Aspekte der Phytoremediation organischer Schadstoffe

Phytoremediation is the quite novel technique of cleaning polluted sites through the use of plants. Phytoremediation methods are comparatively cheap, are accepted by the public and are ecologically advantageous, compared to common technological approaches. Until today, there have been only a few examples for successful applications. One reason is that the processes occurring are complex, and a full clean up may require many years. Plants have an influence on the water balance of a site, they change redox potential and pH, and stimulate microbial activity of the soil. These indirect influences may accelerate degradation in the root zone or reduce the leaching of compounds into the groundwater. Compounds taken up into plants may be metabolised, accumulate, or volatilise into air. Based on these processes, several phytoremediation methods have been developed: Phytoextraction, rhizofiltration, phytostabilisation, rhizound phytodegradation, pump and tree, land farming, phytovolatilisation, hydraulic control and even more. Already in use are plants (and here mainly willows, poplars and grasses) for the degradation of petroleum products, aromatic hydrocarbons (BTEX), chlorinated solvents, explosives and cyanides. Phytotoxicity and pollutants mass balance have rarely been documented carefully. Often, the success of the projects was not controlled, and only estimates can be made about the applicability and the potential of phytoremediation. This lack of experience about possibilities and limitations seems to be a hindrance for a broader use of these techniques.     

Einfluss organischer Substanz auf die Reproduktion, Biomasse und Akkumulation hydrophober Schadstoffe in Lumbriculus variegatus

Background, aim, and scope Sediment-Water Toxicity Tests are an important instrument for the environmental risk assessment of native, contaminated sediments within the European Water Framework Directive. Thus, it must be guaranteed to distinguish between natural and anthropogenic adverse effects. The content of particulate (POC) and dissolved (DOC) organic carbon can affect the mobility of sediment pollutants. Different studies demonstrated that the DOC-content can influence the bioavailability of contaminants and can directly affect aquatic organisms. The aim of this study was to investigate the influence of increasing sediment organic matter on reproduction and growth of the benthic oligochaete Lumbriculus variegatus. Furthermore, the accumulation factors of the hydrophobic substances 1,1-dichloro-2,2-bis(p-chlorphenyl)ethylene (p,p'-DDE), 2´, 3, 4, 4´, 5´-Hexachlorbiphenyl (PCB 138) und 2, 2´, 4, 4´, 5, 5´-Hexachlorbiphenyl (PCB 153) were calculated considering the TOC-content and the uptake route (water-only exposure or sediment ingestion). Materials and methods The test was performed according to the OECD Guideline 225 (2007) using artificial sediment with different peat concentrations. The effect of an increasing TOC-concentration was studied in three different testmodifications with and without spiked sediment. The nominal concentration of the contaminants in spiked sediment was 50?µg/kg. Results The results showed maximum accumulation factors of 13 for both, PCB 138 and 153 and 11 for p,p'-DDE in sediments with low organic carbon content. With increasing peat content accumulation factors decreased. Thereby the ingestion of sediment was the main exposure route. Moreover preponderantly negative correlations between the organic carbon content in unspiked sediments and reproduction as well as growth of the testorganisms were detected. In combination with the test substances reproduction and growth increased with increasing organic carbon content. Discussion Hence it can be assumed that organic matter, especially humic substances, directly effected the testorganisms in the tests without spiked sediment. Due to the decrease of accumulation factors in spiked sediment with increasing TOC-content it might be possible that the availability of humic substances was reduced by conglomeration with the tested chemicals. Conclusions Therefore the possible influence of dissolved organic matter on the testorganism should be considered when assessing the results of toxicity tests and bioaccumulation studies with Lumbriculus variegatus. Recommendations and perspectives To receive detailed information about a critical DOC-concentration influencing the testorganisms further investigations about the amount of organic matter in the sediment and the DOC-concentration in the overlaying water are recommended.     

Aufnahme von Cyanid in Pflanzen

Cyanides are waste products from the pyrolysis of coal and are frequent soil pollutants in cities nowadays. Prussic acid (HCN) is a fast acting, highly toxic poison, but iron-complexed cyanides in soil are far less toxic. The phytotoxicity of free CN to basket willows (Salix viminalis) was determined with the tree transpiration test. The EC₁₀ for t=72 h is 0.76 mg KCN (0.3 mg CN) per liter, the EC₅₀ is 4.47 mg/l. 5 mg/l KCN are ultimately lethal. Balsam poplars (Populus trichocarpa) can survive concentrations of up to 2500 mg/l ferroferricyanide (Prussian blue), although with reduced growth. Willows survived in gas work soils with up to 452 mg/kg total CN. More CN was taken up from nutrient solution than from the soil. Complexed cyanide is probably translocated into the leaves as well. Free CN was readily eliminated from Erlenmeyers with plants growing in nutrient solution. Planting appropriate vegetation might be a suitable solution for many former gas work and mining sites.     

