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Biodegradation of polyesters and other polymers in soil and compost
Papala, František ; Smilek, Jiří (referee) ; Obruča, Stanislav (advisor)
This diploma thesis studies the biodegradation of polyhydroxybutyrate (PHB) and polylactic acid (PLA) within soil and compost environments. The experimental part of this work is concerned with the differences in degradation across environments and the effects of degraded polymers on the environment itself. Experiments revealed that higher temperature and potentially also higher humidity substantially affect the rate of biodegradation. A significant degradation of all the polymers was observed in the compost medium, while polymers within the soil medium did not demonstrate any visible change nor change in mass after the 8th week of experiment. Even though SEM images revealed slow microbial degradation of soil PHB, this was not seen in any of the soil-incubated PLA samples. This might indicate primarily abiotic mechanism of PLA degradation. Germination and grow tests, which used the prepared polymer-enriched compost as a substrate and fertilizer, respectively, did not in most cases reveal any significant differences between individual plants across substrates. This seems to imply that neither the examined polymers nor their degradation products generated during composting are phytotoxic.
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Biodegradation of polyesters and other polymers in soil and compost
Papala, František ; Smilek, Jiří (referee) ; Obruča, Stanislav (advisor)
This diploma thesis studies the biodegradation of polyhydroxybutyrate (PHB) and polylactic acid (PLA) within soil and compost environments. The experimental part of this work is concerned with the differences in degradation across environments and the effects of degraded polymers on the environment itself. Experiments revealed that higher temperature and potentially also higher humidity substantially affect the rate of biodegradation. A significant degradation of all the polymers was observed in the compost medium, while polymers within the soil medium did not demonstrate any visible change nor change in mass after the 8th week of experiment. Even though SEM images revealed slow microbial degradation of soil PHB, this was not seen in any of the soil-incubated PLA samples. This might indicate primarily abiotic mechanism of PLA degradation. Germination and grow tests, which used the prepared polymer-enriched compost as a substrate and fertilizer, respectively, did not in most cases reveal any significant differences between individual plants across substrates. This seems to imply that neither the examined polymers nor their degradation products generated during composting are phytotoxic.
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Changes of biochemical parameters in fish after nitrite exposure
PODLESNÝ, Martin
The aim of this thesis was to assess the effects of long-term nitrite exposure on mortality, growth rate and blood biochemistry in rainbow trout (Oncorhynchus mykiss). Furthermore, acute toxicity tests with nitrite were performed on rainbow trout (Oncorhynchus mykiss) and sheatfish (Silurus glanis). The theoretical part focuses on aquatic toxicology including toxicity evaluation of substances and preparations for water organisms. Detailed information on nitrite are summarized there, namely information on nitrite occurrence and sources in aquatic environment and the mechanism of their uptake and toxic influence on fish including factors influencing their toxicity. The practical part consists of methodology and results of acute toxicity tests on rainbow trout and sheatfish and sub-chronic test on rainbow trout. According to the acute toxicity tests results, 96hLC50 values were estimated at 11.2 mg.l-1 NO2- for rainbow trout and 15.3 mg.l-1 NO2- for sheatfish. Sub-chronic exposure of rainbow trout to nitrite concentrations ranging from 0.01 to 3.0 mg.l-1 lasting 28 days caused an increase of glucose concentration and a decrease of potassium concentration in the blood plasma among all experimental fish compared to control. Elevated nitrite levels were found in the plasma of the fish exposed to concentrations of 0.6 mg.l-1 NO2- and greater. The plasma nitrite levels did not reach those applied in any experimental group in the present study. At highest nitrite concentration (3.0 mg.l-1 NO2-), 42 % growth inhibition and 65 % mortality among fish was noticed. On the basis of growth rate inhibition data, the values of NOEC and LOEC were estimated at 0.01 mg.l-1 and 0.2 mg.l-1 NO2-, respectively.
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