Shake flask and microcosm studies were conducted to determine the fate of parachlorophenol (p-CP) in water and sediment systems and the role of sediment and nonsediment surfaces in the biodegradation process. Biodegradation of p-CP in estuarine water samples in shake flasks was slow over incubation periods of 300 hours. The addition of detrital sediment resulted in immediate and rapid degradation evidenced by the production of 14CO2 from (14C) p-CP. The addition of sterile sediment, glass beads or sand resulted in an approximately 4 to 6 times faster biodegradation than observed in the water alone. Densities of p-CP degrading bacteria associated with the detrital sediment were 100 times greater than those enumerated in water. Bacteria in the water and associated with the sediment after preexposure of both water and sediment to p-CP demonstrated enhanced biodegradation. In some microcosms, p-CP was degraded completely in the top 1.0 cm of intact sediment beds. Sediment reworking activities by benthic invertebrates from one site were sufficient to mi p-CP deep into the sediment bed faster than biodegradation or molecular diffusion. p-CP was persistant at lower depths of the sediment, possibly a result of reduced oxygen conditions preventing aerobic biodegradation.