The Study Of Heavy Metal Ions Association With DOM From Different Aquatic Macrophytes Areas

Heavy metal ions’ shape, solubility and bioavailability affects not only the water quality and aquatic biological behavior but also food safety. In particular, dissolved organic matter (DOM) plays an important role in heavy metals distribution between water and sediment because there are many active points that can association with heavy metals. However, because of the great complexity and heterogeneous composition, DOM from different sources puts in significance difference on the content, composition and structure, and then affects its association characteristic with heavy metals.This work focused on the composition, structure and association characteristic with heavy metals of DOM from overlying water or sediment in different aquatic macrophytes areas. In combination with spectroscopy and morphology characterization, these works are helpful in explaining DOM environmental effects and understanding the impacts on migration and transformation of heavy metals by DOM. The main results are as following:1. There are differences in macro-structure of DOM from overlying water or sediment in different aquatic macrophytes areas. DOM from Phragmites australis Area has the highest aromaticity than the other areas. DOM from overlying water in Myriophyllum spicatum L. Area has the most substituent group on aromatic nucleus and the highest molecular weight, while DOM from sediment in Potamogeton pectinatus Area is the lest and the lowest. DOM in this study is mainly humic components, of which DOM from sediment in Phragmites australis Area has the highest flurophore. DOM from all sources has aliphatic hydrocarbon and aromatic hydrocarbon, functional group including carbonxyl, hydroxyl and amide. DOM from sediment in Potamogeton pectinatus Area has more carbonxyl than hydroxyl, and more total acidity functional group concentrations than the other areas, indicating more active points on it.2. The association ability with heavy metals of DOM which comes from overlying water in different aquatic macrophytes areas is different. DOM from Potamogeton pectinatus Area or Phragmites australis Area shows higher aromaticity and smaller molecular weight, and can associate with more heavy metal ions, especially with Cu2+, of which the association rate can exceed 96%. DOM from Phragmites australis Area has most hydroxyl content, while carboxyl content is close to other area, indicating that DOM in this area has most active group for heavy metals. What’s more, DOM in this area has the highest saturation association capacity for heavy metals, indicating that hydroxyl plays an important role in the associating interaction. Because of the higher aliphatic compound content and molecular weight, DOM from Myriophyllum spicatum L. Area has larger radius colloid, which effects its association characteristics with heavy metals. DOM from overlying water in Potamogeton pectinatus Area can form more stable complex with heavy metals, which the association constant (1gK) can be 2.69 and 2.34 with Cu2+、Pb2+ respectively.3. DOM concentration is an important factor for the association percentage of the DOM and heavy metals. The results showed that DOM has higher association percentage with heavy metal ions when its concentration increased, and the associative constant is bigger and has larger influence on heavy metal’s mobility. However, there’s interaction between the organic matter molecules in DOM with its concentration increasing, and the saturation association capacity of heavy metals will decrease. Compared with the other heavy metals, the association constant of Cu2+ with DOM is higher, meaning that the reaction product is relatively stable, and there is more possibility to form DOM-Cu complex in natural water environment.4. There are differences in functional group between DOM in sediment from different aquatic macrophytes areas. Among DOM in Potamogeton pectinatus Area and Myriophyllum spicatum L. Area carbonxyl is more active, while hydroxyl is more active in Phragmites australis Area. DOM in Phragmites australis Area has relatively stronger association ability with heavy metals in certain concentration ranges. In conclusion, DOM from different aquatic macrophytes areas has different structural feature such as molecular weight, aliphaticity and functional group, and those differences can effect the associating reaction between DOM and heavy metals.