Impact of TiO2 and ZnO nanoparticles on an aquatic microbial community: effect at environmentally relevant concentrations

Can titanium dioxide nanoparticles modulate the effects of zinc oxide nanoparticles on aquatic leaf litter decomposition?

The potential impacts of metallic nanoparticles (NPs) at environmental levels on freshwater ecosystems cannot be ignored due to their frequent release. The most widely used metallic oxide, ZnO NPs and TiO₂ NPs (100 ng L^-1) were applied to explore their single and combined effects on leaf litter decomposition. Although ZnO NPs and TiO₂ NPs alone or in combination increased 22.68%-41.17% of the leaf decomposition rate, they performed different toxic mechanisms in ecological processes. The microbial mass and enzyme activities significantly increased after acute exposure, but significantly decreased after chronic exposure to ZnO NPs. The activity of BG was the most sensitive factor that was decreased by 66.22%, 56.97%, and 39.39% after 21-day exposure to ZnO NPs, TiO₂ NPs, and in combination, respectively. In addition, the analysis of Fourier transform infrared spectroscopy suggested a novel perspective on understanding the promoting mechanism. The promotion effect of ZnO NPs relied on the enhanced decomposition of refractory organics and easily degradable substances due to the contribution of Anguillospora, Pyrenochaetopsis, and Bipolaris. The single exposure to TiO₂ NPs and combined exposure with ZnO NPs promoted microbial mass and hydrolase activities, with the stimulating effect attributed to the enhanced decomposition of soluble substances. Therefore, the results highlight the importance of chemical analysis of decomposed leaves to evaluate the potential threat of metallic NPs to the function of freshwater ecosystems.

Clue of zinc oxide and copper oxide nanoparticles in the remediation of cadmium toxicity in Phaseolus vulgaris L. via the modulation of antioxidant and redox systems

The present study represents new evidence of the successful use of metal oxide nanoparticles in the remediation of heavy metals. Zinc oxide nanoparticles (ZnO NP) and copper oxide nanoparticles (CuO NP) were assessed to alleviate cadmium (Cd) toxicity in Phaseolus vulgaris L. seedlings and plants. Monitoring physiological and metabolic parameters allowed to elucidate Cd mechanism and process whereby it exerts phytotoxic effects on bean. The response of P. vulgaris seedlings is NP dose-dependent (10 mg/L, 50 mg/L, 100 mg/L, and 200 mg/L). Similarly, applied concentrations triggered a differential response of growing plants in terms of length and biomass. Our physiological data allowed to select 100 mg/L as the most appropriate concentration to apply, in order to avoid any risk of phytotoxicity. The regulatory mechanisms by which ZnO NP and CuO NP act are for the first time compared in the embryonic axes of bean seedlings under Cd stress. Both NP were able to reduce the hypergeneration of hydrogen peroxide (H₂O₂). They also acted via enhancing ROS scavenging enzymatic capacity, and activity of antioxidant enzymes CAT, APX, GPOX, GPX, and GR, and inhibited the activity of ROS producing enzymes such as GOX and NOX. Another mechanistic effect of NP consisted of the modulation of redox enzymes Trx, NTR, Fd, and FNR evolved in cellular homeostasis and maintaining reduced status in cells. Taken together, ZnO NP triggered more significant metabolic regulations allowing to mitigate the oxidative damage caused by Cd.

The Widespread Use of Nanomaterials: The Effects on the Function and Diversity of Environmental Microbial Communities

In recent years, as an emerging material, nanomaterials have rapidly expanded from laboratories to large-scale industrial productions. Along with people's productive activities, these nanomaterials can enter the natural environment of soil, water and atmosphere through various ways. At present, a large number of reports have proved that nanomaterials have certain toxic effects on bacteria, algae, plants, invertebrates, mammalian cell lines and mammals in these environments, but people still know little about the ecotoxicology of nanomaterials. Most relevant studies focus on the responses of model strains to nanomaterials in pure culture conditions, but these results do not fully represent the response of microbial communities to nanomaterials in natural environments. Over the years, the effect of nanomaterials infiltrated into the natural environment on the microbial communities has become a popular topic in the field of nano-ecological environment research. It was found that under different environmental conditions, nanomaterials have various effects on the microbial communities. The medium; the coexisting pollutants in the environment and the structure, particle size and surface modification of nanomaterials may cause changes in the structure and function of microbial communities. This paper systematically summarizes the impacts of different nanomaterials on microbial communities in various environments, which can provide a reference for us to evaluate the impacts of nanomaterials released into the environment on the microecology and has certain guiding significance for strengthening the emission control of nanomaterials pollutants.

