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Ionic silver is a potential hazard to aquatic life forms because of the increasing usage of silver based materials. The need for developing a sustainable and ecofriendly process to minimize the toxic effects of the free ions burden is now a scientific consensus. Therefore, we report the latest results in cyanobacterium Leptolyngbya JSC-1 investigating the tolerance towards toxic doses of silver, its extracellular biomineralization and silver nano-deposits formation inside the cells, and speculate about potential environmental impacts. In this study, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) analysis reveal the extracellular biomineralization of soluble silver (1-100 μM) into corresponding nanoparticles (50-100 nm in diameter) by JSC-1, while X-ray photoelectron spectroscopy (XPS) examination divulged the presence of both Ag + and Ag 0 in extracellularly biomineralized silver, depicting a mixture of both Ag x O and elemental Ag. The scanning transmission electron microscopy (STEM), EDS and elemental mapping visualized the formation of intracellular silver nanoparticles. Moreover, this feature of silver tolerance in JSC-1 was further exploited and a novel protocol was developed for isolation and maintenance of axenic culture of this filamentous cyanobacterium. Consequently, this capability of silver biomineralization by JSC-1, both extra- and intra-cellularly might be useful for modeling the Ag resistance mechanism in cyanobacteria and also might be a sustainable alternative for heavy metals bioremediation in aquatic environments., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Silver nanomaterials (AgNMs) are widely used in many fields because of their antimicrobial properties. Depending on the shapes and dimensions of the AgNMs, their potential uses and needs vary. Consequently, vast quantities of multi-dimensional AgNMs are being manufactured and released into aquatic ecosystems, where they have toxic effects on aquatic organisms. Therefore, an assessment of the toxicities of each multi-dimensional AgNM on aquatic ecosystems is necessary. In this study, important aquatic model species, Daphnia magna and Daphnia galeata, were used to assess and compare the toxic effects of silver ions (Ag + ions) and multi-dimensional AgNMs, including silver nanoparticles (AgNPs), silver nanowires (AgNWs), and silver nanoplates (AgPLs). The results indicated that Ag + ions were more toxic than AgNMs of different dimensions and sizes, and that AgPLs were the most toxic of the AgNMs. In the case of AgNWs, the longer (20 μm) nanowire was more toxic than the shorter (10 μm) one. In addition, D. galeata was more sensitive than D. magna to both Ag + ions and AgNMs. This study elucidates the dimension-dependent toxicity of and silver ions and nanomaterials in the cladocerans D. magna and D. galeata. Further studies will be necessary to further elucidate the actual risk of multi-dimensional nanomaterials in ecosystems., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

This study describes the morphology of inner shell surface (ISS) of the blue mussel Mytilus edulis Linnaeus after short-term exposures to radiolabeled silver in free-ionic ((110m)Ag(+)) and engineered nanoparticulate ((110m)AgNPs, <40 nm) phases. Radiolabeled silver in starting solutions was used in a similar low concentration (∼15 Bq mL(-1)) for both treatments. After exposure experiments radiolabeled silver was leached from the ISS using HCl. It concentration for shells from both treatments was ∼0.5 Bq mL(-1). Whole ISS of young individuals and prismatic layer of adults showed no evidence of any major alteration process after silver uptake. However, the nacre portion of adult mussels exposed to both treatments revealed distinct doughnut shape structures (DSS) formed by calcium carbonate micrograins that covered the surface of aragonite tablets. Scanning electron microscope (SEM) imaging revealed the existence of only minor differences in DSS morphology between mussels exposed to Ag(+) and AgNPs. From literature survey, DSS were also found in bivalves exposed to Cd(2+). The DSS occurring in a specimen of a field-collected bivalve is also shown. Formation of distinctive DSS can be explained by a disturbance of the shell calcification mechanism. Although the occurrence of DSS is not exclusively associated with metal bioavailability to the mussels, the morphology of DSS seems to be linked to the speciation of the metal used in the uptake experiments., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

