This study proposes a method based on solid-phase extraction using a minicolumn with sugarcane bagasse for pre-concentration uranium in water samples. The first optimization step was used factorial design in two levels (2⁵) for the preliminary assessment of factors: elution flow, sample flow, pH, buffer concentration, and eluent concentration. From this design, it was found that all variables showed significant influence. In the second stage, using the Doehlert design with 5 variables, the optimal conditions were determined: pH 8.3, flow elution 5.5 mL min⁻¹, buffer concentration 0.045 mol L⁻¹, sample flow 5.5 mL L⁻¹, and eluent solution (ascorbic acid 0.6% w/v in medium of hydrochloric acid at a final concentration of 0.06 mol L⁻¹). The method was applied to the determination of uranium with a detection limit (LD) of 0.41 μg L⁻¹ and quantification (LOQ) of 1.40 μg L⁻¹, Relative standard deviation (RSD) 2.5 and 1.3% uranium concentration of 20 and 60 μg L⁻¹, respectively. The factor of pre-concentration for the system is 46 for a sample volume of 50 mL. The accuracy was confirmed by the spike test. The procedure was applied for the determination of uranium in tap water, well water, and human consumption; the samples were collected in the municipalities of Caetité, Cruz das Almas, Itabuna, Aramari-BA, and seawater samples from Todos os Santos Bay. Uranium concentrations were found in the analyzed samples varying from 7.0 to 16.5 μg L⁻¹.

Catalysts of Pd-In supported on activated carbon fiber were synthesized, characterized, and evaluated for the removal of nitrogen oxyanions from water. The work was carried out aiming the development of a green synthesis process, and the studies were accomplished with the following objectives: (a) to evaluate whether catalysts produced by wet impregnation (WI) and autocatalytic deposition (AD) have enough catalytic activity for the removal of oxyanions in water; (b) to determine the efficiency of ion removal using formic acid as a reducing agent; (c) to determine which synthesis method produces less waste. It was found that the two synthesis processes modified the properties of the support and that the distribution of the particles of the metallic phase was of the nanometric order, being these particles found predominantly at the support surface. By using formic acid as a reducing agent, although low nitrate conversions were obtained (32%), a selectivity to N₂ higher than 99% was achieved. These findings were attributed to the low decomposition of formic acid on the catalyst surface. The Pd:In (0.45:0.2) catalyst prepared by WI was the most suitable for the catalytic reduction of both nitrate and nitrite oxyanions. Regarding the green point of view of the synthesis method, catalysts prepared by WI generated less waste. Graphical abstract

In this study, La(OH)₃-modified magnetic sodium carboxymethyl cellulose (La-MC) was prepared as adsorbents for phosphate, which exhibited excellent adsorption performance up to 62.98 mg P/g and magnetic property for easy recovery. The recovered adsorbents after phosphate sorption were subsequently used for photocatalytic reduction of Cr(VI) and possessed good photocatalytic activity. This work provided an excellent reference for developing a new way of extending life cycle of adsorbents by combining phosphate adsorption with photocatalysis for sequential removal of pollutants from water in the future.

Microplastics in marine organisms are nowadays considered a worldwide phenomenon. An action plan needs to establish to solve this marine pollutant. It requires multidisciplinary information, including the accumulation of data on microplastics in marine biota. The research of microplastic ingestion in the marine environment and organisms of Thailand is limited. As a result, this study was conducted to evaluate the accumulation of microplastics in marine fish from Thailand and to investigate whether the different foraging mechanisms of fish impact the occurrence of microplastics in their gastrointestinal tract. A total number of 361 demersal fish and 131 pelagic fish were investigated. The collected microplastics were counted according to their shape and color. Their polymer type was identified by FT-IR for the first time in fish from Thailand. Moreover, microplastics ingestion sorted by fish size was noted. The number of ingested microplastics in this study was relatively low compared to other locations. There was no significant difference in the number of microplastics ingested between demersal and pelagic fish (p = 0.132). Microplastic fibers were the dominant shape found in both demersal (82.76%) and pelagic fish (57.14%). The most common polymer type was polyamide in both demersal (55.17%) and pelagic fish (50.00%). The dominant microplastics color in both demersal and pelagic fish was red (31.03% and 28.57%, respectively). Microplastics ingestion along different fish sizes fluctuated. This study provides evidence to fill a gap of research relating to microplastic ingestion by fish from Thailand.

