Coupled Abiotic/Biotic Degradation of N-Nitrosodimethylamine in Subsurface Sediments

摘要

N-nitrosodimethylamine (NDMA) is a byproduct of propellant manufac- ture, which, even at trace levels (0.7 parts per trillion), poses a considerable threat to health and ecology. Unintentional surface and subsurface releases of NDMA in water re- sults in rapid subsurface transport due to minimal NDMA sorption and negligible degradation. In this study, abiotic, biotic, and coupled degradation/mineralization proc- esses were investigated, with the field application of a permeable reactive barrier. When subsurface sediments are chemically reduced, abiotic surface phase reactions rapidly de- graded NDMA to nontoxic dimethylamine (DMA), primarily by adsorbed Fe(II). The NDMA mineralization rate and extent in oxic systems was oxygen dependent, which was indicative of microbial oxygenase pathway(s) promoting mineralization. Propane addi- tion did promote more rapid oxic NDMA mineralization. Mineralization rates were ～10x slower under iron reducing conditions for the same sediment, but the NDMA mineraliza- tion extent was still significant (10% to 15% for reducing systems, 35% to 65% for oxic systems). Results suggest that while abiotic NDMA degradation to DMA may be suffi- cient for remediation, sequential abiotic NDMA degradation (in reduced sediment) to intermediates followed by down gradient biotic mineralization of intermediates (in oxic sediment) may yield the most rapid rates for complete mineralization of NDMA mass to field-relevant (ppt) concentrations.