Adsorption behavior of sulfamethoxazole on 11 soils and its co-adsorption with Ca~(2+),Mg~(2+) or Zn~(2+)

This study investigated the adsorption behavior of sulfamethoxazole(SMX) on 11 soils collected in Yunnan Province.The correlation between individual soil properties and the apparent sorption coefficients was not significant,indicating that SMX sorption on the soil may be controlled by various mechanisms.The presence of Ca2+,Mg2+ or Zn2+ in the sorption system showed distinct influences on SMX adsorption.Among the three metal ions,Zn2+ dramatically increased SMX sorption,while Ca2+ and Mg2+ did not alter SMX sorption significantly.The sorption of SMX also decreased Ca2+ or Mg2+ adsorption,but didn′t decrease Zn2+ adsorption.This phenomenon may be resulted from inner-sphere complexation of Zn2+ with soil particles,which consequently resulted in the occupation of the internal sites and replacement of H+.This process led to the decrease of the negative surface charge,and decline of the repulsion between soil and SMX.