Short- and long-term sorption/desorption of polycyclic aromatic hydrocarbons onto artificial solids: effects of particle and pore sizes and organic matters

In order to elucidate the effect of nanopores and organic matters on sequestration of contaminants, short- and long-term sorption and desorption of naphthalene and pyrene in seven artificial solid–water systems were studied. Fast sorption occurred in every case; steady states were reached within 1–5 h. Sorption constants varied drastically among the seven absorbents, ranging from 1.19 to 5.29×103 for naphthalene, and from 24.3 to 6.52×10^4 for pyrene. Slow sorption continued to take place in some cases, especially on absorbents containing humic matter. Desorption usually took place in two stages, fast and slow, on both unaged and aged absorbents. Irreversibility of desorption occurred for every absorbent except for silica particles modified with octadecyl silyl. Aging led to a reduction of fast desorption fraction due to entrapment of the chemicals into nanopores and partitioning of the chemicals into condensed areas of humic matters, and showed no effect on slow desorption and irreversibility of desorption. On the whole, entrapment into nanopores and partitioning into humic matters are considered to be important for sequestration of contaminants. Irreversibility of desorption is considered to be a more influencing factor than percentage of desorption for describing the extent of sequestration.