Quecksilber in Boden und Pflanzen

The former mercury mining districts in Platina (Rheinland-Pfalz, Germany) are now overgrown with a more-or-less dense cover of vegetation. Much of the area is in agricultural use. Cultivated fields around the community of Mörsfeld have been analyzed. The mercury concentration in soil samples exceeds the threshold values set for sewage sludge by up to 10. 000 fold. Wheat grain cultivated in this area has a Hg content of up to 100 times higher than the threshold values set by the WHO/FAO. The accummulation was found to be organ specific and varies by species. The highest Hg concentration was measured in mosses, the lowest in leaves of shrubs.     

Phytovolatilisation organischer Chemikalien

During the phytoremediation of contaminated soils and water, a multitude of pathways, partly not yet quantified, are activated. ‘Phytovolatilisation’ is considered to be a process, where primarily organic compounds are emitted from the above-ground sections of the plant into the atmosphere. Thus, all compounds are included which are taken up by the root, partly transformed within the roots and transported into the sprout. The phytovolatilisation is particularly suitable for the elimination of volatile compounds in shallow groundwater contaminations. In gas exchange experiments, the dynamics of these emissions were examined and, on the basis of a model, the compounds which are preferentially emitted by plants due to their physical characteristics was estimated.     

Aufnahme von 2,4,6-Trinitrotoluol in Pflanzen

Soil contaminations with the explosive 2,4,6-TNT are a major problem at many sites of former ammuniton plants in Germany. But only little is known about its environmental or metabolic fate in soil or plants. A field study was conducted on a former ammunition plant in Stadtallendorf/Hessen. Three areas with different TNT concentrations were planted with 8 different crops. After harvest plants were analyzed for TNT, ADNTs and DNTs. Soil contamination decreased in the rhizosphere compared to unplanted areas and there was a transfer of TNT from soil to the plants. Accumulation in plants was dependent on soil contamination and also specific for different plant parts or plant species. The contamination spectrum of TNT and derivatives was different in soil or plant tissue, respectively. After acid hydrolysis of bean roots, 2,6-DNT and 2,4-DNT could be identified in the extract.     

Salzgehalt und Photosynthese bei marinen Pflanzen

Marine plants — phanerogams as well as algae — show a proportional decrease of photosynthetic rate, when the salinity is lowered by dilution with distilled water. Using natural water instead of distilled water, it is absolutely indispensable to take into consideration the carbon supply. Normally, the photosynthetic rate decreases in freshwater with low alcalinity, in comparison to marine water. On the other hand, using water with high contents of bicarbonates, assimilation rate is higher than in marine water. These results show that salinity may indirectly affect photosynthesis due to differences in carbon supply. The direct influence is caused by exosmosis in hypotonic media and is irreversible. — The author cannot but agree with the statement by Ogata and Matsui (1965): “It may generally be said that the changes in salinity, osmotic pressure, pH, and also carbon dioxide supply, particularly in natural sea-water, are rather inseparably associated.”     

Experimente zum Verbleib von Cyanid nach Aufnahme in Pflanzen

Free cyanide (prussic acid) can be degraded by many organisms. Experimental data on the kinetics of degradation by plants, however, are rare. We experimentally determined the mass balance of potassium cyanide in the system nutrient solution/plant/air In the presence of living willows (Salix alba) and light, free cyanide is almost completely eliminated from the nutrient solution, also by a willow cell suspension (> 99%) and even by a dried-out stem (> 80%). The loss is smaller when the willow is autoclaved (30%). Without a willow, the CN can be recovered to more than 89%. The loss depends on light and transpiration. Volatilization and the formation of complexed cyanide are of minor relevance for the elimination of free CN. The most plausible loss process is metabolism by plants. The transfer into the roots and stem does not change with the light/dark-rhythm. The transfer factor (mg CN/kg plant fw/mg CN/l solution) after 24 h, and related to the initial concentration in solution, is between 2 and 3 for roots, 0.1 to 0.6 for leaves and 0.2 for stems. In the roots of willows and elderberries which were growing on the former gas worksite in Holte, Denmark, high concentrations of cyanides were found. In leaves and fruits, concentrations are a factor of 10 to 1000-fold lower and up to as high as that found in non-exposed control plants. Due to these results, a cyanide-polluted site in Denmark has been remediated with poplar trees.