| Water quality of the drinking water source is strong and direct link between people’s health and improvement of communities. The pollution by heavy metal has been a serious impact on the safety of drinking water. Humic acid, the most widely distributed in natural environment, can effectively react on inorganic and organic pollutants, and is very important in the formation of a variety of complexes. In general, heavy metals can be substracted from water environment by humic acid. However, the ability of binding capacity and affinity depends on the chemical structure and composition of humic acid. The different complexion strength can determine to the "sink" and "source" for heavy metals in the water environment. Therefore, the metal binding capacities of Humic acid are important to practical signification for the the environmental protection of drinking water source.Miyun Reservoir has been used as unique surface drinking water storage for Beijing. The sediments of Miyun Reservoir are an important repository for nutrient substances and heavy metals from rivers and surrounding environment. The water quality of Miyun Reservoir directly affects health and safety of residents in Beijing. The sediments of Miyun Reservoir were studied as the research object. Humic acid extracted from surface sediment followed by a method from the International Humic Substance Society (IHSS). The structural characterization of humic acid was investigated by solid state NMR, and the content and distribution of humic acid and TOC were determined to the nutrient levels. The concentration and distribution of metal binding humic acid and corresponding sediments were analyzed for the sources of heavy metals, the capacities of metal binding by humic acid and the environmental effects. Cu, Cd and Pb were chosen for adsorption on sedimentary humic acid at different location of Miyun Reserovior, the characterization of the adsorption and the impact factors were discussiong. The main results are following:1. The average content of total organic carbon in the surface sediments was about16.40mg/g, and the average concentration of humic acid was0.71mg/g. The spatial distribution of total organic carbon was the order of the middle region> the flow area of Bai River> the flow area of Chao River. The main source of organic carbon in the surface sediments were the runoff by Bai River and Chao River. However, a large of farmland in north of middle reservoir had become an important source of organic carbon. The content of humic acid and organic carbon appeared an unconsistent relationship, and the concentration of humic acid was relatively higher in the flow area of Bai River.2. The sedimentary humic acids in Miyun Reservor were found to be quiet similar, the main structure of sedimentary humic acid was comprised of non-polar aliphatic chain, carboxyl groups, aromatic group, methoxy group and carbohydrates. Partial of humic acid also included aromatic C-O, O-C-O anomerics and carbonyl. However, carbonyl occurred mainly at the middle region and the flow area of Chao River in Miyun Reservior, and this group was not found at in the flow area of Bai River. Among all the groups, the content of non-polar aliphatic chain was the highest and the average value reached to42.79%, the following was carboxyl groups (about20.38%), oxygen-containing groups (including methoxy group and carbohydrates, about19.03%), aromatic group (about14.11%), and other groups were smaller. Howerver, the structure of humic acids were diversity at different regions, such as the carboxyl group was higher at the flow area of Chao River than other regions. Aliphaticity of humic acid was higher, and armoaa’ city and degree of oxidation were lower. At the near of infall to Chao River and Bai River, humic acid mainly came from land-based biological origin, and the other regions suffered from weak water flow were derived from aquatic organisms within the reservoir.3. The contents of heavy metals in surface sediments were at a low level comparing with the average shale values. Index of geoaccumluation showed heavy metals were uncontamination. Heavy metals in surface sediments were mainly carried by the river into the reservoir and deposition, The spatial distribution of heavy metals at Miyun Reservior was different due to the geographical environment of the two rivers. At the flow area of Chao River, the higher contents of metals were found near the input of reservoir and Chao Dam, and the lower was at the middle of the flow direction. However, at the flow area of Bai River, the lower concentrations of metals were found near the the input of reservoir and Bai Dam, and the hiher was at at the middle of the flow direction. At the middle of Miyun Reservoir, the contents of most metals were lower, but there were a