6 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
Extraction and Analysis of Silver and Gold Nanoparticles from Biological Tissues Using Single Particle Inductively Coupled Plasma Mass Spectrometry
Expanded use of engineered nanoparticles
(ENPs) in consumer products
increases the potential for environmental release and unintended biological
exposures. As a result, measurement techniques are needed to accurately
quantify ENP size, mass, and particle number distributions in biological
matrices. This work combines single particle inductively coupled plasma
mass spectrometry (spICPMS) with tissue extraction to quantify and
characterize metallic ENPs in environmentally relevant biological
tissues for the first time. ENPs were extracted from tissues via alkaline
digestion using tetramethylammonium hydroxide (TMAH). Method development
was performed using ground beef and was verified in Daphnia magna and Lumbriculus variegatus. ENPs investigated include 100 and 60 nm Au and Ag stabilized by
polyvynylpyrrolidone (PVP). Mass- and number-based recovery of spiked
Au and Ag ENPs was high (83–121%) from all tissues tested.
Additional experiments suggested ENP mixtures (60 and 100 nm Ag ENPs)
could be extracted and quantitatively analyzed. Biological exposures
were also conducted to verify the applicability of the method for
aquatic organisms. Size distributions and particle number concentrations
were determined for ENPs extracted from D. magna exposed to 98 μg/L 100 nm Au and 4.8 μg/L 100 nm Ag
ENPs. The D. magna nanoparticulate
body burden for Au ENP uptake was 613 ± 230 μg/kg<sub>ww</sub>, while the measured nanoparticulate body burden for D. magna exposed to Ag ENPs was 59 ± 52 μg/kg<sub>ww</sub>. Notably, the particle size distributions determined from D. magna tissues suggested minimal shifts in the
size distributions of ENPs accumulated, as compared to the exposure
media
Assessing nanomaterial exposures in aquatic ecotoxicological testing: Framework and case studies based on dispersion and dissolution
<p>The unique behavior of engineered nanomaterials (ENM) in aqueous media and dynamic changes in particle settling, agglomeration and dissolution rates is a challenge to the consistency, reliability and interpretation of standard aquatic hazard bioassay results. While the toxicological endpoints (e.g., survival, growth, reproduction, etc.) in ecotoxicity bioassays are largely applicable to ENMs, the standard methods as written for dissolved substances are confounded by the dynamic settling, agglomeration and dissolution of particulate ENMs during the bioassay. A testing framework was designed to serve as a starting point to identify approaches for the consistent conduct of aquatic hazard tests that account for the behavior of ENMs in test media and suitable data collection to support representative exposure metrology. The framework was demonstrated by conducting three case studies testing ENMs with functionally distinct characteristics and behaviors. Pretests with a temporal sampling of particle concentration, agglomeration and dissolution were conducted on each ENM in test media. Results indicated that a silver nanoparticle (AgNP) powder was not dispersible, a nano-TiO<sub>2</sub> powder was dispersible but unstable, and a polyvinylpyrrolidinone-coated AgNP was relatively stable in test media. Based on these functional results, <i>Ceriodaphnia dubia</i> bioassays were conducted to compare different exposure summary methods (nominal, arithmetic average, geometric average, time-weighted average) for calculating and expressing toxicity endpoints. Results indicated that while arithmetic means were effective for expressing the toxicity of more stable materials, time-weighted averaged concentrations were appropriate for the unstable nano-TiO<sub>2</sub>.</p
Tungsten Toxicity, Bioaccumulation, and Compartmentalization into Organisms Representing Two Trophic Levels
Metallic tungsten has civil and military applications
and was considered
a green alternative to lead. Recent reports of contamination in drinking
water and soil have raised scrutiny and suspended some applications.
This investigation employed the cabbage Brassica oleracae and snail Otala lactea as models
to determine the toxicological implications of sodium tungstate and
an aged tungsten powder-spiked soil containing monomeric and polymeric
tungstates. Aged soil bioassays indicated cabbage growth was impaired
at 436 mg of W/kg, while snail survival was not impacted up to 3793
mg of W/kg. In a dermal exposure, sodium tungstate was more toxic
to the snail, with a lethal median concentration of 859 mg of W/kg.
While the snail significantly bioaccumulated tungsten, predominately
in the hepatopancreas, cabbage leaves bioaccumulated much higher concentrations.
Synchrotron-based mapping indicated the highest levels of W were in
the veins of cabbage leaves. Our results suggest snails consuming
contaminated cabbage accumulated higher tungsten concentrations relative
to the concentrations directly bioaccumulated from soil, indicating
the importance of robust trophic transfer investigations. Finally,
synchrotron mapping provided evidence of tungsten in the inner layer
of the snail shell, suggesting potential use of snail shells as a
biomonitoring tool for metal contamination
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
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