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Environmental nanoscientists and nanotoxicologists have made significant progress towards understanding the various factors and processes that impact the environmental fate and effects of engineered nanomaterials (ENMs); nevertheless, many knowledge gaps remain. This is partly due to a disconnect that occurs when these factors or processes are elucidated in simplified experimental systems and then applied to predict ENM behavior in significantly more complex real-world systems. To aid the translation of findings between these two extremes, we have outlined and demonstrated the use of a Framework for Relevance And Methods Evaluation (FRAME) based on three components or pillars that collectively define the “environmental realism” of a given experimental design. The three pillars include (1) the properties of the ENMs, (2) the experimental conditions, and (3) the exposure scenario and endpoints that are assessed. FRAME provides researchers with an approach for assessing the environmental relevance of alternative experimental designs. It also provides a basis for reporting how an individual study fits within the broader body of scientific knowledge and for identifying areas where additional research is needed. The proposed framework is intended to be used throughout the scientific process, from the initial conception of the experimental design and continuing through to the interpretation of experimental results. Committing to a more complete assessment of environmental realism has the potential to prevent the overgeneralization of results determined in simplified experimental systems and move the field forward more quickly through the identification of critical knowledge gaps.

Copper based nanoparticles (NPs) are used extensively in industrial and commercial products as sensors, catalysts, surfactants, antimicrobials, and for other purposes. The high production volume and increasing use of copper-based NPs make their ecological risk a concern. Commonly used copper-based NPs are composed of metallic copper or copper oxide (Cu and CuO NPs); however, their environmental toxicity can vary dramatically depending on their physico-chemical properties, such as dissolution, aggregation behavior, and the generation of reactive oxygen species. Here, we investigated the NP dissolution, organismal uptake and aquatic toxicity of Cu and CuO NPs at 0, 0.1, 1, 5 or 10 mg Cu per L using a previously developed multi-species microcosm. This 5 day microcosm assay was comprised of C. reinhardtti, E. coli, D. magna, and D. rerio. We hypothesized that Cu and CuO NPs can elicit differential toxicity to the organisms due to alterations in particle dissolution and variations in organismal uptake. The actual concentrations of dissolved Cu released from the NPs were compared to ionic copper controls (CuCl2) at the same concentrations to determine the relative contribution of particulate and dissolved Cu on organism uptake and toxicity. We found that both NPs had higher uptake in D. magnaand zebrafish than equivalent ionic exposures, suggesting that both Cu-based NPs are taken up by organisms. Cu NP exposures significantly inhibited algal growth rate, D. magnasurvival, and zebrafish hatching while exposure to equivalent concentrations of CuCl2(dissolved Cu fraction) and CuO NPs did not. This indicates that Cu NPs themselves likely elicited a particle-specific mechanism of toxicity to the test organisms, or a combination effect from ionic Cu and the Cu NPs. Overall, this work was the first study to utilize a small-scale rapid assay designed to evaluate the fate and ecotoxicological impacts of Cu and CuO NPs in a mixed aquatic community.

The widespread use of silver nanoparticles (AgNPs) in various applications and industries has brought to light the need for understanding the complex relationship between the physicochemical properties (shape, size, charge, and surface chemistry) of AgNPs that affect their ability to enter cells and cause toxicity. To evaluate their toxicological outcomes, this study systematically analyzed a series of homogeneous hybrid lipid-coated AgNPs spanning sizes from 5 to 100 nm with diverse shapes (spheres, triangles, and cubes). The hybrid lipid membrane comprises hydrogenated phosphatidylcholine (HPC), sodium oleate (SOA), and hexanethiol (HT), which shield the AgNP surface from surface oxidation and toxic Ag+ion release to minimize its contribution to toxicity. To reduce any significant effects by surface chemistry, the HPC, SOA, and HT membrane composition ratio was kept constant, and the AgNPs were assessed using embryonic zebrafish (Danio rerio). While a direct comparison cannot be drawn due to the lack of complementary sizes below 40 nm for triangular plates and cubes due to synthetic challenges, significant mortality was observed for spherical AgNPs (AgNSs) of 5, 20, 40, and 60 nm at 120 h postfertilization at concentrations ≥6 mg Ag/L. In contrast, the 10, 80, and 100 nm AgNSs, 40, 70, and 100 nm triangular plate AgNPs (AgNPLs), and 55, 75, and 100 nm cubic AgNPs (AgNCs) showed no significant mortality at 5 days postfertilization following exposure to AgNPs at concentrations up to 12 mg Ag/L. With constant surface chemistry on the AgNPs, size is the dominant factor driving toxicological responses, with smaller nanoparticles (5 to 60 nm) being the most toxic. Larger AgNSs, AgNCs, and AgNPLs from 75 to 100 nm do not show any evidence of toxicity. However, when closely examining sizes between 40 and 60 nm for AgNSs, AgNCs, and AgNPLs, there is evidence that discriminates shape as a driver of toxicity since sublethal responses generally were observed to follow a pattern, suggesting toxicity is most significant for AgNSs followed by AgNPLs and then AgNCs, which is the least toxic. Sum frequency generation vibrational spectroscopy showed that irrespective of size or shape, all hybrid lipid-coated AgNPs interact with membrane surfaces and “snorkel” between phases into the lipid monolayer with minimal energetic cost. These findings decisively demonstrate that not only smaller AgNPs but also the shape of the AgNPs influences their biological compatibility.

