Impact of nCuO containing treated wastewater on soil microbes and dissolved organic matter in paddy field leachate.

Using treated wastewater (TWW) resources in agriculture is a major pathway for disseminating nanoparticles. Copper-oxide nanoparticles (nCuO) offer potential benefits, but their presence in the environment poses risks to agricultural and environmental sustainability. This study examined soil microbial transformations and the composition of leachate dissolved organic matter (DOM) of paddy soils irrigated with nCuO-contaminated TWW at different concentrations (T2: 0.02 mgL-1, T3: 0.2 mgL-1, T4: 2.0 mgL-1) and examined the differences in Cu source (T5: 0.2 mgL-1 CuSO4). Results showed negative impacts on the absolute microbial abundance with up to 46 % reduction relative to the control treatment (T1). Changes in relative abundance of specific microbes at the genus level deviated from the corresponding phyla. Acidobacteria, Actinobacteria, Chloroflexi, and Verrucomicrobia phyla increased in the surface (0-3 cm) and subsurface (3-15 cm) layers responding differently to nCuO. In the 0-3 cm layer, Nitrospirae, Euryarchaeota, and Crenarchaeota increased, but only Dechloromonas genus from Proteobacteria increased with increasing nCuO. No significant variations were observed in the DOM composition, except in T4, which had a significantly low content of dissolved organic carbon (DOC), total dissolved nitrogen, and terrestrial humic-like and protein-like components. Ninety-eight distinct genera were identified, of which 44%, including 15 bacteria and two archaea, varied between the surface and subsurface, among treatments, and significantly correlated with more DOM parameters in the subsurface. T4 had the highest microbial diversity in the 0-3 layer, and Cu treatments slightly increased the diversity index in the subsurface. Moreover, the effects differed by Cu source, with T3 showing 10 % more reduction in the subsurface and 17 % less reduction in the surface than T5. The variable microbial responses to nCuO and their strong correlations with DOM highlight the need to consider the potential consequences of low nCuO concentrations on biogeochemical cycles.

Tracing the pathways by which flood duration impacts soil bacteria through soil properties and water-extractable dissolved organic matter: A soil column experiment.

Soil microbial communities control biogeochemical processes, nutrient cycling, and organic carbon storage and release in wetlands, which are influenced by flooding. To predict soil nutrient function in wetland ecosystems, understanding the effect of flooding on soil biogeochemical cycling and energy flux, including soil properties, dissolved organic matter (DOM), and microbial communities is essential. This study investigated how different flood durations (1, 3, 8, 16, and 30 d) affect the interactions between physicochemical properties and bacterial communities in a river wetland. The DOM composition was measured using ultraviolet/visible spectrophotometry coupled with fluorescence spectroscopy, and the bacterial communities were identified using 16S rRNA sequencing. Simpson's diversity index varied from 0.92 to 0.94, indicating high bacterial diversity throughout the treatments; the highest and lowest bacterial diversities were found at 1 and 8 flooding days, respectively. The abundance of Desulturomonadales, Clostridiales, Bacteroidales, and Gaiellales was positively correlated with pH, electrical conductivity, water-extractable dissolved organic carbon (WEOC), and water-extractable total dissolved nitrogen (TDN) but negatively correlated with dissolved oxygen (DO) and soil organic matter (SOM), suggesting complex interactions among these factors in response to flooding. Structural equation model revealed that flooding directly increased TDN but indirectly increased WEOC through increasing soil pH; and directly decreased DO and SOM, leading to decreases in total protein-like fraction. Three significant pathways were identified, showing the impacts of flooding on bacterial diversity: (1) flood duration decreased DO, resulting in decreased bacterial diversity; (2) flood duration decreased SOM, leading to increased bacterial diversity; and (3) flood duration decreased DO and SOM, leading to increased bacterial diversity via decreased total protein-like fraction. This study indicated that prolonged flooding has both positive and negative impacts on bacterial diversity, depending on environmental factors. It highlights the importance of flooding in shaping soil bacterial communities, with implications for nutrient cycling and carbon storage in wetlands.

