Three-layered silver nanoparticles to trace dissolution and association to a green alga.

Core-shell silver nanoparticles (NPs) consisting of an inner Ag core and successive layers of Au and Ag (Ag@Au@Ag) were used to measure the simultaneous association of Ag NPs and ionic Ag by the green alga Chlamydomonas (C.) reinhardtii. Dissolution of the inner Ag core was prevented by a gold (Au) layer, while the outer Ag layer was free to dissolve. In short-term experiments, we exposed C. reinhardtii to a range of environmentally realistic Ag concentrations added as AgNO3 or as NPs. Results provide three lines of evidence for the greater cell-association of NPs compared to dissolved Ag over the concentration range tested, assuming that cell-association comprises both uptake and adsorption. First, the cell-association rate constants (kuw) for total Ag (AgNP+D), NPs (AgNP) and AuNP were similar and 2.2-fold higher than the one from AgD exposure, suggesting predominant association of the particles over the dissolved form. Second, model calculations based on Ag fluxes suggested that only 6-33% of algal burden was from AgD. Third, the significantly lower AgNP/Au ratio measured with the algae after exposure (2.1 ± 0.1) compared to the AgNP/Au ratio of the NPs in the media (2.47 ± 0.05) suggests cell-association of NPs depleted in Ag. Core-shell NPs provide an innovative tool to understand NP behavior and to directly delineate Ag accumulation from ion and NPs in aquatic systems.

Modernizing Water Quality Criteria in the United States: A Need to Expand the Definition of Acceptable Data.

The development of water quality criteria (WQC) for the protection of aquatic life is a fundamental component of the Clean Water Act-the primary US legislation responsible for protecting aquatic ecosystems from pollution. Water quality criteria define acceptable levels of contamination in the environment and thus play an important role in society. Rules for how science is used to develop WQC were created in 1985. Most rely on only data and knowledge obtained through a single methodology, the single-species laboratory toxicity test. Since 1985, understanding of the fate and effects of environmental contaminants has advanced markedly from multiple perspectives and disciplines. However, many of these advances are routinely discarded in WQC development because they do not adhere to data limits imposed by the 1985 guidelines. The present Focus article outlines how multiple lines of inquiry have played important roles in improving understanding of the ecological implications of environmental contaminants. The authors focus on gains in understanding that would not have been possible through traditional toxicity bioassays alone and argue that more robust scientific understanding can be used to modernize WQC development. In particular, the present article highlights ways to increase the relevance of toxicity testing (at different spatiotemporal scales) and incorporate all relevant lines of evidence into WQC modernization. Environ Toxicol Chem 2017;36:285-291. © 2017 SETAC.

Opportunities and challenges of integrating ecological restoration into assessment and management of contaminated ecosystems.

Ecosystem restoration planning near the beginning of the site assessment and management process ("early integration") involves consideration of restoration goals from the outset in developing solutions for contaminated ecosystems. There are limitations to integration that stem from institutional barriers, few successful precedents, and limited availability of guidance. Challenges occur in integrating expertise from various disciplines and multiple, sometimes divergent interests and goals. The more complex process can result in timing, capacity, communication, and collaboration challenges. On the other hand, integrating the 2 approaches presents new and creative opportunities. For example, integration allows early planning for expanding ecosystem services on or near contaminated lands or waters that might otherwise have been unaddressed by remediation alone. Integrated plans can explicitly pursue ecosystem services that have market value, which can add to funds for long-term monitoring and management. Early integration presents opportunities for improved and productive collaboration and coordination between ecosystem restoration and contaminant assessment and management. Examples exist where early integration facilitates liability resolution and generates positive public relations. Restoration planning and implementation before the completion of the contaminated site assessment, remediation, or management process ("early restoration") can facilitate coordination with offsite restoration options and a regional approach to restoration of contaminated environments. Integration of performance monitoring, for both remedial and restoration actions, can save resources and expand the interpretive power of results. Early integration may aid experimentation, which may be more feasible on contaminated lands than in many other situations. The potential application of concepts and tools from adaptive management is discussed as a way of avoiding pitfalls and achieving benefits in early integration. In any case, there will be challenges with early integration of restoration concepts for contaminated ecosystems, but the benefits are likely to outweigh them.

Influence of hardness on the bioavailability of silver to a freshwater snail after waterborne exposure to silver nitrate and silver nanoparticles.

