13 research outputs found
Функционирование маркетинговых терминов в английском языке и способы их перевода на русский язык
Целью исследования является определение способов перевода английской терминологии на русский
язык
DataSheet1_Methylmercury content in soil and litter from the Amazonian rainforest and its potential fate during forest fires.PDF
Methylmercury in soils and vegetation from the Amazonian rainforest is still poorly studied. Hence, the aim of this work was to determine the total mercury [THg] and methylmercury [MeHg] concentrations in litter and surface soil, MeHg deposition via litterfall, and the MeHg fate during a forest fire in the Amazonian rainforest. Sampling of litter, soil (0–1, 1–2, and 2–5 cm), and ash was carried out before (BB) and after (AB) a prescribed forest fire. The results showed a low [THg] (34 ± 8 ng g-1) and [MeHg] (0.16 ± 0.03 ng g-1) value in litter, with a correspondingly low estimate of the MeHg litterfall flux (0.13 ± 0.03 μgm-2 yr-1) which has been probably underestimated due to potential losses during the field experiment. In ashes, [THg] and [MeHg] values were 23 ± 8 ng g-1 and 0.11 ± 0.04 ng g-1, respectively. Although a significant part of Hg contained in the biomass was lost during the fire, the [MeHg]/[THg] ratio was not affected by it and was the same in litterfall and ash (∼0.5%). In soil, the average [THg] BB value was 149 ± 12 ng g-1 in the three layers and [MeHg] was between 0.8 and 1.0 ng g-1. The forest fire only affected the superficial soil, with a significant decrease of [THg] and [MeHg] in the 0-1 cm layer. Similarly, the decrease of the [MeHg]/[THg] ratio in the surface soil layer suggested that MeHg was more readily emitted or degraded than the other Hg species present.</p
Transformation, Localization, and Biomolecular Binding of Hg Species at Subcellular Level in Methylating and Nonmethylating Sulfate-Reducing Bacteria
Microbial activity is recognized to play an important
role on Hg
methylation in aquatic ecosystems. However, the mechanism at the cellular
level is still poorly understood. In this work subcellular partitioning
and transformation of Hg species in two strains: <i>Desulfovibrio</i> sp. BerOc1 and <i>Desulfovibrio desulfuricans</i> G200
(which exhibit different Hg methylation potential) are studied as
an approach to the elucidation of Hg methylation/demethylation processes.
The incubation with isotopically labeled Hg species (<sup>199</sup>Hgi and Me<sup>201</sup>Hg) not only allows the determination of
methylation and demethylation rates simultaneously, but also the comparison
of the localization of the originally added and resulting species
of such metabolic processes. A dissimilar Hg species distribution
was observed. In general terms, monomethylmercury (MeHg) is preferentially
localized in the extracellular fraction; meanwhile inorganic mercury
(Hgi) is associated to the cells. The investigation of Hg binding
biomolecules on the cytoplasmatic and extracellular fractions (size
exclusion chromatography coupled to ICP-MS) revealed noticeable differences
in the pattern corresponding to the Hg methylating and nonmethylating
strains
Identical Hg Isotope Mass Dependent Fractionation Signature during Methylation by Sulfate-Reducing Bacteria in Sulfate and Sulfate-Free Environment
Inorganic
mercury (iHg) methylation in aquatic environments is
the first step leading to monomethylmercury (MMHg) bioaccumulation
in food webs and might play a role in the Hg isotopic composition
measured in sediments and organisms. Methylation by sulfate reducing
bacteria (SRB) under sulfate-reducing conditions is probably one of
the most important sources of MMHg in natural aquatic environments,
but its influence on natural Hg isotopic composition remains to be
ascertained. In this context, the methylating SRB <i>Desulfovibrio
dechloracetivorans</i> (strain BerOc1) was incubated under sulfate
reducing and fumarate respiration conditions (SR and FR, respectively)
to determine Hg species specific (MMHg and IHg) isotopic composition
associated with methylation and demethylation kinetics. Our results
clearly establish Hg isotope mass-dependent fractionation (MDF) during
biotic methylation (−1.20 to +0.58‰ for δ<sup>202</sup>Hg), but insignificant mass-independent fractionation (MIF)
(−0.12 to +0.15‰ for Δ<sup>201</sup>Hg). During
the 24h of the time-course experiments Hg isotopic composition in
the produced MMHg becomes significantly lighter than the residual
IHg after 1.5h and shows similar δ<sup>202</sup>Hg values under
both FR and SR conditions at the end of the experiments. This suggests
a unique pathway responsible for the MDF of Hg isotopes during methylation
by this strain regardless the metabolism of the cells. After 9 h of
experiment, significant simultaneous demethylation is occurring in
the culture and demethylates preferentially the lighter Hg isotopes
of MMHg. Therefore, depending on their methylation/demethylation capacities,
SRB communities in natural sulfate reducing conditions likely have
a significant and specific influence on the Hg isotope composition
of MMHg (MDF) in sediments and aquatic organisms
Higher Mass-Independent Isotope Fractionation of Methylmercury in the Pelagic Food Web of Lake Baikal (Russia)
Mercury undergoes several transformations that influence
its stable
isotope composition during a number of environmental and biological
processes. Measurements of Hg isotopic mass-dependent (MDF) and mass-independent
fractionation (MIF) in food webs may therefore help to identify major
sources and processes leading to significant bioaccumulation of methylmercury
(MeHg). In this work, δ<sup>13</sup>C, δ<sup>15</sup>N,
concentration of Hg species (MeHg, inorganic Hg), and stable isotopic
composition of Hg were determined at different trophic levels of the
remote and pristine Lake Baikal ecosystem. Muscle of seals and different
fish as well as amphipods, zooplankton, and phytoplankton were specifically
investigated. MDF during trophic transfer of MeHg leading to enrichment
of heavier isotopes in the predators was clearly established by δ<sup>202</sup>Hg measurements in the pelagic prey–predator system
(carnivorous sculpins and top-predator seals). Despite the low concentrations
of Hg in the ecosystem, the pelagic food web reveals very high MIF
Δ<sup>199</sup>Hg (3.15–6.65‰) in comparison to
coastal fish (0.26–1.65‰) and most previous studies
in aquatic organisms. Trophic transfer does not influence MIF signature
since similar Δ<sup>199</sup>Hg was observed in sculpins (4.59
± 0.55‰) and seal muscles (4.62 ± 0.60‰).
