5 research outputs found
Comparison of acute to chronic ratios between silver and gold nanoparticles, using <i>Ceriodaphnia dubia</i>
<p>As integration of nanoparticles (NPs) into products becomes more common, the need to address the paucity of chronic hazard information for aquatic environments required to determine risk potential increases. This study generated acute and chronic toxicity reference values for <i>Ceriodaphnia dubia</i> exposed to 20 and 100 nm silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) to generate and evaluate potential differences in acute-to-chronic ratios (ACR) using two different feeding methods. A modified feeding procedure was employed alongside the standard procedures to investigate the influence of food on organism exposure. An 8-h period before food was added allowed direct organism exposure to NP dispersions (and associated ions) without food-to-NP interactions. The AgNPs [chronic lethal median concentrations (LC50) between 18.7 and 31.9 µg/L] were substantially more toxic than AuNPs (LC50 = 21 507 to >26 384 µg/L). The modified chronic testing method resulted in greater sensitivity in AgNPs exposures. However, the modified feeding ration had less of an effect in exposures to the larger (100 nm) AgNPs compared to smaller particles (20 nm). The ACRs for AgNPs using the standard feeding ration were 1.6 and 3.5 for 20 nm and 100 nm, respectively. The ACRs for AgNPs using the modified feeding ration were 3.4 and 7.6 for 20 nm and 100 nm NPs, respectively. This supports that the addition of the standard feeding ration decreases <i>C. dubia</i> chronic sensitivity to AgNPs, although it must also be recognized organisms may be sensitized due to less access to food. The ACRs for 20 nm and 100 nm AuNPs (standard ration only) were 4.0 and 3.0, respectively. It is important to also consider that dissolved Ag<sup>+</sup> ions are more toxic than AgNPs, based on both acute toxicity values in the cited literature and chronic toxicity thresholds generated in this study that support existing thresholds that Ag<sup>+</sup> are likely protective of AgNPs effects.</p
Gill Histopathologies Following Exposure to Nanosilver or Silver Nitrate
<div><p>Fish gill is the site for many crucial physiological functions. It is among the first sites of xenobiotic exposure, and gill histopathological alterations may be detected soon after toxicant exposure. Silver (Ag) is one of the most toxic metals to aquatic organisms mainly due to its ability to disrupt ionic regulation. The goal of this study was to determine the effect of ionic and nanoscale Ag on fathead minnow gills by examining gill histology and Na<sup>+</sup>/K<sup>+</sup>-ATPase immunoreactivity. Fathead minnows were exposed to two measured concentrations of silver nitrate (AgNO<sub>3</sub>: 1.3 or 3.7 μg/L as Ag<sup>+</sup>), citrate silver nanoparticles (citrate-AgNP: 15 or 39 μg/L), and polyvinylpyrrolidone-AgNP (PVP-AgNP) (AgNP: 11 or 50 μg/L). Circulatory disturbances were the most prevalent gill alterations detected and were significantly increased in all Ag treatment groups compared to control. AgNO<sub>3</sub> (1.3 μg/L) was the only treatment that significantly elevated the number of total mucous goblet cells present. In all other Ag treatments, the percent of degenerated goblet cells was significantly increased compared to control. When the sum of all histopathological abnormalities (weighted index) was calculated, all Ag groups displayed a significantly higher index, with citrate-AgNP having the highest toxicity (index of 10 ± 0.32 versus 2.4 ± 0.6 in controls). Gill Na<sup>+</sup>/K<sup>+</sup>-ATPase immunoreactivity was decreased by Ag. These results indicated that both AgNO<sub>3</sub> and AgNP created similar disruptions in gill structure and ionic regulation, possibly due to the ionic Ag portion of each treatment.
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Gaining a Critical Mass: A Dose Metric Conversion Case Study Using Silver Nanoparticles
Mass concentration is the standard
convention to express exposure
in ecotoxicology for dissolved substances. However, nanotoxicology
has challenged the suitability of the mass concentration dose metric.
