23 research outputs found
Low Concentrations of Silver Nanoparticles in Biosolids Cause Adverse Ecosystem Responses under Realistic Field Scenario
A large fraction of engineered nanomaterials in consumer and commercial products will reach natural ecosystems. To date, research on the biological impacts of environmental nanomaterial exposures has largely focused on high-concentration exposures in mechanistic lab studies with single strains of model organisms. These results are difficult to extrapolate to ecosystems, where exposures will likely be at low-concentrations and which are inhabited by a diversity of organisms. Here we show adverse responses of plants and microorganisms in a replicated long-term terrestrial mesocosm field experiment following a single low dose of silver nanoparticles (0.14 mg Ag kg−1 soil) applied via a likely route of exposure, sewage biosolid application. While total aboveground plant biomass did not differ between treatments receiving biosolids, one plant species, Microstegium vimeneum, had 32 % less biomass in the Slurry+AgNP treatment relative to the Slurry only treatment. Microorganisms were also affected by AgNP treatment, which gave a significantly different community composition of bacteria in the Slurry+AgNPs as opposed to the Slurry treatment one day after addition as analyzed by T-RFLP analysis of 16S-rRNA genes. After eight days, N2O flux was 4.5 fold higher in the Slurry+AgNPs treatment than the Slurry treatment. After fifty days, community composition and N2O flux of the Slurry+AgNPs treatment converged with the Slurry. However, the soil microbial extracellular enzymes leucine amino peptidase and phosphatase had 52 and 27% lower activities, respectively, while microbial biomass was 35% lower than the Slurry. We also show that the magnitude of these responses was in all cases as large as or larger than the positive control, AgNO3, added at 4-fold the Ag concentration of the silver nanoparticles
A perturbation-based balance training program for older adults: study protocol for a randomised controlled trial
<p>Abstract</p> <p>Background</p> <p>Previous research investigating exercise as a means of falls prevention in older adults has shown mixed results. Lack of specificity of the intervention may be an important factor contributing to negative results. Change-in-support (CIS) balance reactions, which involve very rapid stepping or grasping movements of the limbs, play a critical role in preventing falls; hence, a training program that improves ability to execute effective CIS reactions could potentially have a profound effect in reducing risk of falling. This paper describes: 1) the development of a perturbation-based balance training program that targets specific previously-reported age-related impairments in CIS reactions, and 2) a study protocol to evaluate the efficacy of this new training program.</p> <p>Methods/Design</p> <p>The training program involves use of unpredictable, multi-directional moving-platform perturbations to evoke stepping and grasping reactions. Perturbation magnitude is gradually increased over the course of the 6-week program, and concurrent cognitive and movement tasks are included during later sessions. The program was developed in accordance with well-established principles of motor learning, such as individualisation, specificity, overload, adaptation-progression and variability. Specific goals are to reduce the frequency of multiple-step responses, reduce the frequency of collisions between the stepping foot and stance leg, and increase the speed of grasping reactions. A randomised control trial will be performed to evaluate the efficacy of the training program. A total of 30 community-dwelling older adults (age 64–80) with a recent history of instability or falling will be assigned to either the perturbation-based training or a control group (flexibility/relaxation training), using a stratified randomisation that controls for gender, age and baseline stepping/grasping performance. CIS reactions will be tested immediately before and after the six weeks of training, using platform perturbations as well as a distinctly different method of perturbation (waist pulls) in order to evaluate the generalisability of the training effects.</p> <p>Discussion</p> <p>This study will determine whether perturbation-based balance training can help to reverse specific age-related impairments in balance-recovery reactions. These results will help to guide the development of more effective falls prevention programs, which may ultimately lead to reduced health-care costs and enhanced mobility, independence and quality of life.</p
Sulfidation Processes of PVP-Coated Silver Nanoparticles in Aqueous Solution: Impact on Dissolution Rate
PMID: 21598969International audienceDespite the increasing use of silver nanoparticles (Ag-NPs) in nanotechnology and their toxicity to invertebrates, the transformations and fate of Ag-NPs in the environment are poorly understood. This work focuses on the sulfidation processes of PVP-coated Ag-NPs, one of the most likely corrosion phenomena that may happen in the environment. The sulfur to Ag-NPs ratio was varied in order to control the extent of Ag-NPs transformation to silver sulfide (Ag2S). A combination of synchrotron-based X-ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure spectroscopy shows the increasing formation of Ag2S with an increasing sulfur to Ag-NPs ratio. TEM observations show that Ag2S forms nanobridges between the Ag-NPs leading to chain-like structures. In addition, sulfidation strongly affects surface properties of the Ag-NPs in terms of surface charge and dissolution rate. Both may affect the reactivity, transport, and toxicity of Ag-NPs in soils. In particular, the decrease of dissolution rate as a function of sulfide exposure may strongly limit Ag-NPs toxicity since released Ag+ ions are known to be a major factor in the toxicity of Ag-NPs