Tracking Fecal Bacterial Dispersion from Municipal Wastewater to Peri-Urban Farms during Monsoon Rains in Hue City, Vietnam.

Disease outbreaks attributed to monsoon flood-induced pathogen exposure are frequently reported, especially in developing cities with poor sanitation. Contamination levels have been monitored in past studies, yet the sources, routes, and extents of contamination are not always clear. We evaluated pollution from municipal wastewater (MWW) discharge and investigated fecal contamination by Escherichia coli (E. coli) in three agricultural fields on the outskirts of Hue City, Vietnam. After E. coli concentration was determined in irrigation water (IRW), MWW, soil, vegetables (VEG), and manure, its dispersion from MWW was tracked using multilocus sequence typing (MLST) and phylogenetic analyses during the wet and dry seasons. IRW was severely contaminated; 94% of the samples were positive with E. coli exceeding the stipulated standards, while VEG contamination was very low in both seasons. The confirmed total number of isolates was comparable between the seasons; however, results from MLST and phylogenetic clustering revealed more links between the sites and samples to MWW during the wet season. The wet season had four mixed clusters of E. coli isolates from multiple locations and samples linked to MWW, while only one mixed cluster also linking MWW to IRW was observed during the dry season. The most prevalent sequence type (ST) complex 10 and two others (40 and 155) have been associated with disease outbreaks, while other STs have links to major pathotypes. Irrigation canals are significant routes for E. coli dispersion through direct links to the urban drainage-infested river. This study clarified the genotype of E. coli in Hue city, and the numerous links between the samples and sites revealed MWW discharge as the source of E. coli contamination that was enhanced by flooding.

Prevalence of Antibiotic-Resistant Bacteria ESKAPE among Healthy People Estimated by Monitoring of Municipal Wastewater.

There is increasing attention toward factors that potentially contribute to antibiotic resistance (AR), as well as an interest in exploring the emergence and occurrence of antibiotic resistance bacteria (ARB). We monitored six ARBs that cause hospital outbreaks in wastewater influent to highlight the presence of these ARBs in the general population. We analyzed wastewater samples from a municipal wastewater treatment plant (MWWTP) and hospital wastewater (HW) for six species of ARB: Carbapenem-resistant Enterobacteria (CARBA), extended-spectrum ß-lactamase producing Enterobacteria (ESBL), multidrug-resistant Acinetobacter (MDRA), multidrug-resistant Pseudomonas aeruginosa (MDRP), methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococci (VRE). We registered a high percentage of ARBs in MWWTP samples (>66%) for all ARBs except for MDRP, indicating a high prevalence in the population. Percentages in HW samples were low (<78%), and no VRE was detected throughout the study. CARBA and ESBL were detected in all wastewater samples, whereas MDRA and MRSA had a high abundance. This result demonstrated the functionality of using raw wastewater at MWWTP to monitor the presence and extent of ARB in healthy populations. This kind of surveillance will contribute to strengthening the efforts toward reducing ARBs through the detection of ARBs to which the general population is exposed.

Water extractable organic matter and iron in relation to land use and seasonal changes.

The soil carbon pool is an essential part of the global carbon cycle although it is sensitive to climatic changes and the local environment. Terrestrial areas are important sources of organic matter for aquatic ecosystems and the fluctuation of different soil minerals and elements is largely influenced by land use and season changes. We studied water-extractable organic matter (WEOM) properties including iron (Fe), water extractable organic carbon (WEOC) and spectral characteristics from forests and arable soils to evaluate the effects of land use and seasonal change on WEOM and Fe in terrestrial areas. We collected soil samples randomly from arable land (AR), broadleaf (BL) and aged needle leaf forests (NL) and extracted WEOM for analysis using rainwater. Results of WEOC and Fe showed similar trend seasonally and were higher in forest sample than in AR. WEOC was high in the upper layer while Fe was independent of the depth and higher in AR. On the other hand, specific ultra-violet absorbance at 254 nm (SUVA254) and a proxy for aromaticity significantly varied with both land use and season and was on average two times higher in arable land than forests during spring and summer. Humic-like components significantly varied between the studied sites seasonally while tyrosine-like was affected by season only. The relative abundance of both humic-like and tryptophan-like components were significantly affected by land use while [Fe]: [WEOC] ratio was also high in arable land and negatively correlated with humic-like components in forest sites. As observed from ratio and Fe oxidation rate constant, summer presented ideal conditions for WEOM interactions. The synchronized seasonal WEOC and Fe changes indicate an enhancement of Fe mobility by DOM whereas the differences observed between sites especially from the high humic- and protein-like components in NL and BL reflects the effect of land use.

