The aim of the present experimental study was to perform a technical-economic evaluation of a combined treatment system, consisting of coagulation-flocculation or rapid sand filtration as pre-treatment followed by column adsorption, for reducing the arsenic concentration from approximately 1 mg/L to below the limit set for groundwater remediation and drinking water, i.e., 0.01 mg/L, according to the legislation in force. A wide number of operating conditions were experimentally evaluated in the different tests. In the coagulation-flocculation study, it was initially investigated if the iron contained in a mining drainage co-mixed with the groundwater would be able to achieve a better As content reduction by adsorption/precipitation, thus avoiding fresh coagulant addition. Then, different polyelectrolyte dosages were tested varying the mixing ratio. None of the tested conditions allowed to improve the arsenic removal so significantly to warrant the consequent incremental costs. Therefore, the optimal condition was considered any mixing with a different liquid stream and any polyelectrolyte dosage. The iron content naturally present in the groundwater and contact with air was capable alone of reducing As concentration of about 80%. Sand filtration reached approximately the same removal efficiency (about 80%) at the lower surface loading rate among the values tested. Between coagulation and sand filtration, in terms of costs, the latter showed to be more convenient than coagulation-flocculation, at the same removal efficiency: therefore, it was considered the optimal pre-treatment. The following adsorption column plant was capable of further reducing As concentration up to the required value of 0.01 mg/L. Among the two iron-based commercial adsorbents applied in the adsorption column tests, the hybrid media consisting of an exchange resin with iron oxides showed to be preferable under the selected operating conditions: it offered higher adsorption capacity at breakthrough and, after exhaustion, could be regenerated for a number of cycles. The influent pH showed to have a great influence on the duration of the adsorbent media, and values around neutrality were considered preferable. The estimated cost of the full treatment was computed to be about 0.50 €/m³ of purified water. Therefore, the capacity of achieving the required remediation goal, the limited cost, and simplicity of operation make the proposed combined treatment being potentially suitable for real application.

In this study, we investigated the Sb(V) adsorption on ferrihydrite (Fh) at different pH values, in the presence and absence of common competing anions in soil such as phosphate (P(V)) and arsenate (As(V)). Batch adsorption experiments, carried out at pH 4.5, 6.0, and 7.0, showed a greater affinity of Fh towards P(V) and As(V) with respect to Sb(V), especially at higher pH values, while the opposite was true at acidic pH. The capacity of Fh to accumulate greater amounts of phosphate and arsenate in the 6.0–7.0 pH range was mainly linked to the different acid properties of P(V), As(V), and Sb(V) oxyanions. The Sb(V) adsorption on Fh was highly pH-dependent and followed the following order: pH 4.5 (0.957 mmol·g⁻¹ Fh) > pH 6.0 (0.701 mmol·g⁻¹ Fh) > pH 7.0 (0.583 mmol·g⁻¹ Fh). Desorption of antimonate from Sb(V)-saturated Fh, treated with citric and malic acid solutions, was ~equal to 55, 68, and 76% of that sorbed at pH 4.5, 6.0, and 7.0, respectively, while phosphate, arsenate, and sulfate were able to release significantly lower Sb(V) amounts. The FT-IR spectra revealed substantial absorbance shifts related to the surface hydroxyl groups of Fh, which were attributed to the formation of Fe-O-Sb(V) bonds and supported the formation of inner-sphere bonding between Sb(V) and Fh.

