The aim of the present study was to evaluate the efficiency of removal of microcystin-LR from drinking water using a three-stage bench-scale treatment comprising Fenton oxidation/coagulation/flocculation/sedimentation, filtration through a sand column (15 cm bed), and adsorption onto a granular activated carbon (GAC) column with 15-cm (GAC1) or 20-cm bed (GAC2). Optimal first-stage conditions were determined to be FeSO₄∙7H₂O 0.054 mM, H₂O₂ 0.162 mM, coagulation pH 8.4, sedimentation time 15 min, and flow rate 2 L h⁻¹. Under these conditions, water turbidity was reduced from 5.8 to 3.0 uT, apparent color from 115 to 81 uH, and the concentration of microcystin-LR from 18.52 to 9.59 μg L⁻¹. Column GAC2 was more efficient than GAC1, as shown by the higher adsorption capacity (4.15 μg g⁻¹) and lower carbon usage rate (1.70 g L⁻¹). Microcystin breakthrough occurred after 2 h of operation with GAC1 column and after 6 h with GAC2 column, and the greater efficiency of the latter column was confirmed by the high qe (4.15 μg g⁻¹) and low CUR (1.70 g L⁻¹) values attained. The results demonstrate that adsorption on a GAC column plays an essential role in reducing the concentration of microcystin-LR to levels compatible with current legislation. By-products of the Fenton oxidation of microcystin-LR were analyzed by mass spectrometry, and the ADDA amino acid present in the analyte was identified from its characteristic fragment at m/z 135. It is concluded that the combination of Fenton oxidation and adsorption on a GAC column represents a viable option for purifying eutrophic water containing high concentrations of microcystin-LR.

Saline melt water from road salt applications that has percolated into a fine sandy soil in winter is rinsed out of the soil by infiltrating rainwater in the following warmer seasons. This sequence of saturated and unsaturated flow processes associated with saline water transport in a fine sandy soil was studied by simulation and exploratory laboratory experiments. Experiments in soil columns of 300-μm sand revealed that two rinses of pure water, each of one pore volume, were sufficient to reduce the salt concentration by 99% of its original value in the soil column. Simulated time variations of salt concentration in the effluent from the column agreed with experimental results. Based on simulated and experimental results, a sandy soil must become saturated to experience pore water flow in order to efficiently rinse saline snowmelt water. Depending on the saturated hydraulic conductivity and the soil depth, days, weeks, or months of freshwater infiltration in summer are needed to rinse saline melt water from an unsaturated sandy soil after road salt applications in winter. This explains findings of significant salt concentrations in surface and shallow groundwater during summer months, long after road salt application and infiltration has ceased.

In tropical countries like Colombia, a large variety of available aquatic plants have yet to be investigated for phytodepuration processes. The aim of this study was to assess the effect of Cyper-us ligularis and Echinocloa colona¸ two local plants of Colombian Caribbean region, on removal of dissolved organic matter (COD) and nutrients (N-NH₄⁺, N-NO₃⁻ and P-PO₄⁻³) from domestic wastewater. Experiments were conducted in replicate pilot-scale Horizontal Subsurface Flow Constructed Wetlands (HSSF CWs) (0.66 m²). Four wetland treatment units were installed in parallel. Two were planted with C. ligularis and the other two remained with E. colona. The experimental system was connected to a 0.76-m³ primary sedimentation tank that fed experimental wetland treatment units. Wetlands were filled with granite gravel (~8 mm and 0.4 of porosity). During a period of 4 months, each treatment unit received a continuous loading at the rate of 42 L day⁻¹ and a hydraulic retention time of 2.3 days approximately. Wastewater samples from influent and effluents were collected three times each week in order to monitor temporal/spatial changes in removals efficiencies of COD, N-NH₄⁺, N-NO₃⁻, and P-PO₄⁻³. Results showed that removals of COD, N-NH₄⁺, and N-NO₃⁻ were not significantly different between treatments (p > 0.05). Nevertheless, P-PO₄⁻³ removal for E. colona was significantly higher than C. ligularis (p < 0.05), showing that this plant can assimilate important amounts of P. Further investigations must be conducted to evaluate the potential of native aquatic macrophytes for phytodepuration.

