It is now widely recognized that dissolution plays an important role in metallic nanoparticle toxicity, but to what extent remains unclear. In the present study, it was found that ZnO-engineered nanoparticle (ZnO-EN) toxicity to the marine diatom Thalassiosira pseudonana could be solely explained by zinc ion (Zn(2+) ) release. This is based on comparable inhibitive effects from ZnO-EN addition media, with or without the ultrafiltration through a 3-kD membrane, and from the media in which only Zn(2+) was added. Considering the importance of dissolution in ZnO-EN toxicity, Zn(2+) release kinetics was systematically examined under different conditions for the first time. It was found to be mainly influenced by pH as well as the specific surface area of the nanoparticles. In contrast, natural organic compounds either enhance or reduce Zn(2+) release, depending on their chemical composition and concentration. Compared with deionized water, ZnO-EN dissolution rates were accelerated in seawater, whereas ZnO-EN concentration itself only had a very small effect on Zn(2+) release. Therefore, dissolution as affected by several physicochemical factors should not be neglected in the effects, behavior, and fate of ENs in the environment.

We present a novel approach for the ultra-rapid direct patterning of complex three-dimensional, stacked polystyrene (PS) microfluidic chips. By leveraging the inherent shrinkage properties of biaxially pre-stressed thermoplastic sheets, microfluidic channels become thinner and deeper upon heating. Design conception to fully functional chips can thus be completed within minutes.

The behavior and toxicity of silver engineered nanoparticles (Ag-ENs) to the mixotrophic freshwater alga Ochromonas danica were examined in the present study to determine whether any other mechanisms are involved in their algal toxicity besides Ag+ liberation outside the cells. Despite their good dispersability, the Ag-ENs were found to continuously aggregate and dissolve rapidly. When the initial nanoparticle concentration was lower than 10 µM, the total dissolved Ag+ concentration ([Ag+]T) in the suspending media reached its maximum after 1 d and then decreased suggesting that Ag+ release might be limited by the nanoparticle surface area under these conditions. Furthermore, Ag-EN dissolution extent remarkably increased in the presence of glutathione. In the Ag-EN toxicity experiment, glutathione was also used to eliminate the indirect effects of Ag+ that was released. However, remarkable toxicity was still observed although the free Ag+ concentration in the media was orders of magnitude lower than the non-observed effect concentration of Ag+ itself. Such inhibitive effects were mitigated when more glutathione was added, but could never be completely eliminated. Most importantly, we demonstrate, for the first time, that Ag-ENs can be taken in and accumulated inside the algal cells, where they exerted their toxic effects. Therefore, nanoparticle internalization may be an alternative pathway through which algal growth can be influenced.

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In order to assess the overall risk posed by engineered nanoparticles (ENPs), the biological effects of this emergent pollutant to aquatic ecosystems must be evaluated. We present findings from studies conducted with a diversity of ENPs (metallic, quantum dots) on a variety of freshwater and marine algae (phytoplankton) illustrating both their direct and indirect effects. We show that in general, while the surface properties of ENPs govern their aggregation behavior and ionic strength controls their dissolution, exopolymeric substances (EPS) produced by algae determine their potential to be toxic and thereby movement through the water column and food web. The production of EPS reduces the impact of ENPs (bioavailability and toxicity) and/or their ions on cellular activities of algae. It does not however directly reduce the aggregation and/or solubility of ENPs but rather affects their stability. Complicating understanding of these interactions is the great assortment of surface coatings for ENPs. This perspective is intended to highlight our current knowledge and the need for future research particularly focused on determining the fate and transport of ENPs in the aquatic environment.