Hysteresis in the sorption and desorption of hydrophobic organic contaminants by soils and sediments: 1. A comparative analysis of experimental protocols

Sorption and desorption equilibria were measured for an organic contaminant probe, phenanthrene, and five EPA reference soils and sediments to evaluate the existence and extent of apparent isotherm hysteresis. Three different experimental protocols were tested to assess their relative potentials for introduction of artifact. The results reveal that: i) all systems studied exhibit apparent sorption–desorption hysteresis; ii) the three protocols tested yield significantly different degrees of apparent hysteresis; iii) principal sources of artifact are solute losses to reactor components and failure to achieve equilibrium sorption conditions; iv) isotherm nonlinearity elevates the potential for introduction of artifacts in the quantification of desorption hysteresis; and v) little if any ‘solids effectʹ was observed. A single-cycle decant-refill batch reactor technique employing sealed and resealed glass ampules was found to involve minimal potential for introduction of artifacts. The general suitability of the procedure is confirmed in additional studies described in the companion paper of this two-part series.