Biomedical subjects

Liselotte Clausen

Publications and source records attributed to Liselotte Clausen.

3 recordsLinked to original sources

PubMed2006

Controls on atrazine leaching through a soil-unsaturated fractured limestone sequence at Brévilles, France.

The objective of this study was to identify the main controls on atrazine leaching through luvisols and calcisols overlying fissured limestone using the dual-permeability model MACRO. The model parameterisation was based on a combination of direct measurements (e.g. hydraulic properties, adsorption and degradation), literature data and calibration against bromide leaching experiments in field plots. A Monte Carlo sensitivity analysis was carried out for a typical application pattern, considering two different depths of unsaturated limestone (15 and 30 m). MACRO calibrations to the field experiments demonstrated the occurrence of strong macropore flow in the luvisol, while transport in the calcisol could be described by the advection-dispersion equation. MACRO simulations of tritium and atrazine leaching qualitatively matched tritium concentration profiles measured in the limestone and atrazine concentrations measured in piezometers and in aquifer discharge via a spring. The sensitivity analysis suggested that the thickness of the limestone, as well as the transport properties and processes occurring in the unsaturated rock (e.g. matrix vs. fissure flow) will have little significant long-term effect on atrazine leaching, mainly because degradation is very slow in the limestone. No mineralization of atrazine was detected in one-year incubations and a mean half-life of 10 years was assumed in the simulations. Instead, processes occurring in the soil exerted the main control on predicted atrazine leaching, especially variations in the degradation rate and the strength of sorption and macropore flow. However, fissure flow in unsaturated rock is expected to exert a much more significant control on groundwater contamination for compounds that degrade more readily in the deep vadose zone.

Atrazine↗

PubMed2004

Sorption of the herbicide dichlobenil and the metabolite 2,6-dichlorobenzamide on soils and aquifer sediments.

The worldwide used herbicide dichlobenil (2,6-dichlorobenzonitrile) has resulted in widespread presence of its metabolite 2,6-dichlorobenzamide (BAM) in pore- and groundwater. To evaluate the transport of these compounds we studied the sorption of dichlobenil and BAM in 22 sediment samples of clayey till, sand, and limestone including sediments exhibiting varying oxidation states. Dichlobenil sorbed to all investigated sediments, with a high sorption in topsoils (Kd = 7.4-17.4 L kg(-1)) and clayey till sediments (Kd = 2.7-126 L kg(-1)). The sorption of the polar metabolite BAM was much lower than the sorption of dichlobenil but followed the same tendency with the highest sorption in the topsoils (Kd = 0.24-0.66 L kg(-1)) and in the clayey till sediments (Kd = 0.10-0.93 L kg(-1)). The sorption of both compounds was significantly higher (2-47 times) in the unoxidized (reduced) clayey till than in the weathered (oxidized) clayey till. Such a difference in sorption capacity could neither be explained by a higher organic carbon content, sorption to clay minerals, differences in clay mineralogy, nor by blocking of reactive surface sites on clay minerals by iron oxides. However, by removing an average of 81% of the organic carbon from the reduced clayey till with H2O2, the sorption decreased on average 50%. Therefore, most of the sorption capacity in the reduced clayey till was related to organic carbon, which indicates that sorption processes are affected by changes in organic compound composition due to weathering.

Adsorption↗

PubMed2004

Quantitative microarray pesticide analysis.

To replace a pesticide immunoassay based on microtiter plates, we have developed a quantitative, competitive microarray immunoassay, which permits rapid and highly sensitive quantification of the dichlobenil degradation product 2,6-dichlorobenzamide (BAM), and the prominently used herbicide atrazine. The pesticide analysis is based on the competitive binding of fluorescence conjugated monoclonal antibodies (mAb) to their respective analytes. Lowest detection limits were calculated to 1 ng/l (5 pM) for BAM and 3 ng/l (10 pM) for atrazine. Corresponding IC(50) values were, 10 ng/l (50 pM) for BAM and 34 ng/l (160 pM) for atrazine, respectively. In comparison to the existing microtiter plate immunoassay, the microarray was found to be up to 20-fold more sensitive. Compared to the gas chromatography with mass spectroscopy (GCMS) analysis performed on more than 1000-fold concentrated samples, the microarray-based immunoassay was even 10-fold more sensitive using non-concentrated samples. Measuring both analytes simultaneously did not affect assay sensitivity compared to single analyte quantification. Besides a gain in sensitivity and the possibility of multiplex quantification, assay times and assay complexity were reduced drastically with the microarray platform compared to the microtiter plate immunoassay and GCMS, suggesting that the microarray based immunoassay is a viable method for measuring picomolar amounts of analytes, e.g. clinically relevant analytes.

Antibodies, Monoclonal↗