Studies in the Biodegradation of 5 PAHs (Phenanthrene,Pyrene, Fluoranthene,Chrysene und Benzo(a)pyrene) in the Presence of Rooted Poplar Cuttings

Cuttings of Populus nigra L. cv. Loenen were cultivated in sand treated with one of the following PAHs: phenanthrene (Phen), fluoranthene (Flt), pyrene (Pyr), chrysene (Chr) and benzo[a]pyrene (BaP). The PAHs were applied at varying levels of concentration to each test series. After 6 weeks the concentration and the distribution of the PAHs in the substrate of the various sets of tests were compared with the concentration in the substrate of the control. Additionally the substrate and the plant roots were tested for evidence of degradation products of PAHs. The results revealed that the levels of concentration of Phen and Pyr detected in the substrate surrounding the roots was in some cases significantly lower than in the corresponding section of substrate in the unplanted set (= control). This phenomenon did not occur for Flt and BaP and in the case of Chr only in those substrates, which had been treated with the highest levels of concentration. As the presence of lesser amounts of Phen and Pyr in the plant pots cannot only be attributed to their accumulation and metabolism in the roots, it is fair to assume that the chemical transformation of these three PAHs took place outside the roots. The set of tests treated with Phen revealed the presence of 2- or 3-hydroxy-Phen (main components), a hydroxy-methoxy-Phen, 9,10-Phenanthrenequinone and one unidentified compound in metabolite form. Altogether eleven metabolites of Pyr were identified in the root extracts, which can be divided into three groups: 1-Hydroxy-Pyr and derivatives, dihydroxy-Pyr and derivatives and ring fission products (4-Hydroxy-Pyr and a derivative of the 4-Phen-carbonic acid). However, the metabolite mass detected for Phen and Pyr represents only an insignificant percentage in comparison with the lesser amounts of PAHs observed in the planted set of tests. This indicates that the three PAHs were reduced to lower molecular compounds, which are methodically impossible to record, and subsequently translocated to other parts of the plant and integrated into the biomass. Although no lesser amount for Flt and BaP was found in the plant pots, 1-Hydroxy-Flt, an unidentified compound of Flt and 1-Methoxy-BaP were detected. These are presumably end products which were enhanced in the roots. It was not possible to identify any transformation products of Chr. It can be assumed that the majority of metabolites were not synthesised in the roots but are a result of microbial degradation in the rhizosphere. The test plants improved the conditions for the biotransformation of Phen and Pyr significantly and accumulated Flt, Pyr, Chr and BaP in their roots. It can therefore be concluded that the use of plants in the bioremediation of contaminated soils is a promising option.     

Biodegradation of anthracene in the roots and growth substrate of poplar cuttings

Following their exposure to anthracene, the roots of Populus nigra L. Loenen showed traces of 9 substances classed as products of biodegradation. The main substances detected were phthalic acid and 9,10-anthraquinone, followed by hydroxyanthracene and methoxyanthracene and five other compounds which could not be identified. Due to the relatively low concentration of degradation products found in the roots, further degradation to lower molecular compounds are discussed. The presence of 9,10-anthraquinone as the main product of the degradation of anthracene was also evident in the control tests with unplanted sandy substrate, although the content was higher in the planted series of tests. As a non-sterile approach was chosen, it may be assumed that a microbial degradation for 9,10-anthraquinone took place in the control series. However, it is difficult to differentiate clearly between a microbial degradation of anthracene in the substrate and metabolization in the roots due in part to the absence of specific degradation products in the various reaction areas.     

Exposure of the Roots of <Emphasis Type="Italic">Populus nigra</Emphasis> L. cv. Loenen to PAHs and its Effect on growth and water balance

Poplar cuttings were cultivated for 4 weeks in a substrate, which consisted of a combination of sand and nutrient solution. The plants were treated for 24 days with BaP, Chr, Ant, Phen, P and Flt, single or in combination. The concentration of the PAHs ranged from 0.1-200 mg/kg substrate. The results of the pollution experiments can be summarized as follows: 1. The most significant deviations between the test groups and the control can be observed for transpiration, nutrient solution uptake, and root mass. 2. Although transpiration and nutrient solution uptake are significantly lower for all the treated groups than for the control group, the water content of the leaves was not affected by PAHs. 3. The biomass of the shoots and the growth in shoot length do not react as strongly to exposure to PAHs as transpiration, nutrient solution uptake and the volume of the roots. 4. The differences in leaf weight and leaf surface area are significantly less pronounced compared to the control groups. Growth inhibition is most evident with Flt. Growth and absorption of the nutrient solution dropped with just Flt 0.1 mg/kg substrate. When the substrate concentration was increased, growth and nutrient solution uptake dropped considerably and at a concentration of Flt 200, 5 of the 11 test plants died before the end of the period of exposure. Nutrient solution uptake and shoot development of the test plants decreased in the following order: BaP H approximately = Chr > Ant > Phen > Pyr > Flt.