Shannon K. Hanna

Impacts of Metal Oxide Nanoparticles on Marine Phytoplankton

Information on the toxicity of environmentally relevant concentrations of nanoparticles in marine ecosystems is needed for informed regulation of these emerging materials. We tested the effects of two types of metal oxide nanoparticles, TiO(2) and ZnO, on population growth rates of four species of marine phytoplankton representing three major coastal groups (diatoms, chlorophytes, and prymnesiophytes). These metal oxide nanoparticles (NPs) are becoming common components in many industrial, household, and cosmetic products that are released into coastal ecosystems. Titania NPs showed no measurable effect on growth rates of any species, while ZnO NPs significantly depressed growth rate of all four species. ZnO NPs aggregated rapidly in seawater, forming particles >400 nm hydrodynamic diameter within 30 min, and dissolved quickly, reaching equilibrium concentrations within 12 h. Toxicity of ZnO NPs to phytoplankton was likely due to dissolution, release, and uptake of free zinc ions, but specific nanoparticulate effects may be difficult to disentangle from effects due to free zinc ions. A modeling approach based on a Dynamic Energy Budget (DEB) framework was used to estimate sublethal effects of the two NPs on phytoplankton populations. Concentrations that were estimated to have no effect on population growth (NEC) were (one standard error in parentheses) 428 (58) μg L(-1) ZnO for the diatom Skeletonema marinoi and 223 (56) μg L(-1) for Thalassiosira pseudonana. NEC could not be estimated for the other taxa but were within the range of 500-1000 μg L(-1). Our results suggest that effects of metal oxide NPs on marine organisms is likely to vary with particle type and organism taxonomy.

Uptake, accumulation, and biotransformation of metal oxide nanoparticles by a marine suspension-feeder

A growing body of evidence indicates that some engineered nanoparticles (ENPs) are toxic to organisms that perform important ecosystem services in terrestrial and aquatic ecosystems. However, toxicity can be influenced by the biotransformation of contaminants, including ENPs, as it may alter the fate and transport of these substances. In turn, fate and transport can influence their bioavailability. To understand how biotransformation influences the fate and transport of ENPs in marine ecosystems, we exposed suspension-feeding mussels, Mytilus galloprovincialis, to two common nano-metal oxides, CeO(2) and ZnO, over a range of concentrations from 1mg L(-1) to 10mg L(-1), in a laboratory experiment. Mussels exposed to 10mg L(-1) accumulated 62μg g(-1) of Ce and 880μg g(-1) of Zn on a dry tissue basis but rejected 21,000μg g(-1) for Ce and 63,000μg g(-1) for Zn in pseudofeces. Scanning electron microscope evidence indicates CeO(2) remained as ENPs but ZnO did not after being rejected by the mussels. Mussels filtered most of the CeO(2) from the aqueous media, while a significant fraction of Zn remained in solution. Differences in ENP solubility affect ENP uptake, excretion, and accumulation in mussels. Our study highlights the potential role of marine suspension feeders in biotransformation of ENPs.

Accumulation and toxicity of metal oxide nanoparticles in a soft-sediment estuarine amphipod

Estuarine and marine sediments are a probable end point for many engineered nanoparticles (ENPs) due to enhanced aggregation and sedimentation in marine waters, as well as uptake and deposition by suspension-feeding organisms on the seafloor. Benthic infaunal organisms living in sediments encounter relatively high concentrations of pollutants and may also suffer toxic effects of ENPs. We tested whether three heavily used metal oxide ENPs, zinc oxide (ZnO), copper oxide (CuO), and nickel oxide (NiO) were toxic to an estuarine amphipod, Leptocheirus plumulosus. We used results from 10-day laboratory bioassays to estimate potential demographic impacts of ENP exposure. We also evaluated fate and transport pathways of the ENPs in the experiments to elucidate routes of uptake and exposure. Dissolved Zn was found in sediment pore water and overlying water samples at 10 fold the concentrations of Cu or Ni, a pattern indicative of the relatively high dissolution rate of ZnO ENPs compared with CuO and NiO ENPs. Accumulation of metals in amphipod tissues increased with exposure concentrations for all three ENPs, suggesting possible exposure pathways to higher taxa. Amphipods accumulated ≤600 μg Zn and Cu g(-1) and 1000 μg Ni g(-1). Amphipod mortality increased with ZnO and CuO concentrations, but showed no significant increase with NiO to concentrations as high as 2000 μg g(-1). The median lethal concentration in sediment (LC50) of ZnO was 763 μg g(-1) and 868 μg g(-1) for CuO ENPs. Our results indicate that ZnO and CuO ENPs, but not NiO ENPs, are toxic to L. plumulosus and that ZnO toxicity primarily results from Zn ion exposure while CuO toxicity is due to nanoparticle exposure.