It is of great importance to determine the risk grades of the leakage and non-leakage cases of concentrated saltwater from an underground reservoir for the safe operation of reservoirs and environmental protection. In this paper, the model of risk evaluation for environmental pollution of an underground reservoir stored with concentrated saltwater is established. Moreover, the effects of different influencing factors on the risk grades are investigated, along with an uncertainty analysis. In addition, the risk grade of Lingxin Mining Area is calculated, which can contribute to the prevention and control of pollution in the future for that area. The results show that the water quality complexity of mine water is the most significant indicator for risk grade determination. The certainty of weak-risk grade for environmental pollution caused by an underground reservoir when there is no leakage is more than 60% in the Lingxin Mining Area, and the risk grade becomes a strong-risk grade rapidly after concentrated saltwater leakage is considered. This research can provide a theoretical basis for risk control and management of underground reservoirs storing concentrated saltwater.

China has become the largest carbon-emitting country in the world since 2007. To achieve national environmental goals by 2030, the carbon emissions per unit of gross domestic product (GDP) will need to fall to 60–65% of 2005 levels. Such a dramatic decrease presents a challenge for a nation in adjusting its energy source and usage, but via monitoring of reductions, greater understanding can be gained of how carbon emitters are responding to national goals. We analyzed the change in carbon emissions from China’s fossil energy consumption from population, per capita GDP, energy efficiency improvements and energy structure using a Kaya identity model and Logarithmic Mean Divisia Index (LMDI) factor decomposition method from 2006 to 2018. Results suggest that trends in carbon emissions from 2006 to 2018 can be broken down into four periods: a rapid increase period during 2006–2011, a slowdown increase period during 2011–2014, a consecutive decline period during 2014–2016 and a rebound during 2017–2018. Trends in carbon emissions were greatly affected by per capita GDP and energy efficiency. While per capita GDP increased carbon emissions, energy efficiency had a countering effect on carbon emissions. Our results suggests that China’s measures in the past decade to reduce carbon emissions (i.e. carrying out carbon emissions trading on a fixed basis, readjusting the economic structure, optimizing the energy structure, improving energy efficiency and increasing forest carbon sinks) have helped to reduce carbon emissions. However, China should continue to actively respond to climate change while striving to achieve of economic sustainable development and social progress.

Generation, storage, and management of waste coming from industrial processes are a growing worldwide problem. One of the main contributors is the mining industry, in particular tailings generated by historical mining, which are barely maintained, especially in developing countries. Assessing the impact of a mining site to surrounding soils and ecosystems can be complex, especially when determining mobility and accessibility of the contaminants is required to perform ecological and human health risk assessment. As an effort to obtain information regarding mobility and accessibility of some potentially toxic elements (Zn, Pb, and As) from an historical mining site of northwestern Mexico, the abandoned mine tailings of San Felipe de Jesús in central Sonora and adjacent agricultural soils were investigated. Mobility and accessibility were assessed by means of sequential extraction procedures and using simulated physiological media. Additionally, an assessment of accidental oral intake was calculated considering the bioaccessible fractions. Results show that higher concentrations of contaminants were found in sulfide-rich tailings (Zn = 92,540; Pb = 21,288; As = 19,740 mg kg⁻¹) compared with oxide-rich tailings (Zn = 43,240; Pb = 14,763; As = 13,401 mg kg⁻¹). Concentrations in agricultural soils were on average Zn = 4755, Pb = 2840, and As = 103 mg kg⁻¹. Zinc was mainly recovered from labile fractions in oxide-rich tailings (~ 60%) and in a lower amount from sulfide-rich tailings (~ 30%). Pb and As were mainly associated with residual fractions (80–95%) in both types of tailings. The percentage of mobile fractions (sum of water-soluble, exchangeable, and bound to carbonate fractions) in agricultural soils was as follows: Zn ~ 60%, Pb ~ 15%, and As ~ 70%. Regarding the phytoaccessible fraction, the studied elements in mine tailings and agricultural soil samples exceeded the threshold limits, except for As in agricultural soils. According to data obtained, toxic effects were also calculated. As for daily oral intake for non-carcinogenic effects in adults and children, only Pb and As exceeded reference dose values, especially in children exposed to sulfide-rich tailings and agricultural soils. Regarding carcinogenic effects of Pb and As, most of the samples were above acceptable risk values.

