Particle size dependence of slow desorption of in situ PAHs from sediments

The desorption kinetics of in situ contaminations of phenanthrene, anthracene, pyrene, benzo(a)anthracene, benzo(b)fluoranthene, and benzo(a)pyrene have been measured for four size fractions of three sediments, with a technique in which the porous polymer Tenax serves as an infinite sink for desorbed PAH. For one of the sediments, there appears to be a slight tendency of increasing (slowly + very slowly) desorbing fractions (Fslow+very slw) and decreasing first-order rate constants of slow desorption (kd, low) with increasing particle size. However, for the two other sediments Fslow+very slow and kd, slow showed no relation with particle size. Fslow+very slow values ranged from 7 to 90% of the total extracted PAH amount; kd, slow ranged from 0.23•10−3 h−1 to 1.52•10−3 h−1. The present results indicate that whole-particle size and, thus, overall particle size distribution are not determinants for the slow desorption of organic chemicals. This means that it is probably not diffusion on the whole-grain scale which determines slow desorption of organic compounds from sediments.