Hans-Dieter Narres

Physicochemical interactions between atrazine and clay minerals

The aim of this work was to study the sorption behaviour of atrazine on clay minerals at low environmentally relevant concentrations. Adsorption and desorption isotherms of atrazine were determined on different clay minerals using the 14C tracer technique. The adsorption isotherms are linear at pH 5.8 in the low concentration range studied. The adsorption constant Kd is proportional to the external surface in Na+ layer silicates, such as kaolinite, illite and montmorillonite. This implies that atrazine molecules do not intercalate even in swelling Na+ clay minerals. The experiments with homoionic montmorillonites (Na+, Ca2+, Ni2+, Cu2+ and Fe3+) indicate a correlation between the adsorption constant and the hydrolysis constant of the exchangeable cation. This suggests a participation of the protonated atrazine molecules in sorption due to electrostatic interactions. It is assumed that adsorption shifts the chemical equilibrium to the side of the protonated form for Men+ montmorillonites with a low hydrolysis constant of Men+. In contrast, protonation clearly dominates in Fe3+ montmorillonite because of the high hydrolysis constant of the Fe(III) ion and the adsorption isotherm obtained is not linear. The desorption isotherms show a hysteresis on all the Men+ montmorillonites examined for the time interval of 3.5 weeks. It is suggested that only that fraction of the bound atrazine, which is adsorbed due to the relatively weak physical forces, can be desorbed. The larger the fraction of protonated atrazine molecules on the surface, the less is remobilized.

Effect of organic carbon and mineral surface on the pyrene sorption and distribution in Yangtze River sediments

The effect of organic carbon (OC) and mineral surface on the sorption of polycyclic aromatic hydrocarbon (PAH) pyrene molecule to four Yangtze River sediments was investigated by sorption batch techniques using fluorescence spectroscopy. Pyrene sorption to the mineral fraction was estimated with model sorbent illite, the main clay mineral in Yangtze sediment. The Freundlich model fitted sorption to illite and to sediments was normalized to the specific surface area (SSA). Comparison of the SSA-normalized sorption capacities of illite and sediments suggests a negligible contribution of the pyrene sorption to the mineral fraction. In addition, composite models, such as the linear Langmuir model (LLM) and the linear Polanyi-Dubinin-Manes model (LPDMM) were applied for fitting the sorption of pyrene to the pristine sediments. The application of composite models allows assessing the partition of pyrene into amorphous organic carbon (AOC) and the adsorption in the porous structure of black carbon (BC). The modelling results indicate that the pyrene adsorption to the minor BC components (<0.2%) is more effective than the partition to AOC (0.5-1.3%). Besides the pristine sediments, sediments preheated at 375 degrees C were also studied, in which the AOC fraction was removed during the preheating treatment. The modelling results with LPDMM and Polanyi-Dubinin-Manes model (PDMM) indicate a similar adsorption capacity of BC in pristine and preheated sediments, respectively. The low AOC concentrations in sediments do not diminish the BC micropore filling with pyrene. Simulation of pyrene distribution in the investigated Yangtze River sediments support the importance of the BC fraction in the PAH immobilization under environmental conditions.

Pyrene and Phenanthrene Sorption to Model and Natural Geosorbents in Single- and Binary-Solute Systems

Sorption of pyrene and phenanthrene to model (illite and charcoal) and natural (Yangtze sediment) geosorbents were investigated by batch techniques using fluorescence spectroscopy. A higher adsorption of phenanthrene was observed with all sorbents, which is related to the better accessibility of smaller molecules to micropores in the molecular sieve sorbents. In addition, pyrene sorption in binary-solute systems with a constant initial concentration of phenanthrene (0.1 μmol L(-1) or 2 μmol L(-1)) was studied. A 0.1 μmol L(-1) concentration of phenanthrene causes no competitive effect on the pyrene sorption. A 2 μmol L(-1) concentration of phenanthrene significantly suppresses the sorption of pyrene, especially in the low concentration range; nonlinearity of the pyrene sorption isotherms thus decreases. The competitive effect of 2 μmol L(-1) phenanthrene on the pyrene sorption is overestimated by the ideal adsorbed solution theory (IAST) using the fitted single sorption results of both solutes. An adjustment of the IAST application by taking into account the molecular sieve effect is proposed, which notably improves the IAST prediction for the competitive effect.

Interactions of 15 N-Sulfadiazine and Soil Components As Evidenced by 15 N-CPMAS NMR

The extensive use of sulfonamides (SNs) in animal husbandry has led to an unintentional widespread occurrence in several environmental compartments. The implementation of regulations and management recommendations to reduce the potential risk of development of antibiotic resistances necessitates detailed knowledge on their fate in soil. We present results from two independent incubation studies of 15N-labeled sulfadiazines (SDZ) which focused on identifying binding types in bound residues. In the first study 15N-amino labeled SDZ was incubated with two previously isolated humic acids in the presence and absence of Trametes versicolor laccase, while in the second study 15N-double-labeled SDZ was incubated with a typical agricultural Luvisol and the humic acid fraction isolated after sequential extraction of the soil. The freeze-dried humic acid fractions of both studies were then analyzed by 15N-CPMAS NMR and compared with the 15N-spectra of synthesized model compounds. In both studies amide bonds and Michael adducts were identified, while formation of imine bonds could be excluded. In the humic acid study, where less harsh extraction methods were applied, possible formation of H-bridging and sequestration were additionally detected.