Silver speciation during chronic toxicity tests with the mysid, Americamysis bahia

Environmental Fate of Metal Nanoparticles in Estuarine Environments

In the last decade, metal engineered nanomaterials (ENMs) have seen an exponential use in many critical technologies and products, as well an increasing release into the environment. Coastal ecosystems worldwide may receive ENM-polluted waters and wastes, with a consequent alteration of habitats and contamination of aquatic biota. There is a scarcity of data regarding the fate of these emerging contaminants in such environments. Open issues include the determination of the sources, the quantification of the interactions with marine sediments, the bioaccumulation pathways, the ecotoxicology on marine fauna and the identification of the principal biotic and abiotic factors that may alter metal ENMs toxicity. Little is known about their potential transference into the food web, as well toxicity features and co-stressors of single or multiple ENMs under laboratory and real environmental conditions for various taxonomic phyla. This review reports current knowledge on the ecological impact of ENMs under the complex environmental conditions of estuary systems, identifies gaps in current knowledge and provides directions for future research.

Influence of salinity on the toxicity of silver nanoparticles (AgNPs) and silver nitrate (AgNO3) in halophilic microalgae, Dunaliella salina

This study aim to evaluate the potential toxic effects of citrate coated silver nanoparticles (AgNPs) and ionic silver (AgNO₃) on marine microalgae Dunaliella salina under three different salinities (35, 70, and 140 g/L). The toxicity was investigated according to modified OECD guideline (No. 201) by 72 h exposure of microalgae to various concentrations of each of the chemicals in Walne's saline media. According to the results, the growth inhibitory effects of AgNPs and AgNO₃ increased significantly coincidence with increasing time and concentration compared to control (P < 0.05). The values of median inhibitory concentrations (IC₅₀) of AgNPs and AgNO₃ based on average specific growth rate and yield for D. salina increased significantly with elevation of water salinity from 35 to 140 g/L (P < 0.05). Toxicity of AgNO₃ based on IC₅₀ to D. salina was significantly higher than AgNPs at all salinities (P < 0.05). In conclusion, both AgNPs and AgNO₃ inhibited the growth of D. salina at different saltwater medium.

Relating metals with major cations in oyster Crassostrea hongkongensis: A novel approach to calibrate metals against salinity

Despite salinity has been well documented for its significant effects on the bioaccumulation of many trace elements in biomonitors, no calibration method has been proposed to reduce such influences. For the first time, the present study established a novel method to calibrate biomonitoring data against salinity. Relationships between trace element concentration in oyster Crassostrea hongkongensis and the biological proxy for salinity were quantified based on laboratory exposure experiments. The method was then verified by the biomonitoring data of Pearl River Estuary (PRE). Tissue concentrations of trace elements (Cu, Zn, Ag, Cd, Pb, Cr, As, Se, and Ni) and major cations (Na, Mg, K, and Ca) in oysters exposed at 4 salinities (5, 12, 20, and 28psu) and low concentrations for 6weeks were measured to establish such quantitative relationships. Tissue Na, Mg, and K could be the proxy for salinity, while Na was the best one. Negative correlations between tissue concentrations of trace elements and Na after exposure were observed for metal cations such as Cu, Zn, Ag, Cd, and Pb, while tissue As, Se, and Ni were positively correlated with Na. In PRE, salinity significantly influenced the bioaccumulation of trace elements even under the multifactor-affected field conditions. The calibration method applied to the biomonitoring of PRE was verified to be feasible, and effectively reduced the influences of salinity. Therefore, calibration against salinity could facilitate the interpretation, comparability, and analysis of biomonitoring data.

Silver nanoparticles: a microbial perspective

Silver nanoparticles (NPs) are used for a wide range of commercial reasons to restrict microbial growth. The increasing use of silver NPs in modern materials ensures they will find their way into environmental systems. The mode of action which makes them desirable as an antimicrobial tool could also pose a severe threat to the natural microbial balance existing in these systems. Research into the potential environmental threats of silver NPs has mainly focused on particular areas, such as their influence in rivers and estuaries or their effect on organisms such as earthworms and plants. There is a need to focus studies on all aspects of the microbial world and to highlight potential risks and methods of overcoming problems before significant damage is done. This review focuses on the antimicrobial uses, mechanisms of toxicity, and effects on the environment (mainly soil) of silver NPs, illustrating gaps in current knowledge.

