Contents And Sources Of Organic Colloid And Its Effect On Heavy Metals Behavior In Yangtze River Estuary

Organic colloids (1nm～0.45μm) is the main component of colloids in natural aquatic environment. It is particularly important due to its high specific surface area and strong potential adsorptive capacity. Most of heavy metals in natural water are combined in various organic colloids. Thus, organic colloids play a critical role in the biogeochemical cycles and bioavailability of heavy metals in aquatic environment, implying a reversibility of the "colloidal pumping" process (transformation between the particulate and dissolved phases through colloidal intermediates).Yangtze River estuary is the main channel to transport terrigenous material from Yangtze River basin to the East China Sea. Yangtze River estuarine area is an important transportation and business hub, and it also is a highly urbanization and industrialization region. Organic colloid in this area is not only from upstream runoff, but also from municipal sewage and industrial wastewater. These organic colloids become the carrier of heavy metals due to huge specific surface. Thus, we would understand more about heavy metals’biogeochemical cycle by researched on character of organic colloids and its effects on heavy metals behavior in Yangtze River estuary. These researches have important theoretical sense to to prevent pollution, and to protect human health, meanwhile, they have important practical significance to monitor water quality, to make the theory of governance, and to ensure safety of water supply.In this paper,111water samples were collected from south branch of the Yangtze River estuary during flood and ebb periods of spring and neap tides in different seasons throughout a year. To investigate the content, types, distribution and source of colloidal organic carbon and its effected on heavy metals behavior in the water from Yangtze River estuary (China). Water samples were fractionated into total dissolved (<0.45μm), high molecular weight colloidal (500kDa-0.45μm), medium molecular weight colloidal (5-500kDa), low molecular weight colloidal (1-5kDa) and truely dissolved (<1kDa) fractions with the filters and cross-flow ultrafiltration (CFF) systems, and then all fractions were subsequently characterized for organic carbon content, three dimensional fluorescence spectral characterization and heavy metals content. The main conclusions were showed as follow:(1) Concentration of colloidal organic carbon (COC) can be used as an indicator of organic colloids concent. A significant proportion of dissolved organic carbon (DOC) was found in colloidal fractions in estuarine water. In Yangtze River estuary, colloidal organic carbon (COC) concentrations was high (20.29μmol·L-1-154.16μmol·L"1, the average was50.78μmol·L-1), and ratios of COC in DOC varied from14.11%to50.50%(the average was31.93%). In COC, the ratio of medium molecular weight colloidal organic carbon (COC5k) was higher than high molecular weight (COCsook) and low molecular weight colloidal organic carbon (COCik). There was a significant temporal variation of COC in the Yangtze River estuary, such as: winter>summer>autumn>spring, spring tide> neap tide, and flood period> ebb period. In Spatial, COC concentrations in coast were higher than in middle of south branch, and water from coast of Shanghai urban slightly higher than from coast of Chongming. In addition, COC seasonal variation in coast was significantly larger than the other sampling sites, due to human activities.(2) In2009, COC annual flux was0.7*106t. Yangtze River runoff in summer is huge, but few in winter, so COC seasonal flux in Yangtze River estuary was summer>autumn>spring>winter. A large number of COC were transported to estuary through Yangtze River.(3) In Yangtze River estuary, seven types of fluorescence peaks were observed in three dimensional fluorescence spectrums of dissolved organic matter (DOM) and colloidal organic matter (COM). They were:UV fulvic-like fluorescence peak A, marine sources visible fulvic-like fluorescence peak C, low and high excitation tyrosine peak B1and B2, low and high excitation tryptophan fluorescence peak D1and D2, terrigenous visible fulvic-like fluorescence peak E. Peak A, B1, B2, D1, D2fluorescent substances were mainly existed in the truly dissolved organic matter (UOM,<1kDa), then in low and medium molecular weight colloidal organic matter (COM1k and COMsk,1-500kDa), last in the high molecular weight colloidal organic matter (COM500k). However peak D2and E fluorescent substances were mainly in the colloidal phase.