In this work, trace determination of nitrite in river water samples was studied using solvent stir bar microextraction system with three-hollow fiber configuration (3HF-SSBME) as a preconcentration step prior to UV–Vis spectrophotometry. The obtained results showed that the increase in the number of solvent bars can improve the extraction performance by increasing the contact area between acceptor and sample solutions. The extraction process relies on the well-known oxidation–reduction reaction of nitrite with iodide excess in acidic donor phase to form triiodide, and then its extraction into organic acceptor phase using a cationic surfactant. Various extraction parameters affecting the method were optimized and examined in detail. Detection limit of 1.6 μg L⁻¹ and preconcentration factor of 282 can be attained after an extraction time of 8 min under the optimum conditions of this technique. The proposed method showed a linear response up to 1000 μg L⁻¹ (r² = 0.996) with relative standard deviation values less than 4.0%. The accuracy of the developed method was assessed using the Griess technique. Finally, the proposed method was successfully employed for quantification of nitrite in river water samples (Ghezelozan, Zanjan, Iran).

Phosphate solubilizing bacteria (PSB) can convert insoluble forms of phosphorus (P) to accessible forms. 11 strains of PSB, including five inorganic phosphate solubilizing bacteria (IPSBs) and six organic phosphate solubilizing bacteria (OPSBs), were isolated from rhizosphere soils of three plants Scirpus planiculmis, Zizania latifolia, and Phrnagmites australis in the Yeyahu Wetland of Beijing, China to investigate P-solubilizing activities. In addition, the distributions of P fractions in soil samples were also observed. All strains evaluated above 1.0 by the ratio of transparent circle diameter to colony diameter (D/d) on Ca₃(PO₄)₂ or lecithin plates were identified by 16S rRNA sequencing. Results showed that Ca-bound P (Ca-P) was the main species of inorganic P (IP), and highly resistant organic P (HR-OP) accounted for the most part of organic P (OP). These strains were identified as bacterial species of Enterobacter asburiae, Acinetobacter sp., Bacillus cereus strain, and so on. The most efficient IPSB strain could convert over 430 mg L⁻¹ orthophosphate, while the equivalent OPSB strain only liberated less than 4 mg L⁻¹ in liquid culture, which indicated that IPSBs have a better P-solubilizing ability than OPSBs in rhizosphere soils of the Yeyahu Wetland and IPSBs are likely to regulate the P transformation process in this wetland. Graphical abstract ᅟ

Design and synthesis of arsenic adsorbents with high performance and excellent stability has been still a significant challenge. In this study, we anchored nano-zero-valent iron (NZVI) on the surface of graphene-silica composites (GS) with high specific surface area, forming the NZVI/GS nano-composite. The prepared nano-materials were used to remove As(III) and As(V) through adsorption from aqueous solutions. The results indicated that NZVI particles were dispersed well on the surface of GS, and the NZVI/GS showed great potential to remove As(III) and As(V). Adsorption performance of NZVI/GS for As(III) and As(V) highly depended on the pH of solutions. The experimental data fitted well with the pseudo-second-order kinetic model and the Langmuir isotherm model. The calculated maximum adsorption capacities of NZVI/GS for As(III) and As(V) were up to 45.57 mg/g and 45.12 mg/g at 298 K, respectively, and the adsorption equilibrium could be reached within 60 min. The residual concentrations of As(III) and As(V) after treatment with 0.4 g/L NZVI/GS can meet with the drinking water standard of WHO when the initial concentrations were below 4 mg/L and 3 mg/L, respectively. Moreover, the as-prepared NZVI/GS had excellent anti-interference ability during the process of As removal in the presence of foreign ions. During the As removal process, As(III) was oxidized to As(V), which could be removed through adsorption by electrostatic attraction and complexation. These results indicated that the as-synthesized NZVI/GS composite is a promising adsorbent for the removal of arsenic from aqueous solutions.

