The level of radioactivity in the soil has been increasing unpredictably due to the human uranium mining exploitation of uranium over the past 100 years. Remediation of metals in actual soil confronts many challenges, remaining poorly understood. This study intends to investigate the concentrations and distributions of U, Cd, Zn, Pb, and Cu in soils surrounded by a uranium mill tailing pond. Furthermore, a phosphorus-modified bio-char was prepared in order to determine its role in immobilizing uranium in soil samples. Results show that the contents of U and Pb are much higher than that of the background values, due to the influence of the uranium mill tailing pond. Phosphorus can enhance the immobilization efficiency of U, Cd, Pb, and Cu in soil samples. The concentration of uranium in the leaching supernatant of phosphorus-modified bio-char group is lower than that of control and unmodified bio-char groups due to the fact that the biosorption occurred in the exterior surface of the biomass, which imply that phosphorus-modified bio-char is a potential immobilization material to reduce the leaching rate of metals. These findings can provide references for remediation technology of metals in natural soil.

The presence of potentially toxic metals such as Cu(II) and Pb(II) in aquifers and industrial effluents represents a serious health problem due to their high toxicity, non-biodegradability, and ability to bioaccumulate. In this study, the removal of these pollutants individually and as a binary mixture has been studied, using solid coffee waste modified with 0.6 M citric acid as the adsorbent, and a mathematical model based on the ion exchange mechanism was implemented to elucidate the adsorption equilibrium. The characterization of modified coffee waste showed a pH value at the point of zero charge of 2.97 and a high concentration of carboxylic groups, which are susceptible to ion exchange. Furthermore, the quantification of interchangeable ions confirmed that the main mechanism of adsorption is the ion exchange of metal ions with the protons present on the adsorbent’s surface. The experimental data of the individual and binary adsorption equilibrium using a model based on a phenomenological approach was analyzed. The phenomenological model was compared with the Freundlich and Langmuir empirical solid-liquid adsorption models. The results showed that the adsorption capacities of Cu(II) and Pb(II) individually were 1.46 and 1.18 meq/g, and in a binary mixture were 1.43 and 1.24 meq/g, respectively, at pH 5 and 30 °C. In addition, the separation coefficients from ion exchange model revealed the predominance of protons as an exchangeable ion, which is in accordance with the experimental evidence. Finally, the correlation coefficient showed that the proposed model predicts accurately the adsorption equilibrium.

The study investigated species composition and polysaccharides, proteins, and eDNA content in EPS fractions (soluble, Sol-EPS; loosely bound, LB-EPS; tightly bound, TB-EPS) in nitrifying aerobic granules from reactor operated at a high load of nitrogen 0.5 kg TKN/(m³ × day). In the study, polysaccharides predominated in Sol-EPS, whereas proteins were the main component of bound EPS. eDNA was only detectable in TB-EPS. In Sol-EPS, eDNA originating from Pseudomonales predominated; species belonging to Pseudomonales produce glue-like polysaccharides that enable surface colonization. In all EPS fractions, high abundance of Acinetobacter sp. was noted. In TB-EPS, Thauera sp. was present in high abundance (25.6%) that produce polymers ensuring compact granule structure and that participate in many key metabolic processes for nitrogen conversions in wastewater treatment plants such as heterotrophic nitrification or denitrification. The study indicates that each EPS fraction in aerobic granules represents micro-environment facilitating the growth of species that produce a component of EPS with function essential for surrounding cells.

This paper investigated the photodegradation of oxytetracycline (OTC) in the presence of dissolved organic matter (DOM) and chloride ions, which is relevant to the estuary environment. The separate effects of chloride ions and DOM on the photodegradation of OTC were first studied, and then, the combined effects were studied. The photodegradation of OTC showed a tendency to decrease with increasing DOM levels: a low concentration of DOM (< 2 mg/L) enhanced the degradation of OTC, and a high concentration of DOM (> 5 mg/L) inhibited it. The addition of chloride ions (10–500 mmol/L) to DOM solutions (20 mg/L) significantly increased the degradation rate of OTC. The observed promotion effects may be a consequence of the participation of reactive chlorine species. Quenching experiments verified that the main active species in the presence of chloride ions and DOM are radicals including Cl•/Cl₂•⁻ and HO•. These results indicate a promotion of OTC degradation in saline water compared with fresh water, and this finding is important to better understand the environmental fate of OTC in estuarine and coastal waters.