The release of Ag nanoparticles (AgNPs) into the aquatic environment is likely, but the influence of water chemistry on their impacts and fate remains unclear. Here, we characterize the bioavailability of Ag from AgNO(3) and from AgNPs capped with polyvinylpyrrolidone (PVP AgNP) and thiolated polyethylene glycol (PEG AgNP) in the freshwater snail, Lymnaea stagnalis, after short waterborne exposures. Results showed that water hardness, AgNP capping agents, and metal speciation affected the uptake rate of Ag from AgNPs. Comparison of the results from organisms of similar weight showed that water hardness affected the uptake of Ag from AgNPs, but not that from AgNO(3). Transformation (dissolution and aggregation) of the AgNPs was also influenced by water hardness and the capping agent. Bioavailability of Ag from AgNPs was, in turn, correlated to these physical changes. Water hardness increased the aggregation of AgNPs, especially for PEG AgNPs, reducing the bioavailability of Ag from PEG AgNPs to a greater degree than from PVP AgNPs. Higher dissolved Ag concentrations were measured for the PVP AgNPs (15%) compared to PEG AgNPs (3%) in moderately hard water, enhancing Ag bioavailability of the former. Multiple drivers of bioavailability yielded differences in Ag influx between very hard and deionized water where the uptake rate constants (k(uw), l g(-1) d(-1) ± SE) varied from 3.1 ± 0.7 to 0.2 ± 0.01 for PEG AgNPs and from 2.3 ± 0.02 to 1.3 ± 0.01 for PVP AgNPs. Modeling bioavailability of Ag from NPs revealed that Ag influx into L. stagnalis comprised uptake from the NPs themselves and from newly dissolved Ag.

Inhibition of potential uptake pathways for silver nanoparticles in the estuarine snail Peringia ulvae.

Mechanisms involved in the uptake of Ag NPs, and NPs in general, have been long debated within nano-ecotoxicology. In vitro studies provide evidence of the different available uptake pathways, but in vivo demonstrations are lacking. In this study, pharmacological inhibitors were employed to block specific uptake pathways that have been implicated in the transport of metal NPs and aqueous metal forms; phenamil (inhibits Na(+) channel), bafilomycin A1 (H(+) proton pump), amantadine (clathrin-mediated endocytosis), nystatin (caveolae-mediated endocytosis) and phenylarsine oxide (PAO, macropinocytosis). Peringia ulvae (snails) were exposed to 150 µg Ag L(-1) added as citrate capped Ag NPs or aqueous Ag (AgNO3) in combination with inhibitor treatment (determined by preliminary studies). Reductions in accumulated tissue burdens caused by the inhibitors were compared to control exposures (i.e. no inhibition) after 6 and 24 h. No inhibitor treatment completely eliminated the uptake of Ag in either aqueous or NP form, but all inhibitor treatments, except phenamil, significantly reduced the uptake of Ag presented as Ag NPs. Clathrin- and caveolae-mediated endocytosis appear to be mechanisms exploited by Ag NPs, with the latter pathway only active at 24 h. Inhibition of the H(+) proton pump showed that a portion of Ag NP uptake is achieved as aqueous Ag and is explained by the dissolution of the particles (∼25% in 24 h). This in vivo study demonstrates that uptake of Ag from Ag NPs is achieved by multiple pathways and that these pathways are simultaneously active.

Bioaccumulation and toxicity of CuO nanoparticles by a freshwater invertebrate after waterborne and dietborne exposures.

The incidental ingestion of engineered nanoparticles (NPs) can be an important route of uptake for aquatic organisms. Yet, knowledge of dietary bioavailability and toxicity of NPs is scarce. Here we used isotopically modified copper oxide ((65)CuO) NPs to characterize the processes governing their bioaccumulation in a freshwater snail after waterborne and dietborne exposures. Lymnaea stagnalis efficiently accumulated (65)Cu after aqueous and dietary exposures to (65)CuO NPs. Cu assimilation efficiency and feeding rates averaged 83% and 0.61 g g(-1) d(-1) at low exposure concentrations (<100 nmol g(-1)), and declined by nearly 50% above this concentration. We estimated that 80-90% of the bioaccumulated (65)Cu concentration in L. stagnalis originated from the (65)CuO NPs, suggesting that dissolution had a negligible influence on Cu uptake from the NPs under our experimental conditions. The physiological loss of (65)Cu incorporated into tissues after exposures to (65)CuO NPs was rapid over the first days of depuration and not detectable thereafter. As a result, large Cu body concentrations are expected in L. stagnalis after exposure to CuO NPs. To the degree that there is a link between bioaccumulation and toxicity, dietborne exposures to CuO NPs are likely to elicit adverse effects more readily than waterborne exposures.