Due to its unique properties, the potential application of graphene oxide (GO) in treating environmental pollution has attracted wide attention. In this study, the UV-light catalyzed photoreduction of Cr(VI) by GO was assessed as well as its adsorption toward Cr(VI), and FTIR and XPS techniques were adopted to reveal the underlying mechanisms. The surfaces of GO were negatively charged across the pH range examined. Therefore, the increase in pH resulted in the decrease in Cr(VI) adsorption due to the enhancement in repulsion between Cr(VI) and GO surfaces. The kinetic studies showed that the Cr(VI) adsorption proceeded quickly during the 0–24 h stage, followed by a slow process until to the end of reaction (96 h). Additionally, the kinetic data could be properly described with the pseudo-first-order rate equation (R² = 0.9754). With the UV-light irradiation, Cr(VI) reduction in the presence of 0.5 g L⁻¹ GO was observed with the concentration of Cr(VI) decreased from 0.1 mM to zero within 12 h at pH 3.0, while which would be suppressed as the pH increased. The addition of EDTA could enhance the photocatalytic Cr(VI) reduction due to the consumption of the photogenerated holes (h⁺), leaving more Cr(III) species present in solution. The generation of h⁺ was further confirmed by the complete photodegradation of 4-CP during 48 h. Moreover, the changes in FTIR and XPS spectrum of GO before and after reaction indicated the oxidization of epoxy and hydroxyl groups by holes or reduction by electrons was involved in the photoreaction. The photoreduction of Cr(VI) could was also observed in an oxisol with the existence of GO, with the disappearance of 0.1 mM of aqueous Cr(VI) at pH 4.40 after 36 h. The results above could enhance our understanding on the essence of photoreactivity of GO, and indicated that the potential release of GO into soil environments would be helpful to eliminate the risk posed by Cr(VI) through the UV-light irradiated photocatalytic reduction.

Chromium (Cr(VI)) causes serious impacts on the environment and human. In this study, the commercial activated carbon-loaded silver nanoparticle (AgNPs-AC) was used as a new adsorbent to remove Cr(VI) from the aqueous solution. Batch adsorption experiments were conducted to evaluate the effects of pH, the initial concentration of Cr(VI), contact time, and dose of AgNPs-AC upon removal of Cr(VI) from the aqueous solution. The results showed that at pH of 4, the contact time of 150 min, 40 mg/L of initial Cr(VI), and dosage of 20 mg AgNPs-AC/25 mL were the most suitable condition for absorption of Cr(VI) onto AgNPs-AC from the aqueous solution. The maximum adsorption capacity achieved at abovementioned conditions was 27.70 mg/g. Meanwhile, the adsorption capacity of commercial activated carbon from a coconut shell obtained only 7.61 mg/g in the case where the initial Cr(VI) concentration is 10 mg/L and the contact time is 60 min. The adsorption kinetic data were found to fit best to the pseudo-second-order model with a high correlation coefficient (R² = 0.9597). The adsorption process was controlled by chemisorption due to the appearance of new chemical species on the adsorbent surface. The positively charged functional groups rapidly reduced Cr(VI) to Cr(III), and Cr(III) was subsequently adsorbed by the carboxyl group on the adsorbent’s surface. From this study, it can be concluded that AgNPs-AC is a fully promising, low-cost adsorbent in the removal of Cr(VI) from the aqueous solution.

In this study, organoclay and clay-biopolymer composites were evaluated for the adsorption process of an anionic red dye, Allura Red (AR), in aqueous solution. For this purpose, the cationic exchange capacity (CEC) of a natural bentonite was calculated, and it was modified with the cationic surfactant hexadecyltrimethylammonium bromide (OB). Furthermore, a commercial montmorillonite modified with dimethyldialkyl ammonium (OM) was also employed. These organo-modified clays were used for the synthesis of two series of composites, with alginate as the polymer matrix, and were identified as OBC and OMC, respectively; composites were obtained in the wet (W) and dry (D) states. The adsorbent materials were characterized by means of infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and dispersive energy spectroscopy (EDS). Afterwards, kinetics and isotherms studies were performed in batch systems, with dye solutions of different concentrations, without pH adjustment. Some parameters were evaluated, such as the variation of the pH value of the solution and the concentration of the dye with the organoclays and composites. Chemisorption was considered as the main mechanism that follows the adsorption processes of AR. Results demonstrated that the pseudo-second order was the kinetics model that best described the adsorption process of the AR dye, with both, hydrated and dry composites. Finally, the Freundlich and the Langmuir–Freundlich isotherms were the best models that described the hydrated and dry composites behavior, respectively.

