Manganese oxides are considered an essential component of natural geochemical barriers due to their redox and sorptive reactivity towards essential and potentially toxic trace elements. Despite the perception that they are in a relatively stable phase, microorganisms can actively alter the prevailing conditions in their microenvironment and initiate the dissolution of minerals, a process that is governed by various direct (enzymatic) or indirect mechanisms. Microorganisms are also capable of precipitating the bioavailable manganese ions via redox transformations into biogenic minerals, including manganese oxides (e.g., low-crystalline birnessite) or oxalates. Microbially mediated transformation influences the (bio)geochemistry of manganese and also the environmental chemistry of elements intimately associated with its oxides. Therefore, the biodeterioration of manganese-bearing phases and the subsequent biologically induced precipitation of new biogenic minerals may inevitably and severely impact the environment. This review highlights and discusses the role of microbially induced or catalyzed processes that affect the transformation of manganese oxides in the environment as relevant to the function of geochemical barriers.

• Klíčová slova
• biotransformation, manganese, manganese oxides, microorganisms, sorption,
• MeSH
• mangan * chemie   MeSH
• minerály chemie   MeSH
• oxidace-redukce MeSH
• oxidy * chemie   MeSH
• sloučeniny manganu chemie   MeSH
• životní prostředí MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• mangan * MeSH
• manganese oxide MeSH Prohlížeč
• minerály MeSH
• oxidy * MeSH
• sloučeniny manganu MeSH

An amorphous Mn oxide (AMO), nanomaghemite, and nanomagnetite were used as potential amendments reducing the mobility of As in three contrasting contaminated soils differing in origin of As contamination. Adsorption experiments and XPS analyses combined with incubation batch experiments and pH-static leaching tests were used. The AMO showed excellent adsorption capacity for As(V) reaching a maximum of 1.79 mmol g(-1) at pH 7 and 8. Interestingly, the adsorption capacity in this case decreases with decreasing pH, probably as a result of AMO dissolution at lower pH values. Chemical sorption of As(V) onto AMO was further confirmed with XPS. Both Fe nano-oxides proved the highest adsorption capacity at pH 4 reaching 11 mg g(-1) of adsorbed As(V). The AMO was also the most efficient amendment for decreasing As concentrations in soil solutions during 8 weeks of incubation. Additionally, pH-static leaching tests were performed at pH 4, 5, 6, 7, and natural pH (not adjusted) and AMO again proved the highest ability to decrease As content in leachate. On the other hand, strong dissolution of this amendment at lower pH values (especially pH 4) was observed. For that reason, AMO appears as a promising stabilizing agent for As, especially in neutral, alkaline, or slightly acidic soils, where As(V) species are expected to be more mobile.

• Klíčová slova
• Adsorption, Arsenic, Immobilization, Mn oxide, Nanomaghemite, Nanomagnetite,
• MeSH
• adsorpce MeSH
• arsen analýza   chemie   MeSH
• kinetika MeSH
• koncentrace vodíkových iontů MeSH
• látky znečišťující půdu analýza   chemie   MeSH
• nanočástice chemie   MeSH
• oxidy chemie   MeSH
• půda chemie   MeSH
• regenerace a remediace životního prostředí MeSH
• sloučeniny manganu chemie   MeSH
• železité sloučeniny chemie   MeSH
• znečištění životního prostředí analýza   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• arsen MeSH
• ferric oxide MeSH Prohlížeč
• látky znečišťující půdu MeSH
• manganese oxide MeSH Prohlížeč
• oxidy MeSH
• půda MeSH
• sloučeniny manganu MeSH
• železité sloučeniny MeSH

The application of nanomaterials in commercially available products is increasing rapidly for agriculture, phytoremediation and biotechnology. Since plants suppose the first sink for the accumulation of nanoparticles from the environment, emerging studies have focused on the general consequences for plants and their effects on the biomass production. However, effects on the root surface, as well as blockage of nutrients and water uptake by the roots, may also occur. This experiment was designed to prove if the plant water relations can be affected by the adsorption of nanoparticles on the root surface, causing a consequent stress for the plants. With this goal, plants of Helianthus annuus were previously grown in a hydroponic culture, and at age of 55 days, their roots were exposed to three different concentrations of nanomaghemite (NM) in the hydroponic solution for 5 days: control without NM; 50 and 100 mg l(-1) NM. The main effect was related to the reduction of the root hydraulic conductivity (Lo) and the nutrients uptake. The concentrations of the macronutrients Ca, K, Mg and S in the shoot were reduced relative to the control plants, which resulted in lower contents of chlorophyll pigments. Although stress was not detected in the plants, after the analysis of stress markers like the accumulation of proline or ascorbate in the tissues, reduction of the root functionality by nanoparticles has been identified here, manifested as the effect of NM on Lo. The treatment with 50 mg l(-1) NM significantly reduced the Lo, by up to 57% of its control value, and it was reduced by up to 26% at 100 mg l(-1) NM. These results will be an important factor to take into account with regard to the applicability of NM for long-term use in crops, particularly during privative water conditions.

• Klíčová slova
• Chlorophylls, Metals, Nano-oxide, Root hydraulic conductivity, Sunflower, Uptake,
• MeSH
• biologický transport MeSH
• biomasa MeSH
• chlorofyl metabolismus   MeSH
• Helianthus účinky léků   růst a vývoj   metabolismus   MeSH
• kořeny rostlin účinky léků   růst a vývoj   metabolismus   MeSH
• nanočástice toxicita   MeSH
• prolin metabolismus   MeSH
• voda metabolismus   MeSH
• železité sloučeniny farmakologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• chlorofyl MeSH
• ferric oxide MeSH Prohlížeč
• prolin MeSH
• voda MeSH
• železité sloučeniny MeSH