TiO2 nanoparticles exert an adverse effect on aquatic microbial communities

Titanium dioxide nanoparticle (n-TiO₂) is a widely used nanomaterial, which is inevitably released as a residue into aquatic ecosystems during material production and usage. However, the effects of n-TiO₂ on aquatic microbial communities have not been completely elucidated. This study examined the toxic effects of n-TiO₂ on eukaryotic and prokaryotic microbial communities in freshwater environments. We determined that n-TiO₂ had a greater inhibitory effect on the growth of eukaryotic algae than cyanobacteria in monocultures. A similar phenomenon was observed in a microcosm experiment, revealing that n-TiO₂ slightly reduced the content of chlorophyll-a but evidently increased the phycocyanin content. Moreover, the alpha diversity of the eukaryotic community was not affected, whereas its beta diversity increased with exposure to n-TiO₂. Although n-TiO₂ altered the composition of freshwater microbial communities, it did not change the functions of the prokaryotic community, which might be attributed to the functional redundancy of microbiota. Co-occurrence network analysis indicated that n-TiO₂ destabilized the freshwater community, especially the eukaryotic community, and potentially disturbed the aquatic ecosystem. Our study revealed that the ecological risk of n-TiO₂ on aquatic microbial communities is complex; hence, rational utilization of n-TiO₂ should be emphasized.

Comparative study of the effects of biocides and metal oxide nanoparticles on microbial community structure in a stream impacted by hydraulic fracturing

Our study goal was to investigate the impact of biocides and nanoparticles (NPs) on the microbial diversity in a hydraulic fracturing impacted stream. Biocides and NPs are known for their antimicrobial properties and controlling microbial growth. Previous work has shown that biocides can alter the microbial community composition of stream water and may select for biocide-resistant bacteria. Additional studies have shown that nanoparticles can also alter microbial community composition. However, previous work has often focused on the response to a single compound. Here we provide a more thorough analysis of the microbial community response to three different biocides and three different nanoparticles. A microcosm-based study was undertaken that exposed stream microbial communities to either biocides or NPs. Our results showed a decrease in bacterial abundance with different types of nanoparticles, but an increase in microbial abundance in biocide-amended treatments. The microbial community composition (MCC) was distinct from the controls in all biocide and NP treatments, which resulted in differentially enriched taxa in the treatments compared to the controls. Our results indicate that NPs slightly altered the MCC compared to the biocide-treated microcosms. After 14 days, the MCC in the nanoparticle-treated conditions was similar to the MCC in the control. Conversely, the MCC in the biocide-treated microcosms was distinct from the controls at day 14 and distinct from all conditions at day 0. This finding may point to the use of NPs as an alternative to biocides in some settings.

The Biolog EcoPlate™ Technique for Assessing the Effect of Metal Oxide Nanoparticles on Freshwater Microbial Communities

The application of Biolog EcoPlate™ for community-level physiological profiling of soils is well documented; however, the functional diversity of aquatic bacterial communities has been hardly studied. The objective of this study was to investigate the applicability of the Biolog EcoPlate™ technique and evaluate comparatively the applied endpoints, for the characterisation of the effects of metal oxide nanoparticles (MONPs) on freshwater microbial communities. Microcosm experiments were run to assess the effect of nano ZnO and nano TiO2 in freshwater at 0.8-100 mg/L concentration range. The average well colour development, substrate average well colour development, substrate richness, Shannon index and evenness, Simpson index, McIntosh index and Gini coefficient were determined to quantify the metabolic capabilities and functional diversity. Comprehensive analysis of the experimental data demonstrated that short-term exposure to TiO2 and ZnO NPs affected the metabolic activity at different extent and through different mechanisms of action. TiO2 NPs displayed lower impact on the metabolic profile showing up to 30% inhibition. However, the inhibitory effect of ZnO NPs reached 99% with clearly concentration-dependent responses. This study demonstrated that the McIntosh and Gini coefficients were well applicable and sensitive diversity indices. The parallel use of general metabolic capabilities and functional diversity indices may improve the output information of the ecological studies on microbial communities.