Determining the specific nanomaterial features that elicit adverse biological responses is important to inform risk assessments, develop targeted applications, and rationally design future nanomaterials. Embryonic zebrafish are often employed to study nanomaterial-biological interactions, but few studies address the role of the chorion in nanomaterial exposure and toxicity. Here, we used chorion-intact (CI) or dechorionated (DC) embryonic zebrafish to investigate the influence of the chorion on copper-based nanoparticle toxicity. We found that despite higher dissolution and uptake, CuO NPs were less toxic than Cu NPs regardless of chorion status and did not cause 100% mortality at even the highest exposure concentration. The presence of the chorion inhibited Cu toxicity: DC exposures to Cu NPs had an LC50of 2.5 ± 0.3 mg L−1compared to a CI LC50of 13.7 ± 0.8 mg L−1. This highlights the importance of considering zebrafish chorion status during nanotoxicological investigations, as embryo sensitivity increased by one order of magnitude or more when chorions were removed. Agglomerate size, zeta potential, and dissolved Cu did not sufficiently explain the differences in toxicity between Cu NPs and CuO NPs; however, reactive oxygen species (ROS) generation did. Cu NPs generated ROS in a concentration-dependent manner, while CuO did not and generated less than Cu NPs. We believe that the differences between the toxicities of Cu NPs and CuO NPs are due in part to their ability to generate ROS which could and should be a hazard consideration for risk assessments.

Surface functionalization can minimize nanoparticle agglomeration and expand their applications; however, these modifications can also alter particle stability, dissolution, bioavailability and toxicity. Here we investigated how silver nanoparticles (AgNPs) with different surface chemistries affect community health, and how increased trophic complexity affects the interactions between organisms and nanomaterials. We compared AgNP exposures in simple microcosms comprised of algae (Chlamydomonas reinhardtii) and bacteria (Escherichia coli) to increasingly complex microcosms containing predatory invertebrates (Daphnia magna) and developing vertebrates (Danio rerio). Each microcosm was exposed to one of three 70 nm AgNPs [polyethylene glycol (PEG–AgNP), silica (Si–AgNP), or aminated silica-coated AgNP (Ami-Si–AgNP)] at 0, 0.1, 1, and 5 mg L−1to investigate the relative influence of surface charge, composition and dissolution on organismal uptake and toxicity. All three AgNPs released more dissolved Ag into solution when organisms were present than was measured in the same media without organisms. PEG–AgNPs had the highest overall toxicity in all scenarios, followed by Si–AgNPs, and lastly Ami-Si–AgNPs. Toxicity correlated with the amount of Ag measured in the exposure media and the amount taken up by the organisms. Our findings indicate that surface functionalization plays an important role in determining dissolution, uptake and toxicity of AgNPs. Increasing trophic complexity decreased organismal susceptibility under the same AgNP concentration exposures, likely due to the change in bioavailable Ag that each organism experienced. This implies that tests using individual species provide conservative estimates of environmental impacts, while exposure may be mitigated in more realistic multi-species scenarios like those found in nature.

The complexity of engineered nanomaterials with regard to their structure and system-dependent properties, and limits of instrumentation to fully characterize nanomaterials in aqueous suspensions or biological media make it difficult to understand how material structure invokes biological response. In this work, a data visualization tool was developed to explore the results of 151 zebrafish assays stored in the Nanomaterial-Biological Interactions Knowledgebase. Visualizations generated using the tool indicated that some nanomaterials exhibited a tendency to cause death, others, sublethal abnormalities. The visualizations also showed that combinations of characteristics, such as the material of the core, shell, and surface, more than any individual characteristic, influenced toxicity. Notably, the size of the nanoparticle did not appear significant in determining toxicity across studies. There was an indication that surface charge could affect toxicity, but a distinct relationship between charge and biological response was not identified. Through exploration of the Knowledgebase using the tool, it was determined that it is possible to alter the toxicity of a nanomaterial of a certain core composition by adding different combinations of a shell and/or a functional outer surface, suggesting that proper design choices, as required to achieve a specific function of a material, could mitigate or exacerbate toxicity.

The challenge of optimizing both performance and safety in nanomaterials hinges on our ability to resolve which structural features lead to desired properties. It has been difficult to draw meaningful conclusions about biological impacts from many studies of nanomaterials due to the lack of nanomaterial characterization, unknown purity, and/or alteration of the nanomaterials by the biological environment. To investigate the relative influence of core size, surface chemistry, and charge on nanomaterial toxicity, we tested the biological response of whole animals exposed to a matrix of nine structurally diverse, precision-engineered gold nanoparticles (AuNPs) of high purity and known composition. Members of the matrix include three core sizes and four unique surface coatings that include positively and negatively charged headgroups. Mortality, malformations, uptake, and elimination of AuNPs were all dependent on these parameters, showing the need for tightly controlled experimental design and nanomaterial characterization. Results presented herein illustrate the value of an integrated approach to identify design rules that minimize potential hazard.

The article focuses on the study regarding the effect of nanomaterials on consumer products. It states that several nanomaterials used in sunscreens and other consumer products can damage the deoxyribonucleic acid (DNA) of human lung cells. Researchers found that different nanomaterials cause different types of adverse responses in the lung cells, while two ingredients found in sunscreens and cosmetics such as zinc oxide and titanium dioxide nanoparticles kill cells or damage the DNA.