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Silver nanoparticles (AgNPs) are of great interest due to their antimicrobial properties, but their reactivity and toxicity pose a significant risk to aquatic ecosystems. In biological systems, AgNPs tend to aggregate and dissolve, so they are often stabilized by agents that affect their physicochemical properties. In this study, microalga Chlorella vulgaris was used as a model organism to evaluate the effects of AgNPs in aquatic habitats. Algae were exposed to AgNPs stabilized with citrate and cetyltrimethylammonium bromide (CTAB) agents and to AgNO3 at concentrations that allowed 75% cell survival after 72 h. To investigate algal response, silver accumulation, ROS content, damage to biomolecules (lipids, proteins, and DNA), activity of antioxidant enzymes (APX, PPX, CAT, SOD), content of non-enzymatic antioxidants (proline and GSH), and changes in ultrastructure were analyzed. The results showed that all treatments induced oxidative stress and adversely affected algal cells. AgNO3 resulted in the fastest death of algae compared to both AgNPs, but the extent of oxidative damage and antioxidant enzymatic defense was similar to AgNP-citrate. Furthermore, AgNP-CTAB showed the least toxic effect and caused the least oxidative damage. These results highlight the importance of surface-stabilizing agents in determining the phytotoxicity of AgNPs and the underlying mechanisms affecting aquatic organisms.

Silver nanoparticles represent a threat to biota and have been shown to cause harm through a number of mechanisms, using a wide range of bioassay endpoints. While nanoparticle concentration has been primarily considered, comparison of studies that have used differently sized nanoparticles indicate that nanoparticle diameter may be an important factor that impacts negative outcomes. In considering this, the aim of the present study was to determine if different sizes of silver nanoparticles (AgNPs; 10, 20, 40, 60 and 100 nm) give rise to similar effects during embryogenesis of Mediterranean sea urchins Arbacia lixula and Paracentrotus lividus, or if nanoparticle size is a parameter that can modulate embryotoxicity and spermiotoxicity in these species. Fertilised embryos were exposed to a range of AgNP concentrations (1–1000 µg L−1) and after 48 h larvae were scored. Embryos exposed to 1 and 10 µg L−1 AgNPs (for all tested sizes) showed no negative effect in both sea urchins. The smaller AgNPs (size 10 and 20 nm) caused a decrease in the percentage of normally developed A. lixula larvae at concentrations ≥50 µg L−1 (EC50: 49 and 75 μg L−1, respectively) and at ≥100 µg L−1 (EC50: 67 and 91 μg L−1, respectively) for P. lividus. AgNPs of 40 nm diameter was less harmful in both species ((EC50: 322 and 486 μg L−1, for P. lividus and A. lixula, respectively)). The largest AgNPs (60 and 100 nm) showed a dose-dependent response, with little effect at lower concentrations, while more than 50% of larvae were developmentally delayed at the highest tested concentrations of 500 and 1000 µg L−1 (EC50(100 nm); 662 and 529 μg L−1, for P. lividus and A. lixula, respectively. While AgNPs showed no effect on the fertilisation success of treated sperm, an increase in offspring developmental defects and arrested development was observed in A. lixula larvae for 10 nm AgNPs at concentrations ≥50 μg L−1, and for 20 and 40 nm AgNPs at concentrations >100 μg L−1. Overall, toxicity was mostly ascribed to more rapid oxidative dissolution of smaller nanoparticles, although, in cases, Ag+ ion concentrations alone could not explain high toxicity, indicating a nanoparticle-size effect.

The widespread occurrence of plastic has become a significant problem in the natural environment and may give rise to a range of deleterious impacts in biota, particularly where plastic particles overlap in size with that of the particles that are naturally ingested by filter-feeders. In this context, the effects of two particle sizes (10 μm and 50 μm) of polymethylmethacrylate (PMMA) on ecologically and commercially significant mussel Mytilus galloprovincialis have been investigated. Mussel health status was evaluated by measuring the condition index and stress-on-stress test during and after 72 h exposure to PMMA microparticles in the 0.1–10 mg L−1 concentration range. The decreased condition and fitness indices in the exposed mussels pointed to significant physiological effects at the entire organism level. The 10 μm and 50 μm PMMA particles were noted to rapidly increase the total haemocytes count in haemolymph, and significantly reduce cell viability at higher concentrations of both particle sizes. The results also indicated a significant increase in levels of vacuolised haemocytes as a result of PMMA exposure. While both microparticles were detected in the haemolymph, only the 10 μm PMMA was observed in the gill tissue and digestive gland by histological cryosections, indicating their rapid uptake, transport, and accumulation in tissue. Lack of accumulation of 50 μm microparticles in tissue may be related to a combination of chemical identity and size considerations, enabling more efficient depuration of microparticles in pseudofaeces. The PMMA particles did not induce significant changes in activity of a range of enzymes involved in neurotransmission and responses to oxidative stress.

