Mercuric ion reduction and resistance in transgenic Arabidopsis thaliana plants expressing a modified bacterial merA gene.

With global heavy metal contamination increasing, plants that can process heavy metals might provide efficient and ecologically sound approaches to sequestration and removal. Mercuric ion reductase, MerA, converts toxic Hg2+ to the less toxic, relatively inert metallic mercury (Hg0) The bacterial merA sequence is rich in CpG dinucleotides and has a highly skewed codon usage, both of which are particularly unfavorable to efficient expression in plants. We constructed a mutagenized merA sequence, merApe9, modifying the flanking region and 9% of the coding region and placing this sequence under control of plant regulatory elements. Transgenic Arabidopsis thaliana seeds expressing merApe9 germinated, and these seedlings grew, flowered, and set seed on medium containing HgCl2 concentrations of 25-100 microM (5-20 ppm), levels toxic to several controls. Transgenic merApe9 seedlings evolved considerable amounts of Hg0 relative to control plants. The rate of mercury evolution and the level of resistance were proportional to the steady-state mRNA level, confirming that resistance was due to expression of the MerApe9 enzyme. Plants and bacteria expressing merApe9 were also resistant to toxic levels of Au3+. These and other data suggest that there are potentially viable molecular genetic approaches to the phytoremediation of metal ion pollution.

Disponibilidade de níquel no sistema solo-planta: efeito de doses e saturações por bases

Por se tratar de um elemento essencial às plantas e um metal pesado ao mesmo tempo, o níquel requer atenção quanto aos aspectos da fisiologia de plantas e ambiental. Além disso, existe um intervalo estreito entre as exigências nutricionais e os teores tóxicos às plantas. Neste contexto, objetivou-se avaliar o efeito do Ni no sistema solo-planta, com foco no ciclo do N e a disponibilidade do elemento no solo, por meio de experimento em condições controladas, utilizando vasos distribuídos inteiramente ao acaso, utilizando-se esquema fatorial 2 x 5, com sete repetições cada tratamento. O primeiro fator foi constituído de duas saturações por base (50 e 70%) e o segundo de cinco doses de Ni (0; 0,1; 0,5; 1,0 e 10,0 mg dm-3 de solo). Os vasos foram preenchidos com 8 dm3 de terra e cultivados com soja [Glycine max (L.) Merrill] sucedida por girassol (Helianthus annuus L.). Os parâmetros qualitativos e quantitativos: altura de plantas (AP), diâmetro do caule (DC), número de nós (NN), estádio fenológico (EF), índice SPAD e, diâmetro do capítulo (DCap) (para girassol) foram avaliadas aos 30 e 60 dias após a emergência (d.a.e.) de cada cultivo. Plantas inteiras de soja, amostradas em quatro vasos de cada tratamento, foram coletadas no estádio R1. Na mesma ocasião foram coletadas amostras de solo da rizosfera. Em seguida, as plantas coletadas foram divididas em: folhas; raízes (nódulos na soja) e parte aérea. Foram determinados nas folhas utilizadas para diagnose em soja e girassol: os teores de macro e micronutrientes, as atividades da redutase do nitrato e da urease e as concentrações dos ácidos orgânicos: oxálico, malônico, succínico, málico, tartárico, fumárico, oxaloacético, cítrico e lático. Os mesmos ácidos orgânicos foram determinados em raízes secundárias de girassol e nódulos de soja. Foram realizadas avaliações ultraestruturais por meio de microscopia eletrônica de transmissão (MET) em raízes de girassol, e estruturais e de tonalidade em nódulos de soja, por meio de microscopia de luz. No solo, foram determinadas: atividade urease, desidrogenase, Ni total e fitodisponível pelos métodos: Mehlich-1, Mehlich-3 e DTPA. No período de maturidade fisiológica de cada cultura foi realizada a colheita das plantas dos vasos restantes para determinação de produção de grãos, teores de Ni na planta inteira e Ni e N nos grãos. Ao final dos dois experimentos foi realizada nova coleta de solo para extração sequencial de Ni. O índice SPAD em soja aos 60 d.a.e., a produção de massa seca da parte aérea da soja e da raiz de girassol foram influenciados pela saturação por bases, doses de níquel e pela a interação destes. Foram influenciados pelas saturações por base e doses de níquel (fatores isolados): para soja: AP aos 60 d.a.e., NN aos 30 e 60 d.a.e., SPAD aos 30 d.a.e.; para girassol: AP e NN aos 30 e 60 d.a.e., DC e SPAD aos 30 d.a.e. As demais variáveis avaliadas aos 30 e 60 d.a.e. foram influenciadas apenas pela saturação por bases, ou doses de Ni separadamente. As plantas de soja e girassol apresentaram maiores teores de Ni nos diferentes tecidos avaliados (exceto grãos) quando cultivadas sob V50%. A produção de grãos de soja e girassol não foi influenciada pelos tratamentos, porém o teor de N dos grãos de soja influenciado pelas doses de Ni na V70%. A atividade da enzima urease nas folhas de soja e girassol foi responsiva positivamente ao aumento das doses de Ni. Quatro dos ácidos orgânicos avaliados e o teor de N nas folhas e nos grãos foram maiores nas plantas cultivadas sob V70% com a dose de 0,5 mg dm-3 de Ni. As doses de Ni bem com as saturações por bases influenciaram diretamente o balanço de nutrientes das plantas. Os extratores Mehlich-1, Mehlich-3 e DTPA apresentaram elevado coefienciente de correlação entre a fração de Ni disponível no solo e a concentração do elemento nas plantas de soja e girassol, sendo o extrator DTPA o que apresentou maior coeficiente de correlação. O Ni apresentou distribuição variável entre as diferentes frações do solo em função dos tratamentos. Os solos dos tratamentos com saturação por bases de 70% apresentaram maior concentração de Ni ligado a carbonato, comparado aos tratamentos sob saturação por bases de 50%. A distribuição do Ni entre as frações do solo seguiu a seguinte orgem: ligado a carbonato < trocável < ligado a óxidos < matéria orgânica < residual. A saturação por bases exerceu efeito diferenciado para a atividade da urease no solo em função da cultura avaliada. Por sua vez, o Ni exerceu efeito diferenciado sobre a atividade de desidrogenase em função da cultura estudada