Particle-induced x-ray emission (PIXE) spectroscopy has been used to characterize soil samples from two relatively old gold mine sites (Iperindo and Itagunmodi) in the Ilesha schist belt of Southwestern Nigeria. This is with a view to identifying the indicator or pathfinder elements of gold for fingerprinting and toxicity potential assessment purposes. Average elemental concentrations of 19 major, minor, and trace elements were determined, and the geochemical data of Mn, Ni, Cu, Zn, Ag, As, Pb, and Au together with multivariate factor and cluster statistical analyses allowed to identify As and Ag as the pathfinder elements of gold. The high concentration of the determined pathfinder elements (As and Ag) as well as other toxic metals (Pb and Cu) implies a relatively high metal contamination risk to the miners and the ecosystem. The major hazard is represented by the abandoned mining wastes, pits, and ponds, already serving as fish ponds.

The present systematic experiment was conducted to estimate the impact of behavioral and pathological indices on freshwater fish Channa punctatus exposed to sub-lethal concentration (5 ppm) of an organophosphorus insecticide chlorpyrifos (CPF). Fish were segregated into four experimental groups (G1, control; G2, 10 days; G3, 20 days; and G4, 30 days exposure), each group comprises 15 fish in triplicate. The behavioral and histological changes were assessed in each group. Severe behavioral changes were observed in the 30 days, moderate changes in the 20 days, and mild changes in the 10 days exposure groups respectively when compared with the control group. The pathologic lesions such as inter lamellae space, necrotic lamellae, fused lamellae, and lifting of lamellae epithelium in gills; vacuolation, blood conjunctions, and necrotic hepatocytes in the liver; and lamina propria, fusion of villi, and flattened villi in the intestine were observed. These structural alterations of the gills, liver, and intestine could affect respiration, osmotic and ionic regulation; absorption, storage and secretion; digestion; and absorption of nutrients respectively, which in turn could adversely affect the growth and survival of freshwater fish Channa punctatus. This study serves as a biomonitoring tool for the effects of organophosphorus insecticide CPF on the aquatic biota.

Polycyclic aromatic hydrocarbons (PAHs) are toxic organic pollutants and omnipresent in the aquatic and terrestrial ecosystems. A high-efficient pyrene-degrading strain CP13 was isolated from activated sludge and identified as Mycobacterium gilvum based on the analysis of 16S rRNA gene sequence. More than 95% of pyrene (50 mg L⁻¹) was removed by CP13 within 7 days under the alkaline condition. Pyrene metabolites, including 4-phenanthrenecarboxylic acid, 4-phenanthrenol, 1-naphthol, and phthalic acid, were detected and characterized by GC-MS. Results suggested that pyrene was initially attacked at positions C-4 and C-5, then followed by ortho cleavage, and further degraded following the phthalate metabolic pathway. Analysis of pyrene-induced proteins showed that the extradiol dioxygenase, a key enzyme involved in pyrene degradation, was highly up-regulated in pH 9 incubation condition, which illustrated the high efficiency of CP13 under alkaline environment. The present study demonstrated that the isolated bacterial strain CP13 is a good candidate for bioremediation of alkaline PAH-contaminated sites.

The aim of this study was to determine the distribution of cadmium (Cd) and lead (Pb) in muscle and liver tissue of Haemulopsis axillaris and Diapterus peruvianus from the Eastern Pacific in Mexico and to assess the health risk to consumers. Fish were collected as bycatch on the continental shelf between the coasts of Sinaloa and Guerrero (Eastern Pacific). Cd and Pb were quantified in muscle and liver tissue using graphite-furnace atomic absorption spectrophotometry (GF-AAS).Concentration of Cd was greater in muscle tissue than in liver tissue; with Pb, however, the opposite pattern was found. The highest concentration of Cd (0.177 μg g⁻¹) was found in muscle tissue of H. axillaris from Sinaloa. For Pb, the highest level (0.692 μg g⁻¹) was found in the liver tissue of H. axillaris also from Sinaloa. Levels of Cd and Pb in muscle tissue were both below Mexican Guidelines (0.5, 1.0 μg g⁻¹ wet weight for Cd and Pb respectively) and International Guidelines. The hazard index (HI) for both metals in the edible portion of studied considering metal levels in the edible portion and the rate of fish consumption by the Mexican population (in adults and children) was less than 1 (HI < 1), values which do not represent a health risk to consumers.