Nanoparticles: Weighing the Pros and Cons from an Eco-genotoxicological Perspective

The exponential growth of nanotechnology and the industrial production have raised concerns over its impact on human and environmental health and safety (EHS). Although there has been substantial progress in the assessment of pristine nanoparticle toxicities, their EHS impacts require greater clarification. In this review, we discuss studies that have assessed nanoparticle eco-genotoxicity in different test systems and their fate in the environment as well as the considerable confounding factors that may complicate the results. We highlight key mechanisms of nanoparticle-mediated genotoxicity. Then we discuss the reliability of endpoint assays, such as the comet assay, the most favored assessment technique because of its versatility to measure low levels of DNA strand breakage, and the micronucleus assay, which is complementary to the former because of its greater ability to detect chromosomal DNA fragmentation. We also address the current recommendations on experimental design, including environmentally relevant concentrations and suitable exposure duration to avoid false-positive or -negative results. The genotoxicity of nanoparticles depends on their physicochemical features and the presence of co-pollutants. Thus, the effect of environmental processes (e.g., aggregation and agglomeration, adsorption, and transformation of nanoparticles) would account for when determining the actual genotoxicity relevant to environmental systems, and assay procedures must be standardized. Indeed, the engineered nanoparticles offer potential applications in different fields including biomedicine, environment, agriculture, and industry. Toxicological pathways and the potential risk factors related to genotoxic responses in biological organisms and environments need to be clarified before appropriate and sustainable applications of nanoparticles can be established.

Fate and transport of per- and polyfluoroalkyl substances (PFASs) in the vadose zone

Per- and polyfluoroalkyl substances (PFASs) are a heterogeneous group of persistent organic pollutants that have been detected in various environmental compartments around the globe. Emerging research has revealed the preferential accumulation of PFASs in shallow soil horizons, particularly at sites impacted by firefighting activities, agricultural applications, and atmospheric deposition. Once in the vadose zone, PFASs can sorb to soil, accumulate at interfaces, become volatilized, be taken up in biota, or leach to the underlying aquifer. At the same time, polyfluorinated precursor species may transform into highly recalcitrant perfluoroalkyl acids, changing their chemical identity and thus transport behavior along the way. In this review, we critically discuss the current state of the knowledge and aim to interconnect the complex processes that control the fate and transport of PFASs in the vadose zone. Furthermore, we identify key challenges and future research needs. Consequently, this review may serve as an interdisciplinary guide for the risk assessment and management of PFAS-contaminated sites.

Fates of Au, Ag, ZnO, and CeO2 Nanoparticles in Simulated Gastric Fluid Studied using Single-Particle-Inductively Coupled Plasma-Mass Spectrometry

The increasing use of engineered nanoparticles (ENPs) in many industries has generated significant research interest regarding their impact on the environment and human health. The major routes of ENPs to enter the human body are inhalation, skin contact, and ingestion. Following ingestion, ENPs have a long contact time in the human stomach. Hence, it is essential to know the fate of the ENPs under gastric conditions. This study aims to investigate the fate of the widely used nanoparticles Ag-NP, Au-NP, CeO2-NP, and ZnO-NP in simulated gastric fluid (SGF) under different conditions through the application of single-particle inductively coupled plasma-mass spectrometry (SP-ICP-MS). The resulting analytical methods have size detection limits for Ag-NP, Au-NP, ZnO-NP, and CeO2-NP from 15 to 35 nm, and the particle concentration detection limit is 135 particles/mL. Metal ions corresponding to the ENPs of interest were detected simultaneously with detection limits from 0.02 to 0.1 μg/L. The results showed that ZnO-NPs dissolved completely and rapidly in SGF, whereas Au-NPs and CeO2-NPs showed apparent aggregation and did not dissolve significantly. Both aggregation and dissolution were observed in Ag-NP samples following exposure to SGF. The size distributions and concentrations of ENPs were affected by the original ENP concentration, ENP size, the contact time in SGF, and temperature. This work represents a significant advancement in the understanding of ENP characteristics under gastric conditions.

Antibiotic resistance genes (ARGs) and their associated environmental factors in the Yangtze Estuary, China: From inlet to outlet

The occurrence of antibiotic resistance genes (ARGs) and their associated environmental factors in estuaries are poorly understood. In this study, we comprehensively analyzed ARGs in both water and sediments from inlet to outlet of the Yangtze Estuary, China. The relative abundances of ARGs were higher in the turbidity maximum zone (TMZ) than other sites, implying that suspended particulate matter (SPM) was the major reservoir for ARGs in water. ARGs showed an increasing trend from inlet to outlet in sediments. Positively correlation between intI1 and sul1 in both water and sediments indicated that sul1 may be regulated by intI1. Correlation analysis and redundancy analysis showed that the spatial variations of estuarine ARGs were positively correlated with sample properties (e.g., temperature, SPM, pH) and chemical pollutants (e.g., heavy metals and antibiotic residues), among which chemical pollutants were the major drivers for the ARG distribution in both water and sediments.

