The aqueous solubility, adsorption, mobility, and microbial degradation of polybrominate biphenyls (PBBs) and hexachlorobenzene (HCB) were studied under laboratory conditions. Studies indicated that PBBs were more than 200 times and HCB more than 2.5 times more soluble in landfill leachate than in distilled water. Also, the solubilities of PBBs and HCB were higher in creekwater and landfill leachates than in purified waters: this was correlated with a level of dissolved organics in the waters. HCB showed a greater tendency for adsorption than did PBBs. There was a high direct correlation between the total organic carbon (TOC) content of soils and the amount adsorbed. PBBs and HCB were strongly adsorbed by the Ambersorb XE-348, but not so by organic solvents. PBBs and HCB remained immobile when leached with water or landfill leachate but were highly mobile when leached with organic solvents. PBBs and HCB were found to be resistant to microbial degradation.