Preliminary Studies On The Kinetics Of Bioconcentration And Depuration Of Heavy Metals In Biavlves

With the development of modern industry and agriculture,coastal marine environment was increasingly polluted by heavy metals.Bivalves can concentrate heavy metals in seawater because of their ability of bioconcentration,which is harmful to them.More importantly,those heavy metals will be biomagnified and transferred alone with food chains, which will threaten the health of human beings.Based on above reasons,in this study two cultured bivalves Tegillarca granosa Linnaeus and Ostrea plicatula Gmelin in costal of Zhejiang province were selected,and kinetic characteristics of bioconcentration of three representative heavy metals(copper,lead and cadmium)in the two bivalves were investigated in a semi-static system in the lab.On the basis of kinetics study,more exploratory researches on the depuration of heavy metals in O.plicatula were conducted.The distribution of the three heavy metals in O.plicatula was also studied. The objective of this study was to have a full realization of the kinetic characteristics of bioconcentration,which can be used in estimating the degree of heavy metals pollution,indicating the quality of marine environment,and predicting the latency threaten to human beings. Another aim is to further discuss the feasibility of the depuration of heavy metals in bivalves.This work can provide scientific basis and basic data for preparing pollution-free culturing norm of shellfish,the study on the depuration of heavy metals,the safety of diet,and development of shellfish product.Kinetic parameters of bioconcentration were obtained form the two-compartment model by nonlinear curve fitting,including uptake rate constant(K₁),elimination rate constant(K₂),bioconcentration factor (BCF),and biological half-life(B_1/2).It was found that the metal concentration data were fitted to the two-compartment model,and good agreement was found between the predicted and observed metal concentration using the goodness-of-fit test.The modeling results indicated that,the uptake rate constant(K₁)and bioconcentration factor (BCF)generally decreased with the increase of heavy metal exposure concentration in ambient seawater,the bioconcentration ability order of T. granosa to the three heavy metals is Pb＞Cd＞Cu,the elimination ability is Cu＞Cd＞Pb,for O.plicatula,the bioconcentration ability of the three metals is Cd＞Cu＞Pb,and the elimination ability is Cu＞Cd＞Pb.Maximal content in the organism(C_Amax)at the theoretic equilibrium increased and was basically directly proportional with increasing metal concentration in the outside seawater.So it could be regarded that the heavy metal concentration in those two bivalves faithfully reflected the contamination status and process of the ambient surroundings,accordingly they could be regarded as the indicator of the three heavy metals in coastal waters of China.According to safety consumption limits of Ministry of Agriculture about Cu,Pb and Cd in shellfish,safety levels of Cu,Pb,and Cd in the culturing waters were obtained respectively through the calculation of the bioconcentration kinetic parameters.For T.granosa,the results is Cu 0.065mg/L,Pb 0.0007mg/L,Cd 0.0010mg/L,and for O.plicatula Cu 0.028mg/L,Pb 0.0019mg/L,Cd 0.0005mg/L.Although there were some difference between the result of former and the standard of marine culture water quality,the latter was approximately match with the limit of standard.This work provided a new thought and reference for preparing the norm for the safety levels of heavy metals in those two bivalves Pollution-free Culturing.The influences on the deputation of heavy metals and nutritional value in O.plicatula by salinity,alga,CaNa₂EDTA,vitamine C and chitosan were investigated.The results showed that,increasing salinity was propitious to the depuration of lead,but made against the depuration of cadmium.Both increasing and decreasing salinity can improve the depuration of copper,but the nutritional value was damaged at low salinity.Feeding some alga will be helpful to the depuration of all of those heavy metals.Adding CaNa₂EDTA into the culturing water had no meaning to the depuration,but adding vitamine C and chitosan will accelerate the depuration of heavy metals,meanwhile there were no influence on nutritional value.So there are a certain degree of feasibility on adding vitamine C and chitosan into the O.plicatula culturing water to advance the depuration,but further study must be paid into the application and the detailed mechanism of their influence on the depuration of heavy metals.The content of the three heavy metals in different organs are greatly different.Gill and viscera are the main part of accumulating and holding heavy metals.From the view of diet safety and development of product,it is more safety to eat muscle than the whole soft parts,and the part of gill that were badly contaminated and had low nutritional value are suggested to discard selectively.