Methylation of Mercury by Bacteria Exposed to Dissolved, Nanoparticulate, and Microparticulate Mercuric Sulfides
PMID: 22145980International audienceThe production of the neurotoxic methylmercury in the environment is partly controlled by the bioavailability of inorganic divalent mercury (Hg(II)) to anaerobic bacteria that methylate Hg(II). In sediment porewater, Hg(II) associates with sulfides and natural organic matter to form chemical species that include organic-coated mercury sulfide nanoparticles as reaction intermediates of heterogeneous mineral precipitation. Here, we exposed two strains of sulfate-reducing bacteria to three forms of inorganic mercury: dissolved Hg and sulfide, nanoparticulate HgS, and microparticulate HgS. The bacteria cultures exposed to HgS nanoparticles methylated mercury at a rate slower than cultures exposed to dissolved forms of mercury. However, net methylmercury production in cultures exposed to nanoparticles was 6 times greater than in cultures treated with microscale particles, even when normalized to specific surface area. Furthermore, the methylation potential of HgS nanoparticles decreased with storage time of the nanoparticles in their original stock solution. In bacteria cultures amended with nano-HgS from a 16 h-old nanoparticle stock, 6–10% of total mercury was converted to methylmercury after one day. In contrast, 2–4% was methylated in cultures amended with nano-HgS that was aged for 3 days or 1 week. The methylation of mercury derived from nanoparticles (in contrast to the larger particles) would not be predicted by equilibrium speciation of mercury in the aqueous phase (<0.2 μm) and was possibly caused by the disordered structure of nanoparticles that facilitated release of chemically labile mercury species immediately adjacent to cell surfaces. Our results add new dimensions to the mechanistic understanding of mercury methylation potential by demonstrating that bioavailability is related to the geochemical intermediates of rate-limited mercury sulfide precipitation reactions. These findings could help explain observations that the “aging” of mercury in sediments reduces its methylation potential and provide a basis for assessing and remediating methylmercury hotspots in the environment
Cysteine-Induced Modifications of Zero-valent Silver Nanomaterials: Implications for Particle Surface Chemistry, Aggregation, Dissolution, and Silver Speciation
The persistence of silver nanoparticles in aquatic environments
and their subsequent impact on organisms depends on key transformation
processes, which include aggregation, dissolution, and surface modifications
by metal-complexing ligands. Here, we studied how cysteine, an amino
acid representative of thiol ligands that bind monovalent silver,
can alter the surface chemistry, aggregation, and dissolution of zero-valent
silver nanoparticles. We compared nanoparticles synthesized with two
coatings, citrate and polyvinylpirrolidone (PVP), and prepared nanoparticle
suspensions (approximately 8 μM total Ag) containing an excess
of cysteine (400 μM). Within 48 h, up to 47% of the silver had
dissolved, as indicated by filtration of the samples with a 0.025-μm
filter. Initial dissolution rates were calculated from the increase
of dissolved silver concentration when particles were exposed to cysteine
and normalized to the available surface area of nanoparticles in solution.
In general, the rates of dissolution were almost 3 times faster for
citrate-coated nanoparticles relative to PVP-coated nanoparticles.
Rates tended to be slower in solutions with higher ionic strength
in which the nanoparticles were aggregating. X-ray absorption spectroscopy
analysis of the particles suggested that cysteine adsorbed to silver
nanoparticles surfaces through the formation of Ag(+I)sulfhydryl
bonds. Overall, the results of this study highlight the importance
of modifications by sulfhydryl-containing ligands that can drastically
influence the long-term reactivity of silver nanoparticles in the
aquatic environment and their bioavailability to exposed organisms.
Our findings demonstrate the need to consider multiple interlinked
transformation processes when assessing the bioavailability, environmental
risks, and safety of nanoparticles, particularly in the presence of
metal-binding ligands
Methylation of Mercury by Bacteria Exposed to Dissolved, Nanoparticulate, and Microparticulate Mercuric Sulfides
The production of the neurotoxic methylmercury in the
environment
is partly controlled by the bioavailability of inorganic divalent
mercury (Hg(II)) to anaerobic bacteria that methylate Hg(II). In sediment
porewater, Hg(II) associates with sulfides and natural organic matter
to form chemical species that include organic-coated mercury sulfide
nanoparticles as reaction intermediates of heterogeneous mineral precipitation.
Here, we exposed two strains of sulfate-reducing bacteria to three
forms of inorganic mercury: dissolved Hg and sulfide, nanoparticulate
HgS, and microparticulate HgS. The bacteria cultures exposed to HgS
nanoparticles methylated mercury at a rate slower than cultures exposed
to dissolved forms of mercury. However, net methylmercury production
in cultures exposed to nanoparticles was 6 times greater than in cultures
treated with microscale particles, even when normalized to specific
surface area. Furthermore, the methylation potential of HgS nanoparticles
decreased with storage time of the nanoparticles in their original
stock solution. In bacteria cultures amended with nano-HgS from a
16 h-old nanoparticle stock, 6–10% of total mercury was converted
to methylmercury after one day. In contrast, 2–4% was methylated
in cultures amended with nano-HgS that was aged for 3 days or 1 week.