The denitrifying anaerobic methane oxidation (DAMO) process can achieve methane oxidation and denitrification at the same time by using nitrate or nitrite as an electron acceptor. The short- and long-term effects of nitrite on DAMO organisms were studied from macro (such as denitrification) to micro (such as microbial structure and community) based on two types of DAMO microbial systems. The results showed that the inhibitory effects of nitrite on the two DAMO microbial systems increased with rising concentration and prolonged time. In the short-term inhibitory phase, nitrite with concentrations below 100 mg N L⁻¹ did not inhibit the two distinct DAMO enrichments. When nitrite concentration was increased to 950 mg N L⁻¹, the nitrogen removal performance was completely inhibited. However, in the long-term inhibition experiment, when nitrite concentration was increased to 650 mg N L⁻¹, the nitrogen removal performance was completely inhibited. In addition, in acidic conditions, the real inhibitor of nitrite is FNA (free nitrous acid), while in alkaline conditions, the real inhibitor is the ionized form of nitrite. By using high-throughput sequencing technology, the species abundance and diversity of the two DAMO microbial systems showed an apparent decrease after long-term inhibition, and the community structure also changed significantly. For the enrichment culture dominated by DAMO bacteria, the substantial drop of Methylomonas may be the internal cause of the decreased nitrogen removal rate, and for the coexistence system that hosted both DAMO bacteria and archaea, the reduction of Nitrospirae may be an internal reason for the decline of the denitrification rate.

Investigations of deleterious effects on non-target species, including earthworms, have been conducted for a number of pesticides, but there is a need for additional assessments of potential adverse effects. In the present study, the acute toxicity of eight pesticides to the earthworm Eisenia andrei was assessed and compared. The exposures were conducted using the filter paper contact toxicity method. Based on the 48-h LC₅₀ values, one pesticide was classified as supertoxic (combined fungicide containing difenoconazole and fludioxonil), four as extremely toxic (combined herbicide containing pethoxamide and terbuthylazine, combined fungicide containing fluopyram and tebuconazole, fungicide containing pyrimethanil, and combined fungicide containing thiram and carboxin), two as very toxic (combined fungicide containing flutriafol and thiabendazole, and herbicide containing fluroxypyr-meptyl), and one as moderately toxic (insecticide containing thiamethoxam). Additionally, effects of pesticides on the multixenobiotic resistance (MXR) activity were measured. Results showed that four pesticides caused significant effects with a recorded inhibition of the activity, which can consequently lead to a higher toxicity due to longer retention of the pesticides in the cells. Finally, for three chosen pesticides, gene expression of cat, sod, and gst was measured, and significant changes were observed. The obtained results show that earthworms could be significantly affected by pesticides commonly used in agriculture.

Pesticides are used worldwide in farming activities to guarantee crop yields. In southeastern Mexico, groundwater is the primary source of water for humankind. However, because of the soil characteristics and of intensive agricultural practices, the aquifer is vulnerable to pollution as shown by the regular detection of pesticide residues in groundwater. Within this context, the dissipation and adsorption of four of most used pesticides (2,4-D, atrazine, diazinon, and glyphosate) by farmers in southeastern Mexico were studied to determine their fate in agricultural soil and estimate their risk for the aquifer. Forty-one days after their application, the four pesticides were entirely dissipated from the soil. 2,4-D and glyphosate were the most persistent according to DT₅₀. Diazinon was the most adsorbed to the soil at equilibrium time. All pesticides were volatilized in substantial amounts, reaching 10.1, 22.3, 22.4, and 43.4% of initial amount 72 h after application of glyphosate, atrazine, 2,4-D, and diazinon, respectively. Volatilization was dependent on time and pesticide type (P < 0.05). Following their KOC, diazinon and glyphosate were found to be the most prone to leach. Therefore, in the absence of mitigation measures, their use represents a significant threat for the groundwater in Southeastern Mexico.