Does water chemistry affect the dietary uptake and toxicity of silver nanoparticles by the freshwater snail Lymnaea stagnalis?

Silver nanoparticles (AgNPs) are widely used in many applications and likely released into the aquatic environment. There is increasing evidence that Ag is efficiently delivered to aquatic organisms from AgNPs after aqueous and dietary exposures. Accumulation of AgNPs through the diet can damage digestion and adversely affect growth. It is well recognized that aspects of water quality, such as hardness, affect the bioavailability and toxicity of waterborne Ag. However, the influence of water chemistry on the bioavailability and toxicity of dietborne AgNPs to aquatic invertebrates is largely unknown. Here we characterize for the first time the effects of water hardness and humic acids on the bioaccumulation and toxicity of AgNPs coated with polyvinyl pyrrolidone (PVP) to the freshwater snail Lymnaea stagnalis after dietary exposures. Our results indicate that bioaccumulation and toxicity of Ag from PVP-AgNPs ingested with food are not affected by water hardness and by humic acids, although both could affect interactions with the biological membrane and trigger nanoparticle transformations. Snails efficiently assimilated Ag from the PVP-AgNPs mixed with diatoms (Ag assimilation efficiencies ranged from 82 to 93%). Rate constants of Ag uptake from food were similar across the entire range of water hardness and humic acid concentrations. These results suggest that correcting regulations for water quality could be irrelevant and ineffective where dietary exposure is important.

Toxicity and accumulation of silver nanoparticles during development of the marine polychaete Platynereis dumerilii.

Pollutants affecting species at the population level generate ecological instability in natural systems. The success of early life stages, such as those of aquatic invertebrates, is highly affected by adverse environmental conditions. Silver released into the environment from emerging nanotechnology represents such a threat. Sediments are sinks for numerous pollutants, which aggregate and/or associate with depositing suspended particles. Deposit feeder such as the annelid Platynereis dumerilii, which has a large associated literature on its development, is an excellent model organism for exposure studies in coastal environments. We exposed eggs, larvae, juveniles and adults of P. dumerilii to various concentrations of citrate (cit-Ag NPs) or humic acid (HA-Ag NPs) capped silver nanoparticles (Ag NPs) as well to dissolved Ag (added as AgNO3). We showed that mortality and abnormal development rate increased with younger life stages. While adults and juvenile were the most tolerant life stages, fertilized eggs were highly sensitive to AgNO3, cit-Ag NPs and HA-Ag NPs. Exposures to HA-Ag NPs triggered the highest cute toxicity responses in P. dumerilii and in most cases both Ag NPs were more toxic than AgNO3. Uptake rate of HA-Ag NPs in adult worms was also higher than from other Ag forms, consistent with toxicity to other life stages. The early stages of the life cycle of marine coastal organisms are more affected by Ag NPs than the juvenile or adult life stages, indicating that exposure experiments at the larval level contribute to realistic eco-toxicological studies in aquatic environments.

In vivo retention of ingested Au NPs by Daphnia magna: no evidence for trans-epithelial alimentary uptake.

In vivo studies with Daphnia magna remain inconclusive as to whether engineered nanoparticles (NPs) are internalized into tissues after ingestion. Here we used a three-pronged approach to study the in vivo retention and efflux kinetics of 20 nm citrate stabilized Au NPs ingested by this key aquatic species. Daphnids were exposed to suspended particles (600 µg L(-1)) for 5 h after which they were depurated for 24 h in clean water containing algae. Light microscopy was used to follow the passage of Au NPs through the gastrointestinal tract, Au body burdens were determined by ICP-MS (inductively coupled plasma mass spectrometry), and transmission electron microscopy (TEM) was used to examine the presence and distribution of Au NPs in tissues. Results revealed that the elimination of Au NPs was bi-phasic. The fast elimination phase lasted<1h and the rate constant at which Au (of Au NPs) was eliminated was 1.12 ± 0.34 h(-1) (±SE) which accounted for ∼75% of the ingested Au. The remaining ∼25% of the ingested Au NPs was eliminated at a 100-fold slower rate. TEM analysis revealed that Au NPs in the midgut were in close proximity to the peritrophic membrane after 1 and 24h of depuration. There were no observations of Au NP uptake at the microvilli. Thus, although Au NPs were retained in the gut lumen, there was no observable internalization into the gut epithelial cells. Similar to carbon nanotubes and CuO NPs, our findings indicate that in daphnids the in vivo retention of Au NPs does not necessarily result in their internalization.