South Asia is susceptible to drought due to high variation in monthly precipitation. The drought indices deriving from remote sensing data have been used to monitor drought events. To secure agricultural land in South Asia, timely and effective drought monitoring is very important. In this study, TRMM data was utilized along with remote sensing techniques for reliable drought monitoring. The Drought Severity Index (DSI), Temperature Vegetation Drought Index (TVDI), NDVI, and Normalized Vegetation Supply Water Index (NVSWI) are more helpful in describing the drought events in South Asia due to the dryness and low vegetation. To categorize drought-affected areas, the spatial maps of TRMM were used to confirm MODIS-derived TVDI, DSI, and NVSWI. The DSI, TVDI, NVSWI, and Normalized Monthly Precipitation Anomaly Percentage (NAP) indices with an integrated use of MODIS-derived ET/PET and NDVI were selected as a tool for monitoring drought in South Asia. The seasonal DSI, TVDI, NVSWI, NAP, and NDVI values confirmed that South Asia suffered an extreme drought in 2001, which continued up to 2003. The correlation was generated among DSI, NAP, NVWSI, NDVI, TVDI, and TCI on a seasonal basis. The significantly positive correlation values of DSI, TVDI, and NVSWI were in DJF, MAM, and SON seasons, which were described as good drought monitoring indices during these seasons. During summer, the distribution values of drought indicated that more droughts occurred in the southwest regions as compared to the northeast region of South Asia. From 2001 to 2017, the change trend of drought was characterized; the difference of drought trend was obviously indicated among different regions. In South Asia, generally, the frequency of drought showed declining trends from 2001 to 2017. It was verified that these drought indices are a comprehensive drought monitoring indicator and would reduce drought risk in South Asia.

Advanced oxidation processes (AOPs) have been highly efficient in degrading contaminants of emerging concern (CEC). This study investigated the efficiency of photolysis, peroxidation, photoperoxidation, and ozonation at different pH values to degrade doxycycline (DC) in three aqueous matrices: fountain, tap, and ultrapure water. More than 99.6% of DC degradation resulted from the UV/H₂O₂ and ozonation processes. Also, to evaluate the toxicity of the original solution and throughout the degradation time, antimicrobial activity tests were conducted using Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria, and acute toxicity test using the bioluminescent marine bacterium (Vibrio fischeri). Antimicrobial activity reduced as the drug degradation increased in UV/H₂O₂ and ozonation processes, wherein the first process only 6 min was required to reduce 100% of both bacteria activity. In ozonation, 27.7 mg L⁻¹ of ozone was responsible for reducing 100% of the antimicrobial activity. When applied the photoperoxidation process, an increase in the toxicity occurred as the high levels of degradation were achieved; it means that toxic intermediates were formed. The ozonated solutions did not present toxicity.

Plantago lanceolata L. is a common grassland and roadside plant, widely used in many countries in food and herbal preparations. In this study, samples of this wild plant were collected from rural, suburban/urban, and industrial environments; the concentrations of As, Cd, Co, Cu, Fe, Mn, Ni, P, Pb, V, and Zn were measured in the edible parts of the plant (leaves), in the roots, and in the soils in order to calculate the bioaccumulation and translocation factors. The data obtained were compared with literature data available. Except for samples collected near mines and smelting plants, where Cd, Pb, and Zn concentrations were up to 15 times higher, in all other cases, no differences were observed with respect to samples from rural areas, except for Pb concentration, which was 3 times higher in urban areas. In the samples collected in our study area, the metal content does not pose particular health risks; however, even within a quite restricted region like the investigated area, high metal concentrations, possibly due to the presence of particular substrates, were observed in some samples collected from areas considered “clean” and suitable for wild food plant gathering.

This study reported two-phase electrochemical processes, including struvite electrochemical precipitation and ammonia electrooxidation, for the treatment of supernatant from the hydrolysis sludge. The results showed that in phase I, the removal efficiencies of 92.3% PO₄³⁻-P and 50.1% NH₄⁺-N could be achieved in electrochemical precipitation with magnesium sacrificial anode at pH 9.0 and 40 mA after 120-min electrolysis, and slightly increased to 95.1% and 57.3%, respectively, when current further increased to 120 mA, while the energy consumption (ECS, from 0.6 to 6.7 kWh m⁻³) and specific energy consumption [SECS, from 2.7 to 29.9 Wh g (PO₄³⁻-P)⁻¹] sharply increased. In phase II, the residual NH₄⁺-N is further indirectly electrooxidized to nitrogen with modified Ti anode (Ti/SnO₂-Sb-Pd). With the generation of active chloride, about 83.2% NH₄⁺-N was removed with the molar ratio of Cl/N 5:1 at 50 mA after 120-min treatment, and slightly increased to 92.2%, when current increased to 125 mA, while SECS significantly increased [from 0.027 to 0.117 kWh g (NH₄⁺-N)⁻¹]. The results indicated that current were the crucial factors; meanwhile, lower current and longer reaction time may be the optimal options in electrochemical process with higher efficiency and lower energy consumption. Finally, the integrated process was conducted at the optimal conditions (pH = 9.0, I = 40 mA in phase I; Cl/N = 5, I = 50 mA in phase II) with the supernatant of the alkaline hydrolysis sludge. Removal of ammonia nitrogen (79.3%) and removal of phosphorus (94.3%) were achieved, confirming the feasibility of practical application for the simultaneous phosphorus recovery and ammonia removal.

