Browsing by Subject "environmental ecology"

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  • Pukkila, Veera (Helsingin yliopisto, 2015)
    The worldwide use of pesticides (herbicides, insecticides, and fungisides) currently amounts to 2.4 billion kilos. Only a small proportion of pesticides actually reach the target organism, whereas the majority becomes a potent contaminant that threatens the environment and humans. Microbes, present everywhere in the environment, have the ability to degrade many kinds of man-made chemical compounds, xenobiotics. By studying the degrading microbes and the optimal conditions for microbial degradation, bioremediation techniques may be developed to clean contaminated sites. A metabolite of the herbicide 2,6-dichlorobenzonitrile (dichlobenil), is 2,6-dichlorobenzamide (BAM). BAM is frequently detected in groundwater worldwide, and thus the use of dichlobenil is nowadays banned in the EU. Dichlobenil is degraded in soil relatively quickly, but BAM is much more persistent. Due to its high water solubility and low sorption affinity, BAM easily leaches down to deeper soil layers and even to groundwater where it is considered stable. This study focused on the degradation of dichlobenil and BAM in Finnish groundwater sedimentary deposits and topsoil. The biotic and abiotic factors associated with effective dichlobenil or BAM degradation were studied. The aim was to examine how the presence of microbes and oxygen, and the chemical characteristics of soil and groundwater deposits, affect the degradation rates of dichlobenil and BAM. In addition, the indigenous microbes degrading these compounds were enumerated, and some were isolated and identified. Dichlobenil was degraded in all studied groundwater sedimentary deposits and topsoil. The presence of microbes and oxygen, and high carbon and nitrogen contents enhanced dichlobenil degradation. As expected, BAM was more resilient to microbial degradation than dichlobenil. Significant aerobic microbial degradation of BAM was detected only in one out of five deposits, and in another weak biodegradation was observed. In these two deposits the concentrations of the elements manganese, zinc, cobalt, lead, and nickel were high. Aerobic bacterial strains growing in the presence of dichlobenil or BAM were isolated from all studied groundwater sedimentary deposits and topsoil. The isolates belonged to the phyla Proteobacteria, Actinobacteria, and Bacteroidetes, Gammaproteobacteria being the largest group of isolates. The dichlobenil or BAM degradation capacity of the isolates was rather low (5-46%) and not demonstrated for all isolates. In conclusion, the diversity of dichlobenil and BAM degrading aerobic microbes in Finnish groundwater sedimentary deposits and topsoil was relatively high. Especially the high number and diversity of isolated BAM degrading strains was unexpected, as only few BAM degrading strains have been reported earlier. Due to their low degradation capacity the potential of these isolates in bioremediation is not considered high, but they could be used e.g. to identify the genes and enzymes involved in the degradation of dichlobenil and BAM.
  • Li, Ling (Helsingin yliopisto, 2017)
    The increasing use of titanium dioxide nanoparticles (TiO2 NPs) and their consequent release into the environment, make it important to understand the behaviour, fate and potential adverse effects that TiO2 NPs may have upon organisms. After being introduced into the aquatic environment, TiO2 NPs will undergo transformation processes, which will affect their properties, including, chemical composition, size, surface charge and coating, and these may also have substantial implications on the fate and toxicity of the NPs. This highlights the importance of physiochemical characterization of the NPs in conjunction with a toxicological assessment. The transformation processes are dependent both on the physicochemical properties of the NPs and on the physicochemical properties of the ambient environment. However, these properties have been seldom studied in complex natural waters. Therefore, the research done for this PhD dissertation aimed to investigate the behaviour of TiO2 NPs in natural waters, and to associate the NPs colloidal stability with various water properties. The toxicity tests of TiO2 NPs were performed on two aquatic organisms each of which represent different trophic levels: Lemna minor (L. minor) and Daphnia magna (D. magna) according to ISO 20079 and OECD test 202, respectively. The specific aim was to assess the possible toxic effects of TiO2 NPs with maintained colloidal stability in an optimized ecotoxicological test medium. Given the potential of TiO2 NPs to carry other pollutants, the mixture toxicity of TiO2 NPs with cadmium (Cd) and lead (Pb) on D. magna were also investigated. TiO2 NPs exhibited different colloidal stability, which depend on the physicochemical properties of the natural waters. Total phosphorus, total nitrogen, alkalinity, pH, electrical conductivity and turbidity were shown by experimental and linear regression analysis to be the main water properties that negatively influence NPs stability among 14 water properties that were compared. All six of these physicochemical properties of water had positive correlations on the deposition of TiO2 NPs in lake waters. TiO2 NPs showed low colloidal stability in standard ecotoxicological test media, but modification of the current standard medium enabled the steady exposure of L. minor and D. magna. TiO2 NPs showed no adverse effect on the growth rate or chlorophyll a content of L. minor, or immobility of D. magna. However, TiO2 NPs were found to become attached to the cell wall of L. minor and to the body surface of D. magna, both of which may cause the potential transfer of TiO2 NPs into the aquatic food chains. Such a transfer would lead to an exposure of other organisms and contribute to the environmental fate of NPs. The presence of TiO2 NPs also influenced the bioaccumulation and toxicity of Cd and Pb in D. magna. TiO2 NPs increased the bioaccumulation and toxicity of Cd in daphnia, whereas it reduced the toxicity of Pb regardless of the 3- to 4-fold increase of bioaccumulation found. Surface attached TiO2 NPs combined with adsorbed heavy metals, caused adverse effects on D. magna swimming and moulting behaviour, which was assumed to lead to chronic toxicity. The research findings presented in this thesis elucidate the water physicochemical properties that control the aggregation and deposition of TiO2 NPs in complex natural waters, and offer an insight into their biological effects and accumulation potential upon aquatic organisms.
