To investigate the long-term nitrogen treatment efficiency in vertical-flow (VF)–horizontal-flow (HF) hybrid constructed wetlands (CWs), the nitrogen removal efficiency under different seasons, N loads, and three operating stages (representing age of the wetland) were evaluated over a 12-year period. The average total nitrogen (TN) removal efficiencies in the effluent during the operation period were in the following order: summer (75.2 %) > spring (73.4 %) ≒ autumn (72.6 %) > winter (66.4 %). The removal efficiencies of TN in summer, autumn, and spring were generally higher than those in winter. At different stages of operation (years), the average TN removal rates in the effluent were in the following order: middle stage (73.4 %; years 2006–2009) > last stage (72.0 %; years 2010–2013) > beginning stage (70.1 %; years 2002–2005). In VF–HF CWs, the amount of average TN removal (mg N m⁻² day⁻¹) over the 12-year period was in the order of summer (5.5) ≒ autumn (5.1) > spring (4.3) ≒ winter (4.2) for the VF bed and in the order of summer (3.5) ≒ spring (3.5) ≒ autumn (3.3) > winter (2.7) for the HF bed, showing that the amount of TN removal per unit area (m²) in summer was slightly greater than that in other seasons. The amount of TN removal in the VF bed was slightly greater than that in the HF bed. Using three-dimensional simulation graphs, the maximum TN removal rate was at inflow N loads below 2.7 g m⁻² day⁻¹ in the summer season, whereas the minimum TN removal rate was at inflow N loads below 1.4 g m⁻² day⁻¹ in the winter season. Consequently, the TN removal efficiency was very stable over the 12 years of operation in VF–HF hybrid CWs. Results demonstrate that the VF–HF hybrid CWs possess good buffer capacity for treating TN from domestic sewage for extended periods of time.

High alkalinity (pH > 12) of bauxite-residue leachates presents challenges for the long-term storage and managements of the residue. Recent evidence has highlighted the potential for constructed wetlands to effectively buffer the alkalinity, but there is limited evidence on the potential for wetland plants to establish and grow in soils inundated with residue leachate. A pot-based trial was conducted to investigate the potential for Phragmites australis to establish and grow in substrate treated with residue leachate over a pH range of 8.6–11.1. The trial ran for 3 months, after which plant growth and biomass were determined. Concentrations of soluble and exchangeable trace elements in the soil substrate and also in the aboveground and belowground biomass were determined. Residue leachate pH did not affect plant biomass or microbial biomass. With the exception of Na, there was no effect on exchangeable trace elements in the substrate; however, increases in soluble metals (As, Cd and Na) were observed with increasing leachate concentration. Furthermore, increases in Al, As and V were observed in belowground biomass and for Cd and Cr in aboveground biomass. Concentrations within the vegetation biomass were less than critical phytotoxic levels. Results demonstrate the ability for P. australis to grow in bauxite-residue leachate-inundated growth media without adverse effects.

Periphyton is ubiquitous in paddy field, but its importance in influencing the bioavailability of phosphorus (P) in paddy soil has been rarely recognized. A paddy field was simulated in a greenhouse to investigate how periphyton influences P bioavailability in paddy soil. Results showed that periphyton colonizing on paddy soil greatly reduced P content in paddy floodwater but increased P bioavailability of paddy soil. Specifically, all the contents of water-soluble P (WSP), readily desorbable P (RDP), algal-available P (AAP), and NaHCO₃-extractable P (Olsen-P) in paddy soil increased to an extent compared to the control (without periphyton) after fertilization. In particular, Olsen-P was the most increased P species, up to 216 mg kg⁻¹ after fertilization, accounting for nearly 60 % of total phosphorus (TP) in soil. The paddy periphyton captured P up to 1.4 mg g⁻¹ with Ca-P as the dominant P fraction and can be a potential crop fertilizer. These findings indicated that the presence of periphyton in paddy field benefited in improving P bioavailability for crops. This study provides valuable insights into the roles of periphyton in P bioavailability and migration in a paddy ecosystem and technical support for P regulation.

