Thermally robust hydroxylated biochar (HBC) and sulphonated biochar (SBC) were synthesised from paper and pulp sludge (PPS) and used for the adsorption of Zn²⁺ from synthetic wastewater through batch experiments. FTIR analyses proved successful incorporation of the hydroxyl and sulphonic functional groups in HBC and SBC, respectively. The effects of initial solution pH, initial Zn²⁺ concentration, solution temperature and equilibrium contact time were investigated. The removal efficiency of Zn²⁺ increased with increase in both solution temperature and initial Zn²⁺ concentration. Adsorption of Zn²⁺ was greatest at pH 3. HBC and SBC removed 38–99% and 68–90% of Zn²⁺ from solution, respectively. Zn²⁺ adsorption on SBC followed both Langmuir (R ² = 0.994) and Freundlich isotherm models (R ² = 0.999), while adsorption on HBC followed the Freundlich model (R ² = 0.989). Zn²⁺ adsorption on both biosorbents followed pseudo-second-order kinetics (R ² = 0.994–0.999). The increase in enthalpy of adsorption indicated the adsorption process was endothermic and a decrease in Gibbs free energy signified the spontaneity of adsorption. Positive entropy change values imply that the adsorbed Zn²⁺ ions are randomly distributed over the adsorbent surface. The research demonstrated that although their adsorption mechanisms had salient differences, HBC and SBC can effectively remove Zn²⁺ from wastewater. Development of HBC and SBC from PPS provides potential low-cost biosorbents for water and wastewater, while simultaneously minimising the environmental and public health risks associated with current disposal practices of PPS.

Pig slurry contains sufficient amount of nitrogen, phosphorus, and potassium for plant growth. If appropriately administered, this could substitute significant amounts of fertilizer. However, excessive fertilization with slurry causes environmental problems. To reduce environmental issues, solid-liquid separation or anaerobic digestion is needed to obtain a better distribution of nutrients. Solid-liquid separation produces a solid fraction rich in phosphorus and a liquid fraction containing ammonia, potassium, and high water content. Therefore, further concentration of ammonia is desired for any practical use. In this study, ammonia membrane stripping was carried out using polypropylene membranes and the impact of temperature, flow velocities, and liquid fraction pretreatment on the membrane contactor performance was tested. Sieved liquid effluents from a decanter centrifuge, a screw press, an AL-2 system (flocculation and filtration), and an anaerobic digester were tested. Since the properties of these liquid effluents vary, they might affect ammonia recovery. Thus, it is essential to investigate which effluent is most suitable as a feed for a membrane contactor and what is the cost of preprocessing. The mean ammonia mass transfer coefficient at 30 °C was found to be equal to 17 ± 2 × 10⁻³ m h⁻¹. At 50 °C, it was found to be equal to 29 ± 2 × 10⁻³ m h⁻¹ for all the tested effluents. This means that sieving after slurry separation or anaerobic digestion alleviates the influence the solid-liquid separation has on ammonia membrane stripping. However, the cost evaluation showed that solid-liquid separation using a decanter centrifuge followed by sieve draining is the cheapest of the methods investigated.

Agricultural practices and industrial growth have contaminated the environment with heavy metals and many other harmful compounds. Arsenic (As) has been highlighted as a major heavy metal affecting growth and development of plants as well as causing severe human health hazards through food chain contamination. Most studies of heavy metal impacts address only one of these aspects, overlooking the effect of pollution on the plant as a whole. In this work, our objective was to determine the effect of arsenic stress on physiological, biochemical, and morphological characteristics in seedlings of two cultivars of maize with different arsenic tolerance. This study investigated the effects of varying levels of arsenic (As) stress on growth, enzymatic characteristics, and cell ultrastructure in seedlings of As-sensitive and As-tolerant maize cultivars (Shiyu No. 9 and Dongdan90, respectively) grown in hydroponic culture. Compared to Shiyu No. 9 at the same As concentration, Dongdan90 maintained higher values of biomass, shoot length, root length, and activity of superoxide dismutase, peroxidases, and catalase, but had lower malondialdehyde content, As accumulation, and non-protein thiol. High As concentrations inhibited the growth of both cultivars, while lower concentrations stimulated it. The As-tolerant cultivar also maintained the structural integrity of cells and tissues more efficiently under As stress. These findings demonstrate a link between the physiological and physical impacts of heavy metals on crop plants that paves the way for improved interventions to deal with heavy metal pollution.

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.

Oil spills might lead to severe environmental impacts to the affected fauna, disrupting local food webs, and causing mass mortality in many species. However, little is known about long-term impacts of oil spills, or even if such impacts can be detectable after several generations. In this study, we investigate the genetic variability of three freshwater species—Mimagoniates microlepis (Characiformes: Characidae), Scleromystax barbatus (Siluriformes: Callichthyidae), and Phalloceros harpagos (Cyprinodontiformes: Poeciliidae)—in rivers that were affected by a large oil spill in the state of Paraná, southern Brazil, on February of 2001. Samples were obtained from nine different locations, such that rivers that were directly affected by the oil spill could be compared with similar rivers in the same region that were unaffected. A fragment of the cytochrome C oxidase subunit I mitochondrial gene was sequenced from each specimen, and the level of genetic variability was assessed. Based on estimates of haplotype and nucleotide diversity, no impact of the oil spill could be detected in impacted rivers. These results suggest that fish populations in the region showed resilience to the pollutant, such that immigration from other locations was able to reestablish levels of genetic variability comparable to those of unimpacted rivers.

