Temporal and spatial variation of perchlorate in streambed sediments: results from in-situ dialysis samplers

The fate of perchlorate (ClO4−) in streambed sediments is becoming a concern due to the increasing number of groundwater and surface water contamination sites in the United States. Dialysis samplers were deployed at three sites over a period of 1 year to determine the vertical distribution of ClO4− in sediment pore water. Results indicated that the spatial and temporal ClO4− penetration into sediments could be affected by numerous factors, such as temperature, microbial degradation, ClO4− surface water concentration, and sediment physico-geological properties. In general, maximum ClO4− penetration into sediments at the studied sites was 30 cm below the sediment-water surface. The vertical sequential depletion of electron acceptors in sediments suggested that microbial reduction was responsible for ClO4− depletion in stream sediments. Biodegradation of ClO4− occurred over a seasonally variable active depth zone of 1–10 cm. Results implied that there was a rapid natural attenuation potential of perchlorate in saturated near-surface sediments.