In the present study, the toxic effects of 1-octyl-3-methylimidazolium chloride ([Omim]Cl) and 1-octyl-3-methylimidazolium tetrafluoroborate ([Omim]BF₄) on the zebrafish livers were studied at 0, 5, 10, 20, and 40 mg L⁻¹ on the 7th and 14th days. In addition, the concentrations of [Omim]Cl and [Omim]BF₄ in the test water, the acute toxicity of the two ionic liquids (ILs), and the influence of anions on the toxicity of the ILs were evaluated. The acute toxicity test results showed 50 % lethal concentration (LC₅₀) values of 152.3 ± 12.1 mg L⁻¹ for [Omim]Cl and 144.0 ± 11.4 mg L⁻¹ for [Omim]BF₄. At the lowest concentration investigated (5 mg L⁻¹), [Omim]Cl and [Omim]BF₄ did not significantly affect zebrafish during the exposure period. However, the toxic effects of these substances were enhanced as dosing concentrations and exposure times were increased. Levels of reactive oxygen species (ROS) were significantly enhanced on the 7th day after 20 mg L⁻¹ and on the 14th day after 10 mg L⁻¹ of either substance was applied, resulting in oxidative damage, such as lipid peroxidation and DNA damage. The experimental results also indicated little effect of the anions on the toxicity of ILs and consistent toxic effects of [Omim]Cl and [Omim]BF₄. Graphical Abstract The graphical abstract for the present study after exposure to [Omim]Cl and [Omim]BF₄. The letter R represents the anions Cl⁻ and BF₄ ⁻

Emerging contaminants including pharmaceuticals are a class of compounds that are causing great concern due to several environmental problems. Conventional water and wastewater treatments do not achieve high removal efficiencies for many of these drugs. Therefore, the present work investigated the removal of ibuprofen (IBP) by heterogeneous photocatalysis using TiO₂ irradiated with artificial UV light or solar radiation. The treated solutions were tested against Daphnia similis and Raphidocelis subcapitata, which are species commonly used as bioindicators of environmental conditions. The results indicated that IBP removal reached 92 % after 1 h of treatment using artificial UV and 1000 mg L⁻¹ of TiO₂, which was the optimum catalyst concentration in the range studied (20–1000 mg L⁻¹). TOC removal reached up to 78 % after 60 min of treatment using TiO₂/artificial UV. Ecotoxicological bioassays indicated that the treated solutions had acute effects, with 30 % immobilization of D. similis and 40 % growth inhibition of R. subcapitata.

The present study was done to elucidate the effects of vanadium (V) on photosynthetic pigments, membrane damage, antioxidant enzymes, protein, and deoxyribonucleic acid (DNA) integrity in the following chickpea genotypes: C-44 (tolerant) and Balkasar (sensitive). Changes in these parameters were strikingly dependent on levels of V, at 60 and 120 mg V L⁻¹ induced DNA damage in Balkasar only, while photosynthetic pigments and protein were decreased from 15 to 120 mg V L⁻¹ and membrane was also damaged. It was shown that photosynthetic pigments and protein production declined from 15 to 120 mg V L⁻¹ and the membrane was also damaged, while DNA damage was not observed at any level of V stress in C-44. Moreover, the antioxidant enzyme activities such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were increased in both genotypes of chickpea against V stress; however, more activities were observed in C-44 than Balkasar. The results suggest that DNA damage in sensitive genotypes can be triggered due to exposure of higher vanadium.

