The effect of exogenously applied citric acid (CA) on phytoextraction and antioxidant defense was analyzed using willow species (Salix viminalis, S. alba, and S. matsudana) grown in soil contaminated with cadmium (Cd). Citric acid has been used as a chelating agent for the purpose of accelerating the solubility of Cd in soil and enhancing the phytoextraction of selected plants. Willows were exposed to 6 mg/kg of Cd, following the same with citric acid (20 mM/kg soil). Results revealed a positive effect of citric acid in mobilization of accumulated Cd from roots to shoots and leaves. The addition of citric acid alleviated Cd toxicity by helping plants to overcome oxidative stress, through CA’s chelating properties and the increased activity of antioxidant enzymes. Different protection strategies were evident through modification of activities of antioxidant enzymes such as catalase (CAT), ascorbate-peroxidase (APx), and guaiacol peroxidase (GPx) in young versus mature leaves in plants exposed to Cd. Furthermore, results revealed that addition of citric acid may be beneficial in the reduction of the negative effect of Cd stress on photosynthesis. The efficiency of coupling phytoextraction with the chelating agents represents a good strategy for decreasing damages caused by cadmium and has good potential in decontamination of a polluted environment.

Vanadium has the potential to be released as a by-product of the combustion of fossil fuels such as oil and coal in the aquatic system. Presence of tailing ponds and other mining operations may pose the largest threat to downstream users and to the long-term aquatic health of the Mackenzie River Basin (MRB, Canada). The need for developing a solid baseline for the MRB aquatic ecosystem against which future changes can be measured is urgent. In this study, 36 sets of triplicate diffusive gradients in thin films (DGT) samplers were deployed in MRB during the 2012–2014 ice-free seasons to investigate temporal and spatial changes in the concentration of DGT-labile vanadium (V) as part of a Northwest Territories community-based project. Average DGT-labile V concentration (5.9 ± 0.9 nmol L⁻¹) was comparable with non-contaminated aquatic systems, suggesting no significant impact of human activities on V speciation in MRB in 2012–2014. The V concentrations reported in this study constitutes a baseline that can be used to enhance ongoing monitoring efforts. Although the DGT samplers were deployed in collaboration with northern communities, the absence of temporal changes in DGT-labile V indicated that in situ DGT passive samplers constitute a reliable and robust alternative for community-based monitoring programs. Excitation emission matrix (EEM) fluorescence combined with parallel factor analysis (PARAFAC) validated three humic-like (C1–C3) and one protein-like (C4) fluorescent component. However, no significant relationships were apparent between DGT-labile V and dissolved organic carbon (DOC), the PARAFAC loadings, and composition (p > 0.05). Hierarchical cluster analysis revealed that DGT-labile V concentration was negatively correlated with aromatic and humified DOM (r = − 0.70 to − 0.84, p < 0.05).

Acid deposition and temperature variation could lead to changes of physiological characteristics of plants in response to stress. In this paper, Medicago sativa CV. Dongmu–1 was investigated to test the effects of freeze-thaw circle and acid deposition upon the changes of osmotic adjustment substances, biological membrane permeability, and antioxidant enzymes. The experiment was conducted under laboratory conditions, and the seedlings were divided into four groups (group I: no treatment, group II: acid stressed only, group III: freeze-thaw stressed only, group IV: both freeze-thaw and acid stressed). Results indicated that under freeze-thaw circle and acid deposition, the contents of malondialdehyde (MDA) and proline increased respectively by 0.6~203.4 and 19.3~68.8% when compared with group I, while protein content declined by 4.1~31.7%, and the effects were even significant than freeze-thaw-only stressed groups. In the freeze-thaw process, superoxide dismutase (SOD) activity dropped at first and then increased with the increase of temperature, peaking at − 3 °C by 1118.45 U g⁻¹; peroxidase (POD) activity showed a brief rise and declined rapidly below 0 °C. By increasing the potentials of antioxidant enzymes and MDA, the membrane lipid peroxidation inside alfalfa was prevented; meanwhile, several indexes changed adaptively in resisting hurts. Variation of SOD and POD was induced by the defense mechanism, which showed alfalfa’s satisfactory cold resistance and acid tolerance. Further research on acid deposition and freeze-thaw circle would be beneficial for the global cultivation of forage grass.

