Developing understanding of the fate and behaviour of silver in fresh waters and waste waters

Characterization and quantification of silver complexes with dissolved organic matter by size exclusion chromatography coupled to ICP-MS

The fate and behavior of silver in aquatic systems is intricately determined by its interactions with dissolved organic matter (DOM). In this study, we have introduced a method for identification and quantification of silver-DOM complexes using size exclusion chromatography-inductively coupled plasma mass spectrometry (SEC-ICP-MS). Our findings revealed that silver(I) was weakly bound to Suwannee River humic acid, fulvic acid, and natural organic matter (SRHA, SRFA, and SRNOM) in various media, resulting in facile dissociation during chromatographic separation. Suitable chromatographic conditions were determined for the elution of Ag-DOM complexes, involving the use of 0.5 mM ammonium acetate (pH 7) as the mobile phase and silver-aged column (pre-absorbing 0.1-0.7 μg silver(I)). SEC-UV and SEC-ICP-MS chromatograms revealed that Ag-binding fractions of DOM were dominated by its aromatic compounds. The quantification of silver-DOM complexes was achieved by SEC-ICP-MS combination with on-line isotope dilution. Silver at concentrations below 20 µg L-1 was mainly present in the form of organic complexes in low salinity water. These measurements aligned well with the results obtained using the equilibrium dialysis method. Species analyses of Ag-DOM complexes provide a deeper understanding of the reactivity, transport, and fate of silver in aquatic environments. ENVIRONMENTAL IMPLICATION: Ionic silver is highly toxic to aquatic organisms such as fish and zooplankton. The complexation of silver with binding sites within DOM significantly influences its speciation, mobility, and toxicity. Despite the complex and unknown structure of silver-DOM complexes, this study provided a SEC-ICP-MS method to identify and quantify these complexes in a range of media. By uncovering the formation of silver-DOM complexes across diverse media, this work enhances the comprehension of silver transformation processes and associated environmental risks in aquatic environments.

Ambivalent effects of dissolved organic matter on silver nanoparticles/silver ions transformation: A review

The numerous applications of silver nanoparticles (AgNPs) lead to their spread in aquatic systems and the release of silver ions (Ag⁺), which brings potential risks to environment and human health. Owing to the different toxicity, the mutual transformations between AgNPs and Ag⁺ has been a hot topic of research. Dissolved organic matter (DOM) is ubiquitous on the earth and almost participates in all the reactions in the nature. The previous studies have reported the roles of DOM played in the transformation between AgNPs and Ag⁺. However, different experiment conditions commonly caused contradictory results, leading to the difficulty to predict the fate of AgNPs in specific reactions. Here we summarized mechanisms of DOM-mediated AgNPs oxidation and Ag⁺ reduction, and analyzed the effects of environmental parameters. Moreover, the knowledge gaps, challenges, and new opportunities for research in this field are discussed. This review will promote the understanding of the fate and risk assessments of AgNPs in natural water systems.

European freshwater silver monitoring data do not suggest a potential European-wide risk

European legislations frequently focus on substances that are of potential concern to human or environmental health, such as "priority substances" under the Water Framework Directive 2000/60/EC ("WFD") that are identified as substances posing a significant risk to or via the aquatic environment. The EU REACH regulation also requires the assessment of the environmental risks of chemicals put on the EU market. To properly assess the potential risk of a substance, high-quality representative monitoring data should be compared with a safe threshold concentration. The objective of this article is to evaluate different publicly available freshwater monitoring data sets for silver and investigate them for a potential European-wide risk according to the methodology used by the European Commission. Most available silver monitoring data sets contain a large proportion of undetected samples with a reported concentration below the limit of quantification (LOQ) of the analytical technique, leading to considerable uncertainty in the data set. For silver, this LOQ is often at or above the safe threshold concentration, and the method used to handle undetected samples during the data processing considerably impacts the data assessment. We demonstrate that for large data sets covering many European countries (and often a wide range of LOQs), the uncertainty in the data set does not allow us to make a general conclusion about European-wide risk. However, by examining the data sets in more detail and assessing three additional country-specific monitoring data sets, we show that silver does not pose a risk to the freshwater environment in several countries. We conclude that the available data sets need careful assessment to account for the values that are below the LOQ, and that there is currently no reliable evidence indicating a European-wide risk for silver in the aquatic environment, meaning it should not be selected as  priority substance under the WFD. Integr Environ Assess Manag 2023;00:1-10. © 2022 SETAC.

Asymmetrical Flow Field-Flow Fractionation Methods for Quantitative Determination and Size Characterization of Thiols and for Mercury Size Speciation Analysis in Organic Matter-Rich Natural Waters

Asymmetrical flow field-flow fractionation (AF4) efficiently separates various macromolecules and nano-components of natural waters according to their hydrodynamic sizes. The online coupling of AF4 with fluorescence (Fluo) and UV absorbance (UV) detectors (FluoD and UVD, respectively) and inductively coupled plasma–mass spectrometry (ICP-MS) provides multidimensional information. This makes it a powerful tool to characterize and quantify the size distributions of organic and inorganic nano-sized components and their interaction with trace metals. In this study, we developed a method combining thiol labeling by monobromo(trimethylammonio)bimane bromide (qBBr) with AF4–FluoD to determine the size distribution and the quantities of thiols in the macromolecular dissolved organic matter (DOM) present in highly colored DOM-rich water sampled from Shuya River and Lake Onego, Russia. We found that the qBBr-labeled components of DOM (qB-DOM) were of humic type, characterized by a low hydrodynamic size (dh < 2 nm), and have concentrations <0.3 μM. After enrichment with mercury, the complexes formed between the nano-sized components and Hg were analyzed using AF4–ICP-MS. The elution profile of Hg followed the distribution of the UV-absorbing components of DOM, characterized by slightly higher sizes than qB-DOM. Only a small proportion of Hg was associated with the larger-sized components containing Fe and Mn, probably inorganic oxides that were identified in most of the samples from river to lake. The size distribution of the Hg–DOM complexes was enlarged when the concentration of added Hg increased (from 10 to 100 nM). This was explained by the presence of small iron oxides, overlapping the size distribution of Hg–DOM, on which Hg bound to a small proportion. In addition, to provide information on the dispersion of macromolecular thiols in colored DOM-rich natural water, our study also illustrated the potential of AF4–FluoD–UVD–ICP-MS to trace or quantify dynamic changes while Hg binds to the natural nano-colloidal components of surface water.