Nanoclay-based Pigments: synthesis, characterization and application

Nanoclay-based pigments are promising colorants. They enhance the colorimetric properties of the dye giving more intense and saturated colours. In addition, they act as reinforce additive when they are dispersed into polymers. They can be applied in a wide variety of substrates: printing inks, textiles, acrylic paints and concrete; and more applications are being developed. One important advantage of the nanoclay-based pigments is the fact that they can be considered an ecological alternative to contaminant colorants, in contrast to some traditional inorganic pigments that contend heavy metal in their structure.

Quantum Dot-Sensitized Solar Cells Based on Directly Adsorbed Zinc Copper Indium Sulfide Colloids

Heavy metal-based quantum dots (QDs) have demonstrated to behave as efficient sensitizers in QD-sensitized solar cells (QDSSCs), as attested by the countless works and encouraging efficiencies reported so far. However, their intrinsic toxicity has arisen as a major issue for the prospects of commercialization. Here, we examine the potential of environmentally friendly zinc copper indium sulfide (ZCIS) QDs for the fabrication of liquid-junction QDSSCs by means of photoelectrochemical measurements. A straightforward approach to directly adsorb ZCIS QDs on TiO2 from a colloidal dispersion is presented. Incident photon-to-current efficiency (IPCE) spectra of sensitized photoanodes show a marked dependence on the adsorption time, with longer times leading to poorer performances. Cyclic voltammograms point to a blockage of the channels of the mesoporous TiO2 film by the agglomeration of QDs as the main reason for the decrease in efficiency. Photoanodes were also submitted to the ZnS treatment. Its effects on electron recombination with the electrolyte are analyzed through electrochemical impedance spectroscopy and photopotential measurements. The corresponding results bring out the role of the ZnS coating as a barrier layer preventing electron leakage toward the electrolyte, as argued in other QD-sensitized systems. The beneficial effect of the ZnS coating is ultimately reflected on the power conversion efficiency of complete devices, reaching values of 2 %. In a more general vein, through these findings, we aim to call the attention to the potentiality of this quaternary alloy, virtually unexplored as a light harvester for sensitized devices.

