| Natural aquatic colloids are defined as materials with dimension between1nm-1μm, are ubiquitous in various aquatic environments. Compared with larger particles, colloids have the properties of large number, high abundance and high specific surface areas, thus pollutants and trace metals can strongly bound to colloids. They draw great attention at home and broad due to they play a significant role in pollution, bioavailability and toxicology, even colloid themselves be bioavailable and pose potential risk on the aquatic organisms. Taking the Yangtze estuary as an example, which is characterized by complex environmental factors and intensive human activities. Cross flow ultrafiltration technique is effectively applied to separate colloids from bulk water of research region. Colloidal stability and morphology were characterized, meanwhile, colloidal elements spatial and temporal distribution were analyzed, and further explored the composition of colloidal compound and functional group. Therefore, these studies provided data base for pollutant and trace element environmental and geochemical behavior in the Yangtze estuary.The concentration of total dissolved organic carbon ranged from33.33-932.5μM, colloidal organic carbon were9.33-91.73μM, and colloidal organic carbon account for1.7-41.7%of total dissolved organic carbon. The seasonal distribution of colloidal organic carbon concentration were accordance with total dissolved fraction. Finally, the result showed that colloidal fraction was an important fraction of dissolved organic carbon. There were no significant correlation between total dissolved organic carbon and salinity, between colloidal organic carbon and salinity.The morphologies of aquatic colloids in Yangtze estuary included roughly spherical, thin platy, irregular debris, rod and fibrillar shape. These materials may be biological cells, biological exudates, clay minerals, bacteria, polysaccharide and diatoms. Main colloids of estuary and coastal area were spherical, platy particles or aggregates, however, estuarine colloids were much abundance than those of coastal areas. The morphologies of aquatic colloids at different sampling stations behaved similar, suggested the common source of these colloids. The colloidal or aggregates size much smaller, and their number much larger. Aggregation appeared between materials with similar and different structure, indicated that colloids were system that homogeneity and heterogeneity particles interacted with each other.The research of colloidal stability showed that colloidal size increased with increasing salinity, colloidal size and zeta potential decreased with dispersant at low salinity, as well as desalted colloidal or further with dispersant. The relationships between pH and size, between pH and zeta potential, suggested that natural aquatic colloidal stability was in accordance with DLVO theory. Colloids tend to aggregate at acidic condition, and tend to stable alkaline condition. Meanwhile, estuarine colloidal organic carbon decreased with increased size, but there was no significant change in coastal area.The sediment, suspended particles and colloids of station XP, LHK and WSK in Yangtze estuary were qualitatively and quantitatively analyzed. The results showed that main clay minerals were smectite (montmorillonite), illite, chlorite and kaolinite, non-clay minerals were quartz, potassium feldspar, calcite and dolomite, quartz was the highest non-clay minerals component. The main mineral components of colloids were similar with corresponding sediments and suspended particles. The relative percentage of smectite, illite, chlorite and kaolinite of XP colloid were5.13%,56.41%,17.95%and20.51%, respectively; Those of LHK colloid were14.61%,40.45%,31.46%and13.48%, respectively; Those of WSK colloid were33.33%,37.04%,7.41%and22.22%. Illite was the highest clay mineral of three types of colloids. The clay minerals components were similar with suspended particles and sediments, and also similar with previous researches on sediments of the Yangtze estuary, suggested that mutual transformation occurred among colloids and suspended particles, sediments. The research of13C NMR of three colloids showed that alkyls-C was the highest, O-alkyls-C and carbonyl/acyls-C followed, aromatic-C was the lowest. There were difference between different type of carbon percentage, suggested that three colloids had different structure. According to the characteristic peaks, three colloids process terminal methyl and-CH2CH2CH2COO-, polysaccharide structure. Particularly, XP colloids had rich polysaccharide materials and LHK colloids had more carbonyl/acyls/carboxyl-C. The infrared spectroscopic analysis of three colloids, suspended particles and sediments showed characteristic peaks of carbohydrate, protein and phenyl, also adsorption peaks of C=C of