Silver nanoparticle and Ag+-induced shifts of microbial communities in natural brackish waters: Are they more pronounced under oxic conditions than anoxic conditions?

With the burst of silver nanoparticles (AgNPs) applications, their potential entry into the environment has attracted increasing concern. To date, researches about the impacts of AgNPs on microbial communities have been scarcely conducted in the brackish waters. Here, the effects of interactions of AgNPs and Ag⁺ (as a positive control) with dissolved oxygen on natural brackish water microbial communities were investigated for 30 d. The introduction of AgNPs and Ag⁺ in natural brackish waters resulted in distinct bacterial community composition and structure as well as reduction of the richness and diversity, effects that were not eliminated completely during the tested periods. Anoxic conditions could attenuate the effects of AgNPs and Ag⁺ on the community, and dissolved oxygen made more contributions to community compositions for short-term exposure. High doses of AgNPs had more pronounced long-term impacts than Ag⁺ amendment. Compared with the controls, two general AgNP and Ag⁺ responses, namely, sensitivity and resistance, were observed. Sensitive species mainly included those of the genera Synechococcus and unclassified_f_Rhodobacteraceae, while resistant species mostly belonged to the phylum Bacteroidetes and participated in carbon metabolic processes. Our results indicated that the microbial communities that were involved in nutrient cycles (such as carbon, nitrogen, and sulfide) and photoautotrophic bacteria that contained bacteriochlorophyll were adversely affected by AgNPs and Ag⁺. In addition, dissolved oxygen could further change the microbial communities. These results implied that under different oxygen conditions AgNPs possibly resulted in varying microbial survival strategies and affected the biogeochemical cycling of nutrients in natural brackish waters.

Effects of food-borne ZnO nanoparticles on intestinal microbiota of common carp (Cyprinus carpio L.)

Ingestion of nanoparticles (NPs) with antimicrobial properties may disrupt the balance of intestinal microbiota. To investigate the effects of zinc oxide (ZnO) NPs on intestinal flora, common carp Cyprinus carpio were fed a commercial feed containing 500 mg kg^-1 ZnO NPs for 6 weeks and compared to a control group receiving a similar feed-only regime. Sequencing data were analyzed both in individual fish and in pooled samples. Sequencing of 16S rRNA encoding gene of individual specimens revealed high variation in intestinal microbial composition. Assessment of pooled results can obscure high individual variation in data. ZnO NPs consumption was not associated with a significant difference in the intestinal microbial community compared to untreated controls. Our results indicated a high individual variation in the intestinal microbiome, which may further point out the importance of functional study over microbial composition to address nanomaterials-microbiome relationship.

Exposure to TiO2 nanoparticles induces shifts in the microbiota composition of Mytilus galloprovincialis hemolymph

It is now recognized that host microbiome, the community of microorganisms that colonize the animal body (e.g. microbiota) and their genomes, play an important role in the health status of all organisms, from nutrient processing to protection from disease. In particular, the complex, bilateral interactions between the host innate immune system and the microbiota are crucial in maintaining whole body homeostasis. The development of nanotechnology is raising concern on the potential impact of nanoparticles-NPs on human and environmental health. Titanium dioxide-nTiO₂, one of the most widely NP in use, has been shown to affect the gut microbiota of mammals and fish, as well as to potentially alter microbial communities. In the marine bivalve Mytilus galloprovincialis, nTiO₂ has been previously shown to interact with hemolymph components, thus resulting in immunomodulation. However, no information is available on the possible impact of NPs on the microbiome of marine organisms. Bivalves host high microbial abundance and diversity, and alteration of their microbiota, in both tissues and hemolymph, in response to stressful conditions has been linked to a compromised health status and susceptibility to diseases. In this work, the effects of nTiO₂ exposure (100 μg/L, 4 days) on Mytilus hemolymph microbiota were investigated by 16S rRNA gene-based profiling. Immune parameters were also evaluated. Although hemolymph microbiota of control and nTiO₂-treated mussels revealed a similar core composition, nTiO₂ exposure affected the abundance of different genera, with decreases in some (e.g. Shewanella, Kistimonas, Vibrio) and increases in others (e.g. Stenotrophomonas). The immunomodulatory effects of nTiO₂ were confirmed by the increase in the bactericidal activity of whole hemolymph. These represent the first data on the effects of NPs on the microbiome of marine invertebrates, and suggest that the shift in hemolymph microbiome composition induced by nTiO₂ may result from the interplay between the microbiota and the immune system.