significant increase near the import of the Mangniu River. The results of principal component and correlation analysis showed there were two main sources for metals in surface sediments. The first principal component, including Ni, Cr, Cu, V, Zn, Mn, and part of Pb, represented the source of rock wreathing and soil erosion. The second principal component, consisting of Cd and Pb, and partial concentration of Cr, Cu, V, Zn and Mn, represented the source of industrial mining. The gold mine tailings stacked at the upstream of Mangniu River were potential threat to heavy metals pollution for drinking water source.4. The order of the heavy metals binding to humic acid in surface sediments was as follows:Zn (143.21-2858.13μg/g)> Cu (236.07-4887.07μg/g)> Cr (18.17-2137.81μg/g)> Ni (13.56-1757.58μg/g)> V (0.55-46.97μg/g)> Pb (0.71-29.04μg/g)>Cd (0-2.59μg/g). Of the studied metals, the concentrations of Cu and Zn in humic acid were significantly higher than the corresponding sediments, and Cu and Zn showed a greater affinity for humic acid than sediment, suggesting the possible formation of more stable complexes with humic acid, and it could reduce the bioavailability of these contaminats. With lower content of humic aicd, respectively0.31%-4.16%and0.11%-1.91%of the total Cu and Zn in surface sediments were recovered into humic acid, and other metals were lower than1%. Other metals seemed to prefer sediment, even though Cr and Ni were found a general increase in its content in humic acid in some areas, probably because of the structure of humic acid and environmental conditions (such as oxic to anoxic conditions). The results of index of geoaccumluation showed Cu and Zn had a stronger enrichment in humic acid, but the contents of other metals showed no obvious enrichment in humic acid. The contents of heavy metals in humic acid reflected the source and pollution of heavy metals in water environment, and provided valuable information on drinking water source for environmental safe assessment.5. The adsorption of Cu2+、Cd2+and Pb2+on the different surface sedimentary humic acids (CHHA and BHA) were investigated under different conditions. Under the different initial concentrations of heavy metals, the adsorptive capacity of Cu2+、 Cd2+and Pb2+was increased gradually and eventually equilibrium with the ions of three heavy metals increased, but the adsorption rate was gradually decreased. The pH value could impact on the adsorption of Cu2+and Cd2+, the adsorptive capacity of Cu2+and Cd2+was increased and eventually up to a certain scope no longer to increase as the pH value increased, and the bound of pH value for Cu2+on humic acid with experimental range was6.0, and Cd2+was5.0, but the pH values palyed a smaller effect on adsorptive capacity of Pb2+. Temperature also affected the adsorptive capacity of Cu2+, Cd2+and Pb2+, and the adsorptive capacities of these three ions were increased as the temperature decreased. Under the same conditions, the size of the amount of adsorption for Cu2+, Cd2+and Pb2+on different humic acid was CHHA> BHA, this was mainly due to the content of the carboxyl and phenolic hydroxyl functional groups in CHHA was higher than BHA.6. The results showed that the adsorption isotherm of Cu2+> Cd2+and Pb2+on humic acids complied with the Freundlich equation, the Langmuir equation and the Temkin equation, and the Langmuir equation showed a significant level. In the same conditions, the order of the highest capacity to metal ions on humic acid was Pb2+> Cu2+>Cd2+. In the conditions of25癈and pH6.0, the highest capacities to Cu2+> Cd2+and Pb2+on CHHA were respectively23.65mg/g,4.64mg/g and44.64mg/g, while on the BHA were respectively17.29mg/g,3.23mg/g and38.09mg/g. However, in15"C and pH6.0, the highest capacities to Cu2+> Cd2+and Pb2+on CHHA were respectively25.49mg/g,5.79mg/g and69.45mg/g, but on BHA were respectively18.30mg/g,4.85mg/g and41.65mg/g.In summary, the structure of humic acid, metal binding by humic acid, and the saturated adsorption capacities of humic acid were differences in different regions. The amount of adsorption capacity was much larger than the content of metal binding to the humic acid, and the reaction of heavy metals on humic acid included both surface adsorption and internal combination. Heavy metals in water environment were effectively removed by humic acid, and bioavailability of heavy metals was reduced. However, when the water environmental conditions were changed, a part of surface adsorptive content on humic acid would be release to water and form a "secondary pollution" for heavy metals. Therefor, the study on the reaction of humic acid and heavy metals can provide an important scientific basis for the environmental protection of water sources. |
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