Fully stabilized FeS nanoparticles were prepared with water-soluble carboxymethyl cellulose (CMC) as a stabilizer, and investigated for adsorption of lead (Pb²⁺) ions from simulated drinking water. The optimum particle stabilization was achieved using 0.0025 wt.% of CMC for 50 mg/L FeS (i.e., CMC-to-FeS molar ratio of 0.0005). The particle stabilization technique increased lead removal from 78.1% to 90.3%. However, further increasing the CMC-to-FeS molar ratio to 0.0025 diminished the removal. Rapid adsorption kinetics of Pb by CMC-FeS was observed with an equilibrium time of 240 min. The kinetic data was adequately fitted by a pseudo-second-order kinetic model. The adsorption isotherm showed a sigmoidal S-shape due to complexation of Pb with soluble CMC molecules, and the Sigmoidal isotherm model well fitted the adsorption isotherm data with a maximum monolayer adsorption capacity of 77.0 mg/g. FTIR and XRD analyses indicated that both surface complexation and chemical precipitation (in the form of PbS) were the dominant adsorption mechanisms. Pb uptake was enhanced with increasing CMC-FeS dosage from 10 to 125 mg/L and increasing pH from 4.5 to 8.5. The material can perform well under typical concentrations of a model humic acid (HA) and salts. Yet, unusually high concentrations of HA or hardness ions may exerted elevated inhibitive effect. The findings indicated that CMC-stabilized FeS nanoparticles are promising for effective immobilization of lead in contaminated water and soil.

Cobalt (Co) adsorption onto saline soil was investigated in this study. The effect of pH, interaction time, and initial concentration of Co on adsorption were evaluated empirically to screen the appropriate operating conditions. Three biosurfactant products (i.e., surfactin, trehalose lipids, rhamnolipid) each at two concentrations (1 and 2 critical micelle concentrations (CMCs)) were applied during Co adsorption. The adsorption kinetic models were explored and results indicated that the pseudo-second-order kinetic model fit the experimental data the best. Four isotherms, including Langmuir, Freundlich, Temkin, and Redlich-Peterson were used for regulating the Co adsorption with and without the addition of each biosurfactant. The research results show that Co has low mobility even with the existence of a biosurfactant. The findings help to better understand the adsorption behaviour of Co in saline soil so as to develop applicable remediation options.

Raw coal fly ash (RCFA) was recycled as three kinds of adsorbents by hydroxyl anion (OH⁻), hydrogen ion (H⁺), and thermal activation, respectively, for the adsorption of Cr(VI) from water. The H⁺ activation can explore the adsorptive potential of RCFA more effectively than the other two methods. The specific surface areas of the adsorbents are 12.33, 16.32, and 13.89 m² g⁻¹ for OH⁻, H⁺, and thermal activation, respectively. The adsorption process follows the pseudo-second-order kinetic model and the Langmuir model better and exhibits exothermic property. The activation energy (20.65–31.88 kJ mol⁻¹) and the negative Gibbs free energy reveal that the adsorption is a physical and spontaneous process. The adsorbents derived from OH⁻, H⁺, and thermal activation can be used at least 5, 7, and 4 times, respectively, while the one from H⁺ activation has the best adsorption capacity (6.41 μg g⁻¹ for the first run). The adsorption process can introduce other metallic/toxic elements, but within the Chinese standard. The preparation cost of the H⁺ activation is $1103 ton⁻¹ adsorbent, while the treatment cost is $1.6 ton⁻¹ water. The more accurate parameters in the pseudo-second-order kinetic model and Langmuir model can be calculated by nonlinear method and provided by the error function of the sum of the squares of the errors.