teaching

Although plastic pollution is receiving worldwide attention, most research targets aquatic environments. Thus, knowledge gaps about the entry, fate, and transport of plastic particles in terrestrial ecosystems are vast. Agricultural plastic covers are assumed to contribute to soil contamination with microplastics by breaking down into smaller debris. Further, the lack of simple and fast analytical methods might contribute to that since no standardized method for the monitoring of polymer particles from soil matrices is available. Therefore, this work refined and validated an already developed analytical method using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) for the detection of polyethylene (PE), polypropylene (PP), and polystyrene (PS) debris form soil. Furthermore, the method was applied to environmental samples from eight agricultural fields covered with different plastic foils. For this purpose, 50 g samples were density separated, filtrated, and extracted prior to thermo-analytical analysis. Moreover, to investigate the potential role of polymer debris as a vector for pollutants, the sorption of two fungicides (cyprodinil and fludioxonil) to mulch foil particles in aqueous solution was investigated in a 72 h batch experiment. In 63 % of the soil samples at least one or a combination of the targeted polymers could be detected. But only 18.3 % of the showed higher polymer content than the respective detection limit. PE was most frequently detected with concentrations up to 94.2 µg g^-1, PP and PS were only sporadically found. Different polymer contents could be found between tracks and furrows of the fields mulched with perforated foil (p = 0.003). Furthermore, thinner mulching films were associated with a higher plastic content in the soil, suggesting their avoidance for long-term applications. However, the general polymer entry by one year mulch application was found in a low order of magnitude compared to other sources such as sludge applications. Sorption of both fungicides onto the plastic particles was only 5 % of the total amount. Thus, particles of this type are considered no essential vectors for similar pesticides. Nevertheless, cyprodinil showed distinct sorption compared to fludioxonil. This suggests lipophilicity as a driving factor for reversable absorption. Future studies could investigate the surface dependent (ab-)sorption of such pesticides to polymer particles to gain deeper understanding of the underlaying mechanisms.

The potential consequences of tire abrasion being released into our environment have been rarely studied. Although the wear of tires is one of the largest sources of microplastics. It is unknown whether tire material can alter the sorption behavior of metals in soil, such as copper, which is often used as a fungicide in organic viticulture. To solve this question, this work investigated the sorption of copper to tire wear, to soil substrate, and to a soil substrate-tire wear mixture in ultrapure water solution. In addition, the copper sorption of tire abrasion in a soil solution was investigated to compare the results of the ultrapure water samples with those of a somewhat more realistic experimental setup. The results showed non-linear sorption of copper to the sorbents for all treatments, with a maximum sorption of copper to tire abrasion in the range of 600 g·g^-1. It was found that copper sorbed more effectively to tire abrasion than to the soil substrate. Consistent with this, higher copper sorption was observed in the mixed samples than in the soil samples. In the soil solution, sorption of copper to tire abrasion proceeded less effective compared to sorption in the ultrapure water solution. This could be explained by the presence of other dissolved ions and substances in the soil solution, which compete with copper for the free sorption sites. The work was able to show that tire abrasion in principle has the potential to alter the amount of copper sorption in soils. At the same time, however, it was shown that the results of the laboratory samples should not be overestimated with regard to an interpretation of sorption behavior in the real world. Many influencing variables, such as the pH-value, the proportion of organic material in the soil, the aging and degradation of the tire material as well as the chemical change of the tire material in the formation of tire abrasion were not taken into account in this work and should be investigated in further work for a better understanding of the processes taking place.