To meet demand for processes that minimize the environmental impact generated by waste, efficient systems that degrade such substances and use them as an alternative source for renewable energy generation are increasingly becoming needed. Increased food production to meet the needs of the world’s increasing population has encouraged the use of agrochemicals in order to ensure productivity in crops. However, excessive use of pesticides has caused contamination of natural systems and, therefore, of living beings. In this context, this work presents an alternative plan for an integrated system that simultaneously remediates contaminated environments and generates electricity using a Cu/CuO electrode as a photocatalyst. The materials were prepared from reagents and accessible metals, which reduced costs and contributed to a clean process, without using organic additives. The results showed that the generation of current in an area 6.9 cm² was 193.37 μA for potassium hydrogen phthalate degradation. The Aminol 806® and Connect® pesticides were degraded by 54.46 and 21.02%, respectively, after 90 min in the system, under ultraviolet radiation. The results showed that, at pH 2.0, the generation of current was 2493.2 mA (36.165 mA m⁻²) for Aminol 806® and 7.894 mA (0.114 mA m⁻²) for Connect®. The degradation of organic contaminants and simultaneous power generation of energy in the integrated system provides a self-sustaining form of environmental remediation and energy recovery, and its use is possible on a large scale.

The release of arsenic (As) from sediments poses a risk to human health especially at high pH levels. Despite this, the distribution and kinetic response of mobile As remains unclear under varying pH conditions. In this study, a microcosm incubation experiment was performed, using sediment cores in combination with dialysis (Peeper) and thin film diffusive gradients (DGT), to investigate the distributions of mobile As (soluble As in pore water and DGT-labile As) at high vertical resolutions (2–4 mm). Results show that the concentrations of soluble As present in the water column increased 1.5-fold with an increase in pH from 5.4 to 11.2. Both soluble As in pore water and DGT-labile As exhibited stable low-level distributions in the uppermost layer beneath the sediment-water interface, followed by increasing concentration distribution with decreasing layers to middle depths. The mean concentrations of mobile As species increased with increased water pH in both sediment profiles and with upward diffusion gradients, showing a 0.2-fold increase of soluble As in the top 20-mm layer and a 0.6-fold increase in deeper 20–52-mm layers, while DGT-labile As showed a 1.0- and 1.1-fold increase in these two layers, respectively. Modeling of DGT-induced flux in sediments (DIFS) showed that the desorption rate constant increased more rapidly than the absorption rate constant, resulting in the increased availability of solid As pools, therefore resupplying the soluble As in pore water from sediments.

The intensive use of pesticides has increased exponentially in Brazil and worldwide due to the need to meet the food demands of a growing population. If the management/monitoring of the use of pesticides is adequately performed, it would not compromise the expected benefits or have negative effects on the environment as a whole. In order to examine the information available on herbicide use in Brazil and worldwide, this paper presents a review of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and its chemical properties, action on target organisms, environmental fate, and toxicity to non-target organisms. This herbicide is a synthetic auxin used to control broad-leaved weeds, and the action in target organisms is well known. Although 2,4-D has been widely used worldwide, many studies have shown that this herbicide induces alterations in non-target organisms. Therefore, ecotoxicology studies are important to assess the risk the herbicides can be to different ecosystems. Thus, it is advised to use this herbicide and other pesticides with caution.

Herein, we report the synthesis of carbon spheres (CS) using a relatively low-temperature hydrothermal technique using lactose as precursor pre-treated with HCl. The successful synthesis, spherical morphology, porous morphology, and monodispersed nature of CS were confirmed via scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Isoelectric point (IEP) was determined as 3.8, and at neutral conditions the prepared carbon particles are negatively charged at − 43 ± 2.50 mV. Owing to their spherical morphology, almost uniform distribution and negatively charged surface at neutral conditions, the prepared CS were used as adsorbent for the removal of methylene blue (MB) and Geimsa stain (GS) from aqueous environments at pH 7. It was shown that CS has 97% adsorption capability for GS, whereas for methylene MB, the maximum adsorption capacity was 67% for 0.1-g CS from 50-ppm dye solutions in DI water. The adsorption studies revealed that the Langmuir and modified Fruendlich (MFE) adsorption models resulted in considerably high linear correlation coefficient (r ²) values and the efficient adsorption of positively charged species on CS can be represented better with the MFE model. Graphical Abstract Carbon spheres from D-lactose for environmental application