(4) COM in Yangtze River estuary were mainly originated from anthropogenic sources, secondly from terrigenous sources, thirdly from autochthonous sources (biological decomposition), and the last from marine sources. The concents of anthropogenic, autochthonous, and marine sources COM1k were higher than COM5k, and higher than COMsook, but the contents of terrigenous sources COMsk were higher than COM1k and COMsook.There was obvious seasonal variation of sources of COM in the Yangtze River estuary. Terrigenous inputs in autumn and winter were significantly larger than spring and summer, and COM5k proportion in autumn and winter was higher than spring and summer. Anthropogenic emissions in spring and autumn were higher than summer and winter; in spring colloidal proteins were mainly tyrosine, in summer tyrosine almost same to tryptophan, but in autumn and winter were mainly tryptophan. The COM from anthropogenic sources were the food of plankton, so autochthonous sources from biological activity significantly in spring and autumn were stronger than summer and winter too. Compare to other seasons, marine origins was weakest in summer, because of the huge runoff in this season. In spatial, anthropogenic sources in coast of Shanghai urban was higher than those in middle of south beanch and coast of Chongming as result of human activities. (5) Heavy metals (Cu, Fe, Mn, Ni, Cr, Pb, Zn, Hg, and As) colloidal fractions were significant in dissolved pool. More than50%of dissolved Fe, Mn, Cu, Ni, Zn, and As were associated with colloidal materials. The distribution of each kind of colloidal heavy metals in different molecular weight was obvious difference. The percentages of Fec500k, Mnc500k were more than65%, the percentages of Pbc1k, Asc1k more than50%, each molecular weight percentages of Cu, Cr, Ni, Hg, and Zn were similarly, all exceed50%.(6) There was a significant temporal and spatial distribution of colloidal heavy metals in Yangtze River estuary.The concentration of Cuc, and Fec was increased from spring to winter, and Fec concentration affected by seasonal factors stronger than other heavy metals. Seasonal variation of Mnc and Crc was summer<autumn<winter<spring; Ni and Zn was spring<summer<autumn<winter; Pb was spring<summer<autumn<winter. In addition, the colloidal heavy metals concentrations in spring tide were higher than neap tide, especially in spring and winter; the colloidal heavy metals concentrations during flood period were lower than ebb period in spring tide; In spring and winter, the concentration of each molecular weight colloidal heave metals concentration during flood period were higher than that of ebb tide, but in summer and autumn which were opposite.The spatial and temporal distribution of colloidal heavy metal concentrations were directly affected by the wastewater and sewage discharged from the industrial enterprises and residents along the Yangtze River and Yangtze River estuary, and navigation of ships in the Yangtze River estuary. Fec1k concentrations in the water from coast of chongming were higher than from coast of Shanghai urban, Fec5k instead; the highest concentrations of Fec500k appeared in the middle of south branch, the rest of the sites increasing from coast of chongming to coast of shanghai urban. k, Mnc5k concentrations in coast were higher than middle, but the highest concentrations of Mncsook, Crc500k were found in middle; Cuc5k, Nic1k, Nic5k, Znc1k concentrations in the water from coast of Shanghai urban were higher than from other sites, but Cuc500k and Znc5k concentrations in the water from coast of Chongming were higher than from other sites.(7) The adsorption abilities among COC1k, COC5k, and COCsook on heavy metal were obvious different; it was easily transferred heavy metals Cu, Mn, Ni, Cr, Pb,and Zn from5-500kDa colloidal phase to1-5kDa and500kDa-0.45μm colloidal phase, becease the adsorption ablility of COCsk on these heavy metals was weakest; it was easily transferred heavy metals Fe from1-5kDa colloidal phase to5-500kDa colloidal phase, becease the adsorption ablility of COC1k on Fe was weakest; it was easily transferred heavy metals Hg, and As easily from500kDa-0.45μm colloidal phase to5-500kDa colloidal phase.The affect of "colloid pump" was strong in Yangtze River estuary, because it has high concentrations of COC. Due to "colloid pump" effect, In Yangtze River estuary, heavy metal Fe, Mn, and Cr easily transferred from true dissolved phase to colloidal phase, then transferred to particle phase. However, heavy metal Cu, Ni, Pb, Zn, Hg, and As easily transferred from particle and turely dissolved phases into colloidal phase. Therefore, organic colloidal would adjust the distribution of these heavy metals, and affect the biogeochemical cycle of these heavy metals in Yangtze River estuary.