[Effect of Dissolved Humic Acid on Thyroid Receptor Antagonistic Activity of Zinc in Aquatic Environment]

A rapid recombinant human thyroid (hTR) gene yeast bioassay was used to evaluate the effect of dissolved humic acid on thyroid receptor antagonistic activity of ZnCl₂.The concentration of bio-available zinc after its reaction with dissolved humic acids was measured by anodic stripping voltammetry (ASV).Furthermore,the reaction mechanism of humic acid and zinc was investigated by three-dimensional excitation-emission matrix fluorescence spectroscopy (3DEEM).The results revealed that ZnCl₂ demonstrated strong thyroid receptor antagonistic activity,and the concentration inhibiting 20% of the maximum effect of ZnCl₂ was 1.70×10^-5 mol·L^-1.The thyroid receptor antagonistic activity of ZnCl₂ was reduced by 30%-50% after the reaction of dissolved humic acids.The results of ASV showed that the concentration of bio-available zinc was decreased after the reaction of dissolved humic acids,the result was similar to that of bioassay test.The thyroid receptor antagonistic activity of the mixed solution of humic acid and ZnCl₂ was increased after UV radiation treatment,however it was still lower than the antagonistic activity induced by ZnCl₂.The results of 3DEEM showed that ZnCl₂ could reduce the fluorescence peak intensity of humic acid,which could intuitively characterize the interaction between humic acid and ZnCl₂.The above results can provide basic data and theoretical support for zinc toxicity study in aquatic environment and the establishment of water quality criteria for znic.