Silver nanoparticles adversely affect the swimming behavior of European Whitefish (Coregonus lavaretus) larvae within the low µg/L range.

The aim of this study was to determine the effects of silver nanoparticles (AgNPs; speciation: NM-300 K) in the lab on the behavior of larvae in European Whitefish (Coregonus lavaretus), a relevant model species for temperate aquatic environments during alternating light and darkness phases. The behavioral parameters measured included activity, turning rate, and distance moved. C. lavaretus were exposed to AgNP at nominal concentrations of 0, 5, 15, 45, 135, or 405 µg/L (n = 33, each) and behavior was recorded using a custom-built tracking system equipped with light sources that reliably simulate light and darkness. The observed behavior was analyzed using generalized linear mixed models, which enabled reliable detection of AgNP-related movement patterns at 10-fold higher sensitivity compared to recently reported standard toxicological studies. Exposure to 45 µg/L AgNPs significantly resulted in hyperactive response patterns for both activity and turning rates after an illumination change from light to darkness suggesting that exposure to this compound triggered escape mechanisms and disorientation-like behaviors in C. lavaretus fish larvae. Even at 5 µg/L AgNPs some behavioral effects were detected, but further tests are required to assess their ecological relevance. Further, the behavior of fish larvae exposed to 135 µg/L AgNPs was comparable to the control for all test parameters, suggesting a triphasic dose response pattern. Data demonstrated the potential of combining generalized linear mixed models with behavioral investigations to detect adverse effects on aquatic species that might be overlooked using standard toxicological tests.

Incubation media modify silver nanoparticle toxicity for whitefish (Coregonus lavaretus) and roach (Rutilus rutilus) embryos.

Toxicological studies were performed to examine silver nanoparticle (AgNP, size: 14.4 ± 2.5 nm) transformation within three different test media and consequent effects on embryos of whitefish (Coregonus lavaretus) and roach (Rutilus rutilus). The test media, namely ASTM very hard water, ISO standard dilution medium, and natural lake water differed predominantly in ionic strength. Total silver was determined using inductively coupled plasma mass spectrometry (ICP-MS), while AgNPs were characterized by transmission electron microscopy and single particle ICP-MS. Silver species distributions were estimated via thermodynamic speciation calculations. Data demonstrated that increased AgNP dissolution accompanied by decreasing ionic strength of the test medium did not occur as noted in other studies. Further, other physicochemical parameters including AgNP size and metallic species distribution did not markedly affect AgNP-induced toxicity. Irrespective of the test medium, C. lavaretus were more sensitive to AgNP exposure (median lethal concentration after 8 weeks: 0.51-0.73 mg/L) compared to R. rutilus, where adverse effects were only observed at 5 mg/L in natural lake water. In addition, AgNP-induced toxicity was lower in the two standard test media compared to natural lake water. Currently, there are no apparent studies assessing simultaneously the sensitivity of C. lavaretus and R. rutilus to AgNP exposure. Therefore, the aim of this study was to (1) investigate AgNP-induced toxicity in C. lavaretus and R. rutilus cohabiting in the same aquatic environment and (2) the role played by test media in the observed effects of AgNPs on these aquatic species.

Investigation of the Fate of Silver and Titanium Dioxide Nanoparticles in Model Wastewater Effluents via Selected Area Electron Diffraction.

The increasing use of manufactured nanomaterials (MNMs) and their inevitable release into the environment, especially via wastewater treatment plants (WWTPs), poses a potential threat for aquatic organisms. The characterization of MNMs with analytical tools to comprehend their fate and effect on the ecosystem is hence of great importance for environmental risk assessment. We herein report, for the first time, the investigation of physicochemical transformation processes during artificial wastewater treatment of silver (Ag-NPs) and titanium dioxide nanoparticles (TiO2-NPs) via selected area electron diffraction (SAED). TiO2-NPs with an anatase/rutile ratio of ∼80/20 were found to not undergo any physicochemical transformation, as shown via previous energy-dispersive X-ray analysis (EDX) elemental mapping and crystal structure analysis via SAED. In contrast, Ag-NPs were colocalized with substantial amounts of sulfur (Ag/S ratio of 1.9), indicating the formation of Ag2S. SAED ultimately proved the complete transformation of face-centered cubic (fcc) Ag-NPs into monoclinic Ag2S-NPs. The size distribution of both nanomaterials remained virtually unchanged. Our investigations show that cloud point extraction of NPs and their subsequent crystal structure analysis via SAED is another valuable approach toward the comprehensive investigation of wastewater-borne MNMs. However, the extraction procedure needs optimization for environmentally low NP concentrations.