aromatic and carbonyl, peaks of C-O of phenol, alcohol, ether and ester, deformation peak of O-H and bending vibration peak of Si-O-Si. The colloidal FTIR spectrogram were similar with corresponding sediments and suspended particles, but absorbance of each sample were different significantly, suggested that common source and different chemical composition and material structure. Compared with three colloids FTIR spectrograms, chemical composition of LHK and WSK colloids were much similar, but much complex of XP colloids. It can be inferred that colloids and sediments, suspended particles existed physiochemical transformation.The analysis of colloidal and truly dissolved fluorescent materials in Yangtze estuary and coastal areas showed that the main fluorescent materials were tryptophan-like and humic-like fluorescent materials, some samples had protein-like, fuvic acid-like and humic acid-like materials. Main colloidal and truly dissolved fluorescent materials of WSK were tryptophan-like materials, also exited colloidal humic-like materials in spring and winter. The intensity of tryptophan-like and humic-like peaks at WSK were higher than other sampling sites, suggesting relative frequent microbial activity and some benzene pollutants contained at WSK. While tryptophan-like and humic-like fluorescent materials were main fluorescent materials at coastal areas, and intensity of colloidal tryptophan-like peak was lower than estuary. However, humic-like fluorescent materials distribution were opposite. The inside estuary Both the two fluorescent materials intensities of inside estuary were higher than outside estuary, indicating that terrestrial input is an important source of dissolved organic matter at sea. The seasonal change was not significant. The intensities of colloidal tryptophan-like and humic-like decreased with increasing salinity, but no significant correlation relationship, reflecting that salinity had effect on colloidal fluorescent materials distribution, but not the primary factor. The intensities of colloidal tryptophan-like and humic-like behaved some positive correlation relationship with COC, and the latter had stronger correlation relationship with COC than the former, suggested that COC play more significant role in distribution of humic-like than tryptophan-like.Concentrations of colloidal Na, Mg, K, Ca and B were0.01-33749μg/L, with average concentrations of1129.7μg/L. The percentage of colloidal to dissolved normal elements were0-80%, and that to total were0-59.74%. Concentrations of colloida Al, Ba, Co, Cr, Cu, Fe, Li, Mn, Ni and Zn ranged from0.003to69.75μg/L, with average concentrations of2.64μg/L. The percentage of colloidal to dissolved phase were0.1-95.73%, and that to total were0-82.97%. The percentage of colloidal Fe to dissolved was the highest, Al, Co, Cu followed, Ba, Cr were much smaller, suggesting that binding capacity of these metals with colloids are stronger than else. Though concentrations of colloidal normal elements were3-4times higher than trace elements, the former accounting for dissolved was much smaller than the latter, indicated that colloids play much significant effect on trace elements than normal elements. The correlation relationship between concentration of colloidal trace elements and salinity showed that all the trace elements behaved non-conservative. Among them, concentration of colloidal Al, Ba, Cu, Fe, Mn, Zn in winter tend to decreased with increased salinity. A distinctive V-shape distribution pattern was presented in the concentration of colloidal Co、Li、Ni, while that of colloidal Cr showed a inverted V-shape distribution pattern. Total concentration of colloidal trace elements increased with increasing concentration of COC, and had some correlation relationship in spring, had well correlation relationship in autumn. There were also some correlation relationships between concentration of colloidal Ba and COC, between colloidal Li and COC, between colloidal Li and COC, between colloidal Zn and COC, between colloidal Mn and COC, between colloidal Fe and COC, reflecting that the above elements had some affinity with colloidal organic matters. Koc and Kop values were defined to analyze binding capacity of colloidal, particle and truly dissolved organic carbon with elements. The binding capacity of colloidal organic carbon with Na, Mg, Ba, Co, Cr, Cu, Li, Mn, Ni and Zn were stronger than particle organic carbon, but other elements prefer combine with particle elements in estuary. While in coastal area, the binding capacity of colloidal organic carbon with most elements were stronger than particle elements. The result showed that colloidal organic carbon had strong combine capacity with most elements, indicated that colloidal organic materials play an important role in elemental form and distribution. |
PDF Full Text Request