Effects and Implications of Trophic Transfer and Accumulation of CeO2 Nanoparticles in a Marine Mussel

Bivalves are hypothesized to be key organisms in the fate and transport of engineered nanomaterials (ENMs) in aquatic environments due to their ability to filter and concentrate particles from water, but how different exposure pathways influence their interactions with ENMs is not well understood. In a five-week experiment, we tested how interactions between CeO2 ENMs and a marine mussel, Mytilus galloprovincialis, are affected through two exposure methods, direct and through sorption to phytoplankton. We found that phytoplankton sorbed ENMs in <1 h. The exposure methods used did not result in significantly different mussel tissue or pseudofeces Ce concentrations. Approximately 99% of CeO2 was captured and excreted in pseudofeces and average pseudofeces mass doubled in response to CeO2 exposure. Final mean dry tissue Ce concentration (±SE) for treatments exposed to 3 mg L(-1) CeO2 directly was 33 ± 9 μg g(-1) Ce, and 0 ± 0, 19 ± 4, 21 ± 3, and 28 ± 5 μg g(-1) for treatments exposed to 0, 1, 2, and 3 mg L(-1) CeO2 sorbed to phytoplankton. Clearance rates increased with CeO2 concentration but decreased over time in groups exposed to CeO2 directly, indicating stress. These results show the feedback between ENM toxicity and transport and the likelihood of biological mediation in the fate and transport of ENMs in aquatic environments.

Impact of Engineered Zinc Oxide Nanoparticles on the Individual Performance of Mytilus galloprovincialis

The increased use of engineered nanoparticles (ENPs) in consumer products raises the concern of environmental release and subsequent impacts in natural communities. We tested for physiological and demographic impacts of ZnO, a prevalent metal oxide ENP, on the mussel Mytilus galloprovincialis. We exposed mussels of two size classes, <4.5 and ≥4.5 cm shell length, to 0.1–2 mg l−1 ZnO ENPs in seawater for 12 wk, and measured the effect on mussel respiration, accumulation of Zn, growth, and survival. After 12 wk of exposure to ZnO ENPs, respiration rates of mussels increased with ZnO concentration. Mussels had up to three fold more Zn in tissues than control groups after 12 wk of exposure, but patterns of Zn accumulation varied with mussel size and Zn concentrations. Small mussels accumulated Zn 10 times faster than large mussels at 0.5 mg l−1, while large mussels accumulated Zn four times faster than small mussels at 2 mg l−1. Mussels exposed to 2 mg l−1 ZnO grew 40% less than mussels in our control group for both size classes. Survival significantly decreased only in groups exposed to the highest ZnO concentration (2 mg l−1) and was lower for small mussels than large. Our results indicate that ZnO ENPs are toxic to mussels but at levels unlikely to be reached in natural marine waters.

Impacts of Silver Nanoparticles on a Natural Estuarine Plankton Community.

Potential effects of metal nanoparticles on aquatic organisms and food webs are hard to predict from the results of single-species tests under controlled laboratory conditions, and more realistic exposure experiments are rarely conducted. We tested whether silver nanoparticles (Ag NPs) had an impact on zooplankton grazing on their prey, specifically phytoplankton and bacterioplankton populations. If Ag NPs directly reduced the abundance of prey, thereby causing the overall rate of grazing by their predators to decrease, a cascading effect on a planktonic estuarine food web would be seen. Our results show that the growth rates of both phytoplankton and bacterioplankton populations were significantly reduced by Ag NPs at concentrations of ≥500 μg L(-1). At the same time, grazing rates on these populations tended to decline with exposure to Ag NPs. Therefore, Ag NPs did not cause a cascade of effects through the food web but impacted a specific trophic level. Photosynthetic efficiency of the phytoplankton was significantly reduced at Ag NPs concentrations of ≥500 μg L(-1). These effects did not occur at relatively low concentrations of Ag that are often toxic to single species of bacteria and other organisms, suggesting that the impacts of Ag NP exposure may not be apparent at environmentally relevant concentrations due to compensatory processes at the community level.

