When soil particles are exposed to a contaminant for a long time, some fraction of the contaminant becomes more difficult to release into the surrounding fluid. This phenomenon is evident in studies of contaminant release from spherical particles, where sometimes the release appears to take place in two distinct steps rather than the single step predicted by theory. Many elaborate explanations have been proposed, including distributions of parallel versus serial pore complexes, and multi-site, multi-rate sorption mechanisms. We hypothesize a different mechanism, based on the observed low connectivity of pores inside crystalline rock, e.g. sand grains and gravel particles. This low connectivity results in both porosity and diffusion path length, as functions of distance from the sphere's surface, being different from that given analytically or in well-connected porespaces. A low-connectivity porespace in a spherical particle therefore produces an anomalous pattern of contaminant desorption over time, and so offers a simple and physically-based explanation for the observed two-step desorption phenomenon.