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In natural systems, organisms are embedded in complex networks where their physiology and community composition is shaped by both biotic and abiotic factors. Therefore, to assess the ecosystem-level effects of contaminants, we must pair complex, multi-trophic field studies with more targeted hypothesis-driven approaches to explore specific actors and mechanisms. Here, we examine aquatic microbiome responses to long-term additions of commercially-available metallic nanoparticles [copper-based (CuNPs) or gold (AuNPs)] and/or nutrients in complex, wetland mesocosms over 9 months, allowing for a full growth cycle of the aquatic plants. We found that both CuNPs and AuNPs (but not nutrient) treatments showed shifts in microbial communities and populations largely at the end of the experiment, as the aquatic plant community senesced. we examine aquatic microbiomes under chronic dosing of NPs and nutrients Simplified microbe-only or microbe + plant incubations revealed that direct effects of AuNPs on aquatic microbiomes can be buffered by plants (regardless of seasonal As mesocosms were dosed weekly, the absence of water column accumulation indicates the partitioning of both metals into other environmental compartments, mainly the floc and aquatic plants photosynthetically-derived organic matter. Overall, this study identifies the potential for NP environmental impacts to be either suppressed by or propagated across trophic levels via the presence of primary producers, highlighting the importance of organismal interactions in mediating emerging contaminants' ecosystem-wide impacts., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Plant nanobiotechnology has the potential to revolutionize agriculture. However, the lack of effective methods to deliver nanoparticles (NPs) to the precise locations in plants where they are needed impedes these technological innovations. Here, model gold nanoparticles (AuNP) were coated with citrate, bovine serum albumin (BSA) as a protein control, or LM6-M, an antibody with an affinity for functional groups unique to stomata on leaf surfaces to deliver the AuNPs to stomata. One-month-old Vicia faba leaves were exposed via drop deposition to aqueous suspensions of LM6-M-coated AuNPs and allowed to air dry. After rinsing, Au distribution on the leaf surface was investigated by enhanced dark-field microscopy and X-ray fluorescence mapping. While citrate-coated AuNPs randomly covered the plant leaves, LM6M-AuNPs strongly adhered to the stomata and remained on the leaf surface after rinsing, and BSA-AuNPs specifically targeted trichome hairs. To the authors' knowledge, this is the first report of active targeting of live leaf structures using NPs coated with molecular recognition molecules. This proof-of-concept study provides a strategy for future targeted nanopesticide delivery research.

Gold nanoparticles (Au NPs) are often used to study the physiochemical behavior and distribution of nanomaterials in natural systems because they are assumed to be inert under environmental conditions, even though Au can be oxidized and dissolved by a common environmental compound: cyanide. We used the cyanogenic soil bacterium, Chromobacterium violaceum, to demonstrate that quorum-sensing-regulated cyanide production could lead to a high rate of oxidative dissolution of Au NPs in soil. After 7 days of incubation in a pH 7.0 soil inoculated with C. violaceum, labile Au concentration increased from 0 to 15%. There was no observable dissolution when Au NPs were incubated in abiotic soil. In the same soil adjusted to pH 7.5, labile Au concentration increased up to 29% over the same time frame. Furthermore, we demonstrated that Au dissolution required quorum-sensing-regulated cyanide production in soil by inoculating the soil with different cell densities and using a quorum-sensing-deficient mutant of C. violaceum, CV026. Au NP dissolution experiments in liquid media coupled with mass spectrometry analysis confirmed that biogenic cyanide oxidized Au NPs to soluble Au(CN) 2 - . These results demonstrate under which conditions biologically enhanced metal dissolution can contribute to the overall geochemical transformation kinetics of nanoparticle in soils, even though the materials may be inert in abiotic environments.