Alleviation of Zn toxicity by low water availability

Heavy metal contamination and drought are expected to increase in large areas worldwide. However, their combined effect on plant performance has been scantly analyzed. This study examines the effect of Zn supply at different water availabilities on morpho-physiological traits of Quercus suber L. in order to analyze the combined effects of both stresses. Seedlings were treated with four levels of zinc from 3 to 150 µM and exposed to low watering (LW) or high watering (HW) frequency in hydroponic culture, using a growth chamber. Under both watering regimes, Zn concentration in leaves and roots increased with Zn increment in nutrient solution. Nevertheless, at the highest Zn doses, Zn tissue concentrations were almost twice in HW than in LW seedlings. Functional traits as leaf photosynthetic rate and root hydraulic conductivity, and morphological traits as root length and root biomass decreased significantly in response to Zn supply. Auxin levels increased with Zn concentrations, suggesting the involvement of this phytohormone in the seedling response to this element. LW seedlings exposed to 150 µM Zn showed higher root length and root biomass than HW seedlings exposed to the same Zn dose. Our results suggest that low water availability could mitigate Zn toxicity by limiting internal accumulation. Morphological traits involved in the response to both stresses probably contributed to this response.

Sources and transport of surface sediment and metals in B.C. fjord, Tahsis and Zeballos Inlets

Senior thesis written for Oceanography 445

Gene-environment interactions between adult lead exposure and Apolipoprotein E4 on adult hippocampal neurogenesis and cognitive behavior in mice

Thesis (Ph.D.)--University of Washington, 2016-06

Testing the 'photoinhibition' model of coral bleaching using chemical inhibitors

Explants of the hard coral Seriatopora hystrix were exposed to sublethal concentrations of the herbicide diuron DCMU (N'-(3,4-dichlorophenyl,-N,N-dimethylurea)) and the heavy metal copper. Pulse amplitude modulated (PAM) chlorophyll fluorescence techniques were used to assess the effects on the photosynthetic efficiency of the algal symbionts in the tissue (in Symbio), and chlorophyll fluorescence and counts of symbiotic algae (normalised to surface area) were used to assess the extent of coral bleaching. At 30 mug DCMU l(-1), there was a reduction in both the maximum effective quantum yield (DeltaF/F-m') and maximum potential quantum yield (F-v/F-m) of the algal symbionts in symbio. Corals subsequently lost their algal symbionts and discoloured (bleached), especially on their upper sunlight-exposed surfaces. At the same DCMU concentration but under low light (5% of growth irradiance), there was a marked reduction in DeltaF/F-m' but only a slight reduction in F-v/F-m and slight loss of algae. Loss of algal symbionts was also noted after a 7 d exposure to concentrations as low as 10 mug DCMU l(-1) under normal growth irradiance, and after 14 d exposure to 10 mug DCMU l(-1) under reduced irradiance. Collectively the results indicate that DCMU-induced bleaching is caused by a light-dependent photoinactivation of algal symbionts, and that bleaching occurs when F-v/F-n, (measured 2 h after sunset) is reduced to a value of less than or equal to 0.6. Elevated copper concentrations (60 mug Cu l(-1) for 10 h) also induced a rapid bleaching in S. hystrix but without affecting the quantum yield of the algae in symbio. Tests with isolated algae indicated that substantially higher concentrations (300 mug Cu l(-1) for 8 h) were needed to significantly reduce the quantum yield. Thus, copper-induced bleaching occurs without affecting the algal photosynthesis and may be related to effects on the host (animal). It is argued that warm-water bleaching of corals resembles both types of chemically induced bleaching, suggesting the need for an integrated model of coral bleaching involving the effect of temperature on both host (coral) and algal symbionts.

