Showing papers by "Stefan B. Haderlein published in 1998"
TL;DR: In this article, the biogeochemical processes controlling the reductive transformation of contaminants in an anaerobic aquifer were inferred from the relative reactivity patterns of redox-sensitive probe compounds.
Abstract: The biogeochemical processes controlling the reductive transformation of contaminants in an anaerobic aquifer were inferred from the relative reactivity patterns of redox-sensitive probe compounds. The fate of five nitroaromatic compounds (NACs) was monitored under different redox conditions in a landfill leachate plume of a sandy aquifer. Results of field experiments (continuous injection and in situ microcosms) were compared to the findings of laboratory batch and column experiments (using aquifer matrix and model systems for sulfate- and iron-reducing conditions). NACs were transformed within 2−70 days in the leachate plume as well as in microbially active and in microbially deactivated experiments. Generally, aromatic amines were the predominant reduction products, and these compounds were stable within the time frame and under the conditions of our experiments. Despite the presence of various potential reductants (e.g., H2S/HS-, Fe(II)aq, reduced organic matter, microorganisms), the patterns of relat...
139 citations
TL;DR: In this paper, enantiomer-specific gas chromatography combined with mass spectrometry was used to detect residues of (R)- and (S)-mecoprop in leachate samples.
Abstract: Leachate samples from a waste disposal site in Switzerland and groundwater samples downstream of the landfill were analyzed for residues of (R)- and (S)-mecoprop [(R)- and (S)-2-(4-chloro-2-methylphenoxy)propionic acid] by means of enantiomer-specific gas chromatography combined with mass spectrometry. (R)- And (S)-mecoprop were found at equal concentrations (up to 124 μg/L) in the landfill leachate, indicating that a racemic mixture of mecoprop leached to the receiving groundwater. Groundwater samples downstream of the landfill contained from <0.001 to 975 μg/L of mecoprop and 16 out of 31 samples showed a significant excess of (R)-mecoprop. Sorption of (R)- and (S)-mecoprop to aquifer matrix and to various reference minerals was generally low and did not discriminate between the mecoprop enantiomers. We conclude that enantioselective microbial degradation increased the enantiomeric ratio of (R)- to (S)-mecoprop during groundwater passage of the landfill leachate. Most leachate-affected groundwaters are ...
92 citations
TL;DR: In this article, the combined effects of nonlinear sorption, nonequilibrium mass transfer and the distribution of sorption sites on transport of organic contaminants has been examined in porous media containing aggregates of clay minerals and organic matter as sorbents.
83 citations
TL;DR: The ability of soil minerals to interact with organic solutes exhibiting π-acceptor properties was studied using batch adsorption experiments in this paper, showing that only phyllosilicates were capable of forming strong electron donor acceptor (EDA) complexes with such solutes, including nitroaromatic explosives (e.g., trinitrotoluene [TNT]) and other priority pollutants.
Abstract: The ability of soil minerals to interact with organic solutes exhibiting π-acceptor properties was studied using batch adsorption experiments. Among the major groups of naturally occurring minerals, only phyllosilicates were capable of forming strong electron donor-acceptor (EDA) complexes with such solutes, including nitroaromatic explosives (e.g., trinitrotoluene [TNT]) and other priority pollutants. Depending on the minerals and the solutes involved, adsorption constants due to such EDA interactions may exceed those caused by nonspecific interactions by several orders of magnitude. Two major factors controlled the ability of phyllosilicates to form EDA complexes: the n-donor properties of their siloxane oxygens and the accessibility of such sites for π-acceptors. The donor properties of siloxane oxygens are enhanced by isomorphic substitution, but their accessibility for π-acceptors is restricted by the steric effects of hydrated exchangeable cations. Relative adsorption constants (K ad values) for a given set of π-acceptors were independent of the mineral structure, indicating that similar sites are involved in EDA complex formation on phyllosilicates. Thus, K ad values measured on any type of model phyllosilicate may be used to estimate the relative extent of adsorption of π-acceptors to natural subsurface matrices, irrespective of the types and abundance of phyllosilicates present. Cation exchange on phyllosilicates is a crucial geochemical process that controls the accessibility of their siloxane sites to π-acceptors due to the different sizes of the hydrated cations. Injection of electrolytes may be a promising but so far unexplored way to control the adsorption and thus the bioavailability and transport of TNT and other contaminants with significant π-acceptor properties in the subsurface.
82 citations
TL;DR: In this article, the authors investigated the transport of solutes exhibiting very different sorption characteristics under steady state conditions at different water contents of the porous medium, in which a substantial part of the sorption sites were concentrated in regions within small grained aggregates that were accessible only by diffusion.
35 citations
Journal Article•
TL;DR: In this article, the authors demonstrate that competition for sorption sites at phyllosilicates may substantially enhance the mobility of individual nitro-aromatic compounds (NACs) in porous media when present in mixtures.
Abstract: Subsurface contamination with nitro-aromatic explosives and related compounds has become a problem at many ordnance and ammunition facilities. Results of our column experiments demonstrate that competition for sorption sites at phyllosilicates may substantially enhance the mobility of individual nitro-aromatic compounds (NACs) in porous media when present in mixtures. Competitive sorption of NACs in mixtures is controlled by two major factors: (a) the relative affinities of the NACs for phyllosilicate sorbents and (b) the degree of surface site saturation of these sorbents. A transport model that accounted for competitive sorption effects by a Langmuir approach successfully predicted the multiple-species transport of three model NACs that exhibited very different affinities for phyllosilicates. Generally, the differences in the mobilities of these compounds were substantially larger when present in mixtures compared to single solute conditions. Differences in NAC mobilities may be further accentuated by nitro-reduction, an important transformation pathway of NACs in the subsurface. The resulting (nitro)anilines exhibit low affinities for phyllosilicates and thus are weak competitors which enhances their mobility in anoxic subsurface environments.
3 citations