Integrated management of water quality is critical for sustaining food production and achieving overall well-being of a community. Further, understanding people’s perceptions and engagement can play an important role in achieving water and food security. The main aim of this study was to investigate the perspectives of community and other stakeholders as to how water quality impacts on agriculture, livelihood and community well-being within rural farming communities of two dry zone districts of Sri Lanka. The study adopted ‘key informant interviews’ as the methodology to investigate community and other stakeholder perspectives to collect primary data over a period of four months. The interview contents were then examined using a frequency matrix and graphed using an Excel graphing tool. The raw text was also analysed to understand the broader patterns in the text. A fuzzy logic cognitive map (FCM) was developed using the relationships between various concepts and linkages provided by the key informants. All key informants were concerned with the quality of drinking water they consume and the water used for their food preparation. Key informants representing the farming community indicated that the use of poor quality groundwater with higher levels of hardness has made growing crops difficult in the region. The key informants also identified extensive and ongoing use of agro-chemicals and fertilisers as a major source of pollution in water bodies in both spatio-temporal scale. Based on key informant interviews, possible initiatives that can help improve surface water and groundwater qualities for both drinking and agricultural use in the dry zone of Sri Lanka can be categorised into four broader themes, viz., provision of filtering/treatment systems, reduction in the use of agro-chemical and fertilisers, education of community stakeholders and support of alternative options for portable water supplies. The study indicates that in the key informants’ view of groundwater and surface waters’ continued deterioration in the absence of a proper governance structure, a majority of farmers will have restricted access to good quality water to meet daily and agricultural needs, and this will affect the health of the elderly and children in the area. Further, a majority of key informants were of the view that management of surface water and groundwater should be a shared responsibility between the government and the community in the region and appropriate policy initiatives that will improve water literacy at all levels are mandatory to address future water quality challenges.

Varying concentrations of soil Cr(VI) were used in order to explore the tolerance thresholds and phytoremediation potential of Greek oregano (Origanum vulgare), in a pot experiment conducted outdoors. Oregano exhibited a rather exceptional capacity to bioaccumulate Cr in both the aerial part (up to 1200 mg of total Cr kg⁻¹ DM) and the root—reaching 4300 mg kg⁻¹ DM when grown in soil [Cr(VI)] of 150–200 mg kg⁻¹. Plant responses indicated that there was a threshold set at 100 mg Cr(VI) kg⁻¹ in the soil, above which the following results were recorded: (i) a restriction of Cr translocation from below- to above-ground plant part, (ii) a raise of the soil-to-root Cr transfer, and (iii) the Cr(III) evolution from the reduction of Cr(VI) was significantly decelerated in the root and accelerated in the aerial part. Soil [Cr] that surpassed this threshold challenged plant tolerance, resulting in a dose-dependent reduction of growth and antioxidant phenolics pool. Nonetheless, the significant Cr uptake capacity at plant level accounted for the considerably short remediation time (i.e., 29 years at soil [Cr(VI)] of 150 mg kg⁻¹) calculated according to these results. The overall performance of oregano indicated that phytoremediation would be feasible at sites with Cr contamination levels ranging within the above-defined thresholds.

Carbon emissions in the power sector are an important part of China’s total carbon emissions and have a significant impact on whether China can achieve the 2030 carbon peak target. Based on the three perspectives of decomposition, decoupling, and prediction, this paper studies the feasibility of carbon emission peaks in eight major regional power sectors in China. First, the generalized Divisia index model (GDIM) is used to decompose the carbon emissions of the eight regional power sectors, and the driving factors and their effects on carbon emissions in the power sector of each region are compared. Then, the decoupling index based on the generalized Divisia index model (GDIM-D) is used to study the decoupling relationship between the carbon emissions of the eight regional power sectors and economic growth. Finally, the carbon emissions and decoupling indices of the power sector from 2017 to 2030 are predicted. The results show the following. First, the gross domestic product (GDP) and output scale are the main factors contributing to the carbon emissions of the eight regional power sectors. The carbon intensity of the power sector in GDP (C/G) and output carbon intensity(C/E) are the main factors that contribute to the reduction. Second, the carbon emissions of the southern coast, the middle Yellow River, and the Southwest peaked in 2013 and have been decoupled from economic growth, while those in the other regions have not peaked or decoupled. Third, if the carbon emissions of the power sector in the Northeast, northern coast, eastern coast, middle Yangtze River, and Northwest reach a peak in 2030, they will face many emission reduction pressures. This paper provides a reference for studying the carbon emissions of China’s regional power sectors and their relationship with economic growth and has important implications for peak carbon emissions at the national level.