Manganese and zinc absorption with octylphenoxyethanol surfactants by soybean leaf tissues

Abstract

Soybean leaf disks were used to study the effect of ethylene oxide (EO) chain length in a homologous series of octylphenoxyethanol surfactants on Mn and Zn absorption while floating on solutions in which CaSO4 was either absent or present. Octylphenoxyethanol surfactants with EO chain lengths of 5, 7–8, 9–10, 12–13, and 30 ethylene oxide groups per molecule of surfactant were included in the study.Zn absorption was enhanced whereas Mn absorption was decreased in the presence of 0.5 mM CaSO4. However, the presence of CaSO4 had relatively little influence on the effectiveness of the surfactants in enhancing Mn or Zn absorption. In general, surfactants of intermediate EO chain length enhanced Mn or Zn absorption to the greatest extent. Triton X-114 (EO = 7–8) generally tended to cause the greatest enhancement.The surface tension generally increased as the EO chain length increased. As the surfactant concentration was increased from 0.075 to 0.75 mM, the surface tension decreased but then tended to increase as the surfactant concentration was increased further to 7.5 mM. The interfacial tension measured at a corn oil/surfactant solution interface generally decreased with EO chain length at the 0.075 mM surfactant concentration. However, the interfacial tension decreased and then increased as the EO chain length increased at the 0.75 and 7.5 mM concentrations. Neither surface tension nor interfacial tension values could be directly associated with enhanced Mn or Zn absorption by soybean leaf disks. Also, the hydrophile–lipophile balance of the surfactants was not directly associable with enhanced Mn or Zn absorption.