CdCC/CuCC In Natural Waters Evaluated By Dynamic Analytical Methods

The toxicity and/or bioavailability of heavy metals in natural waters depend on their chemical forms.Since there are ligands such as humic acid and fulvic acid in natural waters, the toxicity and/or bioavailability of heavy metals would be reduced by forming complexes via the coordination of ligands to the metals.On the other hand,a speciation analysis of a water sample is necessary for understanding the toxicity,bioavailability,bioaccumulation and transport of a particular element such as cadmium and copper.Under such a circumstance,the concept "Complexing Capacity"(CC) has been introduced.The characteristic of occurring ligands can be expressed with the CC which can be deemed to self-purification capacity of natural waters.Up till now,various methods for the measurement of the CC have been reported such as anodic stripping voltammetric(ASV),ion exchange,ion selective electrode and back extraction based on the principle of thermodynamic equilibrium,while dynamics based methods using liquid-liquid extraction and chelating resin enable the simultaneous determination of the CC and the observed lability constants(k_obsd) of metal-complexes involved.In this thesis,diphenyl thiocarbazone(dithizone) and bis(1,1,3,3-tetramethylbutyl)monothiophosphinic acid(HMTP) as well as methylene monoamino diacetic acid chelating resin(MADA) was used to as competing ligands to study and determine Cd and Cu complexing capacities of natural waters and the corresponding Cd/Cu k_obsd.These strategies were applied to evaluate the self-purification capacity of natural waters and predicate the risk of heavy metal pollution in water system.This thesis consists of 5 chapters.In Chapter One,the pollution and subsequent impacts on the environmental and biological systems of heavy metals such as Cd and Cu were briefly reviewed,and the concept of the CC and its significance for evaluating of the self-purification capacity of natural waters and the state of the art for determining the metal CC was introduced.The objectives of this thesis was thus proposed to establish dynamic methods for simultaneous determination of Cd/CuCC and k_obsd as well as the evaluation of the risk of heavy metal pollution. In Chapter two,a theoretic model of the dynamic extraction using dithizone as an competing ligand was established for for determining CdCC and teh corresponding k_obsd of natural waters.The feasibility of the method was validated by using the mimic water samples containing some model chelating agents such as ethylenediaminetraacetic acid(EDTA), N-(2-hydroxyethyl)ethylene-diamine-N,N',N'-triacetic acid(HEDTA),nitrilotriacetic acid (NTA) and humic acid.The method was applied to the real water samples collected from different sites of the Minjiang River which locates in the southeastern China.The CdCC are from 7.20 to 7.78μmol L^-1,and k_obsd from 2.5 to 2.8×10^-2 s^-1,nearly to humic acid model solution.Furthermore,the relationship between CdCC and dissolved organic carbon(DOC), nitrogen and sulfur contents of the water samples was discussed,and the influences from the anthropogenic activities around the sampling sites as well.In Chapter Three,a softer competing ligand HMTP was used to simultaneously determinate Cd/CuCC of natural waters and the corresponding k_obsd of Cd/Cu complexes involved.The obtained extraction dynamic curve(-ln[ML]against t) shows a two-stage stepwise profile that reflected the competition of different ligands existing in the natural waters with HMTP toward Cd/Cu species,suggesting that there are different chemical forms of Cd/Cu in the natural waters.Through the comparison of Cd/CuCC of natural waters which are responsible to the different sampling location from Minjiang River,it was found that a significant correlation between Cd/CuCC and DOC in the water samples,and S/N content played an important role in regulating the self-purification capacity of the waters.On the other hand,the occurrences of the kinds of ligands in the natural waters are much influenced by anthropogenic activities.In Chapter Four,considering the potential toxicity and inconvenience manipulation of dithizone and HMTP,a methylene monoamino diacritic acid chelating resin was used instead of the extracting ligands.Results indicated that the chelating resin is suitable for evaluating CdCC when moderate and strong organic ligands are existing in the water samples. It was successfully applied to the evaluation of the self-purification capacity of Furong Lake in the main campus of Xiamen University,and comparable to that of HMTP-based method. Synthesis of new type of chelating resin and design automatic device to be used for future automation of the CC and the corresponding k_obsd determination procedures should be expected for more objective and efficient evaluation of the risk of heavy metal pollution in water system.In Chapter Five,a summary of this thesis was concluded and the developing trend was also prospected.