Study On The Bioconcentration And Elimination Of Heavy Metals (Cu、Cd) In Crassostrea Plicatula And Related Safety Limits

Heavy metal pollution in benthic filter-feeding bivalves has beenreceived more and more attention due to their stong ability in biologicalenrichment. In the present study, accumulation and elimination of twometals（Cu、 Cd） in Crassostrea plicatula of two sizes by using thetwo-conpartment kinetic model. A semi-static system was maintainedthroughout36d exposure period in different concentrations of heavy metalsat22.3±2.7℃. Then,the seawater with heavy metals was discharged, theflow-through system with clean seawater was adopted during the42delimination period. Through regular sampling and detection the contents ofheavy metals（Cu、Cd） in C. plicatula to study their change trend and ediblerisk assessment. Curves and kinectic parameters of bioconcentration wereobtained by nonlinear fitting of the heavy metals contents in C. plicatula.Serval statistical analysis was adopted to test the data wether suit to themodel or not, the result showed fitting goodness was acceptable. According to safety consumption limits of Ministry of Agriculture aboutCu and Cd in shellfish, safety levels of Cu and Cd in the culturing waterswere obtained repectively through the calculation of the bioconcentrationfactors. The main conclusions are as follows:1. Through the36d enrichment experiment showed that C. plicatulahas great bioaccumulation on Cu and Cd as a type of strong netaccumulation, the contents of heavy metals in C. plicatula were positivelyrelated to the metals’ concentration in seawater, pollution of heavy metalsin C. plicatula could paly a good indicative role of heavy metals pollutionin the marine environment. After the elimination phase of42d,60⁷0%of Cu contents in C. plicatula were removed, but only about50%of Cdcontents in C. plicatula were removed, indicated that C. plicatula has muchmore powerful purification capacity to Cu than Cd. After enrichmentexperiment phase of36d, the enrichment of Cu, Cd by C. plicatula had notreach the equilibrium, proved it wasn’t suit the steady-state model, so wechoosed the two-compartment kinetic model in this study.2. From the results of risk assessment, health risk Cu contents in C.plicatula to humanbeing is very low, but to Cd its much higher and that’snot optimistic.Therefore this research recommend to division the shellfishculture area as serval carefully and meticulously, establishing market accesssystem on different areas, to ensure people’s shellfish food safety from the aquaculture chain.3. Using the combination of R2, X2test and F test to evaluate theadaptable of two-compartment kinetic model with the enrichment of C.plicatula to heavy metals, results showed that the fitness was very good,the two-compartment kinetic model was suit for this study.4. Through nonlinear fitting of contents of heavy metals in C.plicatula with time-varying by, get bioaccumulation curves and kinecticparameters (absorption rate constant k₁, discharge rate constant k₂,bioconcentration factor BCF, biological half-life of B_1/2) of C. plicatulaon Cu, Cd by two stages. Using BCF for comparison, bioaccumulationability order of C.plicatula was Cu>Cd, bioconcentration factor BCFgenerally decreased with the increase of heavy metal concentration in theuptake phase; using B1/2for comparison, the removement and purificationability to heavy metals in C. plicatula was Cu>Cd.5. Individual size on heavy metals enrichment effects of C. plicatulawere very complex. By two phases of enrichment and elimination, the BCFof Cd in C. plicatula were lager in the large size of C. plicatula than in thecorresponding small ones. In enrichment phase,the BCF of0.01,0.05mg/Llarge size groups to Cu were higher than the corresponding smallgroups,but in0.02mg/L group was just opposite, in the eliminationphase,the BCF of large size groups to Cu were lower than the the corresponding small groups. The biological kinetic parameters betweenbody size did not tally with the trend our assumption before as a singlepositive or negative correlation, maybe the experimental condition needmuch optimization in future.6. According to the selecting rules, Using the BCF of small C.plicatula0.010mg/L groups and the Cu,Cd limits in NY5073-2006as basis,the results of calculation were that the the safety limits in culture water ofC. plicatula were8.03（Cu） and0.96（Cd） μg/L. The limits of Cu is close toGB11607-89and higher than the first grade standards in GB3097-1997；The limits of Cu is much strict to GB11607-89and close to the first gradestandards in GB3097-1997. This data could provide information support forrevising fishery water quality standards, particularly shellfish aquaculturewater quality standards, having some economic and social value.