Bioavailability Of Mercury In Agricultural Soils And Its In Situ Stabilization By Chemicals

There has been a big threat to the edible safety of agricultural products due to the increasing contamination of mercury in agricultural soils.Mercury species decide their solubility,mobility and toxicity.The species of mercury were changed and reduced its bioavailability by adding chemicals to the contaminated soil.In this thesis,the characteristics of mercury contamination in agricultural soils were investigated,and the bioavailability of mercury was also determined.Moreover,the contaminated soil was remedied using the in situ chemical stabilization technology.This thesis contains four chapters.Chapter 1,the contamination,harm,and risk assessment method of mercury in agricultural soils and the influence of mercury pollution on food safety were extensively summarized.The research methods of mercury bioavailability in soils were introduced.In addition,this chapter also reviewed the remediation technologies of mercury contamination in soils.Chapter 2,the characteristic of mercury contamination in agricultural soils of Xiamen was investigated and its potential ecological risks were evaluated.Concentrations of mercury in 196surface soils collected from the study areas were measured with the method of atomic fluorescence spectrometry after microwave digestion.The spatial distributions of mercury in soils based on the geographic information system?GIS?were plotted.And the potential ecological risks of mercury in agricultural soils were evaluated.Results showed that Hg concentrations in top-soils ranged from ND to 1321 ng/g among which 32.6%of the samples exceeded the mercury limit?250 ng/g?of soil quality set for edible agricultural products in China?HJ 332-2006?.The highest levels of mercury were found to mainly distribute in the top-soils from the southwestern part of the studied areas.While the lowest contents of mercury distributed in the eastern part of the studied areas.In the profile,mercury concentrations decreased with the increases of profile depth.Most of the soils in the studied areas existed above medium ecological harm.And the strongest potential ecological risks of mercury only distributed several areas.Results of mercury risk evaluation indicated that most of the agricultural soils from the studied areas should be classified into above medium ecological harm,and only several areas were in strong or the strongest degree of mercury ecological risks.Chapter 3,the bioavailability of mercury in contaminated soils was studied.The distribution of mercury species in soils was determined with the sequential extraction procedures based on Kingston method.Moreover,the bioavailability of mercury in soils was researched through the pot experiment.Results indicated that mercury speciation mainly distributed in semi-mobile forms and non-mobile forms accounted for 47.6-63.6%and 33.5-48.8%of the total extracted Hg in soils,respectively.While Hg in the mobile forms only accounted for 3.7-12.4%.Concentrations of mercury in edible parts of Brassica juncea ranged from 0.66 to 2.92 ng/g.Positive correlations were found between the mercury concentrations of edible parts of Brassica juncea and the total mercury concentrations of the corresponding soil?r=0.820,p<0.05?,and the mercury concentrations of mobile forms in the corresponding soil?r=0.891,p<0.05?.Chapter 4,the remediation of mercury contaminated soils was studied using the in situ chemical stabilization technology.The four chemicals of thiol-functionalized cellulose,hydroxyapatite,sodium alga acid and Ca?OH?₂,were selected as stabilizers.The effect of chemicals on inhibiting plant absorbing mercury from soils was investigated by pot experiments.And the interacting mechanism of thiol-functionalized cellulose and mercury was further investigation.Results showed that four chemical stabilizers effectively reduced the concentration of mercury in mobile forms.The optimum concentration of thiol-functionalized cellulose was 40g/kg_?soil?with the reduction values of 70.6%.Meanwhile,the optimum concentration of hydroxyapatite,sodium alga acid and Ca?OH?₂ was 25 g/kg_?soil?,20 g/kg_?soil?and 25 g/kg_?soil?with the reduction values of 44.2%,39.8%and 61.1%,respectively.Thiol-functionalized cellulose reduced the amount of 55.9%mercury accumulated in the edible parts of Brassica juncea.While the composite of hydroxyapatite,sodium alga acid and Ca?OH?₂ reduced the amount of 43.3%mercury accumulated in the edible parts of Brassica juncea.The remedial effect of thiol-functionalized cellulose was better than the composite.The interacting mechanism that thiol-functionalized cellulose reduced the bioavailability of mercury in soils was the reaction between thiol base and mercury.