| Abstract
| - The biogeochemical processes controlling the reductivetransformation of contaminants in an anaerobic aquiferwere inferred from the relative reactivity patterns ofredox-sensitive probe compounds. The fate of fivenitroaromaticcompounds (NACs) was monitored under different redoxconditions in a landfill leachate plume of a sandyaquifer.Results of field experiments (continuous injection and insitumicrocosms) were compared to the findings of laboratorybatch and column experiments (using aquifer matrix andmodel systems for sulfate- and iron-reducing conditions).NACs were transformed within 2−70 days in theleachateplume as well as in microbially active and in microbiallydeactivated experiments. Generally, aromatic amineswerethe predominant reduction products, and these compoundswere stable within the time frame and under theconditions of our experiments. Despite the presenceofvarious potential reductants (e.g., H2S/HS-,Fe(II)aq, reducedorganic matter, microorganisms), the patterns of relativereactivity of the probe compounds indicated that ferrousiron associated with iron(III) (hydr)oxide surfaceswasthe dominant reductant throughout the anaerobic region ofthe plume. Our results suggest that Fe(II) associatedwithferric iron minerals is a highly reactive reductant inanaerobic aquifers, which may also determine the fate ofother classes of reducible contaminants such ashalogenated solvents, azo compounds, sulfoxides, chromate,or arsenate.
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