Dietary bioavailability of cadmium presented to the gastropod Peringia ulvae as quantum dots and in ionic form.

For quantum dots (QDs) synthesized in solvents that are immiscible in water, dietary, rather than aqueous, exposure is expected to be the primary route of uptake. The estuarine snail Peringia ulvae was presented with mats of simulated detritus spiked with oleic acid capped cadmium sulfide (CdS; 3.1 ± 0.4 nm) or cadmium selenide (CdSe; 4.2 ± 0.8 nm) nanoparticles, synthesized using a microfluidics method, or Cd(2+) (added as Cd[NO3 ]2 ) as a control. A biodynamic modeling approach was used to quantify parameters that describe the dietary accumulation of the Cd forms. Ingestion rates decreased across treatments at higher exposure concentrations, indicating a metal-induced stress response related to Cd dose rather than form. Although Cd was bioavailable from both CdS and CdSe QDs, uptake rate constants from diet were significantly lower than that of Cd(2+) (p < 0.05). After 72 h depuration, however, no loss of Cd was observed from snails that had accumulated Cd from either type of QD. In comparison, snails ingesting Cd(2+) -spiked detritus eliminated 39% of their accumulated body burden per day. The almost identical uptake and efflux rates for Cd in both QDs suggest no effect of the chalcogenide conjugates (S or Se). The findings of the present study indicate that the availability of Cd in the form of nanoparticles and its apparent in vivo persistence will lead to bioaccumulation. The implications of this are discussed.

Stable isotope tracer to determine uptake and efflux dynamics of ZnO Nano- and bulk particles and dissolved Zn to an estuarine snail.

Zinc oxide nanoparticles (ZnO NPs) are among the most commercialized engineered nanomaterials. Their biological impact in aquatic organisms has been associated with dissolution, but there is also evidence of nanospecific effects. In this study the waterborne uptake and efflux kinetics of isotopically labeled (68)ZnO NPs (7.8 ± 1.2 nm), in comparison to aqueous (68)Zn and (68)ZnO bulk particles (up to 2 µm), were determined for the estuarine snail Peringia ulvae following a 7 d exposure (nominally 20 µg (68)Zn L(-1)) and 28 d depuration. Detection of the (68)Zn label was achieved by high precision multiple-collector ICP-MS (MC-ICP-MS). Previous characterization in artificial estuarine water revealed that the NPs underwent initial aggregation and solubilized up to 60% within 1-2 days. Bulk and aqueous forms were significantly more bioavailable than (68)ZnO NPs (p < 0.05), but after correcting for dissolution, aqueous (0.074 L(-1) g(-1) d(-1)) and NP (0.070 L(-1) g(-1) d(-1)) uptake rate constants were highly comparable. The rate constant of loss for (68)Zn aqueous (0.012 ± 0.005 d(-1)) and (68)ZnO NPs (0.012 ± 0.007 d(-1)) were identical. These results strongly suggest that in this exposure scenario the bioaccumulation of Zn from ZnO NPs is primarily dependent upon solubility.

The complexity of nanoparticle dissolution and its importance in nanotoxicological studies.

Dissolution of nanoparticles (NPs) is an important property that alters their abundance and is often a critical step in determining safety of nanoparticles. The dissolution status of the NPs in exposure media (i.e. whether they remain in particulate form or dissolve - and to what extent), strongly affects the uptake pathway, toxicity mechanisms and the environmental compartment in which NPs will have the highest potential impact. A review of available dissolution data on NPs demonstrates there is a range of potential outcomes depending on the NPs and the exposure media. For example two nominally identical nanoparticles, in terms of size and composition, could have totally different dissolution behaviours, subject to different surface modifications. Therefore, it is imperative that toxicological studies are conducted in conjunction with dissolution of NPs to establish the true biological effect of NPs and hence, assist in their regulation.

Bioaccumulation dynamics and modeling in an estuarine invertebrate following aqueous exposure to nanosized and dissolved silver.