In this study, five different fillers: coal ash, fiber-ball, polypropylene, ceramic, and polyhedron empty ball were used for cultivating nitrifying bacteria by increasing influent ammonia concentration gradually in sequencing batch reactors (SBRs). The results of ammonia removal performance showed that the reactor with coal ash has the highest NH₄⁺-N removal rate all the time. The ammonia removal rate of it averagely reached ≥ 95% under the condition of hydraulic retention time (HRT), dissolved oxygen (DO), pH was 12 h, 4.5 ± 0.5 mg/L, 7.5–8.5, respectively, even when the ammonia nitrogen loading reached 1000 mg/L. MiSeq Highthrough sequence was used for analyzing microbial community. The results revealed that obvious variation have occurred among the reactors after 48 days of operation; however, Nitrosomonas was enriched in large amount and became the dominant genus except in the reactor with polypropylene. Compared with other carriers, coal ash can enrich more nitrifying bacteria, the cell biomass of Nitrosomonas increased from 12.25 to 384.18 mg/L, which was 5.5 times more than the negative control. The use of coal ash as filler realizes the enrichment of a large amount of nitrifying bacteria in a short period, which guarantees a highly efficient nitrification.

It is now acknowledged that aromatic hydrocarbons present in contaminated soils occur in mixtures. The effect of single, binary and quinary mixtures of phenanthrene and selected nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) were investigated on the survival, growth and behavioural index of earthworms (Eisenia fetida) over a 21-day incubation in soil. The results showed that the LC₅₀ values ranged from (not detected) ND–329.3 mg kg⁻¹ (single mixture), ND–219.8 mg kg⁻¹ (binary mixtures) to 148.4 mg kg⁻¹ (quinary mixture), while the EC₅₀ values (based on weight loss) ranged from 13.3–148.4 mg kg⁻¹ (single mixture), 63.8–148.4 mg kg⁻¹ (binary mixture) to 24.2 mg kg⁻¹ (quinary mixture). Greater impacts were recorded where N-PAHs are present with phenanthrene. Further, behavioural index of E. fetida was affected after 24-h exposure to N-PAH-amended soils. Among the N-PAHs however, benzo[h]quinoline recorded the greatest impact on the survival, growth and behavioural index of E. fetida in soil. Findings from this study showed that three ring-N-PAHs are more toxic than phenanthrene as expected from their physico-chemical properties. The binary and quinary mixtures of phenanthrene and N-PAHs in soil intensified toxicity, suggesting that PAHs-N-PAHs mixtures represent greater risk to soil biota.

This work is dedicated to study the potential application of char byproducts obtained in the gasification of rice husk (RG char) and rice husk blended with corn cob (RCG char) as removal agents of two emergent aquatic contaminants: tetracycline and caffeine. The chars presented high ash contents (59.5–81.5%), being their mineral content mainly composed of silicon (as silica) and potassium. The samples presented a strong basic character, which was related to its higher mineral oxides content. RCG char presented better textural properties with a higher apparent surface area (144 m² g⁻¹) and higher micropore content (V ₘᵢcᵣₒ = 0.05 cm³ g⁻¹). The alkaline character of both chars promoted high ecotoxicity levels on their aqueous eluates; however, the ecotoxic behaviour was eliminated after pH correction. Adsorption experiments showed that RG char presented higher uptake capacity for both tetracycline (12.9 mg g⁻¹) and caffeine (8.0 mg g⁻¹), indicating that textural properties did not play a major role in the adsorption process. For tetracycline, the underlying adsorption mechanism was complexation or ion exchange reactions with the mineral elements of chars. The higher affinity of RG char to caffeine was associated with the higher alkaline character presented by this char.

Treated wastewater (TWW) is an imperative nonconventional water resource for reuse in irrigation to cope with the water shortage and agricultural expansion in Egypt. The Bahr El-Baqar drain in Sharqia, Egypt, is one of the main drains in the Nile Delta that receives various types of wastewater. Monitoring and assessing the drain’s water quality were achieved by collecting georeferenced water samples along the drain during the 2015 summer and winter cropping seasons. Chemical, microbial, and parasitic analyses were performed. Additionally, surface soil samples irrigated with the drain water were gathered from the adjacent area to quantify the main physicochemical properties. Water analysis results revealed that the concentrations of most trace elements were within international standards and the Egyptian allowable levels for TWW reuse in agriculture. Oxygen depletion was observed for all samples collected. The microbial analysis indicated that there was fecal coliform contamination (>1000 per 100 mL) in the summer and winter samples. Concentrations of PO₄ and SO₄ were within the permissible level for irrigation use, whereas NH₄, NO₃, and MoO₄ concentrations were higher than the recommended values for reusing Bahr El-Baqar water in irrigation. Based on the soil analysis results, Cd contamination was observed, whereas the Pb concentration in soils was slightly higher than its normal range. Mixing Bahr El-Baqar water with freshwater and implementing appropriate on-farm treatment before the reuse are recommended as a prerequisite for reusing Bahr El-Baqar water for irrigation. Bio-diesel fuel and energy oil crops are recommended for the studied region.