To investigate the differential contribution of extracellular polymeric substances (EPS) to polycyclic aromatic hydrocarbon (PAH) degradation by fungi and bacteria, the PAH-degrading ability and characteristics of EPS from the bacterium Mycobacterium gilvum SN12 and the fungus Mucor mucedo were compared. The fungus degraded 11% more pyrene and 21% more benzo[a]pyrene (B[a]P) than the bacterium. The biodegradation of pyrene and B[a]P increased after EPS were introduced into the PAH degradation solution, and 5.0% more pyrene and 4.5% more B[a]P were achieved for the added EPS from the fungal compared with the bacterial isolate. The comparison of two EPS indicated that the amount of protein and carbohydrate in EPS from the fungus was greater than that from the bacterium and was especially enriched for tryptophan, which is positively related to the increase of PAH biodegradation by fungal EPS. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) further revealed that higher molecular weight (HMW) of proteins over 200 kDa only existed in EPS from the fungus, and the polymorphism of proteins in EPS from the fungus was more abundant than that from the bacterium. The HMW proteins with stronger hydrophobicity in the fungal EPS also enabled the fungus to absorb more PAH than the bacterium. The results demonstrated that the pronounced differences in the characteristics of EPS from the fungal and the bacterial sources are responsible for the differential effects on PAH biodegradation.

Two species of Pb-adapted shrubs, Alyssum montanum and Daphne jasminea, were evaluated in vitro for their tolerance to elevated concentrations of cadmium. Shoot cultures were treated with 0.5, 2.5, and 5.0 μM CdCl₂ for 16 weeks and analyzed for their organogenic response, biomass accretion, pigment content, and macronutrient status. Cadmium accumulation and its root-to-shoot translocation were also determined. In both species, rooted microplantlets, suitable for acclimatization, were obtained in the presence of Cd applied as selection agent. In A. montanum, low and moderate dose of Cd stimulated multiplication, rooting, and biomass production. Growth tolerance index (GTI) in Cd-treated shoots ranged from 120 to 215%, while in the roots 51–202%. In turn, in Cd-treated D. jasminea proliferation and rooting were inhibited, and GTI for shoots decreased with increasing doses of Cd. However, roots exposed to Cd had higher biomass accretion. Both species accumulated Cd in developed organs, and its content increased with increasing CdCl₂ dose. Interestingly, D. jasminea accumulated higher amounts of Cd in the roots than A. montanum and immobilized this metal in the root system. On the contrary, A. montanum translocated some part of accumulated Cd to the shoots, but with low efficiency. In the presence of Cd, A. montanum maintained macronutrient homeostasis and synthesized higher amounts of phytosynthetic pigments in the shoots. D. jasminea accumulated root biomass, immobilized Cd, and restricted its translocation at the expense of nutrient balance. Considering remediation potential, A. montanum could be exploited in phytoextraction, while D. jasminea in phytostabilization of polluted substrate.

Nanoscale zero valent iron (NZVI) was synthesized by the reduction of natural limonite under hydrogen conditions. The adsorption performance of the as-prepared NZVI on phosphate was evaluated through batch and column experiments. The removal of phosphate (PO₄³⁻) significantly decreased with an increase of pH from 2.0 to 11, whereas a remarkable increase of PO₄³⁻ removal was observed in the presence of SO₄²⁻ and S₂O₃²⁻. In addition, Cl⁻ and NO₃⁻ also improved phosphate removal at concentrations of more than 0.2 mmol/L. Kinetic studies indicated that the removal process of PO₄³⁻ on NZVI can be easily followed with the pseudo-second-order kinetic model. The removal of phosphate from the oxic system was significantly higher than that of the anoxic system, which was attributed to the formation of the secondary phase by the further oxidization of Fe²⁺. The adsorption capacity of the as-prepared NZVI of the oxic system was 16 mg/g, and the pH was 6.3. The column experiments further demonstrated that the as-prepared NZVI presented a high removal capacity for PO₄³⁻-P. These findings indicated that the as-prepared NZVI displayed an excellent ability to remove phosphate from aqueous solutions.