Predicting the environmental impact of engineered nanomaterials (ENMs) is increasingly important owing to the prevalence of emerging nanotechnologies. We derived waterborne uptake and efflux rate constants for the estuarine snail, Peringia ulvae, exposed to dissolved Ag (AgNO(3)) and silver nanoparticles (Ag NPs), using biodynamic modeling. Uptake rates demonstrated that dissolved Ag is twice as bioavailable as Ag in nanoparticle form. Biphasic loss dynamics revealed the faster elimination of Ag from Ag NPs at the start of depuration, but similar slow efflux rate constants. The integration of biodynamic parameters into our model accurately predicted Ag tissue burdens during chronic exposure with 85% of predicted values within a factor of 2 of observed values. Zeta potentials for the Ag NPs were lower in estuarine waters than in waters of less salinity; and uptake rates in P. ulvae were slower than reported for the freshwater snail Lymnaea stagnalis in similar experiments. This suggests aggregation of Ag NPs occurs in estuarine waters and reduces, but does not eliminate, bioavailability of Ag from the Ag NPs. Biodynamic modeling provides an effective methodology to determine bioavailable metal concentrations (originating from metal and metal-oxide nanoparticles) in the environment and may aid future ENM risk assessment.

Caddisflies as biomonitors identifying thresholds of toxic metal bioavailability that affect the stream benthos.

It has been proposed that bioaccumulated concentrations of toxic metals in tolerant biomonitors be used as indicators of metal bioavailability that could be calibrated against the ecological response to metals of sensitive biotic assemblages. Our hypothesis was that metal concentrations in caddisfly larvae Hydropsyche siltalai and Plectrocnemia conspersa, as tolerant biomonitors, indicate metal bioavailability in contaminated streams, and can be calibrated against metal-specific ecological responses of mayflies. Bioaccumulated concentrations of Cu, As, Zn and Pb in H. siltalai from SW English streams were related to the mayfly assemblage. Mayflies were always sparse where bioavailabilities were high and were abundant and diverse where bioavailabilities of all metals were low, a pattern particularly evident when the combined abundance of heptageniid and ephemerellid mayflies was the response variable. The results offer promise that bioaccumulated concentrations of metals in tolerant biomonitors can be used to diagnose ecological impacts on stream benthos from metal stressors.

Isotopically modified nanoparticles for enhanced detection in bioaccumulation studies.

This work presents results on synthesis of isotopically enriched (99% (65)Cu) copper oxide nanoparticles and its application in ecotoxicological studies. (65)CuO nanoparticles were synthesized as spheres (7 nm) and rods (7 × 40 nm). Significant differences were observed between the reactivity and dissolution of spherical and rod shaped nanoparticles. The extreme sensitivity of the stable isotope tracing technique developed in this study allowed determining Cu uptake at exposure concentrations equivalent to background Cu concentrations in freshwater systems (0.2-30 µg/L). Without a tracer, detection of newly accumulated Cu was impossible, even at exposure concentrations surpassing some of the most contaminated water systems (>1 mg/L).

Trophically available metal--a variable feast.

Assimilation of trace metals by predators from prey is affected by the physicochemical form of the accumulated metal in the prey, leading to the concept of a Trophically Available Metal (TAM) component in the food item definable in terms of particular subcellular fractions of accumulated metal. As originally defined TAM consists of soluble metal forms and metal associated with cell organelles, the combination of separated fractions which best explained particular results involving a decapod crustacean predator feeding on bivalve mollusc tissues. Unfortunately TAM as originally defined has subsequently frequently been used in the literature as an absolute description of that component of accumulated metal that is trophically available in all prey to all consumers. It is now clear that what is trophically available varies between food items, consumers and metals. TAM as originally defined should be seen as a useful starting hypothesis, not as a statement of fact.

Silver bioaccumulation dynamics in a freshwater invertebrate after aqueous and dietary exposures to nanosized and ionic Ag.

We compared silver (Ag) bioavailability and toxicity to a freshwater gastropod after exposure to ionic silver (Ag(+)) and to Ag nanoparticles (Ag NPs) capped with citrate or with humic acid. Silver form, exposure route, and capping agent influence Ag bioaccumulation dynamics in Lymnaea stagnalis. Snails efficiently accumulated Ag from all forms after either aqueous or dietary exposure. For both exposure routes, uptake rates were faster for Ag(+) than for Ag NPs. Snails efficiently assimilated Ag from Ag NPs mixed with diatoms (assimilation efficiency (AE) ranged from 49 to 58%) and from diatoms pre-exposed to Ag(+) (AE of 73%). In the diet, Ag NPs damaged digestion. Snails ate less and inefficiently processed the ingested food, which adversely impacted their growth. Loss rates of Ag were faster after waterborne exposure to Ag NPs than after exposure to dissolved Ag(+). Once Ag was taken up from diet, whether from Ag(+) or Ag NPs, Ag was lost extremely slowly. Large Ag body concentrations are thus expected in L. stagnalis after dietborne exposures, especially to citrate-capped Ag NPs. Ingestion of Ag associated with particulate materials appears as the most important vector of uptake. Nanosilver exposure from food might trigger important environmental risks.