An empirically derived model of major ion toxicity was combined with other toxicity assessments to account for the observed toxicity in field-collected produced water and produced water contaminated groundwater. The accuracy and precision of the ion toxicity model, calculated using model deviation ratios (MDR) and simple linear regressions, was determined for fathead minnows, Ceriodaphnia dubia, and Daphnia magna. Model accuracy for produced water fell within a factor of two for all three organisms. The precision, or variability explained by the model, was 47.9%, 56.1%, and 0.00% for fathead minnows, C. dubia, and D. magna, respectively. Incorporating other measured potential toxicants improved predictive precision for fathead minnows to 67.0% using ion toxicity and pH and to 30.9% for D. magna using ion toxicity, pH, and total ammonia. The observed toxicity to Daphnia pulex was also evaluated using D. magna model predictions and other measured parameters, but no consistent relationship was found. Dissimilar results were found for produced water contaminated groundwaters with model predictions for D. magna falling within a factor of two of and explaining 53.8% of the observed variability in D. pulex responses. These results indicate that predicted major ion toxicity, combined with other measured parameters, can accurately and precisely account for observed responses in test organisms to field-collected samples., (2010 Elsevier Ltd. All rights reserved.)

Rejection characteristics of chromate, arsenate, and perchlorate were examined for one reverse osmosis (RO, LFC-1), two nanofiltration (NF, ESNA, and MX07), and one ultrafiltration (UF and GM) membranes that are commercially available. A bench-scale cross-flow flat-sheet filtration system was employed to determine the toxic ion rejection and the membrane flux. Both model and natural waters were used to prepare chromate, arsenate, and perchlorate solutions (approximately 100microgL(-1) for each anion) in mixtures in the presence of other salts (KCl, K(2)SO(4), and CaCl(2)); and at varying pH conditions (4, 6, 8, and 10) and solution conductivities (30, 60, and 115mSm(-1)). The rejection of target ions by the membranes increases with increasing solution pH due to the increasingly negative membrane charge with synthetic model waters. Cr(VI), As(V), and ClO(4)(-) rejection follows the order LFC-1 (>90%) > MX07 (25-95%) congruent withESNA (30-90%)>GM (3-47%) at all pH conditions. In contrast, the rejection of target ions by the membranes decreases with increasing solution conductivity due to the decreasingly negative membrane charge. Cr(VI), As(V), and ClO(4)(-) rejection follows the order CaCl(2)90%) excluding NO(3)(-) (71-74%) than the ESNA NF membrane (11-56%) with a relatively large pore size (0.44nm), indicating that size exclusion is at least partially responsible for the rejection. The ratio of solute radius (r(i,s)) to effective membrane pore radius (r(p)) was employed to compare ion rejection. For all of the ions, the rejection is higher than 70% when the r(i,s)/r(p) ratio is greater than 0.4 for the LFC-1 membrane, while for di-valent ions (CrO(4)(2-), SO(4)(2-), and HAsSO(4)(2-)) the rejection (38-56%) is fairly proportional to the r(i,s)/r(p) ratio (0.32-0.62) for the ESNA membrane.

Following onto our work on the in situ remediation of soils contaminated with PAH's, PCB's and other polychlorinated organic compounds using microwave energy, we now report a preliminary investigation on the in situ remediation of soils contaminated with toxic metal ions: Cd(II), Mn(II), Th(IV), Cr(III) and mainly Cr(VI). The soil is partially vitrified in the process, and extraction with hot (70 degrees C) 35% nitric acid for 4.5 h leads to the recovery of very small amounts of the metals which had been spiked into the clean soil: Cd, Mn, and Cr(III) are completely immobilized (unextractable), Th is mostly unextractable, and Cr(VI) partially extractable at very high levels of spiking, but almost completely unextractable using the US EPA Toxicity Characteristic Leaching Procedure. This suggests that contaminated soils which are not going to be used for agricultural purposes can be remediated safely to preset depths without fear of the toxic metal ions leaching out for a long time.