Alternative metrics often discussed in the literature include particle
number, surface area, and ion release (kinetics, equilibrium). It
is unlikely that any single metric is universally applicable to all
types of nanoparticles. However, determining the optimal metric for
a specific type of nanoparticle requires novel studies to generate
supportive data and employ methods to compensate for current analytical
capability gaps. This investigation generated acute toxicity data
for two standard species (<i>Ceriodaphnia dubia</i>, <i>Pimephales promelas</i>) exposed to five sizes (10, 20, 30,
60, 100 nm) of monodispersed citrate- and polyvinylpyrrolidone-coated
silver nanoparticles. Particles were sized by various techniques to
populate available models for expressing the particle number, surface
area, and dissolved fraction. Results indicate that the acute toxicity
of the tested silver nanoparticles is best expressed by ion release,
and is relatable to total exposed surface area. Particle number was
not relatable to the observed acute silver nanoparticle effects
Differential Effects and Potential Adverse Outcomes of Ionic Silver and Silver Nanoparticles in Vivo and in Vitro
Nanoparticles
are of concern because of widespread use, but it
is unclear if metal nanoparticles cause effects directly or indirectly.
We explored whether polyvinylpyrrolidone-coated silver nanoparticles
(PVP-AgNPs) cause effects through intact nanoparticles or dissolved
silver. Females of the model species fathead minnow (<i>Pimephales
promelas</i>) were exposed to either 4.8 μg/L of AgNO<sub>3</sub> or 61.4 μg/L of PVP-AgNPs for 96h. Microarray analyses
were used to identify impacted receptors and toxicity pathways in
liver and brain tissues that were confirmed using in vitro mammalian
assays. AgNO<sub>3</sub> and PVP-AgNP exposed fish had common and
distinct effects consistent with both intact nanoparticles and dissolved
silver causing effects. PVP-AgNPs and AgNO<sub>3</sub> both affected
pathways involved in Na<sup>+</sup>, K<sup>+</sup>, and H<sup>+</sup> homeostasis and oxidative stress but different neurotoxicity pathways.
In vivo effects were supported by PVP-AgNP activation of five in vitro
nuclear receptor assays and inhibition of ligand binding to the dopamine
receptor. AgNO<sub>3</sub> inhibited ligand binding to adrenergic
receptors α1 and α2 and cannabinoid receptor CB1, but
had no effect in nuclear receptor assays. PVP-AgNPs have the potential
to cause effects both through intact nanoparticles and metal ions,
each interacting with different initiating events. Since the in vitro
and in vivo assays examined here are commonly used in human and ecological
hazard screening, this work suggests that environmental health assessments
should consider effects of intact nanoparticles in addition to dissolved
metals
Fate and Toxicity of CuO Nanospheres and Nanorods used in Al/CuO Nanothermites Before and After Combustion
Although nanotechnology
advancements should be fostered, the environmental
health and safety (EHS) of nanoparticles used in technologies must
be quantified simultaneously. However, most EHS studies assess the
potential implications of the free nanoparticles which may not be
directly applicable to the EHS of particles incorporated into in-use
technologies. This investigation assessed the aquatic toxicological
implications of copper oxide (CuO) nanospheres relative to CuO nanorods
used in nanoenergetic applications to improve combustion. Particles
were tested in both the as-received form and following combustion
of a CuO/aluminum nanothermite. Results indicated nanospheres were
more stable in water and slowly released ions, while higher surface
area nanorods initially released more ions and were more toxic but
generally less stable. After combustion, particles sintered into larger,
micrometer-scale aggregates, which may lower toxicity potential to
pelagic organisms due to deposition from water to sediment and reduced
bioavailability after complexation with sediment organic matter. Whereas
the larger nanothermite residues settled rapidly, implying lower persistence
in water, their potential to release dissolved Cu was higher which
led to greater toxicity to <i>Ceriodaphnia dubia</i> relative
to parent CuO material (nanosphere or rod). This study illustrates
the importance of considering the fate and toxicology of nanoparticles
in context with their relevant in-use applications