Water quality in the Great Barrier Reef region: responses of mangrove, seagrass and macroalgal communities

Marine plants colonise several interconnected ecosystems in the Great Barrier Reef region including tidal wetlands, seagrass meadows and coral reefs. Water quality in some coastal areas is declining from human activities. Losses of mangrove and other tidal wetland communities are mostly the result of reclamation for coastal development of estuaries, e.g. for residential use, port infrastructure or marina development, and result in river bank destabilisation, deterioration of water clarity and loss of key coastal marine habitat. Coastal seagrass meadows are characterized by small ephemeral species. They are disturbed by increased turbidity after extreme flood events, but generally recover. There is no evidence of an overall seagrass decline or expansion. High nutrient and substrate availability and low grazing pressure on nearshore reefs have lead to changed benthic communities with high macroalgal abundance. Conservation and management of GBR macrophytes and their ecosystems is hampered by scarce ecological knowledge across macrophyte community types. (c) 2004 Elsevier Ltd. All rights reserved.

Autocatalytic deposition of composite coatings

The deposition and properties of electroless nickel composite coatings containing graphite, PTFE and chromium were investigated. Solutions were developed for the codeposition of graphite and chromium with electroless nickel. Solutions for the deposition of graphite contained heavy metal ions for stability, with non-ionic and anionic surfactants to provide wetting and dispersion of the particles. Stability for the codeposition of chromium particles was achieved by oxidation of the chromium. Thin oxide layers of 200 nm thick prevented initiation of the electroless reaction onto the chromium. A mechanism for the formation of electroless composite coatings was considered based on the physical adsorption of particles and as a function of the adsorption of charged surfactants and metal cations from solution. The influence of variables such as particle concentration in solution, particle size, temperature, pH, and agitation on the volume percentage of particles codeposited was studied. The volume percentage of graphite codeposited was found to increase with concentration in solution and playing rate. An increase in particle size and agitation reduced the volume percentage codeposited. The hardness of nickel-graphite deposits was found to decrease with graphite content in the as-deposited and heat treated condition. The frictional and wear properties of electroless nickel-graphite were studied and compared to those of electroless nickel-PTFE. The self-lubricating nature of both coatings was found to be dependent on the ratio of coated area to uncoated area, the size and content of lubricating material in the deposit, and the load between contacting surfaces. The mechanism of self-lubrication was considered, concluding that graphite only produced an initial lubricating surface due to the orientation of flakes, unlike PTFE, which produced true self-lubrication throughout the coating life. Heat treatment of electroless nickel chromium deposits at 850oC for 8 and 16 hours produced nickel-iron-chromium alloy deposits with a phosphorus rich surface of high hardness. Coefficients of friction and wear rates were intially moderate for the phosphorus rich layer but increased for the nickel-iron-chromium region of the coating.

Background levels of urban land contamination

The research work reported in this thesis is concerned with the development and application of an urban scale sampling methodology for measuring and assessing background levels of heavy metal soil contamination in large and varied urban areas. The policy context of the work is broadly the environmental health problems posed by contaminated land and their implications for urban development planning. Within this wider policy context, the emphasis in the research has been placed on issues, related to the determination and application of 'guidelines' for assessing the significance of contaminated land for environmental planning. In concentrating on background levels of land contamination, the research responds to the need for additional techniques which address both the problems of measuring soil contamination at the urban scale and which are also capable of providing detailed information for use in the assessment of contaminated sites. Therefore, a key component of the work has been the development of a land-use based sampling framework for generating spatially comprehensive data on heavy metals in soil. The utility of the information output of the sampling method is demonstrated in two alternative ways. Firstly, it has been used to map the existing pattern of typical levels of heavy metals in urban soils. Secondly, it can be used to generate both generalised data in the form of 'reference levels' from which the overall significance of .background contamination may be assessed and detailed data, termed 'normal limit levels' for use in the assessment of site specific investigation data. The fieldwork was conducted in the West Midlands Metropolitan County and surface soil has been sampled and analysed for a measure of plant-available' and 'total' lead cadmium, copper and zinc. The research contrasts with much of the previous work on contaminated land which has generally concentrated on either the detailed investigation of individual sites suspected of being contaminated or the appraisal of land contamination resulting from specific point sources.