Large amounts of sediment are dredged globally every year. This sediment is often contaminated with low concentrations of metals, polycyclic aromatic hydrocarbons, pesticides and other organic pollutants. Some of this sediment is disposed of on land, creating a need for risk assessment of the sediment disposal method, to minimize the degradation of environmental quality and prevent risks to human health. Evaluating the available fractions of certain polycyclic aromatic hydrocarbons is very important, as in the presence of various organisms, they are believed to be easily subject to the processes of bioaccumulation, biosorption and transformation. In order to determine the applicability of applying these methods for the evaluation of pollutant bioavailability in sediments, the desorption kinetics from the sediment of various polycyclic aromatic hydrocarbons in the presence of Tenax and XAD4 were examined over the course of 216 h. Changes in the PAH concentrations in dredged sediments using five different seed plants during a short time of period (10 days) were also followed. Using chemical extraction techniques with Tenax and XAD4, a time of around 24 h is enough to achieve equilibrium for all four PAHs. Results showed good agreement between the seed accumulation and PAH extraction methods with both agents. If we compare the two extraction techniques, XAD4 gave better results for phenanthrene, pyrene and benzo(a)pyrene, and Tenax gave better results for chrysene.

The aim of the study is to evaluate the acute biochemical and histological changes in rat kidneys after treatment with grayanotoxin (GTX) of rhododendron honey (RH). A total of 60 Sprague–Dawley female rats were divided into five groups of 12 rats each, one being a control group (group 1) and group 2 was treated with 0.015 mg/kg/bw of GTX standard preparation via intraperitoneal injection. Groups 3, 4, and 5 were given RH at doses of 0.1, 0.5, and 2.5 g/kg/bw, respectively, via oral gavage. Compared to the control group, significant increases were observed in glucose, blood urea nitrogen (BUN), and creatinine levels of the GTX-injected groups after 1 h. However, in low dose RH group, such an increase was not observed and had a normal appearance histologically. Therefore, low dose (1 g/kg/bw) of RH produces no acute adverse effects on renal functions of rats.

Much attention had been paid to reducing external loading of nutrients to improve water quality, while internal loading from sediment, which has been largely neglected, is also an important source for water eutrophication. The internal load in deep lakes or reservoirs is not easy to be detected and be quantified. In this study, three different methods (mass balance method, Fick’s law, and regression equation) were combined to calculate the gross or/and net P release from sediment using limited data. Our results indicated that (1) the methods of mass balance and regression equation give similar results of sediment P release rate, with values of 0.889 and 0.902 mg m² d⁻¹, respectively, while the result of Fick’s law was much lower (0.400 mg m² d⁻¹); (2) Hot periods of sediment releasing were suggested to occur from March to April and from August to September, which correspond to periods of high risks of algae blooms. The remaining months of the year were shown as net nutrient retention; (3) for the whole region, Baihedam and Chaohekuqu were identified as zones with a higher possibility to release P from sediment. (4) P loading to the Miyun Reservoir was greater in the inflow than in the outflow, suggesting a portion of the inflow P load was retained in the water or sediment; hence, release of sediment P may continue to be a major source of phosphorus in the future.

The distribution and speciation of several heavy metals, i.e., As, Cd, Cr, Cu, Hg, Pb, and Zn, in surface sediments from the karst aquatic environment of the Lijiang River, Southwest China, were studied comparatively. The mean contents of Cd, Cu, Hg, Pb, and Zn were 1.72, 38.07, 0.18, 51.54, and 142.16 mg/kg, respectively, which were about 1.5–6 times higher than their corresponding regional sediment background values. Metal speciation obtained by the optimized BCR protocol highlighted the bioavailable threats of Cd, Cu, and Zn, which were highly associated with the exchangeable fraction (the labile phase). Hierarchical cluster analysis indicated that in sediments, As and Cr were mainly derived from natural and industrial sources, whereas fertilizer application might lead to the elevated level of Cd. Besides, Cu, Hg, Pb, and Zn were related to traffic activities. The effects-based sediment quality guidelines (SQGs) showed that Hg, Pb, and Zn could pose occasional adverse effects on sediment-dwelling organisms. However, based on the potential ecological risk assessment (PER) and risk assessment code (RAC), Cd was the most outstanding pollutant and posed the highest ecological hazard and bioavailable risk among the selected metals. Moreover, the metal partitioning between water and sediments was quantified through the calculation of the pseudo-partitioning coefficient (K P), and result implied that the sediments in this karst aquatic environment cannot be used as stable repositories for the metal pollutants.