Studies On Heavy Metal Complexation Capacity In The Typical Areas Of The Bohai Sea

The heavy metal complexation capacity, CC, of nature waters is a quality parameter which measures the ability of the system to complex heavy metals. The thesis is based on the study to the North area of the Bohai Bay, the Yellow River estuary and the South area of the Bohai Sea, which are selected as typical areas. By using anodic stripping voltammetry (ASV) technique combined with 'pre-equibrium' complexometric titration, the heavy metal complexation capacity (CC) of the seawater and the conditional stability constants (K) of metal-ligands of seawater samples collected in the typical areas of the Bohai Sea are determined. The thesis also studies the changing rules and distribution rules of these typical areas. On this basis, the thesis makes further research on copper ion's toxicity and the self-purification capacity of seawater to copper. The self-purification capacity of seawater to copper in some sea areas is estimated according to observations on seasonal changes. Effect of seasonal changes on the apparent copper complexation capacity (ACuCC) in seawater of the alongshore at Qingdao city has been studied during a year period. All the research provides primary data to heavy metal complexation capacity in the Bohai Sea. In order to assure the reliability of studies, following works are undertaken to expound and prove what has been determined and estimated through condition tests. The first is to select proper experiment condition for obtained CC. The second is to validate the reasonableness of 1:1 complexation model of metal-ligands by theories and experiments. The third is to choose Cu as reference metal used for the measurement. The main results achieved are as follows:1. Determine the study method.The reaction of Cu, Cd, Pb and Zn with the ligands in seawater can be completed in lOmins. The 1:1 complexation model of heavy metal-natural ligands is corroborated on theories and experiments. The Van den Berg linear method is a bettermethod than other methods for determining CC and K. Based on determination of CuCC, CdCC, PbCC and ZnCC, copper is selected as reference metal in complexometric titration to determine the heavy metal complexation capacity to the seawater of the Bohai Sea and the results is proved to be reasonable.2. Seasonal changes of the apparent copper complexation capacity (ACuCC) in seawater of the alongshore at Qingdao city, China.The ACuCC values changes according to seasons. The ACuCC values in the alongshore at Qingdao city were between 271.0 and 474.2nmol/L, with mean value being 362.4nmol/L. The lgK values were between 7.74 and 9.45, with mean value being 8.53. The ACuCC values changed in succession. The maximal ACuCC value appears in August and the minimum appears in February. Seasonal changes have a significant effect on the ACuCC, which must be taken into account in the observation.3. The ACuCC and lgKcu values in the typical areas of the Bohai Sea.The seawater of Bohai Sea has a strong capacity of complexing with Cu, Cd, Pb and Zn. The mean value of ACuCC is 437.5nmol/L in the North area of the Bohai Bay for surface seawater, 210.8nmol/L in the Yellow River estuary for surface seawater and 486.5nmol/L in the South area of the Bohai Sea for seawater. The mean value of lgKcu is 7.89 in the North area of the Bohai Bay for surface seawater, 8.17 in the Yellow River estuary for surface seawater and 8.04 in the South area of the Bohai Sea for seawater.4. Variational characteristics of the heavy metal complexation capacity of surface water in the Yellow River estuary.The surface water heavy metal complexation capacity of the Yellow River estuary increase from the riverway to the entrance of the Yellow River and decrease from the entrance to the sea. Maybe it is the results of the particulate organic carbon (POC) turn to dissolved organic carbon (DOC) and the dilution of seawater.5. Correlation between the complexation parameters and dissolved chemical oxygen demand (DCOD).Using correlation analytical method, the correlation between DCOD and complexation parameters is determined. Comparisons of data for seawater samplescollected from Bohai Sea show no significant correlation.6. Copper ion's toxicity and quantitative calculating the self-purification capacity of seawater to copper in the typical areas of the Bohai Sea.Using Van den Berg function, the amount of free or labile metal in seawater is calculated and it's toxicity to marine organisms is evaluated. The degree of copper contaminated to seawater is relatively serious in the North area of the Bohai Bay, which will do potential harm to marine organisms in a few part of this area. The next serious one is Laizhou Bay and it is the lightest in the middle part of the Bohai Sea. Copper in the studied areas seawater is safely to marine organisms as a whole. As a pilot study, the seawater self-purification capacity to copper is estimated. Seawater self-purification capacity to copper is 16.81 nmol/(L· a)(1.07 μ g/(L ·a)) in the North area of the Bohai Bay include 8.06 nmol/(L · a)(0.51 μ g/(L · a)) remainder, 40.86nmol/(L · a)(2.60 μ g/(L · a)) in the Laizhou Bay include 27.08nmol/(L · a)(1 .72 μ g/(L · a)) remainder and 17.87nmol/(L · a)(1 .14 μ g/(L · a)) in the South half part of the middle part of the Bohai Sea include 13.64nmol/(L · a)(0.87 μ g/(L· a)) remainder.