Diclofenac (hereafter DCF) is an extensively used anti-inflammatory drug; therefore, it is found in many sewage treatment plant effluents and it is one of the most usually reported environmental pharmaceutical contaminants. In this work, the degradation of diclofenac in pure water under UV light was studied, and the influence of some variables, such as humic acids (HA), nitrate anions (NO₃⁻) and titanium dioxide (TiO₂) on DCF photodegradation was investigated. The experimental activity was carried out in a batch reactor of 100 mL equipped with fixed UV light of 254 nm and an irradiation intensity of 400 mJ/m². Diclofenac initial concentration was equal to 10 mg/L in pure water, and its removal was evaluated by varying HA concentration in the range 10–20 mg/L and NO₃⁻ concentration in the range 25–50 mg/L. Furthermore, the heterogeneous catalysis with TiO₂ (1–50 mg/L) was studied. Temperature in all experiments was kept constant at 20 °C. Experimental results show that while HA have a significant influence on DCF photodegradation, nitrate and titanium dioxide seem to be ineffective, at least in the tested conditions. Finally, DCF photolysis modelling was carried out and a pseudo-first-order kinetic model was used.

Nowadays, the increasing pollution of natural water effluents with surfactant, wetting, dispersing, and emulsifying agents which contain nonylphenol ethoxylate (NP₇EO) is an emerging problem that has not received the enough attention. Currently, it is known that degrading this type of highly stable compounds is possible through advanced electrochemical oxidation (AEO), but the degradation of NP₇EO has not been tested yet. Thus, this work carries out a study of the degradation of the NP₇EO (500 mg L⁻¹) through advanced electrochemical oxidation, using a DiaClean® cell, equipped with boron-doped diamond electrodes (BDD, 70 cm²). The cell operated in a recirculation system with a peristaltic pump, which allowed to control the electrolyte flow. The buffer media for degradation was NH₄OH 0.1 M/HCl 0.05 M (pH 9.25). The effect of the current density (j = 20, 30, 40 mA cm⁻²) was studied, and the cell efficiency for each condition was evaluated. The degradation was followed by total organic carbon (TOC), chemical oxygen demand (COD), and absorbance. The cell potential was monitored to determine the operating costs. The best conditions for the mineralization of NP₇EO (initial concentration = 500 mg L⁻¹) were applying 40 mA cm⁻² and at a flow rate of 12.6 L min⁻¹ during 8 h of electrolysis, achieving a 90% of TOC removal. Therefore, this technology appears as a promising alternative for degrading surfactants like NP₇EO in aqueous media.

To evaluate the exposure of children to 14 perfluorinated compounds (PFCs) in a typical and representative industrial city, plasma samples from 476 children aged 0–7 years in Foshan, China, were analysed. Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) were detected in 100% of the samples, accounting for 82.27 and 11.46% of the total PFC concentrations, respectively, while PFOS peaked at age 0–1 years, for which the mean and median concentrations were 113.71 and 83.65 ng/mL, respectively, while PFOA peaked at age 3–4 years, for which the mean and median concentrations were 10.68 and 6.58 ng/mL, respectively. The concentrations of PFOS, perfluorohexane sulfonate and perfluorohexanoic acid decreased with age among children aged 0–7 years, and no gender-related differences were found in the concentrations of PFCs. A high correlation was found among all PFCs, especially between PFCs of similar carbon chains (r = 0.161–0.695, p < 0.05). In addition, the concentrations of PFOS and PFOA in children’s plasma in Foshan were up to 40-fold higher than those reported in China and other countries. In conclusion, children in Foshan have extensive exposure to PFCs, especially in infancy. Further studies are needed to explore the impact of PFCs on children who live in a typical and representative industrial city in China. Graphical abstract ᅟ