Surface solubilization of phenanthrene by surfactant sorbed on soils with different organic matter contents

The effect of sorbed surfactant on the distribution of hydrophobic organic compounds (HOCs) during soil washing was investigated using a mathematical model. Phenanthrene (PHE) as an HOC and Triton X-100 (TX100) as a nonionic surfactant were used with two soils with low (SS) and high (BS) organic matter contents. The available carbon fraction (f(A,soil)(*)) after surfactant sorption was determined from surfactant coverage by measuring soil surface area using a methylene blue method. The sorbed surfactant was greatly effective as a sorbent for PHE, with an effectiveness factor (epsilon(soil)) in the range of 10.9-117.2 for SS and 39.7-121.3 for BS. Surface molar solubilization ratio (MSR(s)) and epsilon(soil) decreased with increasing TX100 dose. The MSR(s) decrement was lower for BS than for SS probably due to stronger affinity of PHE on organic matter in BS than in SS, which cause lower efficiency of soil washing than estimated by intrinsic sorption of PHE. These results suggest that soil washing in the field using surfactant for soils with high organic matter contents may give much lower efficiency than expected due to additional adsorption of HOC onto sorbed surfactant.