PCB-induced changes of a benthic community and expected ecosystem recovery following in situ sorbent amendment.

The benthic community was analyzed to evaluate pollution-induced changes for the polychlorinated biphenyl (PCB)-contaminated site at Hunters Point (HP) relative to 30 reference sites in San Francisco Bay, California, USA. An analysis based on functional traits of feeding, reproduction, and position in the sediment shows that HP is depauperate in deposit feeders, subsurface carnivores, and species with no protective barrier. Sediment chemistry analysis shows that PCBs are the major risk drivers at HP (1,570 ppb) and that the reference sites contain very low levels of PCB contamination (9 ppb). Different feeding traits support the existence of direct pathways of exposure, which can be mechanistically linked to PCB bioaccumulation by biodynamic modeling. The model shows that the deposit feeder Neanthes arenaceodentata accumulates approximately 20 times more PCBs in its lipids than the facultative deposit feeder Macoma balthica and up to 130 times more than the filter feeder Mytilus edulis. The comparison of different exposure scenarios suggests that PCB tissue concentrations at HP are two orders of magnitude higher than at the reference sites. At full scale, in situ sorbent amendment with activated carbon may reduce PCB bioaccumulation at HP by up to 85 to 90% under favorable field and treatment conditions. The modeling framework further demonstrates that such expected remedial success corresponds to exposure conditions suggested as the cleanup goal for HP. However, concentrations remain slightly higher than at the reference sites. The present study demonstrates how the remedial success of a sorbent amendment, which lowers the PCB availability, can be compared to reference conditions and traditional cleanup goals, which are commonly based on bulk sediment concentrations.

Cellular internalization of silver nanoparticles in gut epithelia of the estuarine polychaete Nereis diversicolor.

Silver nanoparticles (AgNPs) are widely used which may result in environmental impacts, notably within aquatic ecosystems. As estuarine sediments are sinks for numerous pollutants, but also habitat and food for deposit feeders such as Nereis diversicolor, ingested sediments must be investigated as an important route of uptake for NPs. N. diversicolor were fed sediment spiked with either citrate capped AgNPs (30 ± 5 nm) or aqueous Ag for 10 days. Postexposure AgNPs were observed in the lumen of exposed animals, and three lines of evidence indicated direct internalization of AgNPs into the gut epithelium. With TEM, electron-dense particles resembling AgNPs were observed associated with the apical plasma membrane, in endocytotic pits and in endosomes. Energy dispersive X-ray analysis (EDX) confirmed the presence of Ag in these particles, which were absent in controls. Subcellular fractionation revealed that Ag accumulated from AgNPs was predominantly associated with inorganic granules, organelles, and the heat denatured proteins; whereas dissolved Ag was localized to the metallothionein fraction. Collectively, these results indicate separate routes of cellular internalization and differing in vivo fates of Ag delivered in dissolved and NP form. For AgNPs an endocytotic pathway appears to be a key route of cellular uptake.

A novel approach reveals that zinc oxide nanoparticles are bioavailable and toxic after dietary exposures.

If engineered nanomaterials are released into the environment, some are likely to end up associated with the food of animals due to aggregation and sorption processes. However, few studies have considered dietary exposure of nanomaterials. Here we show that zinc (Zn) from isotopically modified (67)ZnO particles is efficiently assimilated by freshwater snails when ingested with food. The (67)Zn from nano-sized (67)ZnO appears as bioavailable as (67)Zn internalized by diatoms. Apparent agglomeration of the zinc oxide (ZnO) particles did not reduce bioavailability, nor preclude toxicity. In the diet, ZnO nanoparticles damage digestion: snails ate less, defecated less and inefficiently processed the ingested food when exposed to high concentrations of ZnO. It was not clear whether the toxicity was due to the high Zn dose achieved with nanoparticles or to the ZnO nanoparticles themselves. Further study of exposure from nanoparticles in food would greatly benefit assessment of ecological and human health risks.