Microplastic (MP) is of concern as an emerging pollutant in our plastic age because its ubiquitous presence in the environment poses a potential risk to human and animal health. A better understanding of MP pathways in the environment would benefit the development of mitigation measures for plastic pollution. For this reason, this study investigated potential point sources of land- based MPs into the aquatic environment, focusing on wastewater treatment plant (WWTP) effluent and stormwater from the drainage sewer systems. With the River Weser as the study focus, MPs in the effluent of the WWTP Bremen-Seehausen was monitored for one year to (1) determine the extent to which treated wastewater (TWW) contributes MPs to the recipient and (2) capture the annual variations of MPs. Also, water samples were taken from a runoff storage basin to (3) investigate MP occurrence in stormwater and have it compared to that of TWW. In this study, MPs were isolated from environmental samples through enzymatic-oxidative purification and subsequent density separation with ZnCl₂. For characterization, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and focal plane array (FPA)-based micro-FTIR imaging were applied, allowing the detection down to a size of 11.6 µm. Overall, MPs were present in all analyzed samples. MP concentration in TWW varied throughout the studied year without a clear pattern. Acrylates/polyurethanes/varnish/lacquer, polypropylene, polyethylene, ethylene vinyl acetate and rubber were the most abundant polymers detected. MPs were dominant in subclasses with a size range of 10-100 µm. There was no significant difference found between MP occurrence in TWW and stormwater. In conclusion, this thesis provided a comprehensive data set of MP occurrence in TWW with annual variations observed. Also, the contribution of stormwater to MP pollution in receiving waters was elucidated, in turn emphasizing the need of studying MPs in stormwater.

Although plastic pollution is receiving worldwide attention, research has mainly focused on aquatic ecosystems, leaving a large knowledge gap on the sources, occurrence, fate and effect of microplastics in terrestrial ecosystems. Especially the lack of adequate analytical methods has so far hampered the mass-related quantification of microplastics in complex environmental samples like sediment or soil. To quantitatively investigate the contribution of plastic mulching to (micro)plastic pollution in agricultural soils a previously established method for the selective quantification of polyethylene (PE), polypropylene (PP), and polystyrene (PS) in soil using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was optimized, validated and applied on soil samples. For this purpose, samples of 4 g soil from three strawberry fields covered with different plastic mulches were extracted with 8 mL TCB at 120°C prior to thermoanalytical analysis. To aid the understanding of the ecological impact of plastic pollution in soil, a carbon transformation test according to OECD Guideline 217 was conducted with five concentrations ranging from 0.05 to 500 mg g^-1 of homogeneously mixed PE- and PP-microplastics. The results of the plastic screening revealed increased PE concentrations of up to 136 µg g^-1 in at least one of the investigated fields. While it is likely that these plastic contaminations originated from the mulch film, this could not be ultimately proven, as it was not possible to exclude an input from other sources. Apart from that, valuable insights with regard to future method optimizations were obtained. As the comparison of different decomposition products indicated that especially longer-chained alkadienes are suitable for a specific quantification of PE, 1,19-Eicosadiene was selected for PE analysis. On the basis of solubility tests performed with several polymers and mulch films, a change of the solvent from pure TCB to an n-Xylene/TCB mixture is recommended for future studies. The results of the carbon transformation test revealed no significant effects of microplastics on soil microbial activity compared to the control. A microplastic-driven increase in microbial activity, as described by other authors could not be confirmed. Given that research on fate and effects of microplastics in terrestrial ecosystems is in its infancy, there is still a long way to go for a comprehensive risk assessment. Future studies are facing the challenge to extend analytical analysis to other plastics and matrices and to consider more species in toxicological testing in order to obtain a more complete picture of the consequences of plastic pollution.

Microplastic pollution of aquatic ecosystems is a rapidly evolving research topic, whereas the issue on terrestrial ecosystems has been neglected. Presently, terrestrial ecosystems under influence of human, such as agroecosystems, are possibly to be contaminated by plastic debris. Nevertheless, the boundary of this contamination has not been determined at present due to lack of adequate analytical methods for the quantification of plastic debris in soil. With this thesis, I adapted, developed, and evaluated a suitable extraction procedure for the quantification of poly (ethylene) and poly (ethylene terephthalate) in soil, which are the potential microplastics agricultural soil. Suitability of TGA-MS for the detection and measurement of PE microplastics in soil was also investigated. Various extraction methods were conducted and achieved the recovery rate of -5% to 111%. To evaluate the performance of TGA-MS for PE quantification, the several calibration standards were tested. The calibration curves responded linearly (adj. R² of 0.880-0.992) with instrumental detection limits of 0.40-1.61 mg PE and quantification limits of 1.21-4.87 mg PE. Overall, an appropriate procedure to extract MPs from the soil sample should be a (sequential) density separation followed by SOM digestion using Fenton’s reagent or dissolution combined with SOM removal using Fenton’s reagent. Soils with different organic matter content, and with various kinds of microplastics, and also the real agricultural soil are needed to be examined in further study.

