Noble gas constraints on the fate of arsenic in groundwater

Groundwater contamination of geogenic arsenic (As) remains a global health threat, particularly in south-east Asia. The prominent correlation often observed between high As concentrations and methane (CH$_{4}$) stimulated the analysis of the gas dynamics in an As contaminated aquifer, whereby noble and reactive gases were analysed. Results show a progressive depletion of atmospheric gases (Ar, Kr and N$_{2}$) alongside highly increasing CH$_{4}$, implying that a free gas phase comprised mainly of CH$_{4}$ is formed within the aquifer. In contrast, Helium (He) concentrations are high within the CH$_{4}$ (gas) producing zone, suggesting longer (groundwater) residence times. We hypothesized that the observed free (CH$_{4}$) gas phase severely detracts local groundwater (flow) and significantly reduces water renewal within the gas producing zone. Results are in-line with this hypothesis, however, a second hypothesis has been developed, which focuses on the potential transport of He from an adjacent aquitard into the (CH$_{4}$) gas producing zone. This second hypothesis was formulated as it resolves the particularly high He concentrations observed, and since external solute input from the overlying heterogeneous aquitard cannot be excluded. The proposed feedback between the gas phase and hydraulics provides a plausible explanation of the anti-intuitive correlation between high As and CH$_{4}$, and the spatially highly patchy distribution of dissolved As concentrations in contaminated aquifers. Furthermore, the increased groundwater residence time would allow for the dissolution of more crystalline As-hosting iron(Fe)-oxide phases in conjunction with the formation of more stable secondary Fe minerals in the hydraulically-slowed (i.e., gas producing) zone; a subject which calls for further investigation

Optical Properties of Manganese Doped Wide Band Gap ZnS and ZnO

Optical properties of ZnMnO layers grown at low temperature by Atomic Layer Deposition and Metalorganic Vapor Phase Epitaxy are discussed and compared to results obtained for ZnMnS samples. Present results suggest a double valence of Mn ions in ZnO lattice. Strong absorption, with onset at about 2.1 eV, is tentatively related to Mn 2+ to 3+ photoionization. Mechanism of emission deactivation in ZnMnO is discussed and is explained by the processes following the assumed Mn 2+ to 3+ recharging.Comment: 17 pages, 4 figures, 32 reference

Unsustainable agriculture and its environmental consequences

Intensywny sposób gospodarowania bez wątpienia przyczynił się do zwiększenia efektywności oraz wydajności produkcji roślinnej i zwierzęcej. Wydajność ta wzrosła dzięki szeroko stosowanym nawozom mineralnym, środkom ochrony roślin, a także mechanizacji rolnictwa. Ważnym aspektem intensywnego sposobu gospodarowania jest wprowadzanie nowych odmian roślin uprawnych i zwierząt hodowlanych lepiej przystosowanych do lokalnych warunków klimatycznych. Intensywne rolnictwo niesie jednak ze sobą wiele poważnych konsekwencji środowiskowych. Wiąże się to głównie ze stosowaniem zbyt dużych dawek chemii rolnej, która jest istotnym źródłem zanieczyszczeń. Pestycydy oraz nawozy mineralne mogą stanowić zagrożenie dla zdrowia konsumentów, poza tym zmieniają także chemizm gleb oraz zanieczyszczają wody powierzchniowe. Mechanizacja rolnictwa przyczynia się do erozji gleb oraz zmiany jej struktury. Ponadto uprzemysłowione rolnictwo powoduje obniżenie bioróżnorodności oraz walorów krajobrazowych terenu. Głównym celem tej pracy jest omówienie, w jaki sposób intensywne i niezrównoważone rolnictwo wpływa na poszczególne komponenty środowiska naturalnego.Without any doubt intensive and modern agriculture significantly increased efficiency and productivity of crop and animal production. It became possible mainly thanks to the widely used mineral fertilizers, crop protection chemicals such as pesticides, but also due to constantly developed new varieties of plants and breeds of animals that are more resistant to diseases and better adapted to cold, as well as mechanization of the agriculture. The crop and animal production would not be possible without the use of natural resources such as soil, water, air as well as land together with its ecosystems and biodiversity. The intensive and industrial agriculture might cause very serious environmental consequences and endanger natural resources from which we are dependent. Threat to the environment comes mainly from unsustainable use of these resources as well as overuse of agrochemicals which are the source of various pollution. Pesticides and fertilizers are not only a direct danger to the health of consumers, they might be a source of food contamination. They also importantly affect chemical properties of the soil by changing its pH, contaminate it with heavy metals and pesticide residues that often cumulate in the upper layers over decades and eventually leach to the ground waters. Extensive use of NPK fertilizers leads to the eutrophication of surface waters causing algae bloom in lakes threatening water ecosystems. Use of agricultural machinery and hi-tech equipment certainly increased the efficiency and productivity in the farm. However, it also caused decrease in employment in the rural areas. Works that were used to be performed by people nowadays are carried out by the machines. Furthermore, mechanization and use of heavy equipment lead to the soil erosion and cause changes in soil structure. Intensive agriculture is one of the main sources of greenhouse gases emissions. The greatest portion of methane comes from ruminant animals which are produced during digestive processes. Finally, industrial agriculture negatively influences biological diversity of rural and agricultural ecosystems. Intensive farming often favors large surface monocultures that significantly decrease biodiversity. The main goal of this review is to discuss how modern, unsustainable agriculture affect our environment, its specific components and natural resources

Structural and optical properties of low-temperature ZnO films grown by atomic layer deposition with diethylzinc and water precursors

We report on properties of low-temperature (LT) ZnO films grown by the atomic layer deposition method with diethylzinc (DEZn) precursor. It is shown that the ZnO thin film crystallographic orientation, quality of the surface, and optical properties depend on the main growth parameters like temperature, pulsing, and purging time and thus can be varied in controllable manner. All the presented results were obtained for ZnO layers grown at temperature between 90 and 200 degrees C. (C) 2008 Elsevier B.V. All rights reserved

16S rRNA gene amplicon sequencing of groundwater, sediment and sediment cultures relevant for arsenic mobilization

Arsenic groundwater contamination is threatening health of millions of people. Due to the abundance of As-bearing sediments deposited in river deltas, South and Southeast Asia is a particularly affected part of the world. In many As-contaminated sites high concentrations of CH4 were observed, but it is unknown whether CH4 can function as electron donor for microbial processes in these sediments. This study investigates microbial communities in CH4 rich As-contaminated groundwater and sediment. Additionally, microbial communities are monitored in sediment cultures where As is mobilizing when supplemented with CH4