干旱区研究

Arid Zone Research ›› 2018, Vol. 35 ›› Issue (1): 243-248.doi: 10.13866/j.azr.2018.01.30

• Ecologyand Environment • Previous Articles    

Complexation of As (Ⅲ) with Extracellular Polymeric Substance from Biofilm in the Salt-discharging Channel in Kuytun,Xinjiang

LIN Qing-hua1,2, ZHANG Dao-yong1,3   

  1. 1. State Key Laboratory of Environmental Geochemistry,Chinese Academy of Sciences,Guiyang 550002,Guizhou,China;
    2. University of Chinese Academy of Sciences,Beijing 100049,China;
    3. College of Environment,Zhejiang University of Technology,Hangzhou 310014,Zhejiang,China
  • Received:2017-04-01 Revised:2017-05-26 Online:2018-01-15 Published:2025-11-16

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Abstract: There is a heavy arsenic pollution in the salt-discharging channel due to the geological background in Kuytun,Xinjiang. The complexation between extracellular polymeric substance of the algal biofilm and As (Ⅲ) influences the transportation and diffusion of arsenic and further affects the biological toxicity and the ecological risk of arsenic.At present,the effects of the widespread biofilm on the transport and fate of arsenic in channel are completely unknown.In this study,the interaction of extracellular polymeric substance of the algal biofilm and As (Ⅲ) was investigated by fluorescence quenching test and isothermal titration calorimetry.The results of fluorescence quenching test showed that the fluorescent components of extracellular polymeric substance were composed of three fluorescence peaks: Peak A belonged to aromatic protein Ⅱ,Peak B belonged to soluble microbial by-product-like,and Peak C belonged to humic acid-like.Peak A and B were collectively referred to protein-like substance,and peak B was further intended to be tryptophan-like substance.There was a strong complexation between the protein-like substance and As (Ⅲ),while the interaction between As (Ⅲ) and the humic-like substance was ignorable.Both static quenching and dynamic collision were involved in fluorescence quenching of extracellular polymeric substance by As (Ⅲ).The binding constant,lgKb,for interaction of As (Ⅲ) with the aromatic protein-like substance and tryptophan-like substance were 3.82 and 2.22 respectively,indicating the binding affinity of As (Ⅲ) to the former is one order of magnitude greater than the latter.Multiple sites were involved in competition for binding As (Ⅲ) in the aromatic protein-like substance,and only one class of binding sites were taken part in tryptophan-like substance for their complexation with As (Ⅲ).The data obtained from isothermal titration calorimetry test were fitted by independent model,and the thermal dynamic parameters ΔH,ΔG and ΔS of complexation reaction were acquired.Negative enthalpy change ΔH and negative Gibbs free energy ΔG proved that the complexation between extracellular polymeric substance and the As (Ⅲ) is a spontaneous exothermic reaction.The degree of disorder in the complexing reaction increases,and the reaction is driven by entropy.The protein-like substance in the biofilm in salt-discharging channel may have significant effects on environmental fate and risk of arsenic,while the role of humic acid-like substance in extracellular polymeric substance is ignorable.

Key words: salt-discharging channel, arsenic pollution, biofilm, EPS, fluorescence quenching, isothermal titration calorimetry, Kuytun, Xinjiang