The lack of simple methods for microplastic quantification in non-aquatic environments is deemed from a high concern in times of increasing plastic littering, especially into terrestrial ecosystems. Hence, the first aim of this study was to improve a pyrolysis GC-MS (gas chromatography mass spectrometry) method for plastic quantification using prior liquid extraction. Therefore, the solvent properties of the targeted polymers were to be investigated. The second aim of the study was to adapt the method towards the quantitative extraction of microplastic particles from penguin guano. Guano is assumed to have more matrix interferences than soil because of it’s relatively high organic carbon content (8-15%). For the first aim, the solubility of PE, PP and PS were tested in different solvent combinations, where TCB: xylene 50:50 was found the best. Furthermore, a solubility limit for polyethylene fibers was determined to be 1500 µg/mL and during the experiment the assumption of a cooling-induced coil-to-globule transition (CCGT) was built and strengthened. For the second aim of the study several clean- up procedures were tested whereat quantitative filtration with demineralised water was found to have the highest recoveries. A filter recovery experiment was carried out and averaged recoveries between 40.90 % ± 7.8 % for PP and 71.53 % ± 90.8 % were obtained for PS. For the different PE pyrolysates averaged recoveries between 40.60 % ± 5.7 % for 1,20-henicosadiene and 50.09 % ± 7.4 % for 1,22-tricosadiene were determined. This optimized method was then applied to penguin guano. In the samples from the Antarctic no polypropylene exposure could be monitored. However, PE was quantified in seven of these samples in amounts between 178 µg/g and 2236 µg/g guano. These findings support the existing method with a solvent composition of TCB: xylene (50:50) and provide new indication (CCGT) for more accurate precision. Furthermore, the results add another prove for the existence of plastic debris in the Antarctic. Consequently, the results highlight the need for further assessment of plastic particles in this sensitive ecosystem. Especially temporal trends and potential effects on penguins and other organisms in the arctic food web are to be investigated.

Lindane is a persistent organo-chlorine insecticide which has been extensively used worldwide for the control of agricultural, wood and medical pests, despite known its tendency to bioaccumulate and its toxicity to non-target organisms. As a result of the high persistence and long-time extensive usage, environmental contaminations of global dimensions exist. To bioremediate these soils, different bioremediation strategies were tested, based on biochar application, and degradation by the white rot fungi Pleurotus ostreatus, and a combined approach using biochar and P. ostreatus. In order to simulate realistic in situ remediation treatments, economically and feasible application rates and typical lindane pollution levels were used. The efficiency and effectiveness of each remediation treatment in non-sterile and sterile soils during 50 days of incubation was evaluated according to lindane dissipation processes (extractable, non-extractable, volatilized and mineralized radioactivity) and growth (ergosterol content) and activity (respiration) of P. ostreatus and indigenous soil microbes. Fungal treatment and biochar application showed best remediation success in terms of lindane dissipation either due to mineralization or immobilization. Sterile soils were strongly colonized by P. ostreatus and particularly high lindane mineralization (8.73-11.7 %) and immobilization (16.9-24.5 %) were observed. Non-sterile inoculated soil showed a similar magnitude of immobilization (10.54-24 %) but lower mineralization (2.4-2.7 %). However, the mechanisms of lindane immobilization by P. ostreatus, i.e. whether lindane was only sorbed or also incorporated into fungal tissue, still remains to be clarified. Biochar amendments resulted in lower volatilization of lindane from soil and had a positive effect on fungal growth in terms of respiration rate and visually observable mycelium. Moreover, it enabled a better colonization of the non-sterile soil and therefore, biochar amendments might provide a useful tool to introduce fungal inoculum for future in situ remediation measures. However, the fungal growth (ergosterol content) and lindane mineralization were lower in biochar- amended soils. This may be due to the strong sorption of mineralized lindane (¹⁴CO₂) and ergosterol to biochar, which might have resulted in lower recoveries by the methods used. A lower extraction efficiency for ergosterol-spiked soils has already been demonstrated in this study. It therefore remains to be clarified whether the biochar had a negative effect on fungal growth and mineralization or whether this can be attributed to inadequate extraction methods. Moreover, it should be examined to what extent common methods for measuring the mineralization of a pollutant can be applied to biochar-amended soils, or whether the methodologies must be changed for this purpose. In addition, it remains to be clarified in the future to what extent these results can be transferred to a field trial.