptable to monitor and assess the contamination status of heavy metal Hg in freshwater by means of A. woodiana as a bio-indicator. The mean levels of residual mercury in the swan mussel tissues were significantly lower than the limits specified in corresponding national food standard (GB2762-1994) and agricultural sector standard (NY5073-2001). 4. Difference in element bioaccumulation between farmed and field-transplanted Hyriopsis cumingii:Comparison was conducted in bioaccumulation of trace elements between the mussels H. cumingii reared in aquicultural ponds in Gongan Country (APG) and in the Tongzhuanghe River, a natural waterbody, in the Three Gorges Reservoir Region (NWTR), Hubei Province of China. The mussels in the latter were relocated from the former. After one year of husbandry, the mussels were sampled for analysis of K, Mg, Ca, Fe, Zn, Mn, Cu, As, Al, Cr,Ni, Se, Mo, Ag, Cd, Ti and Pb in their soft tissues, using an Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Although the17elements in these two groups of mussels followed a similar order in concentration, reflecting characteristics of bioaccumulation of the elements by the mussels, those in NWTR were higher than in APG in concentration of9elements (Ca,Mg,Cu,Mn,Zn,Cr,As,Cd and Pb), suggesting that living habitats may have an important impact on bioaccumulation in H. cumingii. The mussels in the natural waterbody were exposed to a higher mean load of the elements in their soft tissues than those in the ponds, demonstrating the mussels’significant capacity of sequestrating those pollutant elements and purifying water bodies.As a first attempt to use the "Freshwater Mussel Watch" approach to monitor the elemental pollution, the present study provided the most recent information on bioaccumulation or contamination of heavy metal and metalloid elements in Taihu Lake and, further, suggested that A. woodiana can be used as a suitable bioindicator for inland water environmental monitoring. At the same time, the findings by the farmed and field-transplanted H. cumingii of the study can serve as scientific basis for rearing the aforementioned "standardized freshwater mussel" to monitor heavy metals and metalloids in natural waterbodies and purify the environment therein. |
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