The methylation of mercury derived from nanoparticles (in contrast
to the larger particles) would not be predicted by equilibrium speciation
of mercury in the aqueous phase (<0.2 μm) and was possibly
caused by the disordered structure of nanoparticles that facilitated
release of chemically labile mercury species immediately adjacent
to cell surfaces. Our results add new dimensions to the mechanistic
understanding of mercury methylation potential by demonstrating that
bioavailability is related to the geochemical intermediates of rate-limited
mercury sulfide precipitation reactions. These findings could help
explain observations that the “aging” of mercury in
sediments reduces its methylation potential and provide a basis for
assessing and remediating methylmercury hotspots in the environment
Low Concentrations of Silver Nanoparticles in Biosolids Cause Adverse Ecosystem Responses under Realistic Field Scenario
<div><p>A large fraction of engineered nanomaterials in consumer and commercial products will reach natural ecosystems. To date, research on the biological impacts of environmental nanomaterial exposures has largely focused on high-concentration exposures in mechanistic lab studies with single strains of model organisms. These results are difficult to extrapolate to ecosystems, where exposures will likely be at low-concentrations and which are inhabited by a diversity of organisms. Here we show adverse responses of plants and microorganisms in a replicated long-term terrestrial mesocosm field experiment following a single low dose of silver nanoparticles (0.14 mg Ag kg<sup>−1</sup> soil) applied via a likely route of exposure, sewage biosolid application. While total aboveground plant biomass did not differ between treatments receiving biosolids, one plant species, <i>Microstegium vimeneum,</i> had 32 % less biomass in the Slurry+AgNP treatment relative to the Slurry only treatment. Microorganisms were also affected by AgNP treatment, which gave a significantly different community composition of bacteria in the Slurry+AgNPs as opposed to the Slurry treatment one day after addition as analyzed by T-RFLP analysis of 16S-rRNA genes. After eight days, N<sub>2</sub>O flux was 4.5 fold higher in the Slurry+AgNPs treatment than the Slurry treatment. After fifty days, community composition and N<sub>2</sub>O flux of the Slurry+AgNPs treatment converged with the Slurry. However, the soil microbial extracellular enzymes leucine amino peptidase and phosphatase had 52 and 27% lower activities, respectively, while microbial biomass was 35% lower than the Slurry. We also show that the magnitude of these responses was in all cases as large as or larger than the positive control, AgNO<sub>3</sub>, added at 4-fold the Ag concentration of the silver nanoparticles.</p> </div
Microbial abundance, activity, and composition affected by Ag.
<p><b>A</b> Microbial biomass in 0–1 cm soils on Day 50 of the experiment; <b>B</b> N<sub>2</sub>O flux from soil on day 8; <b>C</b> activity of the proteolytic extracellular enzyme leucine aminopeptidase (LAP), on day 50; <b>D</b> activity of the organophosphorous degrading enzyme phosphatase on day 50; <b>E</b> NMS ordination of bacterial community composition with day of experiment designated by shapes: Day 0 (triangles), Day 1 (squares), and 50 (circles); and treatment designated by colors: Control (white), Slurry (black), Slurry+AgNPs (gray), and Slurry+AgNO<sub>3</sub> (red). All error bars are standard error of the mean, and shared letters denote no significant difference at p<0.05 between treatments in panels A–D (n = 6)</p
Mesocosm plant aboveground and belowground biomass affected by Ag.
<p><b>A</b> Aboveground plant biomass of <i>Microstegium vimineum</i>, <b>B</b> root biomass in 0–1 cm soils. Error bars are standard error of the mean, and shared letters denote no significant difference at p<0.05 between treatments differences (n = 6)</p
Silver fate in terrestrial mesocosms.
<p><b>A</b> Recovery of silver by ecosystem compartment after 50 days exposure to biosolid Slurry (white bars), Slurry+AgNPs (gray bars), or Slurry + AgNO<sub>3</sub> (black bars), and <b>B</b> EXAFS linear combination fit (k-space) of AgNPs after 15 minute exposure to biosolid slurry. In B, Lines indicate the data (black line), the linear combination fit (light gray dashed line), and the individual fit components Ag<sup>0</sup> (gray line) and Ag<sub>2</sub>S (dark gray line) are shown, and represent 75±2% and 25±6% percent of the silver, respectively. The model R-factor = 0.0672, chi<sup>2</sup> = 86.64, and the reduced chi<sup>2</sup> = 0.4867 (parameters describing goodness of fit of the model to the data). Error bars in panel <b>A</b> are standard errors of the mean (n = 6). Since all treatments showed the same pattern in ANOVA post-hoc testing, differences for each treatment within each ecosystem compartment were denoted with brackets with letters, where shared letters denote no significant difference at p<0.05 between ecosystem compartments within a treatment</p