Biomedical subjects

Joost Groeneweg

Publications and source records attributed to Joost Groeneweg.

4 recordsLinked to original sources

PubMed2006

Transport of sulfadiazine in soil columns: experiments and modelling approaches.

Antibiotics, such as sulfadiazine, reach agricultural soils directly through manure of grazing livestock or indirectly through the spreading of manure or sewage sludge on the field. Knowledge about the fate of antibiotics in soils is crucial for assessing the environmental risk of these compounds, including possible transport to the groundwater. Transport of (14)C-labelled sulfadiazine was investigated in disturbed soil columns at a constant flow rate of 0.26 cm h(-1) near saturation. Sulfadiazine was applied in different concentrations for either a short or a long pulse duration. Breakthrough curves of sulfadiazine and the non-reactive tracer chloride were measured. At the end of the leaching period the soil concentration profiles were determined. The peak maxima of the breakthrough curves were delayed by a factor of 2 to 5 compared to chloride and the decreasing limbs are characterized by an extended tailing. However, the maximum relative concentrations differed as well as the eluted mass fractions, ranging from 18 to 83% after 500 h of leaching. To identify relevant sorption processes, breakthrough curves of sulfadiazine were fitted with a convective-dispersive transport model, considering different sorption concepts with one, two and three sorption sites. Breakthrough curves can be fitted best with a three-site sorption model, which includes two reversible kinetic and one irreversible sorption site. However, the simulated soil concentration profiles did not match the observations for all of the used models. Despite this incomplete process description, the obtained results have implications for the transport behavior of sulfadiazine in the field. Its leaching may be enhanced if it is frequently applied at higher concentrations.

Adsorption↗

PubMed2004

Enumeration of soil bacteria with the green fluorescent nucleic acid dye Sytox green in the presence of soil particles.

Total counts in soils are usually determined using fluorescent dyes, such as DAPI or Sybr green, due to fluorescence enhancement if they are bound to nucleic acids. Unfortunately, these commonly used dyes stain soil particles as well. Therefore, besides fluorescence enhancement, sufficient spectral differentiation is also required. We present a new procedure that overcomes the problems of visualising bacteria on surfaces in soil and avoids the separation of soil particles to a large extent. Spectral differentiation between bacteria and soil matrix is achieved by using Sytox green and a suboptimal excitation wavelength. Bacteria exhibit a bright green fluorescence, while soil particles fluoresce blue or red. Slight homogenisation and sedimentation of the sand and coarse silt that were too big for microscopic investigations were the only separation steps required. We compared the proposed Sytox green staining with Sybr green staining. The recovery of Sybr green-stained cells amounted to 38%, whereas in samples stained by Sytox green 81% of the spiked cells were counted. Sytox green can also be combined with fluorescence in situ hybridisation (FISH) using deep red dyes such as Cy5.

Aluminum Silicates↗

PubMed2002

A filtration, incubation and staining reactor including a new protocol for FISH.

A newly developed device for performing fluorescence in situ hybridization (FISH) is described. An adapted procedure was compared with two typical FISH protocols. Tests were performed with Pseudomonas cells and the gene probe EUB338. With the novel procedure, we obtained a better recovery of cells and less variability in results.

Artifacts↗

PubMed2002

Diffuse atrazine pollution in German aquifers.

Until its prohibition in Germany in 1991, atrazine was the most frequently applied herbicide in maize cultivation. Moreover, it was used in orchards and vineyards and as a total herbicide on non-cultivated grounds (railways, factory grounds). Later on, atrazine was substituted mainly by terbutylazine. Terbutylazine and terbutryn are the only s-triazines presently permitted in Germany. Nevertheless, atrazine and its metabolite desethylatrazine are by far the most abundant herbicides detected in near surface groundwater. This might be due to wash-outs from the pools of atrazine and its metabolites from the soil into the groundwater or continuing illegal applications. Samples taken from maize fields in 1994 showed that 6.2% of 471 fields tested were treated with atrazine despite the prohibition of its use. Nevertheless, the overall trend is in fact a slow decrease in atrazine concentrations where it is detected in groundwater and, simultaneously often a slight increase in desethylatrazine concentrations. But this is not the case for all sampling points, and increasing concentrations in several aquifers are observed as well. Factors governing the adsorption, degradation, persistence and the possible transfer into the aquifer and the current situation concerning atrazine occurrence in German aquifers will be discussed.

Atrazine↗