Role of non-ionic surfactants and plant oils on the solubilization of organochlorine pesticides by oil-in-water microemulsions

Screening low-cost, high efficacy and environmentally safe surface active agents is critical for achieving successful surfactant-enhanced remediation (SER) of soil contaminated with hydrophobic organic compounds. This study reports the solubilization of organochlorine pesticides (DDT or γ-HCH) in oil-in-water (Winsor I) microemulsions (E) composed of non-ionic surfactant (Tween 80 or Triton X-100), plant oil (linseed oil or soybean oil), and the cosurfactant (1-pentanol). Results show that the cosurfactant to surfactant ratio (C/S ratio, w/w) is the major factor influencing the microemulsion formation, and C/S ratios of 1:3 and 1:6 are superior to 1:1 for microemulsion formation. 66.9-95.6% and 51.9-80.9% of DDT solubilization enhancements were achieved by microemulsions based respectively on Tween 80 or Triton X-100 as compared to their respective surfactant solution alone, indicating the higher solubilizing capacities of microemulsion systems. The solubilization of γ-HCH also increased by 40.6-57.5% in microemulsion formed with Tween 80 and 43.0-65.8% in microemulsion formed with Triton X-100, compared with that in corresponding surfactant solutions only. Further studies revealed that both cosurfactant content and oil content could influence the solubilizing capacity of microemulsions system, and higher solubilizing capacity could be obtained when more cosurfactant or oil were emulsified in microemulsion system. Between the two, oil content is more influential than cosurfactant content. The present results affirm the effective role of microemulsions formed with Tween 80 and Triton X-100 in enhancing the solubilization of DDT and γ-HCH which would facilitate remediation of soils contaminated with these compounds.