Association of dissolved organic matter characteristics and trace metals in mountainous streams with sabo dams.

Metals undergo various processes transforming from one phase to another during transportation from head streams to oceans. The major chemical processes in the streams and rivers appear to be strongly dependent on dissolved organic matter (DOM). The mutualistic interactions between DOM and metals are important in determining the fate of many elements. We collected surface water samples from four stations along two mountainous streams in 2015 and analysed DOM quality and quantity and metal concentrations with the aim of understanding how changes in DOM characteristics are associated with dissolved metals along the stream with sabo dams. Both DOM and metal concentration were very low at the upstream site and did not show any significant correlation. However, sites within the dam vicinity (St.2 and St.3) had significantly high concentrations of manganese (Mn) and iron (Fe) which strongly correlated with molecular weight and aromaticity (> 0.6, p ≤ 0.01). Fe, Mn, copper (Cu) and aluminium (Al) significantly varied (p ≤ 0.05) downstream with highest average concentration for Al (17.7 ± 6.0 µg/L) and Cu (0.63 ± 0.3 µg/L). Cu had significant correlation with fluorescence components (fulvic-like, humic-like and protein like) and fluorescence index, while Fe significantly correlated to coloured DOM properties for all the sites. In the midstream section, strong correlations were exhibited by Fe, Cu, Zn and Mn whereas all metals did not show any significant correlation in the upstream site. Additionally, Cu, Mn and lead (Pb) showed strong correlation to DOM properties at the downstream site. The Fe to DOC and Mn to DOC ratios gave significant correlations with aromaticity, molecular weight and fulvic-like component at the midstream sections whereas Cu to DOC ratio lacked significant correlations to DOM at all the stations. Sabo dams enhanced Fe and Mn dissolution, while human activities in the downstream impacted Cu, Al, DOC, Mn and Fe stream concentrations. On the other hand, Fe and Mn were closely associated to DOM properties in regions of changing decreasing redox potential. The significant correlations presented by Mn, Fe and Cu with fluorescence index stresses the role of DOM heterogeneity in natural environments.

Dissolved organic matter characteristics along sabo dammed streams based on ultraviolet visible and fluorescence spectral properties.

Changes in dissolved organic matter (DOM) characteristics were investigated in two mountainous streams with closed-type sabo dams. Surface water was collected from four stations along the two mountainous streams and analyzed using ultraviolet-visible spectrophotometry and excitation-emission fluorescence matrix (EEM) methods. Optical properties of DOM indicated an increase in molecular weight and aromaticity at stations near the sabo dams. Average spectral ratio values were low before and after the dam (i.e., < 0.72) compared to other sections of the stream. Specific ultraviolet absorbance (SUVA254) increased in the vicinities of the dams. While chromophoric DOM characteristics from two sites were influenced by the dam, fluorescence components, however, did not show notable changes around dams. Instead, the three chromophoric components distinguished by EEM-parallel factor analysis, that is, humic-like (C1 and C2) and protein-like (C3) increase along the stream. Fulvic-like component (C1) had a high fluorescence intensity at all stations; all the three components were more abundant in the downstream section. Chromophoric DOM properties varied along the stream based on alterations in molecular size and aromaticity. Using multivariate analysis, the studied sites were grouped into three clusters related to sabo dams and other activities. We conclude that sabo dams modify DOM characteristics which influence the behavior of DOM transported along the stream.