Influence Of DOM In Taihu Lake On Cu Species And Bioavailability

Potential danger raised by metal accumulation in aquatic environments and inaquatic organisms not only poses threat to our environments but also to the food safety.Generally, bioavailability of heavy metals is related to physical and chemicalconditions of the aquatic environment. In particular，the dissolved organic matters isimportant control over the biogeochemical behavior and toxicity of heavy metals innatural waters. The heavy metal pollution in the Taihu Lake has been becoming moreand more serious. So we studied the influence of DOM in Taihu Lake on the speciesand bioavailability of Cu, and this work will provide a data base for the ongoingChina’s criteria strategy, which proposed recently by the Ministry of EnvironmentProtection of China to establish its own water quality criteria system based on China’secological and economic situation. Main contents of the thesis are listed as follows:(1) Metal concentrations in the water column in Taihu Lake were generally lowand would not give rise to ecological risks either for the CCC or CMC values. Theconcentration of most metals in the interstitial water was not higher than in the watercolumn. In the sediment, metals were enriched compared with the background valuesfor local soil. Spatially, many metals presented a clear spatial gradient in both watercolumn and sediment from the Caoqiao River to the lake, which is a reflection of theimpact of river input s to the lake. The potential bio-available fraction of the heavymetals accounted for8.4%(Cr) to55.6%(Cu) of the total metal concentration.Statistical analysis indicated that organic matters had a significantly stronger controlon the metal distribution and species than pH in Taihu sediment.(2) Insoluble organic matter of sediment can absorb most Cu from water phaseand DOM could greatly enhance the sorption capacity. Through quantitativelycharacterizes the Cu binding potential of DOM in sediment from different part ofTaihu Lake, results show that the exogenous DOM included more humic matters thanendogenous DOM and had higher complex capacity than Taihu Lake DOM. Thefluorescence quenching results reflect that the complex capacity of humic componentsin DOM was from111.5mg/g to151.4mg/g, however, the complex capacity of proteincomponents was from26.3mg/g to35.4mg/g. According to the complex capacity andDOM concentration in Taihu Lake, it was calculated that if the Cu concentration inTaihu Lake water was less than7.87mg/l, Cu would exist as DOM complexation inthe water column. The desorption experiment indicated that insoluble organic matters could form the most stable complexes, however, DOM was favorable for the metaltransportation.（3）The equilibrium membrane dialysis method was employed to determine themolecular weight distribution of dissolved organic matters in the Taihu Lake sediment.Results indicate that Taihu DOM was dominated with the molecular weight>3500Dain south lake, while DOM was dominated with the molecular weight between<10000Da. Overall, south lake DOM had a higher molecular weight than that in northlake. Through analyzing the substances in different molecular weight DOM, it wasfound that the high molecular weight DOM was mainly consisted by the humicmatters while the low molecular weight DOM was mainly comprised by theprotein-lake matters. The ISE results and3DEEM spectral characteristics showed thatCu tended to be associated with low molecular weight DOM in Taihu Lake.(4) DOM in the Taihu water was significantly degraded under UV radiation. Theconcentration of TOC declined quickly between72h and168h. UV absorption and3DEEM results showed that the a254decreased quickly and the four fluorescencepeaks also disappeared quickly under UV radiation condition. This indicated a morecomplete degradation under UV radiation. Under the dark condition, the a254andA254/A400ratio showed the action of microorganisms in converting high molecularweight substances into low molecular weight substances. The Variation of degradationbehavior of different components in DOM can caused different effects on theinteraction between DOM and Cu. Under UV condition，Cu can promote thedegradation of DOM by the UV radiation, however, in dark， Cu inhibit thedegradation of DOM by microbes.(5) According the range of DOM concentration and percentage of HA in DOM,BLM was used to predict the species, bio-available and Water quality criteria of Cubased on the investigation of Taihu Lake water quality. The results indicated that theDOM concentration and components significantly influenced the species of Cu andthen influenced the bio-available and water quality criteria of Cu. With the increase ofDOM concentration or the percentage of HA, acute toxicity and water quality criteriaof Cu to Daphnia magna increased with a linear correlation.