Studies On The Speciation Of Mercury And Selenium In The Soft Tissues Of Bay Scallops And The Antagonism Of Selenium Species To Mercury Species

The following facts are appealing：the popularly sea cultivated bay scallops（Argopecten irradias）live in the off-shore waters which are greatly influenced byanthropogenic activities，together with their non-selective filter-feeding characters，they are inevitably affected by the marine environment. Large quantities of harmfulpollutants accumulate in their tissues，but most of them can survive healthily for theirlife time. This proves that，there exits a very important and effective antagonisticmechanism to the poisonous substances in their bodies.Owing to the results of the existing studies， organic mercury species areselected as the representatives of the most dangerous pollutants，and the seleniumspecies are selected as the representatives with antagonistic effects to the mercuryspecies. By the speciation of these two elements in bay scallop samples， thespecies，amounts and distribution among the tissues and the laws are revealed. Therelationship between the mercury species and the selenium species are analyzed byregression analysis. The studies and the results not only provide a scientificprecondition for the control of food safety， but also enrich the knowledge ofmetallomics and proteomics.In the studies，samples are drawn every month at regular intervals. The softtissues are divided into three parts according to food habits：the adductor muscle，the mantle and the visceral mass. Speciation methods are developed and thespecies of mercury and selenium are determined. The antagonism between mercuryand selenium were opened out by the regression analysis. The innovativediscoveries and results are as follows.Organic mercury species，methyl mercury，ethyl mercury and phenyl mercury can be quantitatively released by the mixture made of cupric salt，sodium chlorideand zinc acetate. The use of zinc acetate not only decreases the needed amount ofsodium chloride，leading to the least disturbance to the electron capture detector（ECD），but also enables the thorough release or separation of the mercury speciesfrom the protein residues，which assures the accuracy of the determination.The replacement of the thio-bearing chelate resins to sulfhydryl cotton fibers（SCF）in the concentration of the mercury species totally eliminated the errorscaused by the variable quality of SCF and the severe disturbances by the thiols usedin making SCF. The combination of hydrochloric acid and hyper-chloric acid canquantitively elute the organic mercury species from the concentration resins. Theabsorbed species can then be totally extracted by toluene，effectively separated bygas chromatography and accurately detected by ECD.The soft tissues of bay scallops pre-treated by papain in sodium bicarbonatesolutions made the tissues easy to be totally dissolved in the following enzymatichydrolysis with the combination of the commercially available enzyme Flavourzyme500L，carboxypeptidase Y and trypsin into free forms of selenium species，which canbe separated by high performance liquid chromatography（HPLC）and determined byinductively coupled plasma-mass spectroscopy（ICP-MS）. Sodium thiosulfate is ableto guarantee the integrity of the selenium species during the whole process ofenzymatic extractions without transformations among the species. The combinationof sodium thiosulfate and nitrogen is the most optimal measure to ensure the integrityof selenium species.On the basis of the results of the mercury species and the selenium species inthe soft tissues of bay scallops，close linear relationships among them are found byregression analysis. The relationships should be the antagonism of the seleniumspecies to the mercury species, which are very important to the healthy living of bayscallops.Conclusions are drawn according to the facts above：First, from the end of June to the end of November，2012，only methylmercuryare detected in bay scallop samples drawn from the Yellow Sea and the Bohai Sea. The amounts in the visceral mass are higher than in the other tissues，showing atrend of increase with the living time.Second, no selenate is detected in all the tissues，showing this species can betotally bio-transformed， while the other four species (Se-methyl seleno-cysteine,seleno-cystine, seleno-methionine and selenite) are found higher in the visceralmass than in the other tissues，increase with the living time of bay scallops in thesea.And third, the results of the regression analysis show that there exists anantagonistic effect between methylmercury and the selenium species：The amountsof mercury species coincide with that of the selenium species. That is，the amountand distribution in the tissues are the same and time dependent. With the increase ofthe accumulation of methyl mercury，the most dangerous substance to the healthyliving of bay scallops，the amounts of selenium species increase accordingly，showing an obvious antagonistic effect. The amounts of methylmercury in thesamples from the Yellow Sea are higher than those from the Bohai Sea，accordinglythe amounts of the selenium species are also higher. The molar ratios of theselenium species to methylmercury in bay scallops grown up in both seas are muchlarger than1to1，showing that the selenium species antagonize not only the harmof mercury，but also other poisonous elements and their compounds，and shellfishtoxins. At the same time，meet the needs of making seleno-proteins and enzymes.