Sabine Tischer

Plant--rhizosphere-microflora association during phytoremediation of PAH-contaminated soil.

The capability of plants to promote the microbial degradation of pollutants in rhizosphere soil is a principal mechanism of phytoremediation of PAH-contaminated soil. The formation of a specific rhizosphere microbocenosis with a high degradative potential toward contaminants is largely determined by plant species. The comparative PAH-degradation in unplanted soil and in soil planted with reed (Phragmites australis) and alfalfa (Medicago sativa) was studied in pot experiments during 2 years. Both alfalfa and reed successfully remediated contaminated soil by degrading 74.5 and 68.7% of PAHs, respectively. The study of the rhizosphere, rhizoplane, and unplanted-soil microflora in experimental pots showed that alfalfa stimulated the rhizosphere microflora of PAH-contaminated soil more effectively than did reed. Alfalfa clearly enhanced both the total number of microorganisms (1.3 times, according to fluorescence microscopy data) and the rate of the PAH-degrading population (almost seven times, according to plate counting). The degradative potential of its rhizosphere microflora toward PAHs was higher than the degradative activity of the reed rhizosphere. This study provides relevant information for the successful application of alfalfa to phytoremediate PAH-contaminated soil.

Earthworms as Bioindicators of Soil Quality

Earthworms can indicate soil quality by (1) the abundance and species composition of the earthworm fauna at a particular site, (2) the behavior of individual earthworms in contact with a soil substrate (preference/avoidance/activity), (3) the accumulation of chemicals from the soil into the body, and (4) the biochemical/cytological stress-biomarkers in the earthworm. Earthworms are assessed in several long-term soil monitoring programs in Europe. Abundance data of earthworms may not only represent soil quality because weather and food are also important factors of influence. The ISO-avoidance test and tests with 2D (two-dimensional) terraria are laboratory assays with behavioral endpoints that can supplement the field monitoring of earthworm abundance. The analysis of chemical concentrations in earthworms has been used to indicate the risk of secondary poisoning for worm-feeding predators and to get an estimate of the bioavailability of contaminants in the soil. Bioaccumulation factors (BAF) for chemicals in earthworms can differ considerably from site to site and from species to species indicating that the bioavailability of a contaminant is influenced by chemical, physical, behavioral, and physiological parameters.

Microbial biomass and enzyme activities on soil monitoring sites in Saxony-Anhalt, Germany

Abstract Apart from soil chemical parameters like pH-values, Corg-content and heavy metal amounts, microbial parameters like the microbial biomass, several enzyme activities of different nutrient cycles and the luminescence inhibition were estimated on 68 soil monitoring sites differently used in Saxony-Anhalt (Germany). The microbial biomass, the metabolic quotient, the Cmic/Corg-ratio, the luminescence inhibition, and the enzyme activities ß-glucosidase, protease and arylsulphatase are among the chosen parameters ideal for the microbiological soil quality monitoring. The pH-value was the primary determinant physico-chemical factor in establishing microbial communities. Grassland and forest soils accumulate in particular carbon and are especially suitable for a carbon sink. According to the German soil protection law (BBodSchG) 11 of the 68 studied soil monitoring sites showed increased amounts of heavy metals. The measured microbial parameters were hardly influenced by the heavy metal amounts.

Model Trials for Phytoremediation of Hydrocarbon-Contaminated Sites by the Use of Different Plant Species

ABSTRACT In order to further the development of plant-based remediation of sites contaminated by carbo-chemical and petro-chemical industries, the penetration of the roots of Phragmites australis in contaminated soil substrate was studied in model trials. The series of experiments contained model substrate with firm bitumen and tar. In terms of the level of root penetration, the roots and rhizomes penetrated equally through the middle of the pot and at the edges as well as coming up through the bottom. There were differences between the density of the root systems in the topsoil of the two variations, with the roots in the sample with a 3.5 -cm bitumen layer being more dense. The experiment also showed that shallow rooting plants can penetrate thick barriers and are suitable for planting in contaminated areas. In the subsoil zone, which contained many roots, a reduction of up to 85% in the MOH content was observed. In a second series of long-term pot experiments, the stimulation of hydrocarbon remediation by Phragmites australis, Alnus glutinosa, and Robinia pseudoacacia was studied. In the subsoil zone, which contained many roots, a reduction of up to 64% in the hydrocarbon content was determined. In the comparison between the cropped and noncropped treatments, the decontamination ratio was up to 40% higher in the cropped pots than in the pots without plants. For a determination of microbial activity, two enzymes (catalase, ß-glucosidase) and microbial biomass were measured. Variants with plants showed higher microbial activities than uncropped pots. By increasing “biostimulation,” pollution and also the leaching of pollutants can be reduced.

Lumbricids species diversity and heavy metal amounts in lumbricids on soil monitoring sites in Saxony-Anhalt (Germany)

This paper will contribute to an evaluation of soil monitoring sites. Abundance, biomass and species diversity of lumbricids was evaluated on 68 differently used sites (fields, grassland, deciduous forest, coniferous forest, mine spoil). Eight of the 68 studied soil monitoring sites showed increased amounts of heavy metals. Apart from the assessment of the abundance, of the biomass and the species diversity, the heavy metal accumulation in lumbricids was measured and evaluated. Earthworms are ideal bioindicators for heavy metals in the soil. Additional soil properties (organic matter content, pH, heavy metals) were measured that could explain differences in the bioavailability of the metal burdens of polluted sites. Metal concentrations in lumbricids showed considerable variation between land use type and the individual lumbricid species.