This study was conducted to assess the proximate analysis (protein, carbohydrate, lipid, and moisture content) and concentration levels of metals (Zn, Cu, Cd, Pb, and Cr) in the muscles of selected shellfish (Portunus reticulatus, P. segnis, P. sanguinolentus, Scylla olivaceae, Penaeus monodon, and P. indicus) species. The concentration of metals showed significant difference (p > 0.05) among species. The detected concentrations of the analyzed heavy metals were below the daily intake and legal limits set by national and international standards. The THQs and CR index were calculated to evaluate the risk estimation of the metal contamination associated with the human health. The THQ values of all metals were below 1 in all species, indicated that there is no risk of adverse health effect, but the risk of elevated intakes of heavy metals adversely affecting food safety for the studied species. The CR index indicated that Cd and Pb caused the greatest cancer risk. The correlation and multivariate (principle component analysis) among metal concentration and nutritional quality were also evaluated. The carbohydrate and moisture showed the positive correlation (p > 0.05) with metals. The biochemical results of the present work clearly indicate that there was a significant difference in the muscles of shellfish. It was concluded that more effective controls should be focused on Cd and Pb to reduce pollution for quality and seafood safety concern.

The effects of elevated ozone (O₃) levels (80 ppb and 120 ppb) on photosynthetic efficiency and growth of canola plants were studied in open-top chambers. The chlorophyll a polyphasic fluorescence rise kinetics OJIP, stomatal conductance and Chlorophyll Content Index (CCI) were measured after 15 and 30 days of O₃ fumigation, as well as in control plants; biomass measurements were done only after 30 days with and without fumigation. Analysis of the OJIP kinetics by the JIP-test led to the calculation of several photosynthetic parameters and the total Performance Index (PIₜₒₜₐₗ). The decline of PIₜₒₜₐₗ under the 80 ppb O₃ treatment was due to a lower density of reaction centres (RC/ABS), while the notable decline under the 120 ppb treatment was found to be due both to a further decline of RC/ABS and to a pronounced lowering of the efficiency with which an electron can move from the reduced intersystem electron acceptors to the PSI end acceptors (δRₒ). Stomatal conductance was affected by both treatments. Biomass was found to be affected by O₃ fumigation (for 30 days), decreasing by 40% at 80 ppb and by more than 70% under 120 ppb. Our findings indicate that biomass decline is due both to the lowering of CCI and the lowering of photosynthetic efficiency parameters. They thus suggest that two simple, non-invasive and rapid methods, namely, the analysis of OJIP fluorescence transients and the measurement of CCI, can be used to screen the effect of elevated O₃ on biomass of canola plants.

Biogas reactors are now a common part of wastewater treatment systems. The quality of produced biogas is the result of many factors, mainly the input substrate and microbial composition of the bioreactor. The aim of this research was to evaluate the microbial community of the Modřice biogas reactor together with the possible changes in biogas composition. The key microbial groups and their content in anaerobic digester were identified by sequencing techniques. The most dominant group were sulphate-reducing (45%), followed by methanogenic (19%), acetate (6%) and hydrogen-producing (11%) microorganisms. The remaining microorganisms were identified only to their order (19%). Phylogenetic trees were constructed to show evolutionary relationships of detected microorganisms. The volume of methane in biogas content was 60%, which corresponds with literature data regarding sewage digesters. None of the detected impurities have crossed the safe limits and their volume remained stable during the measurement period. Despite sulphate-reducing bacteria being the dominant group, their produced hydrogen sulphide (H₂S) was detected only in a small quantity (2.43–7.46 ppm) and had no inhibitory effect on the methane production. The mechanism of inhibition by H₂S and the perspective of its biological removal were discussed. Application of phototrophic sulphur bacteria, especially Chlorobiaceae and Chromatiaceae family, and the creation of new photobioreactor systems can be a promising pathway for hydrogen sulphide treatment in biogas plants.

Two nonionic POEA surfactants (CAS No. 61791-26-2), TA15 and TH30, were tested to establish their acute pathological effects and lethal concentrations (LC₅₀) in Piaractus brachypomus. Both compounds are nonionic surfactants produced by the alkoxylation of ethylene oxide with tallow amine, and they are used in variety of industries such as textiles, paints, metal working, agriculture, and polish manufacture. Fish were exposed to six concentrations of TA15 (0.2–4.0 mg/L) or TH30 (8–140 mg/L) for 96 h. The LC₅₀ for TA15 was 2.08 mg/L and for TH30 47.32 mg/L. The main clinical signs observed in fish exposed to 4 mg/L of TA15 and 32 to 140 mg/L of TH30, were lethargy, loss of shoaling behavior, respiratory distress, changes in swimming pattern, such as, loss of balance and abnormal buoyancy, prolapse of the lower lip and superior location in the water column. The highest concentrations of these compounds induced nervous signs and collapse. The relevant macroscopic lesions were skin and fins erosions with necrotic lysis of the caudal peduncle. In addition, hemorrhages in mouth, branchial arches, and petechial hemorrhages in skin were observed. An increased fluid in the celomic cavity and meningeal hemorrhages were also evident. Organs as gills, liver, brain, and anterior kidney presented severe lesions at the highest concentrations of each compound. For the first time, it is reported lesions in interrenal tissues and choroidal bodies, as well as severe telencephalic lesions associated with the POEA toxicity. These last lesions were more severe in fish exposed to TA15 than to TH30, although the pattern of injuries was similar with both substances. According to the Global Harmonized System of Classification and Labelling of Chemical (GHS) by the United Nations, we reported that TA15 is classified as Acute Category 2 and TH30 is Acute Category 3 for white cachama. Due to the low LC₅₀ and the highly toxic effects of both POEA compounds for neotropical fish, a revision of the regulation of the use of herbicide mixtures by Colombian legislation is necessary.

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.