Accumulation and Toxicity of Copper Oxide Engineered Nanoparticles in a Marine Mussel

Cu is an essential trace element but can be highly toxic to aquatic organisms at elevated concentrations. Greater use of CuO engineered nanoparticles (ENPs) may lead to increased concentrations of CuO ENPs in aquatic environments causing potential ecological injury. We examined the toxicity of CuO ENPs to marine mussels and the influence of mussels on the fate and transport of CuO ENPs. We exposed marine mussels to 1, 2, or 3 mg L-1 CuO ENPs for four weeks, and measured clearance rate, rejection, excretion and accumulation of Cu, and mussel shell growth. Mussel clearance rate was 48% less, and growth was 68% less, in mussels exposed to 3 mg L-1 than in control animals. Previous studies show 100% mortality at 1 mg Cu L-1, suggesting that CuO ENPs are much less toxic than ionic Cu, probably due to the slow dissolution rate of the ENPs. Mussels rejected and excreted CuO ENPs in biodeposits containing as much as 110 mg Cu g-1, suggesting the potential for magnification in sediments. Mussels exposed to 3 mg L-1 CuO ENPs accumulated 79.14 ± 12.46 µg Cu g-1 dry weight, which was 60 times more Cu than in control animals. Our results suggest that mussels have the potential to influence the fate and transport of CuO ENPs and potentially cause magnification of CuO ENPs in mussel bed communities, creating a significant source of Cu to marine benthos.

Deposition of carbon nanotubes by a marine suspension feeder revealed by chemical and isotopic tracers

Carbon nanotubes (CNTs) are one of the few truly novel nanomaterials and are being incorporated into a wide range of products, which will lead to environmental release and potential ecological impacts. We examined the toxicity of CNTs to marine mussels and the effect of mussels on CNT fate and transport by exposing mussels to 1, 2, or 3mg CNTsl(-1) for four weeks and measuring mussel clearance rate, shell growth, and CNT accumulation in tissues and deposition in biodeposits. We used metal impurities and carbon stable isotope ratios of the CNTs as tracers of CNT accumulation. Mussels decreased clearance rate of phytoplankton by 24% compared with control animals when exposed to CNTs. However, mussel growth rate was unaffected by CNT concentrations up to 3mgl(-1). Based on metal concentrations and carbon stable isotope values, mussels deposited most CNTs in biodeposits, which contained >110mg CNTsg(-1) dry weight, and accumulated about 1mg CNTsg(-1) dry weight of tissue. We conclude that extremely high concentrations of CNTs are needed to illicit a toxic response in mussels but the ability of mussels to concentrate and deposit CNTs in feces and pseudofeces may impact infaunal organisms living in and around mussel beds.

Separation, Sizing, and Quantitation of Engineered Nanoparticles in an Organism Model Using Inductively Coupled Plasma Mass Spectrometry and Image Analysis.

For environmental studies assessing uptake of orally ingested engineered nanoparticles (ENPs), a key step in ensuring accurate quantification of ingested ENPs is efficient separation of the organism from ENPs that are either nonspecifically adsorbed to the organism and/or suspended in the dispersion following exposure. Here, we measure the uptake of 30 and 60 nm gold nanoparticles (AuNPs) by the nematode, Caenorhabditis elegans, using a sucrose density gradient centrifugation protocol to remove noningested AuNPs. Both conventional inductively coupled plasma mass spectrometry (ICP-MS) and single particle (sp)ICP-MS are utilized to measure the total mass and size distribution, respectively, of ingested AuNPs. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) imaging confirmed that traditional nematode washing procedures were ineffective at removing excess suspended and/or adsorbed AuNPs after exposure. Water rinsing procedures had AuNP removal efficiencies ranging from 57 to 97% and 22 to 83%, while the sucrose density gradient procedure had removal efficiencies of 100 and 93 to 98%, respectively, for the 30 and 60 nm AuNP exposure conditions. Quantification of total Au uptake was performed following acidic digestion of nonexposed and Au-exposed nematodes, whereas an alkaline digestion procedure was optimized for the liberation of ingested AuNPs for spICP-MS characterization. Size distributions and particle number concentrations were determined for AuNPs ingested by nematodes with corresponding confirmation of nematode uptake via high-pressure freezing/freeze substitution resin preparation and large-area SEM imaging. Methods for the separation and in vivo quantification of ENPs in multicellular organisms will facilitate robust studies of ENP uptake, biotransformation, and hazard assessment in the environment.