Vliv nanočástic oxidu ceričitého na sladkovodní mikroorganismy
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S rostoucím používáním nanomateriálů vyvstává i otázka jejich bezpečnosti pro životní prostředí. Jedním z materiálů, kterým je v poslední době věnována pozornost, jsou nano-částice oxidu ceričitého (CeO2). Kromě výhod nanočástic CeO2 se ovšem v literatuře setká-váme i s možnou toxicitou vůči mikroorganismům.Tato práce si klade za cíl zjistit účinky nanočástic CeO2 na říční mikroorganismy - bakterie a řasy, a chování CeO2 v různých typech vodních biotopů (dle pH). Za tímto účelem byly mi-kroorganismy z řeky exponovány CeO2 nanočásticím bez úpravy (naked CeO2 4 nm a 25 nm), a dispergovaným v collyriu (collyrium CeO2 4 nm). Byly aplikovány různé koncen-trace od 0.001 do 0.05 g/L a měření proběhla po 5, 14 a 28 dnech. Pro hodnocení účinků CeO2 na mikroorganismy byl použit epifluorescenční mikroskop (morfologie buněk), a pře-devším molekulárně biologické analýzy (změny v biomase řas a bakterií a zastoupení bak-teriálních populací). Pro studium chování CeO2 při různém pH byly měřeny velikosti a náboj pomocí dynamického rozptylu světla.Celkově bylo relativní množství řas pouze mírně ovlivněno menšími nanočásticemi CeO2 (4 nm naked a 4 nm collyrium), nicméně celkově řasy ve vzorcích narostly a až ke konci studie začaly odumírat pravděpodobně kvůli vyčerpání dostupných živin. Relativní množ-ství bakterií pokleslo ve všech vzorcích oproti původnímu stavu po dobu 14 dnů a mírně se zvýšilo po 28 dnech. Bakteriální populace měli nižší biodiversitu po expozici 4 nm CeO2. Zastoupení Sediminibacterium bylo po celou dobu vyšší a nárůst Cyanobaterium PCC-6307 bylo možné pozorovat po 28 dnech. Ve vzorcích naked CeO2 4 nm Verrucomicrobiae narost-ly po 5 dnech, Candidatus Aquirestis po 14 dnech a Limnobacter po 28 dnech. Niveispirillum se objevilo v obou vzorcích s CeO2 nanočásticemi po 28 dnech. Všechny Ce02 nanočástice byly záporně nabité v rozsahu -5 až -25 mV ve všech pH 6.6, 7.6 a 8.3, měly proto tendenci agregovat při všech pH, kromě obou velikostí naked CeO2, ty byly stabilní při pH 6.6. Nano-částice CeO2 s collyriem byly stabilní při pH 8.3.
With the increasing use of nanomaterials, the question of their safety for the environment also arises. The toxicity of these substances could affect organisms in the environment, including microorganisms. Cerium oxide (CeO2) nanoparticles (NPs) are one of the materi-als that have recently received attention. In addition to the benefits, CeO2 NPs have contra-dictory possible toxicity to microorganisms.This thesis aims to determine the effects of CeO2 NPs on river microorganisms - bacteria and algae and the behavior of CeO2 in different types of aquatic habitats (according to pH). For this purpose, microorganisms from the river were exposed to CeO2 nanoparticles with-out treatment (naked CeO2 4 nm and 25 nm), and dispersed in collyrium (collyrium CeO2 4 nm). Different concentrations were applied, from 0.001 to 0.05 g/L, and the exposure was examined after 5, 14, and 28 days. To evaluate the effects of CeO2 on microorganisms, an epifluorescence microscope (cell morphology) was used, and especially molecular biologi-cal analyses (changes in the biomass of algae and bacteria and the representation of bacte-rial populations). To study the behaviors of CeO2 NPs in different pH, sizes and charge were measured by a dynamic light scattering. Overall, the relative abundance of algae was only slightly affected by the smaller CeO2 NPs (4 nm naked and 4 nm collyrium). However, overall algae in the samples increased and began to die by the end of the study, probably due to the depletion of available nutrients. The relative abundance of bacteria was more stable than of algae over 14 days, and in-creased after 28 days. The composition of bacterial communities changed but diversity re-mained relatively high in the presence of 4 nm CeO2. Sediminibacterium increased over the whole time and Cyanobaterium PCC-6307 was found after 28 days. In naked CeO2 4 nm samples, Verrucomicrobiae developed after 5 days, Candidatus Aquiresis was found after 14 days and Limnobacter found after 28 days. Niveispirillum showed in one sample of both CeO2 after 28 days. All CeO2 NPs were negatively charged in a range of -5 to -25 mV in all pH 6.6, 7.6, and 8.3. They tended to aggregate during 28 days in all pH, except both sizes of naked CeO2 were stable in pH 6.6, and collyrium CeO2 was stable in pH 8.3.
With the increasing use of nanomaterials, the question of their safety for the environment also arises. The toxicity of these substances could affect organisms in the environment, including microorganisms. Cerium oxide (CeO2) nanoparticles (NPs) are one of the materi-als that have recently received attention. In addition to the benefits, CeO2 NPs have contra-dictory possible toxicity to microorganisms.This thesis aims to determine the effects of CeO2 NPs on river microorganisms - bacteria and algae and the behavior of CeO2 in different types of aquatic habitats (according to pH). For this purpose, microorganisms from the river were exposed to CeO2 nanoparticles with-out treatment (naked CeO2 4 nm and 25 nm), and dispersed in collyrium (collyrium CeO2 4 nm). Different concentrations were applied, from 0.001 to 0.05 g/L, and the exposure was examined after 5, 14, and 28 days. To evaluate the effects of CeO2 on microorganisms, an epifluorescence microscope (cell morphology) was used, and especially molecular biologi-cal analyses (changes in the biomass of algae and bacteria and the representation of bacte-rial populations). To study the behaviors of CeO2 NPs in different pH, sizes and charge were measured by a dynamic light scattering. Overall, the relative abundance of algae was only slightly affected by the smaller CeO2 NPs (4 nm naked and 4 nm collyrium). However, overall algae in the samples increased and began to die by the end of the study, probably due to the depletion of available nutrients. The relative abundance of bacteria was more stable than of algae over 14 days, and in-creased after 28 days. The composition of bacterial communities changed but diversity re-mained relatively high in the presence of 4 nm CeO2. Sediminibacterium increased over the whole time and Cyanobaterium PCC-6307 was found after 28 days. In naked CeO2 4 nm samples, Verrucomicrobiae developed after 5 days, Candidatus Aquiresis was found after 14 days and Limnobacter found after 28 days. Niveispirillum showed in one sample of both CeO2 after 28 days. All CeO2 NPs were negatively charged in a range of -5 to -25 mV in all pH 6.6, 7.6, and 8.3. They tended to aggregate during 28 days in all pH, except both sizes of naked CeO2 were stable in pH 6.6, and collyrium CeO2 was stable in pH 8.3.
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Nanočástice, oxid ceričitý, sladkovodní mikroorganismy, toxicita, Nanoparticles, cerium oxide, freshwater microorganisms, toxicity