Global pollution of mercury (Hg) threatens ecosystem and human health. We measured total Hg (THg) and monomethylmercury (MMHg) concentrations in filter-feeding blackfly (Simulium spp.) larvae in the inflows and the outflows of six boreal lakes with no Hg point source pollution. THg in the larvae ranged from 0.03 to 0.31 mg kg⁻¹ dw and MMHg between 0.02 and 0.25 mg kg⁻¹ dw. The proportion of MMHg in the larvae was 74 ± 0.16% and ranged from 43 to 98% of THg, the highest proportions being comparable to those typically found in aquatic predatory insects and fish. We compared the larvae MMHg concentrations to river water quality, catchment land-use, and to size-adjusted lake pike THg data. Two of the investigated catchments have been affected by a multimetal biomine since 2008 and were characterized by higher conductivity and higher urban land-use activity. Larvae THg and MMHg concentrations were higher in the lake inflows than in outflows and associated with water conductivity and catchment land-use activity. Lake pike THg concentrations were highly correlated to lake outflow blackfly larvae MMHg concentrations. Our data illustrate that blackfly larvae take up high percentage of THg that is MMHg, which in turn is available for higher consumers in aquatic and terrestrial food webs.

The decolorization of Reactive Blue 19 (RB19) from aqueous solutions using the Fenton oxidation process was researched. The effects of different operating parameters, e.g., H₂O₂, Fe(II), initial dye concentration, pH, and solution temperature, on the decolorization of RB19 were investigated. Increasing, the H₂O₂ concentration and temperature increased the rate of the decolorization; however, increasing initial RB19 concentration reduced the decolorization. Additionally, modeling of the decolorization obtained by the Fenton oxidation process was researched based on deep neural networks (DNN) architecture providing the best performance in terms of optimum hidden layers and neuron numbers in addition to ideal activation and optimization function pairs. The performances of the models were analyzed on the training, validation, and test data. According to the experimental results, the seven hidden layers DNN model with “relu” activation function and “RMSProp” optimization function provided the best performance with root mean square error (RMSE) of 3.39 and correlation coefficient (R²) of 0.99.

Most studies that address microplastic (MP) ingestion by fish are conducted in marine environments; however, freshwater ecosystems such as rivers and streams are also important sources of these particles in coastal areas. Considering that increasing urbanization surrounding watersheds increases the sources of plastic pollution and that fish feeding behavior may influence the probability of ingestion of these particles, the aim of this study was to evaluate the ingestion of MP by fish of different feeding habits in urbanized and non-urbanized streams. The fish were captured in ten streams in Southern Brazil and the stomach contents of 294 individuals belonging to 13 species were analyzed. Individuals of ten species ingested MP of fiber type. From a generalized linear mixed model, we observed that the urbanized streams and the omnivorous habit showed a positive correlation with MP intake. Our results suggest that both types of streams present MP, but this pollutant is probably more prominent in heavily urbanized sites, which may represent important sources of MP for larger systems along the river basin. This evidences the importance of preserving riparian areas of small order streams as a means to reduce MP inputs into these ecosystems.