Building the Bridge From Aquatic Nanotoxicology to Safety by Design Silver Nanoparticles

Environmental factors modify silver nanoparticles ecotoxicity in Chydorus eurynotus (Cladocera)

Silver nanoparticles (AgNPs) are among the most produced nanomaterials in the world and are incorporated into several products due to their biocide and physicochemical properties. Since freshwater bodies are AgNPs main final sink, several consequences for biota are expected to occur. With the hypothesis that AgNPs can interact with environmental factors, we analyzed their ecotoxicity in combination with humic acids and algae. In addition to the specific AgNPs behavior in the media, we analyzed the mortality, growth, and phototactic behavior of Chydorus eurynotus (Cladocera) as response variables. While algae promoted Ag+ release, humic acids reduced it by adsorption, and their combination resulted in an intermediated Ag+ release. AgNPs affected C. eurynotus survival and growth, but algae and humic acids reduced AgNPs lethality, especially when combined. The humic acids mitigated AgNP effects in C. eurynotus growth, and both factors improved its phototactic behavior. It is essential to deepen the study of the isolated and combined influences of environmental factors on the ecotoxicity of nanoparticles to achieve accurate predictions under realistic exposure scenarios.

Expanding adverse outcome pathways towards one health models for nanosafety

The ever-growing production of nano-enabled products has generated the need for dedicated risk assessment strategies that ensure safety for humans and the environment. Transdisciplinary approaches are needed to support the development of new technologies while respecting environmental limits, as also highlighted by the EU Green Deal Chemicals Strategy for Sustainability and its safe and sustainable by design (SSbD) framework. The One Health concept offers a holistic multiscale approach for the assessment of nanosafety. However, toxicology is not yet capable of explaining the interaction between chemicals and biological systems at the multiscale level and in the context of the One Health framework. Furthermore, there is a disconnect between chemical safety assessment, epidemiology, and other fields of biology that, if unified, would enable the adoption of the One Health model. The development of mechanistic toxicology and the generation of omics data has provided important biological knowledge of the response of individual biological systems to nanomaterials (NMs). On the other hand, epigenetic data have the potential to inform on interspecies mechanisms of adaptation. These data types, however, need to be linked to concepts that support their intuitive interpretation. Adverse Outcome Pathways (AOPs) represent an evolving framework to anchor existing knowledge to chemical risk assessment. In this perspective, we discuss the possibility of integrating multi-level toxicogenomics data, including toxicoepigenetic insights, into the AOP framework. We anticipate that this new direction of toxicogenomics can support the development of One Health models applicable to groups of chemicals and to multiple species in the tree of life.

Nanotechnology-based pesticides: Environmental fate and ecotoxicity

The imminent increase in global food demand inevitably leads to an increase in agricultural practices, with an emphasis on pesticide applications. Nanotechnology-based pesticides, or nanopesticides, have gained importance as they are more efficient and, in some cases, less toxic than their conventional counterparts. However, concerns about these novel products have arisen as evidence about their (eco)safety is controversial. This review aims to: (1) introduce the currently applied nanotechnology-based pesticides and their mechanisms of toxic action; (2) describe their fate when released into the environment, with an emphasis on aquatic environments; (3) summarize available research on ecotoxicological studies in freshwater non-target organisms through a bibliometric analysis; and (4) identify gaps in knowledge from an ecotoxicological perspective. Our results show that the environmental fate of nanopesticides is poorly studied and depends on both intrinsic and external factors. There is also a need for comparative research into their ecotoxicity between conventional pesticide formulations and their nano-based counterparts. Among the few available studies, most considered fish species as test organisms, compared to algae and invertebrates. Overall, these new materials generate toxic effects on non-target organisms and threaten the integrity of the environment. Therefore, deepening the understanding of their ecotoxicity is crucial.

