Heterogeneous dissolution of benzo(a)pyrene by surfactant solutions

The dissolution of a solid deposit of benzo(a)pyrene (BaP) has been investi gated using three surfactants, a cationic (benzyldimethyl dodecylammonium b romide), an anionic (sodium dodecyl sulfate) and a neutral (t-octylphenoxyp olyethoxyethanol). Dissolution is a heterogeneous process characterized by the fragmentation of the solid deposit into solid particles. Successive fil trations have defined three granulometric classes: the coarse fraction grea ter than 0.45 mu m, the fine fraction ranging between 0.05 and 0.45 mu m an d the micellar fraction lower than 0.05 mu m. The chemical nature of the su rfactant influences the repartition into the different classes. The coarse fraction becomes negligible when the concentration of the cationic surfacta nt is increased. It still represents more than 80% of the deposit with neut ral and anionic surfactants, even in a large excess of surfactant concentra tion compared to the critical micellar concentration value. The cationic su rfactant is also the most efficient towards the solubilization in micellar phase. This efficiency is attributed to the contribution of two mechanisms: a partition process into the hydrophobic core of the micelle and a surface solubilization into the palisade layer due to specific interactions, surfa ce solubilization being the major contribution. Electrophoretic mobility me asurements have shown (i) the pronounced negative charge carried by the dep osit surface and by BaP particles (ii) the strong affinity of the cationic surfactant towards these surfaces. The break up of the deposit into fine fr agments and the solubilisation by the cationic surfactant is correlated to this adsorption. (C) 2000 Elsevier Science B.V. All rights reserved.