As nanoparticles have been found to cause a range of harmful impacts in biota, understanding processes and transformations which may stabilize and increase their persistence time in the environment are of great importance. As nanoparticles carried in riverine or wastewaters will eventually reach estuaries, understanding their behavior and transport potential in this transition zone from fresh to marine waters is essential, particularly as estuaries are sensitive ecological zones, oftentimes encompassing ornithologically important areas. In this direction, we report on the influence of combined gradients of riverine and marine natural organic matter (NOM) on the temporal stability of biocorona-encapsulated silver nanoparticles in terms of ion release kinetics. In parallel, salinity, pH and oxygen saturation were simultaneously varied to create a model to mimic the complex estuarine environment. While humic acid (HA) and alginate (Alg) disrupted the stabilizing ability of the nanoparticle protein corona to a greater and lesser degree, respectively, they slowed the rate of ion release in freshwater at pH 6.6 and in saltwater at pH 8, respectively, while oxygen saturation was also found to be an important factor. Thus, as the type of NOM changes with pH along a salinity gradient in an estuary, conditions required to increase the persistence time of nanoparticles are serendipitously met, with greater colloidal stability achieved in cases where there is more rapid replacement of HA with Alg. Despite the strong gradients in ionic strength, pH and oxygen saturation, the protein corona was not sufficiently disrupted at the nanoparticle surface to be substituted by NOM indicating the greater adsorption energy of the protein’s hydrophobic domains. Ultimately, it is the specific NOM profile of individual estuaries that may provide the best indicator for predicting the stability and persistence of silver nanoparticles as they transition from fresh to salt water environments.

Understanding the effect that specific amino acids (AA) exert on calcium phosphate (CaPs) formation is proposed as a way of providing deeper insight into CaPs’ biomineralization and enabling the design of tailored-made additives for the synthesis of functional materials. Despite a number of investigations, the role of specific AA is still unclear, mostly because markedly different experimental conditions have been employed in different studies. The aim of this paper was to compare the influence of different classes of amino acids, charged (aspartic acid, Asp and lysine, Lys), polar (asparagine, Asn and serine, Ser) and non-polar (phenylalanine, Phe) on CaPs formation and transformation in conditions similar to physiological conditions. The precipitation process was followed potentiometrically, while Fourier transform infrared spectroscopy, powder X-ray diffraction, electron paramagnetic spectroscopy (EPR), scanning and transmission electron microscopy were used for the characterization of precipitates. Except for Phe, all investigated AAs inhibited amorphous calcium phosphate (ACP) transformation, with Ser being the most efficient inhibitor. In all systems, ACP transformed in calcium-deficient hydroxyapatite (CaDHA). However, the size of crystalline domains was affected, as well as CaDHA morphology. In EPR spectra, the contribution of different radical species with different proportions in diverse surroundings, depending on the type of AA present, was observed. The obtained results are of interest for the preparation of functionalized CaPs’, as well as for the understanding of their formation in vivo.

Silver nanoparticles (AgNPs) are the most exploited nanomaterial in agriculture and food production, and their release into the environment raises concern about their impact on plants. Since AgNPs are prone to biotransformation, various surface coatings are used to enhance their stability, which may modulate AgNP-imposed toxic effects. In this study, the impact of AgNPs stabilized with different coatings (citrate, polyvinylpyrrolidone (PVP), and cetyltrimethylammonium bromide (CTAB)) and AgNO3 on photosynthesis of tobacco plants as well as AgNP stability in exposure medium have been investigated. Obtained results revealed that AgNP-citrate induced the least effects on chlorophyll a fluorescence parameters and pigment content, which could be ascribed to their fast agglomeration in the exposure medium and consequently weak uptake. The impact of AgNP-PVP and AgNP-CTAB was more severe, inducing a deterioration of photosynthetic activity along with reduced pigment content and alterations in chloroplast ultrastructure, which could be correlated to their higher stability, elevated Ag accumulation, and surface charge. In conclusion, intrinsic properties of AgNP coatings affect their stability and bioavailability in the biological medium, thereby indirectly contributing changes in the photosynthetic apparatus. Moreover, AgNP treatments exhibited more severe inhibitory effects compared to AgNO3, which indicates that the impact on photosynthesis is dependent on the form of Ag.

Silver nanoparticles (AgNPs) are used in a wide range of consumer products because of their excellent antimicrobial properties. AgNPs released into the environment are prone to transformations such as aggregation, oxidation, or dissolution so they are often stabilised by coatings that affect their physico-chemical properties and change their effect on living organisms. In this study we investigated the stability of polyvinylpyrrolidone (PVP) and cetyltrimethylammonium bromide (CTAB) coated AgNPs in an exposure medium, as well as their effect on tobacco germination and early growth. AgNP-CTAB was found to be more stable in the solid Murashige and Skoog (MS) medium compared to AgNP-PVP. The uptake and accumulation of silver in seedlings was equally efficient after exposure to both types of AgNPs. However, AgNP-PVP induced only mild toxicity on seedlings growth, while AgNP-CTAB caused severe negative effects on all parameters, even compared to AgNO3. Moreover, CTAB coating itself exerted negative effects on growth. Cysteine addition generally alleviated AgNP-PVP-induced negative effects, while it failed to improve germination and growth parameters after exposure to AgNP-CTAB. These results suggest that the toxic effects of AgNP-PVP are mainly a consequence of release of Ag+ ions, while phytotoxicity of AgNP-CTAB can rather be ascribed to surface coating itself.