5 research outputs found
Determining the Concentration Dependent Transformations of Ag Nanoparticles in Complex Media: Using SP-ICP-MS and Au@Ag Core–Shell Nanoparticles as Tracers
The
fate, behavior, and impact of engineered nanoparticles (NPs)
in toxicological and environmental media are driven by complex processes
which are difficult to quantify. A key limitation is the ability to
perform measurements at low and environmentally relevant concentrations,
since concentration may be a key factor determining fate and effects.
Here, we use single particle inductively coupled mass spectroscopy
(SP-ICP-MS) to measure directly NP diameter and particle number concentration
of suspensions containing gold–silver core–shell (Au@Ag)
NPs in EPA moderately hard water (MHW) and MHW containing 2.5 mg L<sup>–1</sup> Suwannee River fulvic acid. The Au core of the Au@Ag
NPs acts as an internal standard, and aids in the analysis of the
complex Ag transformations. The high sensitivity of SP-ICP-MS, along
with the Au@Ag NPs, enabled us to track the NP transformations in
the range 0.01 and 50 μg L<sup>–1</sup>, without further
sample preparation. On the basis of the analysis of both Au and Ag
parameters (size, size distribution, and particle number), concentration
was shown to be a key factor in NP behavior. At higher concentration,
NPs were in an aggregation-dominated regime, while at the lower and
environmentally representative concentrations, dissolution of Ag was
dominant and aggregation was negligible. In addition, further formation
of ionic silver as Ag NPs in the form of AgS or AgCl was shown to
occur. Between 1 and 10 μg L<sup>–1</sup>, both aggregation
and dissolution were important. The results suggest that, under realistic
conditions, the role of NP homoaggregation may be minimal. In addition,
the complexity of exposure and dose in dose–response relationships
is highlighted
Stability of Citrate, PVP, and PEG Coated Silver Nanoparticles in Ecotoxicology Media
Silver nanoparticles (AgNPs) are present in the environment
and
a number of ecotoxicology studies have shown that AgNPs might be highly
toxic. Nevertheless, there are little data on their stability in toxicology
media. This is an important issue as such dynamic changes affect exposure
dose and the nature of the toxicant studied and have a direct impact
on all (eco)Âtoxicology data. In this study, monodisperse citrate,
PVP, and PEG coated AgNPs with a core size of approximately 10 nm
were synthesized and characterized; their behavior was examined in
standard OECD media used for <i>Daphnia</i> sp. acute and
chronic tests (in the absence of Daphnia). Surface plasmon resonance,
size, aggregation, and shape were monitored over 21 days, comparable
to a chronic exposure period. Charge stabilized particles (citrate)
were more unstable than sterically stabilized particles. Replacement
of chloride in the media (due to concerns over chloride-silver interactions)
with either nitrate or sulfate resulted in increased shape and dissolution
changes. PVP-stabilized NPs in a 10-fold diluted OECD media (chloride
present) were found to be the most stable, with only small losses
in total concentration over 21 days, and no shape, aggregation, or
dissolution changes observed and are recommended for exposure studies
Synthesis and Characterization of Polyvinylpyrrolidone Coated Cerium Oxide Nanoparticles
There
is a pressing need for the development of standard and reference nanomaterials
for environmental nanoscience and nanotoxicology. To that aim, suspensions
of polyvinylpyrrolidone (PVP)-coated ceria nanoparticles (NPs) were
produced. Four differently sized monodispersed samples were produced
by using different PVP chain lengths. The chemical and physical properties
of these NPs were characterized as prepared and in different ecotoxicology
exposure media. Dynamic light scattering analysis showed that the
samples were monodispersed, with an unchanged size when suspended
in the different media over a 72 h period. Electron microscopy confirmed
this and revealed that the larger (ca. 20 nm) particles were aggregates
composed of the smaller individual particles (4–5 nm). Electron
energy loss spectroscopy (EELS) showed that the smallest and largest
samples were composed almost entirely of ceriumÂ(III) oxide, with only
small amounts of ceriumÂ(IV) present in the largest sample. Dissolved
cerium concentrations in media were low and constant, showing that
the NPs did not dissolve over time. The simple synthesis of the these
NPs and their physical and chemical stability in different environmental
conditions make them potentially suitable for use as reference materials
for (eco)Âtoxicology and surface water environmental studies
A High Resolution Study of Dynamic Changes of Ce<sub>2</sub>O<sub>3</sub> and CeO<sub>2</sub> Nanoparticles in Complex Environmental Media
Ceria nanoparticles (NPs) rapidly
and easily cycle between CeÂ(III)
and CeÂ(IV) oxidation states, making them prime candidates for commercial
and other applications. Increased commercial use has resulted in increased
discharge to the environment and increased associated risk. Once in
complex media such as environmental waters or toxicology exposure
media, the same redox transformations can occur, causing altered behavior
and effects compared to the pristine NPs. This study used high resolution
scanning transmission electron microscopy and electron energy loss
spectroscopy to investigate changes in structure and oxidation state
of small, polymer-coated ceria suspensions in complex media. NPs initially
in either the III or IV oxidation states, but otherwise identical,
were used. CeÂ(IV) NPs were changed to mixed (III, IV) NPs at high
ionic strengths, while the presence of natural organic macromolecules
(NOM) stabilized the oxidation state and increased crystallinity.
The CeÂ(III) NPs remained as CeÂ(III) at high ionic strengths, but were
modified by the presence of NOM, causing reduced crystallinity and
degradation of the NPs. Subtle changes to NP properties upon addition
to environmental or ecotoxicology media suggest that there may be
small but important effects on fate and effects of NPs compared to
their pristine form
Citrate-Coated Silver Nanoparticles Growth-Independently Inhibit Aflatoxin Synthesis in <i>Aspergillus parasiticus</i>
Manufactured silver nanoparticles
(Ag NPs) have long been used
as antimicrobials. However, little is known about how these NPs affect
fungal cell functions. While multiple previous studies reveal that
Ag NPs inhibit secondary metabolite syntheses in several mycotoxin
producing filamentous fungi, these effects are associated with growth
repression and hence need sublethal to lethal NP doses, which besides
stopping fungal growth, can potentially accumulate in the environment.
Here we demonstrate that citrate-coated Ag NPs of size 20 nm, when
applied at a selected nonlethal dose, can result in a >2 fold inhibition
of biosynthesis of the carcinogenic mycotoxin and secondary metabolite,
aflatoxin B<sub>1</sub> in the filamentous fungus and an important
plant pathogen, <i>Aspergillus parasiticus</i>, without
inhibiting fungal growth. We also show that the observed inhibition
was not due to Ag ions, but was specifically associated with the mycelial
uptake of Ag NPs. The NP exposure resulted in a significant decrease
in transcript levels of five aflatoxin genes and at least two key
global regulators of secondary metabolism, <i>laeA</i> and <i>veA,</i> with a concomitant reduction of total reactive oxygen
species (ROS). Finally, the depletion of Ag NPs in the growth medium
allowed the fungus to regain completely its ability of aflatoxin biosynthesis.
Our results therefore demonstrate the feasibility of Ag NPs to inhibit
fungal secondary metabolism at nonlethal concentrations, hence providing
a novel starting point for discovery of custom designed engineered
nanoparticles that can efficiently prevent mycotoxins with minimal
risk to health and environment