Low bioavailability of silver nanoparticles presents trophic toxicity to marine medaka (Oryzias melastigma)

Concerns for the potential risks of silver nanoparticles (AgNPs) to aquatic organisms have increased. The present study investigated the trophic transfer of AgNPs from brine shrimp (Artemia salina) nauplii to marine medaka. We found that the aggregated AgNPs (20 and 80 nm) and well dispersed 80-nm AgNPs (stabilized by 20 μM Tween 20) could be readily accumulated by brine shrimp, while far less well-dispersed 20-nm AgNPs were accumulated. The assimilation efficiency (AE) of AgNPs in medaka fed AgNPs-contaminated brine shrimp was low (<6%), resulting in a low trophic transfer efficiency (0.01-0.04) after 28 days of chronic dietary exposure. However, such low bioavailability of dietary AgNPs could inhibit the whole-body Na+/K+-ATPase and superoxide dismutase (SOD) activity in the fish within the first 2 weeks of exposure. Significant (p<0.05, two-way ANOVA) inhibition occurred in the high AgNPs-contaminated brine shrimp treatment over 28 days of chronic exposure. Furthermore, reduced growth and water content percentage were also observed in fish fed high dosages of AgNPs-contaminated brine shrimp. Our study highlighted the potential of trophically available AgNPs in bringing toxicity to the marine fish.

Evaluation of different extracts and synthesised silver nanoparticles from leaves of Euphorbia prostrata against Haemaphysalis bispinosa and Hippobosca maculata

The present study was based on assessments of the antiparasitic activity to determine the efficacies of hexane, chloroform, ethyl acetate, acetone, methanol and aqueous leaf extracts of Euphorbia prostrata Ait. (Euphorbiaceae) and synthesised Ag nanoparticles (NPs) using aqueous leaf extract against the adult cattle tick Haemaphysalis bispinosa Neumann (Acarina: Ixodidae) and the haematophagous fly Hippobosca maculata Leach (Diptera: Hippoboscidae). Synthesised Ag NPs were characterised with ultraviolet-vis (UV-vis) spectrum, scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) support the biosynthesis of Ag NPs. Parasites were exposed to varying concentrations of plant extracts and synthesised silver NPs for 24 h. All extracts showed the maximum toxic effect on parasites; however, the highest mortality was found in the hexane, chloroform, ethyl acetate, acetone, methanol and aqueous leaf extracts of E. prostrata and synthesised Ag NPs against the adult of H. bispinosa (LC(50)=45.24, 40.07, 21.91, 25.32, 19.30, 10.16 and 2.30 ppm; LC(90)=86.95, 88.66, 70.92, 83.22, 48.28, 70.27 and 8.28 ppm) and against H. maculata (LC(50)=39.37, 41.98, 19.92, 27. 93, 21.97, 9.79 and 2.55 ppm; LC(90)=89.44, 98.52, 76.59, 90.18, 55.07, 54.35 and 9.03 ppm), respectively. Mortality of 100% was found in synthesised Ag NPs at a concentration of 10 mg l(-1). UV-vis spectrograph of the colloidal solution of Ag NPs has been recorded as a function of time. The absorption spectrum of E. prostrata leaf extracts at different wavelengths ranging from 300 to 600 nm revealed a peak at 420 nm after 6 h. The FTIR spectra of Ag NPs exhibited prominent peaks at 3431; 1616; 1381; 1045; 818; 509; and 420 cm(-1). SEM analyses of the synthesised Ag NPs were rod shaped and measured 25-80 nm with an average size of 52.4 nm. The chemical composition of aqueous leaf extract was analysed by gas chromatography-mass spectrometry (GC-MS). The major chemical constituent was identified as 2-phenylethanol. These results suggest that the leaf methanol, aqueous extracts of E. prostrata and green synthesis of Ag NPs have the potential to be used as an ideal eco-friendly approach for the control of H. bispinosa and H. maculata. In addition, toxicity tests were conducted to analyse the toxicological effects of particle size on Daphnia magna and Ceriodaphnia dubia, and the animal model test was evaluated against Bos indicus for 24-h treatment. No toxicity on daphnids and no adverse effects were noted on animals after exposure to solvent extracts and synthesised Ag NPs.

Assessing abalone growth inhibition risk to cadmium and silver by linking toxicokinetics/toxicodynamics and subcellular partitioning

The purpose of this study was to link toxicokinetics/toxicodynamics and subcellular partitioning for assessing the susceptibility and the growth inhibition risks of abalone Haliotis diversicolor supertexta exposed to waterborne and foodborne cadmium (Cd) and silver (Ag). We reanalyzed published data on growth inhibition and subcellular partitioning associated with the present mechanistic model to explore the correlations among elimination (k (e)), detoxification (k (d)), and recovery (k (r)) rate constants and to assess the growth inhibition risk. We found a positive correlation among k (e), k (d), and k (r) in abalone exposed to Ag. We also employed a life-stage based probabilistic assessment model to estimate the growth inhibition risk of abalone to environmentally relevant Cd (5-995 μg l(-1)) and Ag (0.05-9.95 μg l(-1)) concentrations in Taiwan. The results showed that abalone had a minimum 20% probability of the growth inhibition risk exposed to Cd, whereas Ag exposure was not likely to pose the risk. The maximum biomasses were estimated to be 0.0039 and 0.0038, 61.61 and 43.87, and 98.88 and 62.97 g for larvae, juveniles, and adults of abalone exposed to the same levels of Cd and Ag, respectively. Our study provides a useful tool to detect potential growth biomass of abalone populations subjected to Cd and Ag stresses and mechanistic implications for a long-term ecotoxicological risk assessment in realistic situations.