Predicting nanoparticle fate in aquatic environments requires mimicking of ecosystem complexity to observe the geochemical processes affecting their behaviour. Here, 12 nm Au nanoparticles were added weekly to large-scale freshwater wetland mesocosms. After six months, ~70% of Au was associated with the macrophyte Egeria densa, where, despite the thermodynamic stability of Au 0 in water, the pristine Au 0 nanoparticles were fully oxidized and complexed to cyanide, hydroxyls or thiol ligands. Extracted biofilms growing on E. densa leaves were shown to dissolve Au nanoparticles within days. The Au biodissolution rate was highest for the biofilm with the lowest prevalence of metal-resistant taxa but the highest ability to release cyanide, known to promote Au 0 oxidation and complexation. Macrophytes and the associated microbiome thus form a biologically active system that can be a major sink for nanoparticle accumulation and transformations. Nanoparticle biotransformation in these compartments should not be ignored, even for nanoparticles commonly considered to be stable in the environment.

Despite the rapid rise in diversity and quantities of engineered nanomaterials produced, the impacts of these emerging contaminants on the structure and function of ecosystems have received little attention from ecologists. Moreover, little is known about how manufactured nanomaterials may interact with nutrient pollution in altering ecosystem productivity, despite the recognition that eutrophication is the primary water quality issue in freshwater ecosystems worldwide. In this study, we asked two main questions: (1) To what extent do manufactured nanoparticles affect the biomass and productivity of primary producers in wetland ecosystems? (2) How are these impacts mediated by nutrient pollution? To address these questions, we examined the impacts of a citrate-coated gold nanoparticle (AuNPs) and of a commercial pesticide containing Cu(OH) 2 nanoparticles (CuNPs) on aquatic primary producers under both ambient and enriched nutrient conditions. Wetland mesocosms were exposed repeatedly with low concentrations of nanoparticles and nutrients over the course of a 9-month experiment in an effort to replicate realistic field exposure scenarios. In the absence of nutrient enrichment, there were no persistent effects of AuNPs or CuNPs on primary producers or ecosystem productivity. However, when combined with nutrient enrichment, both NPs intensified eutrophication. When either of these NPs were added in combination with nutrients, algal blooms persisted for >50 d longer than in the nutrient-only treatment. In the AuNP treatment, this shift from clear waters to turbid waters led to large declines in both macrophyte growth and rates of ecosystem gross primary productivity (average reduction of 52% ± 6% and 92% ± 5%, respectively) during the summer. Our results suggest that nutrient status greatly influences the ecosystem-scale impact of two emerging contaminants and that synthetic chemicals may be playing an under-appreciated role in the global trends of increasing eutrophication. We provide evidence here that chronic exposure to Au and Cu(OH) 2 nanoparticles at low concentrations can intensify eutrophication of wetlands and promote the occurrence of algal blooms., (© 2018 by the Ecological Society of America.)

Terrestrial plants can internalize and translocate nanoparticles (NPs). However, direct evidence for the processes driving the NP uptake and distribution in plants is scarce at the cellular level. Here, NP-root interactions were investigated after 10 days of exposure of Arabidopsis thaliana to 10 mg·L -1 of negatively or positively charged gold NPs (∼12 nm) in gels. Two complementary imaging tools were used: X-ray computed nanotomography (nano-CT) and enhanced dark-field microscopy combined with hyperspectral imaging (DF-HSI). The use of these emerging techniques improved our ability to detect and visualize NP in plant tissue: by spectral confirmation via DF-HSI, and in three dimensions via nano-CT. The resulting imaging provides direct evidence that detaching border-like cells (i.e., sheets of border cells detaching from the root) and associated mucilage can accumulate and trap NPs irrespective of particle charge. On the contrary, border cells on the root cap behaved in a charge-specific fashion: positively charged NPs induced a higher mucilage production and adsorbed to it, which prevented translocation into the root tissue. Negatively charged NPs did not adsorb to the mucilage and were able to translocate into the apoplast. These observations provide direct mechanistic insight into NP-plant interactions, and reveal the important function of border cells and mucilage in interactions of plants with charged NPs.