Combined Toxicity of Silver Nanoparticles with Hematite or Plastic Nanoparticles toward Two Freshwater Algae.

In the natural environment, the interactions of different types of nanoparticles (NPs) may alter their toxicity, thus masking their true environmental effects. This study investigated the toxicity of silver NPs (AgNPs) combined with hematite (HemNPs) or polystyrene (PsNPs) NPs toward the freshwater algae Chlamydomonas reinhardtii and Ochromonas danica. The former has a cell wall and cannot internalize these NPs, while the latter without a cell wall can. Therefore, the toxicity of AgNPs toward C. reinhardtii was attributed to the released Ag ions, while AgNPs had direct toxic effects on O. danica. Moreover, nontoxic HemNPs ameliorated AgNP toxicity toward C. reinhardtii, by decreasing the bioavailability of Ag ions through adsorption. Despite their role as Ag-ion carriers, HemNPs still reduced the toxicity of AgNPs toward O. danica by competitively inhibiting AgNP uptake. In both algae, Ag accumulation fully accounted for the combined toxicity of AgNPs and HemNPs. However, the combined toxicity of AgNPs and PsNPs was complicated by their significant individual toxicities and the synergistic interactions of these particles with the algae, regardless of differences in Ag accumulation. Overall, in environmental assessments, considerations of the combined toxicity of dissimilar NPs will allow more accurate assessments of their environmental risks.

Bacteria compete with hematite nanoparticles during their uptake by the ciliate Tetrahymena thermophila.

Bacterial accumulation of engineered nanoparticles (NPs) result in their transfer along the food chain. However, there are a lot of NPs not associated with bacteria. Whether bacteria, as representative biotic particles, influence the biological uptake of these non-associated NPs in aquatic ecosystems is unclear. In the present study, we examined the effects of four bacterial species on the uptake kinetics of polyacrylate-coated hematite nanoparticles (HemNPs) by the ciliate Tetrahymena thermophila. The HemNPs were well dispersed. Their adsorption on the bacteria was low with negligible uptake by T. thermophila through bacterial ingestion. This result demonstrated the feasibility of examining the effects of bacteria on the uptake of non-associated HemNPs. Our study further showed that all four bacterial species inhibited the uptake of HemNPs by T. thermophila; however, the effects of the bacterial cells on the physiological activities of the ciliate with respect to its uptake of HemNPs were negligible. In the absence of phagocytosis by T. thermophila, none of the bacteria inhibited HemNP uptake. This observation suggested that bacterial cells competed with the HemNPs for uptake via phagocytosis. Therefore, in evaluations of the environmental risks of NPs, their competition with biotic particles should be taken into account.

Photodegradation of carbon dots cause cytotoxicity.

Carbon dots (CDs) are photoluminescent nanomaterials with wide-ranging applications. Despite their photoactivity, it remains unknown whether CDs degrade under illumination and whether such photodegradation poses any cytotoxic effects. Here, we show laboratory-synthesized CDs irradiated with light degrade into molecules that are toxic to both normal (HEK-293) and cancerous (HeLa and HepG2) human cells. Eight days of irradiation photolyzes 28.6-59.8% of the CDs to <3 kilo Dalton molecules, 1431 of which are detected by high-throughput, non-target high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. Molecular network and community analysis further reveal 499 cytotoxicity-related molecules, 212 of which contain polyethylene glycol, glucose, or benzene-related structures. Photo-induced production of hydroxyl and alkyl radicals play important roles in CD degradation as affected by temperature, pH, light intensity and wavelength. Commercial CDs show similar photodegraded products and cytotoxicity profiles, demonstrating that photodegradation-induced cytotoxicity is likely common to CDs regardless of their chemical composition. Our results highlight the importance of light in cytocompatibility studies of CDs.

Facile synthesis of (55)Fe-labeled well-dispersible hematite nanoparticles for bioaccumulation studies in nanotoxicology.

Although water-dispersible engineered nanoparticles (ENPs) have a wide range of applications, the ENPs used in many nanotoxicological studies tend to form micron-sized aggregates in the exposure media and thus cannot reflect the toxicity of real nanoparticles. Here we described the synthesis of bare hematite nanoparticles (HNPs-0) and two poly(acrylic acid) (PAA)-coated forms (HNPs-1 and HNPs-2). All three HNPs were well dispersed in deionized water, but HNPs-0 quickly aggregated in the three culture media tested. By contrast, the suspensions of HNPs-1 and HNPs-2 remained stable, with negligible amounts of PAA and Fe(3+) liberated from either one under the investigated conditions. To better quantify the accumulation of the coated HNPs, a relatively innocuous (55)Fe-labeled form of HNPs-2 was synthesized as an example and its accumulation in three phytoplankton species was tested. Consistent with the uptake kinetics model for conventional pollutants, the cellular accumulation of HNPs-2 increased linearly with exposure time for two of the three phytoplankton species. These results demonstrate the utility of (55)Fe-labeled well-dispersible HNPs as a model material for nanoparticle bioaccumulation studies in nanotoxicology.

Cd2+ Toxicity to a green alga Chlamydomonas reinhardtii as influenced by its adsorption on TiO2 engineered nanoparticles.

In the present study, Cd(2+) adsorption on polyacrylate-coated TiO(2) engineered nanoparticles (TiO(2)-ENs) and its effect on the bioavailability as well as toxicity of Cd(2+) to a green alga Chlamydomonas reinhardtii were investigated. TiO(2)-ENs could be well dispersed in the experimental medium and their pH(pzc) is approximately 2. There was a quick adsorption of Cd(2+) on TiO(2)-ENs and a steady state was reached within 30 min. A pseudo-first order kinetics was found for the time-related changes in the amount of Cd(2+) complexed with TiO(2)-ENs. At equilibrium, Cd(2+) adsorption followed the Langmuir isotherm with the maximum binding capacity 31.9, 177.1, and 242.2 mg/g when the TiO(2)-EN concentration was 1, 10, and 100 mg/l, respectively. On the other hand, Cd(2+) toxicity was alleviated in the presence of TiO(2)-ENs. Algal growth was less suppressed in treatments with comparable total Cd(2+) concentration but more TiO(2)-ENs. However, such toxicity difference disappeared and all the data points could be fitted to a single Logistic dose-response curve when cell growth inhibition was plotted against the free Cd(2+) concentration. No detectable amount of TiO(2)-ENs was found to be associated with the algal cells. Therefore, TiO(2)-ENs could reduce the free Cd(2+) concentration in the toxicity media, which further lowered its bioavailability and toxicity to C. reinhardtii.