I pursued research in environmental chemistry since the beginning of my master's thesis in 1990, which took place at the University of Berne under the supervision of Prof. Dr. P. W. Schindler and Dr. G. Furrer. During my master's thesis, I developed the computer program SteadyFit for the simultaneous determination of kinetic and thermodynamic parameters in completely mixed flow-through systems at steady state (Gfeller et al., 1993). The program was successfully applied to my own experimental data investigating the proton-induced hydrolysis of the polynuclear Al 13 complex. I could show that the decomposition of the polymer proceeds via two parallel reactions, one first order and the other second order with respect to the hydrogen ion activity. Investigation of the kinetics of proton-promoted decomposition of Al 13 is relevant for the understanding of the aspect of active sites in the dissolution kinetics of aluminium (hydr)oxide minerals in acidic solutions (Furrer, 1993). Further, Al 13 could be formed in soils and through its strong interaction with heavy metal ions influence their chemical speciation and solubility, and therefore their toxicity.
During my Ph.D. at the Institute of Terrestrial Ecology of the ETH Zürich, I investigated the surface-catalysed hydrolysis of pesticides under the supervision of Prof. Dr. R. Schulin and Dr. G. Furrer. There were two major aspects of my work. First, I developed an experimental set-up using flow-through reactors designed by Dr. G. Furrer to investigate the steady-state hydrolysis kinetics of organic compounds in mineral suspensions. The experimental set-up allows the concurrent use of up to eight flow-through reactors with on-line analysis and data acquisition of organic reaction educts and products (with HPLC) and pH. The set-up was tested by re-investigating the surface-catalysed hydrolysis of the carboxylic acid ester phenyl picolinate, which has been thoroughly studied in batch systems (Torrents and Stone, 1991). The program SteadyFit (Gfeller et al., 1993) was used to evaluate the steady-state data. Investigations of environmentally relevant processes and compounds in flow-through reactors is relevant because they represent the natural open systems better than batch reactors. Reaction rates at steady state might be different from initial rates gained from batch experiments. For the hydrolysis of phenyl picolinate in the presence of titanium oxide, steady-state rates were about 1 order of magnitude lower than initial rates in batch systems. The results are published in Gfeller et al. (1997) and Furrer et. al (1999).
Second, I investigated the degradation kinetics of the carbamate insecticide carbosulfan in homogeneous and heterogeneous aqueous batch systems. Carbosulfan (Maitlen and Sladen, 1979) is a pro-pesticide of carbofuran (introduced on the market in 1967, Worthing and Hance, 1991) which was the sixth most-used insecticide on field crops in the major producing States of the USA (Anderson, 1994). In homogeneous systems, the hydrolysis reaction was found to be first order with respect to the hydronium ion concentration with a half-life of about 1 hour at pH 3 and 1000 hours at pH 6. While TiO 2 (0.1, 0.4, 9.9 g L -1) and MnO 2 (5.0, 20.0 g L -1) did not catalyse hydrolysis, the clay-silt fraction from two acidic soils (20.0 g L -1) decreased the half-life slightly. Montmorillonite (10.0 g L -1) decreased the half-life of carbosulfan significantly and revealed a surface-catalysed reaction almost independent of the proton concentration in the pH range 3-6. The effects of the total concentration of carbosulfan and of the cosolvent (acetonitrile) concentration on the hydrolysis rate indicated that the low aqueous solubility of the pesticide is limiting its degradation kinetics.
From September 1996 until September 1997 I worked at the Institute of Freshwater Ecology, Ambleside, UK, in the research group of Dr. E. Tipping. The post-doctoral project entitled "Sorption kinetics of heavy metals on riverine suspended particulate matter" was financed by the European Science Exchange Programme ( Royal Society/ Swiss National Science Foundation). An experimental set-up using 5 completely mixed flow-through reactors arranged in series was developed to study sorption kinetics of metals on riverine suspended metals in open systems. In contrast to the reactors employed in my Ph.D., the ones developed in England are open with regard to particles. This is because steady-state sorption kinetics cannot be observed if the particles are retained in the reactors. The sorption of copper on particles from Whitray Beck (Yorkshire), a small tributary to the River Lune, was studied to test the set-up. Both at pH 4.5 and 5.5 sorption takes place within less than 10 minutes. Desorption, induced by lowering pH from 5.5 to 4.5, was slow and steady-state was not reached after 8 hours (ca 9 times the overall residence time). It has been established that the experimental design is suitable for the investigation of the kinetics of heavy metals interactions with suspended riverine particles, but that a few enhancements are necessary for future work.
Anderson, M. (1994) Agricultural Resources and Environmental Indicators. Vol. 705 of Agricultural Handbook. U.S. Department of Agriculture, Economic Research Service, Natural Resources and Environment Division.
Furrer, G. (1993) New aspects on the chemistry of aluminium in soils. Aquatic Sciences 55: 281-290.
Furrer, G., J. Klausen, and M. Gfeller (1999) The study of surface-catalysed reactions of organic compounds in mixed flow-through reactors with on-line analysis. Wat. Res. 33(1): 286-289.
Gfeller, M., G. Furrer, H. Schärli, and R. Schulin (1998) Abiotic transformation of carbosulfan in batch systems. In preparation.
Gfeller, M., G. Furrer, and P.W Schindler (1993) The determination of kinetic and thermodynamic constants in completely mixed flow-through systems at steady state. Geochim. Cosmochim. Acta 57: 685-695.
Gfeller, M., G. Furrer, and R. Schulin (1997) Use of completely mixed flow-through systems: Hydrolysis of phenyl picolinate. Environ. Sci. Technol. 31: 3692-3701.
Maitlen, E. and N. Sladen (1979) Effectiveness of granular and sprayable formulations of FMC 35001, a new insecticide/nematicide, for use on agricultural crops. Proc. Brit. Crop Prot. Conf. - Pests and Dis. 2:557-564.
Torrents, A. and A. Stone (1991) Hydrolysis of phenyl picolinate at the mineral/water interface. Environ. Sci. Technol. 25: 143-149.
Worthing, C. E. and R. J. Hance (1991) The Pesticide Manual. Brit. Crop. Prot. Counc., Farnham, Surrey, UK.
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Last modification: 2005/11/9 at 20:31