Preliminary Studies On Accumulation And Response Of Heavy Metal (Copper, Lead And Cadmium) In Tegillarca Granosa

At present, heavy mental pollution is aggravating in the coastal areas of China, andthreatened our food security. The paper selected the tidal shellfish Tegillarca granosa （T. granosa）which lived in southeast coast of China as an object, to study the kinetic accumulation characters,accumulation rules in different organs, and response mechanism under the single and combinedheavy metal strss, the results could provide scientific basis for tidal shellfish healthy culture andproduct security monitoring. The details were as follows：（1）Acute toxicity of heavy mentals to T. garnosaThe single and joint toxicity of Cu²⁺, Pb²⁺, Cd²⁺to T. granosa were tested at watertemperature of27.5±2℃. The joint toxicity test was determined using equi-toxic ratio mixing, andthe effects of joint toxicity are evaluated with the Marking’s additive index. The results indicatedthat the median lethal concentrations （LC50） of single acute toxicity of Cu²⁺, Cd²⁺at96hours to T.granosa were363.06μg/L,2249.52μg/L, respectively. but Pb²⁺has very low toxicity for killingnone after96h exposure. The toxicity sequence of the three poisons to T. granosa ranged as Cu²⁺﹥Pb²⁺﹥﹥Cd²⁺. The safety concentrations of Cu²⁺, Cd²⁺on T. granosa were3.63μg/L,22.50μg/L,respectively. Under the low concentrations, the joint toxicities of Cu²⁺-Cd²⁺at96hours wassynergy.（2） Kinetic study on the bioaccumulation of heavy metalsIn the present study，accumulation of three heavy metals（Cu, Pb and Cd）in T. granosa wereinvestigated in a semi-static system. Kinetic parameters of bio-concentration were obtained fromthe two-compartment model by nonlinear curve fitting. The modeling results showed that uptakerate constant（K1） ranged from24.40to57.07, elimination rate constant（K2） ranged from0.01to0.10, bio-concentration factor（BCF） ranged from490.68to1696.02, biological half-life（B1/2）ranged from7.68to46.52. The results also indicated that: the bioaccumulation ability order of T.granosa to the three heavy metals was Cu≥Pb> Cd; the B1/2was Pb>Cu>Cd, Cu had a longer B1/2at the joint heavy metals test, while a longer B1/2of Pb and Cd at the single test.（3） Accumulation rules of heavy metal in T. garnosaSemi-static exposure toxicity test were conducted in laboratory to study the accumulation ofheavy metals （Cu, Pb, Cd） and accumulation pathways in different tissues of T. granosa under single and combined heavy metal exposure. The results indicated that: Under the single heavymetal exposure, the metal contents of Cu in different tissues were with the sequences ofgills>viscera>muscle, and metal contents of Pb and Cd were gills>muscle>viscera. Theaccumulation of Pb in muscle and gill were significantly higher than that in viscera （P<0.05）.Under the combined heavy metal exposure, there was a competitive adsorption relationshipbetween Cu and Cd. A certain amount of Cu could activate a variety of enzymes in the visceralmass, and those enzymes could clear Pb and Cd; in other tissues, Cu and Cd have no influence tothe accumulation of Pb. The results illustrated that the localization of Cu and Cd were in solublefraction mainly, whereas Pb was located in insoluble fraction.（4） Metallothionein gene expression in T. garnosa exposing to CopperThe tissue specific expression of MT mRNA in six kinds of tissues of T. granosa, anddifferent concentration and time sites of copper stress induced effects in visceral mass ware studiedusing real-time quantitative PCR. The results showed that: under the natural conditions, the levelof MT mRNA was highest in visceral mass. Under the50μg/L Cu²⁺exposure, the MT mRNAexpression level in visceral mass of T. granosa had significant time effect. The “pulse-scheme”expression was showed by the time change, which indicated that MT-mRNA expression followingmetal exposure appeared to be largely dependent of time. The negative correlation was showedbetween MT expression and Cu²⁺concentration at3h point.