| Heavy metal bioconcentration and the edible safety analysis of farmed Crassostrea rivularis were carried out in four culture zones of Zhanjiang Bay in January (winter), April (spring), July (summer) and November (autumn), 2010. Four culture zones were Guandu culture zone (S1), Nanyou culture zone (S2), Techeng Island culture zone (S3) and Dongtoushan Island culture zone (S4), respectively. The main environmental factors (pH, DO, COD, temperature, salinity, nutrients, heavy metals in seawater and sediments) of those culture zones were investigated to evaluate the Environmental Quality of different culture areas. Bioconcentration capacities of heavy metals in different tissues were also studied from 0-year-old to 3-year-old Crassostrea rivularis. Combined with survey results of the major environmental factors, heavy metal bioconcentration rules of Crassostrea rivularis in shellfish culture areas were discussed, and the edible safety of Crassostrea rivularis in Zhanjiang Bay was evaluated.Main contents and conclusions were shown as below:(1) Throughout the year, the highest water temperature was Guandu culture zone, the annual average is 26.4℃. The lowest was in Dongtoushan island culture zone, the annual average was 24.8℃; The lowest content of salinity was Guandu culture zone, the annual average was 12.7; The value of pH was 6.02 in winter in Guandu culture zone, it failed to meet water quality standard for fisheries, and other culture zones were in line with standard value of the limit of pH; The content of dissolved oxygen in Guandu culture zones were less than 5mg/L,which failed to meet water quality standard for culture, the annual average is 4.45mg/L; COD in Guandu culture zone was between three to four categories of seawater quality standard, the other three culture areas almost met a class of sewater quality standards; DIN of the culture zones were relatively high. The annual average range of inorganic nitrogen was 0.57 mg/L~1.62 mg/L, the annual average range of DIP was 0.066 mg/L~0.101 mg/L. Four culture zones belonged toⅥP phosphorus limit the potential of eutrophication. (2) The concentration of As,Pb,Cd,Cr and Zn in seawater of culture zones met standards of mariculture, the annual average of Cu in the seawater were 19.36μg/L, 15.19μg/L,17.97μg/L,16.13μg/L, respectively. Except in spring, the contents of Cu were over the limit of standards of mariculture in other seasons; There was no obvious rule within heavy metal content of sediments collected from culture zones. Results showed content of Cr in Techeng island culture zone met the second class sediment quality standard, while the content of other elements met the first class. The heavy metal pollution degree and potential ecological risk were assessed by the method of potential ecological risk index presented by Lars Hakanson.Results showed that this area had no potential ecological risk assessment.(3) The concentration of As, Pb, Cu, Zn, Cd and Cr in Crassostrea rivularis were the lowest in Dongtoushan island cultured zone, the annual average of heavy metals were 0.94μg/g, 0.21μg/g, 82μg/g, 583μg/g , 0.86μg/g, 0.78μg/g, respectively. The highest was in Guandu culture zone, the annual average of heavy metals were 5.44μg/g, 1.51μg/g, 195μg/g, 1169μg/g, 4.61μg/g, 2.23μg/g, respectively. Distribution rules of Cu, Pb and As were S1>S2>S3>S4 ; While distribution rules of Zn, Cd and Cr were S1>S3>S2>S4. The order of the content of As, Pb and Cr in different tissues: As: visceral mass>gills>pallium>adductor muscle, Pb: pallium>gills>visceral mass>adductor muscle, Cr: gills>visceral mass>pallium>adductor muscle, while distribution rules of Cd, Zn,Cu were the same, which were as follows: gills>pallium>visceral mass >adductor muscle.(4) The survey results of heavy metal content in four tissues of Crassostrea rivularis were as follows: The capacity of bioconcentration of six elements were the same in pallium, visceral mass and adductor muscle, the capacity of bioconcentration from high to low is Zn>Cu> As>Cd>Cr>Pb; while gills, Zn>Cu>Cd>As>Cr>Pb. Heavy metals content of Crassostrea rivularis varied with their ages. The concentration of As, Pb and Cu increased with ages, while those of Zn, Cd and Cr decreased with ages.(5) Heavy metal enrichment of Crassostrea rivularis from seawater was much higher than the amount of enrichment from sediments. Heavy metals of tissues associated with the relationship between sediments was not significant. This may be related to follows: Crassostrea rivularis were hanging culture Raft on the scaffolding. Crassostrea rivularis are filter feeders, suspended in the water feed mainly on phytoplankton, detritus-based, including the need to constantly filter set high concentrations of heavy metals in suspended solids, phytoplankton and other organic debris. And they associated with heavy metals in sea water and physical and chemical factors such as salinity, temperature, DO, had significant correlations, but also indirectly affected by the impact of nutrients in seawater. This also may be related to follows: The content increase of some heavy metals, including toxic metals As and essential element Cu, Zn, had effected on metabolism of Crassostrea rivularis. It made metabolic activity, which were respiration, excretion and so on, produce more biological activities such as defecation, resulting in nutrient increase of seawater.(6) Bioconcentration of heavy metals of the same tissue in different ages had some reasons. They were influenced by environmental factors. In addition, they had associated with physiological functions of different tissues in Crassostrea rivularis and physical and chemical state of heavy metals. And the uptake of different tissues of some heavy metals (such as Zn, Cu) in Crassostrea rivularis was highly selective.(7) The concentration of Pb, Cd and Cr in farmed Crassostrea rivularis were in safe state of food quality, but the concentration of As had a warning 7.8 times of food qulity standard. Especially the mean value in adductor muscle was high to 3.3μg/g (wet weight counted), nearly exceeding 6.6 times of allowable value, seriously threating edible value of them. So more attention should be called for. Considering adductor muscle of them, in which heavy metal content was the lowest, it was the main edible part, we can remove potential harmful tissues, leaving adductor muscle for consumers to guarantee the edible safety. |
PDF Full Text Request