Impact of wastewater-borne nanoparticles of silver and titanium dioxide on the swimming behaviour and biochemical markers of Daphnia magna: An integrated approach.

Due to their widespread use, silver (Ag) and titanium dioxide (TiO2) nanoparticles (NPs) are commonly discharged into aquatic environments via wastewater treatment plants. The study was aimed to assess the effects of wastewater-borne AgNPs (NM-300 K; 15.5 ±â€¯2.4 nm; 25-125 µg L-1) and TiO2NPs (NM-105; 23.1 ±â€¯6.2 nm; 12.5-100 µg L-1), from a laboratory-scale wastewater treatment plant, on Daphnia magna, at individual and subcellular level. For effect comparison, animals were also exposed to ASTM-dispersed NPs at the same nominal concentrations. The behaviour of D. magna was evaluated through monitoring of swimming height and allocation time for preferred zones after 0 h and 96 h of exposure. Biochemical markers of neurotransmission, anaerobic metabolism, biotransformation, and oxidative stress were subsequently determined. No 96-h EC50 (immobilization ≤ 4 %) could be obtained with wastewater-borne NPs and ASTM-dispersed TiO2NPs, whereas the ASTM-dispersed AgNPs resulted in an immobilization 96-h EC50 of 113.8 µg L-1. However, both wastewater-borne and ASTM-dispersed TiO2NPs, at 12.5 µg L-1, caused immediate (0 h) alterations on the swimming height. Allocation time analyses showed that animals exposed to ASTM-dispersed AgNPs spent more time on the surface and bottom at 0 h, and in the middle and bottom at 96 h. This pattern was not observed with ASTM-dispersed TiO2NPs nor with wastewater-borne AgNPs and wastewater-borne TiO2NPs. At the biochemical level, the more pronounced effects were observed with wastewater-borne AgNPs (e.g. induction of lactate dehydrogenase and glutathione S-transferase activities, and inhibition of catalase activity). This integrative approach showed that: (i) the behavioural and biochemical response-patterns were distinct in D. magna exposed to environmentally relevant concentrations of wastewater-borne and ASTM-dispersed NPs; (ii) the most pronounced effects on allocation time were induced by ASTM-dispersed AgNPs; and (iii) at the subcellular level, wastewater-borne AgNPs were more toxic than wastewater-borne TiO2NPs. This study highlights the need for the assessment of the effects of wastewater-borne NPs under realistic exposure scenarios, since processes in wastewater treatment plants may influence their toxicity.

Rapid determination of binding parameters of chitin binding domains using chitin-coated quartz crystal microbalance sensor chips.

Chitin present in fungal cell walls has been considered as a diagnostic polymer for the detection of fungal infections. Chitin staining can be achieved with different dyes such as Calcofluor white or Congo red, but these methods have not entered into clinical routine diagnosis due to problems with sensitivity and specificity. More accurate detection can be achieved using chitin binding domains (CBDs) from a large variety of naturally occurring proteins that specifically interact with chitin. The chitin binding properties of most of these proteins have not yet been determined, because chitin is an insoluble fibrillar material rendering accurate determination of chitin binding kinetics challenging. Here we report a quartz crystal microbalance with dissipation monitoring (QCM-D) based method to determine binding constants of CBDs on chitin-coated gold surfaces. For this purpose, chitin was trimethylsilylated and coated onto the sensor chips. After desilylation, regular fibril-like structures with a typical center-to-center spacing of 85 nm were observed by atomic force microscopy. Using different experimental conditions and data evaluation methods for QCM-D measurements, we determined kon and koff and calculated the KD values for binding of a recombinant CBD from Bacillus circulans chitinase A1. Depending on the evaluation method, the KD values ranged between 0.6 and 2.5 µM. The obtained KD values were in good agreement with those measured for other bacterial CBDs usually ranging between 1 to 10 µM. Hence, we propose that the experimental approach developed in this study can be applied to determine yet unknown binding affinities of various CBDs from different origin.

Enhanced gelation properties of purified gellan gum.

Gellan gum is a hydrogel-forming polysaccharide when combined with monovalent or divalent cations such as sodium, magnesium, potassium or calcium. Commercially, gellan gums are sold with trace amounts of these cations, which have been proven to affect the gelation and mechanical properties of the resultant hydrogels. A new method based on impedance analysis for determining the gel transition temperature of purified and un-purified gellan gum is presented. The sodium salt form of gellan gum is shown to have lower dissolution and gel transition temperatures.