The MIF is suggested to be mainly controlled by specific physical
and biogeochemical characteristics of the water column. The higher
level of MIF in pelagic fish of Lake Baikal is mainly due to the bioaccumulation
of residual MeHg that is efficiently turned over and photodemethylated
in deep oligotrophic and stationary (i.e., long residence time) freshwater
columns
Volatile Dimethyl Polonium Produced by Aerobic Marine Microorganisms
The production of volatile polonium (Po<sub>v</sub>),
a naturally
occurring radioactive element, by pure cultures of aerobic marine
tellurite-resistant microorganisms was investigated. <i>Rhodotorula
mucilaginosa</i>, a carotogenic yeast, and a <i>Bacillus</i> sp. strain, a Gram-positive bacterium, generated approximately one
and 2 orders of magnitude, respectively, greater amounts of Po<sub>v</sub> compared to the other organisms tested. Gas chromatography-inductively
coupled plasma-mass spectrometry (GC-ICP-MS) analysis identified dimethyl
polonide (DMPo) as the predominant volatile Po compound in culture
headspace of the yeast. This species assignment is based on the exact
relation between GC retention times and boiling points of this and
other Group VI B analogues (S, Se, and Te). The extent of the biotic
Po<sub>v</sub> production correlates exponentially with elevated particulate
Po (Po<sub>p</sub>): dissolved Po (Po<sub>aq</sub>) ratios in the
cultures, consistent with efficient Po bioaccumulation. Further experimentation
demonstrated that some abiotic Po<sub>v</sub> generation is possible.
However, high-level Po<sub>v</sub> generation in these cultures is
predominantly biotic
Specific Effects of Dietary Methylmercury and Inorganic Mercury in Zebrafish (<i>Danio rerio</i>) Determined by Genetic, Histological, and Metallothionein Responses
A multidisciplinary
approach is proposed here to compare toxicity
mechanisms of methylmercury (MeHg) and inorganic mercury (iHg) in
muscle, liver, and brain from zebrafish (<i>Danio rerio</i>). Animals were dietary exposed to (1) 50 ng Hg g<sup>–1</sup>, 80% as MeHg; (2) diet enriched in MeHg 10000 ng Hg g<sup>–1</sup>, 95% as MeHg; (3) diet enriched in iHg 10000 ng Hg g<sup>–1</sup>, 99% as iHg, for two months. Hg species specific bioaccumulation
pathways were highlighted, with a preferential bioaccumulation of
MeHg in brain and iHg in liver. In the same way, differences in genetic
pattern were observed for both Hg species, (an early genetic response
(7 days) for both species in the three organs and a late genetic response
(62 days) for iHg) and revealed a dissimilar metabolization of both
Hg species. Among the 18 studied genes involved in key metabolic pathways
of the cell, major genetic responses were observed in muscle. Electron
microscopy revealed damage mainly because of MeHg in muscle and also
in liver tissue. In brain, high MeHg and iHg concentrations induced
metallothionein production. Finally, the importance of the fish origin
in ecotoxicological studies, here the seventh descent of a zebrafish
line, is discussed
Comparison of 16S rRNA genes and 16S rRNA transcripts based on T-RFLP analyses from BAL and NEREIS+BAL.
<p>(<b>A</b>) Percentage of Operational Taxonomic Units (OTUs) specific to the 16S rRNA genes (RNA− DNA+) or the 16S rRNA transcripts (RNA+ DNA−), or common to both (RNA+ DNA+). The stars show significant differences obtained by the Duncan test (p-value<0.05) compared to the day 2 value. (B) Relationships between percentage of OTUs common to 16S rRNA genes and transcripts (RNA+ DNA+) with n-alkanes concentrations.</p
Characteristics of the CTRL<sub>270d</sub>, BAL<sub>270d</sub>, NEREIS<sub>270d</sub> and NEREIS+BAL<sub>270d</sub> cDNA libraries.
<p>Characteristics of the CTRL<sub>270d</sub>, BAL<sub>270d</sub>, NEREIS<sub>270d</sub> and NEREIS+BAL<sub>270d</sub> cDNA libraries.</p
Bacterial community structure changes based on the 16S rRNA gene (A) and transcripts (B) for 270 days for the four conditions.
<p>Hierarchical analysis was performed using all replicates but only the average similarity between replicates is represented. CTRL, white circle; BAL, black circle; NEREIS, white triangle; NEREIS+BAL, black triangle. Clusters were formed under the 69.9% threshold.</p