Hexavalent chromium is a type of toxic chemical, it may cause allergies, hereditary genetic defects and cancer in humans by inhalation, and it is also a persistent danger to the environment. However, chromium metal, trivalent chromium and tetravalent chromium have low toxicities. In this study, semiconductor materials (quartz fibre and TiO₂) were added to a hexavalent chromium solution and the removal efficiency of hexavalent chromium as a function of the γ-ray irradiation dose, as well as the catalytic mechanism, was investigated. It was observed that the reduction of hexavalent chromium by γ-ray irradiation was largely promoted in the presence of semiconductor materials; the semiconductor materials act as catalysts under the gamma-ray irradiation. The hexavalent chromium in the solution can be converted to an insoluble precipitate by gamma-ray irradiation. These results are highly beneficial to apply semiconductor materials as catalysts for the removal of contaminants by radiation.

The increase in demand for food due to the rapid population growth in recent years has raised the use of fertilizers, particularly phosphate salts. This fact has contributed to the excess amount of phosphorus species in aquatic systems. This is due to the leaching of these species present in the fertilizers applied to the soil to aquatic environments and may lead to eutrophication in these environments. Substances capable of interacting with the phosphate in the aquatic environment are promising for the reduction on the environmental impact. The humin, an insoluble fraction of humic material, has potential for phosphate retention, behaving like a chelating resin. Thus, the purpose of this research was to study the interaction between humin and phosphate. The equilibrium time between humin and phosphate was 15 min, where hydrogenionic potential (pH) 4.0 was the most effective in the interaction process. In this pH, the humin retained 33% of phosphate added. The complexing capacity of the humin-phosphate system was 11.53 mg g⁻¹. The adsorption studies indicated that the system follows a kinetic pseudo-second-order model. The Freundlich model was the most suitable to describe the phosphate adsorption process in humin. To evaluate the humin application in real systems, humin was added to the domestic wastewater. Sixteen percent of the total phosphate was adsorbed by the humin. Based on these results, humin has the potential to phosphate retention in domestic wastewater and could be used as a chelating resin minimizing environmental impact.

Mercury (Hg) dynamics was evaluated in contaminated sediments and overlying waters from Tagus estuary, in two sites with different Hg anthropogenic sources: Cala Norte (CNOR) and Barreiro (BRR). Environmental factors affecting methylmercury (MMHg) production and Hg and MMHg fluxes across sediment/water interface were reported. [THg] and [MMHg] in solids (0.31–125 μg g⁻¹ and 0.76–201 ng g⁻¹, respectively) showed high variability with higher values in BRR. Porewater [MMHg] (0.1–63 ng L⁻¹, 0.5–86% of THg) varied local and seasonally; higher contents were observed in the summer campaign, thus increasing sediment toxicity affecting the sediment/water Hg (and MMHg) fluxes. In CNOR and BRR sediments, Hg availability and organic carbon were the main factors controlling MMHg production. Noteworthy, an upward MMHg diffusive flux was observed in winter that was inverted in summer. Although MMHg production increases in warmer month, the MMHg concentrations in overlying water increase in a higher proportion compared to the levels in porewaters. This opposite trend could be explained by different extension of MMHg demethylation in the water column. The high concentrations of Hg and MMHg and their dynamics in sediments are of major concern since they can cause an exportation of Hg from the contaminated areas up to ca. 14,600 mg year⁻¹ and an MMHg deposition of up to ca. 6000 mg year⁻¹. The results suggest that sediments from contaminated areas of Tagus estuary should be considered as a primary source of Hg for the water column and a sink of MMHg to the sedimentary column.

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).

Heavy metals, chemical elements considered toxic at certain concentrations, can be considered potential threats to plants, animals, and biological resources of a particular ecosystem. Among them, mercury and aluminum, when involved in bioaccumulation processes, can cause damage to various organ systems of both animals and plants. In vegetables, heavy metals produce reactive oxygen species (ROS), which are involved in the occurrence of malformations and deficits in the growth of roodets and plumule of several species of plants, which justifies the study of natural antioxidant agents that may come to reverse or ameliorate the deleterious effects caused by these compounds. In this sense, this study aims to evaluate the cytoprotective effect of hydroethanolic extract of Stryphnodendron rotundifolium Mart., species popularly known as “barbatimão” against the heavy metals mercury and aluminum in vegetable model, because of its known antioxidant potential. To this end, there was the cytoprotection test in microbial and lettuce seeds (germination) in order to ascertain the potential of the said extract on the protection of roots and stem this. It was observed that the extract showed no allelopathic effect on lettuce seeds at a concentration of 32 μg/mL and in combination with HgCl₂ and AlCl₃, it enabled a higher growth in the roodets and stem Lactuta sativa L. These results demonstrated that the extract of Stryphnodendron rotundifolium can be an alternative to solve the problem with soil contamination by heavy metals, showing thus its promising potential cytoprotective in plant species.