| In recent years,the growing metal pollution has affected the health of estuarine environment in China.As an important component of estuarine ecosystem,marine bivalve has the characteristics of accumulating metals and being sensitive to metals,which make its regular physiological process(such as growth and reproduction)vulnerable to metal pollution,further affecting the stability of whole estuarine ecosystem or economic performance of aquaculture.Razor clam Sinonovacula constricta is a common infaunal bivalve in estuarine area of China and an important species of aquaculture,but currently its living environment is under threat of metal pollution.Therefore,the study of the ecotoxicological effects of metals on Sinonovacula constricta is of great importance.This study mainly consists of four parts:1)investigation of the source of metal accumulation in tissue of S.constricta in estuaries with various metal pollution and the effects of metal accumulation on the growth and reproduction;2)study of the bioavailability of particle-bound metals to S.constricta by measurements of the assimilation efficiency of metals under different particle mixing ratios and particle loads;3)application of PBPK model to study the absorption,distribution,metabolism,and excretion(ADME)of Cu in different organs of S.constricta under dissolved exposure,and analysis of the pathway of Cu entering the tissue as well as the distribution of Cu in each organ;4)application of the TKTD model by comparing the accumulation and sensitivity difference of three common bivalves to Cu,to reveal the mechanisms of interspecific difference of marine bivalve sensitivity to Cu.The main results of the study are summarized below:A eight-month transplantation experiment was conducted at two stations with different pollution levels in the Jiulong River estuary of southern China,and metal concentrations in the dissolved phase,particle phase,surface sediment,whole-body tissue of S.constricta and different tissues were measured every month for eight metals:Ag,As,Cd,Cr,Cu,Ni,Pb and Zn,coupled with measurements of the physiological index of growth and gonad development.By comparing the trends of metal concentrations in the environments and the whole-body tissue of S.constricta,the results showed that the accumulation of Ag,As,Cd,Cu and Zn in the body S.constricta mainly came from the particle phase,while the accumulation of Cr and Ni mainly came from the dissolved phase.The concentrations of Ag,Cu and Ni in the whole-body tissue of S.constricta from the more polluted station were significantly higher than that from the cleaner station,and the accumulated concentration of Cu could reach 61.4 ?g/g.In addition,the shell length,dry weight and condition index of S.constricta was significantly inhibited at the more polluted station.Accordingly,the gonad index of polluted station was also significantly lower than that of the relatively clean station.These results indicated that excessive accumulation of Cu caused adverse effect on the growth and breeding of S.constricta.Excessive accumulation of metals in multi-metal contaminated estuaries will cause ecological risks to the survival of S.constricta.With the application of pulse-feeding technology,the effects of different particle mixing ratios and loads on the assimilation efficiency of Cd and Zn by S.constricta were quantified.By using the dual gamma radiotracers,the effects of corresponding particle mixing ratios and loads on particle sorting(before pre-ingestion)of S.constricta were also studied.The results revealed that the assimilation efficiency of 109Cd and 65Zn was significantly affected by particle mixing ratio and particle load.Furthermore,the presence of one type of particle did not affect the assimilation efficiency of the metal from another type of particle.Dual gamma radiotracer study demonstrated that the particle selection in S.constricta was not obvious under different particle mixing ratios and loads.Both particle type and load can affect the bioavailability of Cd and Zn in S.constricta.These results were of great significance for understanding the metal accumulation of bivalves in the estuary environment where food particle mixing ratio and concentration fluctuate greatly.A long-term dissolved exposure to two Cu concentration(5 ?g L-1 and 15?g L-1)was conducted,and the Cu concentration in each organ of S.constricta was measured.The uptake and elimination process of Cu by S.constricta as well as the transferring process between different organs(blood,digestive glands and the other tissues)was simulated by using a physiologically based pharmacokinetic model(PBPK model).The results showed that the Cu concentrations in gill under two different exposure concentrations were similar during Cu exposure,while the concentrations of Cu in other organs(blood,digestive glands and other tissue)increased with increasing Cu concentration.These results suggested that the digestive system was another pathway for S.to absorb Cu except for the gill.The simulated uptake rate constant of gill was similar to that of the digestive gland(0.294 L g-1 d-1 vs 0.364 L g-1 d-1),indicating that the digestive gland was another pathway for S.constricta to absorb Cu from the dissolve phase.However,elimination rate of Cu from gill was significantly higher than the transfer rate from gill to blood(1.73 d-1 vs 0.100 d-1),indicating that the gill played an important role in regulation during Cu exposure.In addition,the transfer rate of Cu from blood to digestive gland was significantly higher than that from blood to other tissues(219 d-1,0.0131 d-1 and 4.96 d-1),indicating that the blood transferred most of Cu to the digestive gland.This study proved that the digestive system was an important pathway for marine bivalve of absorbing Cu in the dissolve phase besides the gill,and different organs played different roles in Cu metabolic process..Finally,the dynamic changes of metal bioaccumulation and survival under different Cu concentration gradients were examined for three marine bivalves(mussel P.viridis,clam S.constricta and oyster C.angulate).By using a toxicokinetic-toxicodynamic model(TKTD model),the dynamic change of Cu accumulation and survival of three marine bivalves were simulated,and the relationship between accumulation of Cu in the body of three marine bivalves and the toxicity was explained.Parameters estimation showed that the killing rate of mussels was the highest,followed by clams and oysters.Oysters displayed low uptake as well as elimination,and barely eliminated Cu.Mussels had the highest uptake and elimination rate,and the elimination rate of clam was intermediate between mussels and oysters.The estimated toxicity parameters suggested that the detoxification mechanism of oysters to Cu might tend to store the excess Cu in the detoxification from,while mussels and clams tended to eliminate Cu from the body.Comparatively,storing Cu in the detoxification form was the more effective detoxification mechanism than excreting Cu.Thus,difference of bivalve sensitivity to Cu was related to their detoxification mechanism. |
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