Characterization and Behaviour of Silica Engineered Nanocontainers in Low and High Ionic Strength Media

Mesoporous silica engineered nanomaterials are of interest to the industry due to their drug-carrier ability. Advances in coating technology include using mesoporous silica nanocontainers (SiNC) loaded with organic molecules as additives in protective coatings. The SiNC loaded with the biocide 4,5-dichloro-2-octyl-4-isothiazolin-3-one (DCOIT), i.e., SiNC-DCOIT, is proposed as an additive for antifouling marine paints. As the instability of nanomaterials in ionic-rich media has been reported and related to shifting key properties and its environmental fate, this study aims at understanding the behaviour of SiNC and SiNC-DCOIT in aqueous media with distinct ionic strengths. Both nanomaterials were dispersed in (i) low- (ultrapure water-UP) and (ii) high- ionic strength media-artificial seawater (ASW) and f/2 medium enriched in ASW (f/2 medium). The morphology, size and zeta potential (ζP) of both engineering nanomaterials were evaluated at different timepoints and concentrations. Results showed that both nanomaterials were unstable in aqueous suspensions, with the initial ζP values in UP below -30 mV and the particle size varying from 148 to 235 nm and 153 to 173 nm for SiNC and SiNC-DCOIT, respectively. In UP, aggregation occurs over time, regardless of the concentration. Additionally, the formation of larger complexes was associated with modifications in the ζP values towards the threshold of stable nanoparticles. In ASW, SiNC and SiNC-DCOIT formed aggregates (<300 nm) independently of the time or concentration, while larger and heterogeneous nanostructures (>300 nm) were detected in the f/2 medium. The pattern of aggregation detected may increase engineering nanomaterial sedimentation rates and enhance the risks towards dwelling organisms.

Ecotoxicity of nanosilver on cladocerans and the role of algae provision

Silver nanoparticles (AgNPs) are applied in diverse industries due to their biocide and physicochemical properties; therefore, they can be released into aquatic systems, interact with environmental factors, and ultimately exert adverse effects on the biota. We analyzed AgNPs effects on Ceriodaphnia reticulata (Cladocera) through mortality and life-history traits, considering the influence of food (Tetradesmus obliquus, Chlorophyceae) presence and concentration. C. reticulata was exposed to AgNPs in acute (absence and two algae concentrations plus five AgNPs treatments) and chronic assays (two algae concentrations plus three AgNPs treatments). AgNPs did not affect algae flocculation but increased Ag⁺ release, being these ions less toxic than AgNPs (as proved by the exposure to AgNO₃). A reduction in AgNPs acute toxicity was observed when algae concentration increased. Acute AgNP exposure decreased C. reticulata body size and heart rate. The chronic AgNP exposure reduced C. reticulata molt number, growth, heart rate, and neonate size:number ratio, being these effects mitigated at the highest algae concentration. Increases in relative size and number of neonates were observed in AgNP treatments suggesting energy trade off. The increased Ag⁺ release with food presence suggests that the AgNP-algae interaction might be responsible of the decreased toxicity. Although algae reduced AgNP toxicity, they still exerted adverse effects on C. reticulata below predicted environmental concentrations. Since algae presence reduces AgNP effects but increases Ag⁺ release, studies should be continued to provide evidence on their toxicity to other organisms.

Ecologically based methods for promoting safer nanosilver for environmental applications

Nanosilver, widely employed in consumer products as biocide, has been recently proposed as sensor, adsorbent and photocatalyst for water pollution monitoring and remediation. Since nanosilver ecotoxicity still pose limitations to its environmental application, a more ecological exposure testing strategy should be coupled to the development of safer formulations. Here, we tested the environmental safety of novel bifunctionalized nanosilver capped with citrate and L-cysteine (AgNPcitLcys) as sensor/sorbent of Hg²⁺ in terms of behaviour and ecotoxicity on microalgae (1-1000 µg/L) and microcrustaceans (0.001-100 mg/L), from the freshwater and marine environment, in acute and chronic scenarios. Acute toxicity resulted poorly descriptive of nanosilver safety while chronic exposure revealed stronger effects up to lethality. Low dissolution of silver ions from AgNPcitLcys was observed, however a nano-related ecotoxicity is hypothesized. Double coating of AgNPcitLcys succeeded in mitigating ecotoxicity to tested organisms, hence encouraging further research on safer nanosilver formulations. Environmentally safe applications of nanosilver should focus on ecologically relevant exposure scenarios rather than relying only on acute exposure data.