Effects Of Single And Combined Pollution Of Heavy Metals In Seawater And Abiotic Factors On Metallothionein Of Ruditapes Philippinarum

Heavy metals are highly lipophilic, hard to degrade, bioaccumulative. Amplifying through the food chain, trace metals can cause oxidative stress and oxidative damage in organisms, even result in death. Therefore, it is necessary to research suitable methods for monitoring heavy metal pollution in seawater and ecological risk assessment. Biomarkers have high sensitivity and specificity, they can monitor mixed effect of heavy metals in the seawater. Metallothioneins (MTs) of marine bivalves are common biomarkers which are used in monitoring heavy metal toxicity. However, MTs in different species, even in different tissues of the same species, respond differently to the same pollution. To quantify heavy metal pollution, the dose-or time-effect relationships between heavy metal concentrations and MTs contents need to be obtained. Furthermore, the MTs inductions by metals can be influenced by variations of the temperature, salinity, pH value and so on, which can cause inaccuracy of field monitoring.Ruditapes philippinarum are exposed in artificial seawater containing single heavy metal ion Cu2+, Zn2+, Cd2+or Hg2+. The aims of this part is to study the rules of metal enrichment, through determining the total/soluble component of heavy metal in gills and visceral mass; finding the suitable tissue for monitoring single-metal pollution and confirming the concentration range of each metal and exposure time. The experiments indicate that visceral mass can easier accumulate metals than gills. BCF5of gills are53.6,280.8.20.6,282.8after exposed in50μg/L Cu2+,100μg/L Zn2+,50μg/L Cd2+and5μg/L Hg2+, respectively, while BCF5of gills are676.8,268.1,47.4,565.6.Cu2+and Cd2+in gills and visceral mass are mainly in free form, in clams exposed to Zn2+or Hg2+, subcellular fraction C1contained higher Zn or Hg percentage. It is confirmed by the power function or negative exponential relationship between the levels of MTs and the contents of Cu, Cd or Hg in all tissues (gills and visceral mass), while Zn and MTs is in the positive and significant relationship. The MTs of visceral mass are more sensitive to Cu2+exposure, while for monitoring metal ions Zn2+, Cd2+or Hg2+, MTs of gills are more suitable.To better understand the effects of metals in MTs response in Ruditapes philippinarum, these clams are exposed to polymetallic mixtures (Cu2+-Zn2+, Cd2+-Hg2+or Cu2+-Zn2+-Cd2+-Hg2+). The interactions between these metals and induction mechanism of MTs by polymetallic mixtures are discussed. The results show that the MTs in all clams exposed to a mixture of2or4metals are found significantly increase, which compared to control group (p<0.01or p<0.05). During exposed to Cu2+-Zn2+for5days, MTs levels in gills and visceral mass show increase at first, then decreased. The inductive effect of Cu2+-Zn2+compound is showed synergism-addition-antagonism on MTs in gills and synergism-antagonism in visceral mass with the increase concentrations of Cu2+and Zn2+. The inducibility of MTs by Cd2+-Hg2+in lower concentrations is larger than other groups. The inductive effect of Cd2+-Hg2+compound is showed synergism-addition-antagonism on MTs in gills and synergism-antagonism in visceral mass with the increase concentrations of Cd2+and Hg2+. When exposed to polymetallic mixtures(Cu2+-Zn2+-Cd2+-Hg2+), the inductive effect of Cu2+-Zn2+-Cd2+-Hg2+compound is showed addition-antagonism on MTs in gills and antagonism in visceral mass with the increase concentrations of these four metals.The abiotic factors have certain influences on MTs induction by heavy metals in clams. The temperature, salinity and pH value of seawater are common abiotic factors. The present study is designed to examine the interference degree of these factors on MTs induction by polymetallic mixtures and put forward the effective methods to eliminate the unfavorable effects when applying MTs to monitoring heavy metals pollution in seawater. The results indicate that temperature and salinity affect MTs contents in gills and visceral mass notably, while the influences of pH value are relatively minor.①Under the optimal growth temperature5～20℃, there are linear relationship between MTs contents in gills and visceral mass and exposure temperatures (except MTs in visceral mass of clams exposed in lower concentrations of metals). The interpolation method is used to convert actual values of MTs to standard values based on the MTs contents determined at15℃.②Stepped changes are found for MTs with salinity fluctuation. Based on the standard value determined at30ppt salinity, the values of MTs in gills at HPA with salinity range20-35ppt and MTs in visceral mass at LPA or HPA with salinity range20-35ppt don’t need to be adjusted. The MTs contents determined at other salinity ranges need correction by interpolation method.③The impacts on MTs by pH value are relatively minor. Based on the standard value measured at pH8.0, the MTs contents in gills of the clams living at pH7.5-9.0(LPA) or pH7.5-8.0(HPA) don’t need correction, and also for MTs contents in visceral mass at8.0-8.5(LPA, HPA).