Study On The Chemical Speciation Of Mercury And Selenium In Animal And Toxic Interaction Between The Two Elements

The mutual antagonism between mercury and selenium has been considered one of the strongest and the most general examples of interaction between heavy metals. The exact mechanisms of interaction between the two elements are intricate but not well understood. Exploring the possible mechanisms is an important content of bioinorganic chemistry and ecotoxicology, which has signality in modifying contamination effect to animals. This thesis studies on the chemical speciation of mercury and selenium in dolphin livers, sub-chronic toxic effect of Wistar rats of sodium selenite and mercuric chloride and investigates the antagonism mechanism from there aspects: 1. redistribution of mercury in the presence of selenium, 2. transformation of mercury in the presence of selenium, 3. formation of mercury selenium complexes or compounds.The concentrations of mercury and selenium in ten dolphin livers were determined. Mercury and selenium exist in the livers as abnomal high concentrations at approximate 1:1 molar ratio of mercury to selenium. The efficiency of extracting mercury and selenium from livers homogenate by acetone, 80% ethanol, and ammonium acetate all were very low. More than 90% of mercury and selenium were in the indissoluble fraction of the liver (liver powder). Seven proteases were used to dissolve the liver powder, especially alkaline protease with 1%SDS made 99% of liver powder dissolve. Approximate 50% of mercury and selenium presented in the supernatant (liver hydrolysate) and the others in the 1% residue.Gel filtration chromatography of the hydrolysate on Sephadex G-75, Sephacryl S-300HR, Sephacryl S-500HR columns showed that 96% of mercury and 87% of selenium were combined with the high molecular weight proteins (most of it over 1.0 106Da) at 1.98~1.99 molar ratio of mercury to selenium. On the contrary, the others were combined with low molecular weight proteins (lower than 1.0 104Da) at 0.5 molar ratio of it. The high molecular weight fraction was subjected to Dithiothreitol and Selenocysteine respectively. Molecular weight diminished after treatment by DTT in some of it, in which mercury and selenium were not determinated. Mercury transferred from low molecular weight proteins to high molecular weight (1.0 106Da) proteins after treatment by Selenocysteine. Mercury can not be replaced by the complexing reagent of Dithiothreitol, Sodium Diethyl-dithiocarbamate and Selenocysteine. The results indicate that most mercury are combined with high molecular weight proteins stably, and selenium plays an important role in the procedures of transferring mercury to high molecular weight proteins, which has a significant effect on reducing mercury toxicity because mercury is fixed in the high molecular weight protein.In the present study, half of mercury and selenium were recovered in the insoluble powder which couldn't be digested by alkaline protease. HgSe crystal was confirmed in it by scanning electron microscope, energy dispersion of X-ray analysis, and X-ray diffraction analysis. However, HgS or Hg(SexSi.x) is denied though sulfur has a high affinity with Hg2+. Formation of HgSe crystal is considered as ultimate stage on the detoxification by selenium. The fact there aren't formation of HgS and Hg (SexSi-x) shows special and vital function of selenium in the detoxification of mercury.In acute toxicity test, male and female Wistar rats received sodium selenite and mercuric chloride singly or associatively. The values of the LDso show an obvious antagonism between mercury and selenium, and the LDso of the females are higher than that of the males in associated dose but contrary in the single dose. In the sub-chronic toxicity test, Wistar rats were divided into six groups randomly (10 male and 10 female per group), in which one control group, two groups received sodiumselenite (0.4mg/kg) and mercuric chloride (2.4 mg/kg) individually, and three groups received associated dose (2.4 mg/kg HgCl2+0.2mg/kg Na2SeO3, 2.4 mg/kg HgCl2+0.4mg/kg Na2SeO3, 2.4mg/kg HgCl2+0.8mg/kg Na2SeO3) for three month...