  • Yu, Dan (Helsingin yliopisto, 2014)
    An enormous quantity of solid waste is generated annually all over the world. Solid waste can be divided into three main categories: municipal waste, industrial waste and agricultural waste. The focus of the research presented in this thesis was on the biodegradable fraction of municipal solid waste (MSW), and particularly on the biowaste and sewage sludge generated in the Nordic countries. In general, there are two major options for processing biodegradable MSW in a sustainable manner: aerobic treatment (e.g. composting) and anaerobic treatment (e.g. anaerobic digestion). The key interest of this study was in analysing the microbial community composition in composting and anaerobic co-digestion using various types of biodegradable MSW as feedstock. In addition, the aims of this study were to: 1) understand the connections between the microbial communities and the capacities of disease-suppressive composts against the soil-borne plant pathogens Pythium and Fusarium; 2) investigate the effects of pH and microbial composition on odour emission in biowaste composting in Nordic countries; 3) study the connections between microbial communities and the key methanogenesis intermediates under various conditions (e.g. temperature, OLR) in the anaerobic digestion process; and 4) find a functional compromise between the waste treatment capacity of anaerobic digestion, biogas production and a stable microbial community. To achieve the above-mentioned goals, DNA-based microbiological techniques (e.g. DNA extraction, PCR, qPCR, DGGE and cloning) and sequencing techniques (i.e. Sanger sequencing and high-throughput pyrosequencing) were applied. The results are summarized in five articles/manuscripts enclosed with this thesis. Studies on composting (articles I IV) illustrated that the microbial communities were abundant and diverse, with Proteobacteria and Ascomycota as the dominant bacterial and fungal candidates, respectively. The presence of bacterial Acidobacteria Gp14 and fungal Cystobasidiomycetes in Pythium-suppressive composts indicated their possible roles in the suppression of Pythium wilt disease (article I). Actinobacterium and non-pathogenic relatives of the pathogen Fusarium may suppress Fusarium disease on tomato plants (article II). In food waste composting (articles III and IV), results indicated that LAB (e.g. Lactobacillus) together with Clostridia were responsible for the high odour emission in the studied composts. The results suggest that a potential odour reduction strategy would be to rapidly overcome the low pH phase through high initial aeration rates and the use of additives such as bulking material, as well as pre-treatment of the composting feedstock in anaerobic digestion. A study on anaerobic digestion (article V) demonstrated a rather limited methanogenic archaeal community that was dominated by Methanobacteriales and Methanosarcina in both meso- and thermophilic processes, even with Methanothermobacter as an additional abundant genus in the thermophilic production cycle. Key factors such as the acetate concentration and OLR, as well as substrates such as propionate apparently contributed to the dominance of Methanosarcina. Biogas production was greater in the thermophilic process; when the OLR increased to 5 kg VS m-3 d-1, the efficiency maximum was reached. The microbial groups within the microbial community usually remain largely unexplored. In this thesis, the key microbial candidates that are involved in plant disease suppression, composting odour emission and anaerobic co-digestion were revealed. As the rapid progress of high-throughput sequencing approaches continues, better coverage of the microbial community will be achieved.
  • Liu, Xinxin (Helsingin yliopisto, 2016)
    The worldwide use of triazines as pesticides has resulted in their widespread occurrence in groundwater. Within the northern boreal region in Southern Finland, 30% of groundwater sampling points contained pesticides, and acceptable drinking water limits were exceeded in 11%. Atrazine and its degradation products were among the most common pesticides observed. Chemical pesticide degradation in soil is slower than microbial degradation. Biodegradation often decreases with increasing depth. Nutritional factors and soil physicochemical properties affect microbial pesticide degradation. However, their effects on separate microorganisms, and the genetic basis of these responses, are not well documented. The aim of this thesis was to isolate and characterize atrazine-degrading microorganisms, and to find appropriate microbial, physicochemical, and nutritional demands for pesticide degradation. Microbial community composition was studied in farmland, forested farmland, and primary forest soils by pyrosequencing and in gardens, groundwater deposits, and vadose zone sediments by cultivation on mineral medium with atrazine or terbutryn as the nitrogen source. Atrazine dissipation efficiency was additionally compared under stagnant and circulating water conditions. The dominant phyla that increased in atrazine-treated farmland, gardens, deposits, and sediments were Proteobacteria and Actinobacteria. The overlap in genera was less than in phyla, while the isolated Pseudomonas strains only slightly overlapped between isolates from surface soils and subsurface deposits and sediments. Atrazine dissipation was better in circulating than in stagnant water, and aerobic microbes from genera known to have atrazine degradation genes, all from phyla Proteobacteria and Actinobacteria, were simultaneously enriched,. Based on the results, the application of microbial remediation of atrazine and terbutryn requires special attention to soil physicochemical properties and selection of proper microbial strains.