Effect Of Different Molecular Weight Dissolved Organic Matter On Bioavailability Of Cu By Chlorella Pyrenoidosa In Taihu Lake

Heavy metal pollution has become a global environmental problem in freshwater ecosystems,the algae can adsorb heavy metal which is widespread and constitutes an important part in natural freshwater environments.In addition,DOM is a natural organic ligand in aquatic environment,which can affect the migration transformation and bioavailability of heavy metals in water.In this study,we choosed Chlorella pyrenoidosa to investigate the adsorption behavior of Cu²⁺ on it,and longterm bioaccumulation process in the presence of different molecular weight DOM.The main results are shown as the following three parts.In the first part,monitoring the water quality of Taihu Lake,the results showed five sampling points have the same water temperature change trend in Taihu Lake that are reached the lowest in March,the highest temperature in July.Water pH value is in the range of the 6-10,conductivity changes in the range of 327-1202 ?S/cm,Do changes in the range of 5.5-13.2 mg/L.The measured total N and total P show that the water quality is in the state of eutrophication at each sampling point.DOM is extratcted from Taihu Lake.The method?Resin concentration-dialysis bag separation-freeze drying?was used to extract,separate and obtain the dissolved organic matter in Taihu Lake,and divided into three fractions.In the second part,we investigated the adsorption kinetics characteristics of Cu by the freshwater algae C.pyrenoidosa and the influence of environmental factors.The results showed that the adsorption Cu²⁺ on C.pyrenoidosa is a fast adsorption process,and almost complete in 1 h.The biosorption of Cu²⁺ on C.pyrenoidosa well followed the pseudo-second-order kinetic model.As the temperature rised,the adsorption capacity of Cu increased,which indicated that the adsorption of Cu on C.pyrenoidosa was endothermic,when the temperature was higher than 20 ?,the adsorption quantity does not change significantly at first and then decreased.The adsorption capacities of Cu increased as the pH increased in the range that heavy metals did not precipitate.In the third part,we investigated the effect of DOM on bioavailability of Cu²⁺ by C.pyrenoidosa.The results showed the tolerance concentration of Cu²⁺ was increased in the presence of DOM,and the maximum tolerance concentration increased with the increase of molecular weight of DOM,maximum reach 0.028 mmol/L.In the presence of the same fraction?F2 and F3?,the tolerance increases with elevating concentration of the fraction;In the presence of F1,F2 and F3,for the same concentration of Cu²⁺,the absorptive capacity of C.pyrenoidosa was decreased,and the higher the concentration,the fraction of DOM with larger molecular weight,the more obvious inhibitory effect.However,with the increase of equilibrium concentration of Cu²⁺,it had been found that a node exist between adsorption isotherm of ternary system and binary system,which promoted the enrichment of Cu2.A reasonable explanation for this phenomenon might be the complex of DOM-Cu would interact with membrane of C.pyrenoidosa to form DOM-Cu-algae ternary complexes;the EDTA elution reported that when the value at 6.25×10-3 mmol/L copper concentration,extracellular and intracellular copper content of algae both decreased,while the value at 1.56×10-2 mmol/L copper concentration,when added DOM to the solutions,and extracellular and intracellular copper content was both increase for F1,but F2 and F3 had the opposite function.Thus,we speculate that after the note between the ternary system and binary system,that should be formed the DOM-Cu-algae ternary complex,and the formation of the ternary complex required DOM?Cu and algal concentration in a range.Experimental results show that when did not form a ternary complex,DOM inhibit the accumulation of Cu²⁺ by C.pyrenoidosa,reduce the bioavailability of heavy metals,and with larger molecular weight had lower bioavailability.However,when DOM,heavy metal and algae form a ternary complex,the bioavailability of heavy metals incaease.It has great significance to evaluate ecological risk of heavy metals in water environment.