The health effects of potentially toxic elements (PTEs) in airborne particulate matter (PM) are strongly dependent on their size distribution and dissolution. This study examined PTEs within nine distinct sizes of PM in a Chinese megacity, with a focus on their deposited and dissolved bioaccessibility in the human pulmonary region. A Multiple Path Particle Dosimetry (MPPD) model was used to estimate the deposited bioaccessibility, and an in-vitro experiment with simulated lung fluid was conducted for dissolved bioaccessibility. During the non-heating season, the dissolved bioaccessible fraction (DBF) of As, Cd, Co, Cr, Mn, Pb and V were greater in fine PM (aerodynamics less than 2.1 μm) than in coarse PM (aerodynamics between 2.1 and 10 μm), and vice versa for Ni. With the increased demand of heating, the DBF of Pb and As decreased in fine particle sizes, probably due to the presence of oxide/silicate compounds from coal combustion. Inhalation health risks based on the bioaccessible concentrations of PTEs displayed the peaks in <0.43 μm and 2.1–3.3 μm particulate sizes. The non-cancer risk was at an acceptable level (95th percentiles of hazard index (HI) was 0.49), but the cancer risk exceeded the threshold value (95th percentiles of total incremental lifetime cancer risk (TCR) was 8.91 × 10⁻⁵). Based on the results of uncertainty analysis, except for the exposure frequency, the total concentrations and DBF of As and Cr in <0.43 μm particle size segment have a greater influence on the uncertainty of probabilistic risk.

Lead (Pb) is a toxic metal in industrial production, which can seriously threat to human health and food safety. Thus, it is particularly crucial to reduce the content of Pb in the environment. In this study, raw fly ash (FA) was used to synthesise a new active silicate materials (IM) employing the low-temperature-assisted alkali (NaOH) roasting approach. The IM was further synthesised to form zeolite-A (ZA) using the hydrothermal method. The physicochemical characteristics of IM and ZA amendments before and after Pb²⁺ adsorption were analysed using the Scanning electron microscope-Energy Dispersive Spectrometer (SEM-EDS), Fourier Transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) apparatuses. The results revealed the considerably change in the microstructure and functional groups of IM and ZA amendments, conducive to Pb²⁺ removal. Moreover, a 3-year field experiment revealed that the IM and ZA significantly improved the growth of rice and reduced available Pb by 21%–26.8% and 9.7%–16.9%, respectively. After 3 years of remediation, the Pb concentration of the rice grain reached the national edible standard (≤0.2 mg kg⁻¹) of 0.171 mg kg⁻¹ and 0.179 mg kg⁻¹, respectively. Meanwhile, the concentration of acid-exchangeable Pb reduced, while those of reducible and residual fractions of Pb increased. There was no significant difference between the IM and ZA treatments. The potential mechanisms of remediation by the amendments were ion-exchange, complexation, precipitation, and electrostatic attraction. Overall, the results indicate that IM is suitable for the remediation of contaminated soil and promotes safe food production, and develops an environmentally friendly and cost-effective amendment for the remediation of polluted soil.

High-arsenic wastewater derived from the metallurgical industry of nonferrous minerals is one of the most dangerous arsenic (As) sources that usually follow the emission of massive hazardous arsenic-bearing wastes. Considering the properties of red mud (RM), we propose an alternative and environmentally friendly method for the efficient remediation of high-arsenic wastewater using RM through formation of AlAsO₄@silicate precipitate, aiming at ''zero-emission of hazardous solid waste''. The results show nearly 100% of arsenic could be stepwisely removed from high-arsenic wastewater and reduce the arsenic concentration from 6100 mg/L to 40 μg/L using RM at room temperature. The highest arsenic removal capacity of RM reaches 101.5 mg/g at a RM-to-wastewater ratio of 40 g/L due to the superior arsenic adsorption and the co-precipitation of arsenate and Al³⁺ to form insoluble aluminum arsenate. The silicate shell of arsenic-loaded RM created at an alkaline condition acts as an arsenic stabilizer, resulting in a leached arsenic concentration of 1.2 mg/L in TCLP tests. RM acts as a highly effective arsenic remover and stabilizer for the disposal of high-arsenic wastewater. It shows great potential for the remediation of wastewater containing heavy metals with varying concentrations to produce clean water available for industrial purpose.

This study aimed to evaluate the hydrochemistry of the water resources of the Weibei Plain, Northern China, as well as the risks posed by high groundwater nitrate concentrations to human health. Groundwater and surface water samples numbering 168 and 14, respectively, were collected during the dry and wet seasons. Water in the study area was weakly alkaline, falling into a hard-fresh or hard-brackish category. The groundwater chemical types were mainly SO₄·Cl–Ca·Mg (59.5%) and HCO₃–Ca·Mg (28.6%), whereas the dominant chemistry type of surface water was SO₄·Cl–Na (78.6%). Groundwater showed relatively high concentrations of NO₃⁻, with average dry and wet season concentrations of 212 mg·L⁻¹ and 223 mg·L⁻¹, respectively, whereas surface water had a low NO₃⁻ content. The major processes affecting water chemistry were determined to be rock weathering, such as silicate weathering and evaporative dissolution, as well as cation exchange. NO₃⁻ in groundwater was found to mainly originate from anthropogenic inputs such as agricultural production and domestic sewage. The entropy-weight water quality index (EWQI) assessment showed that although the quality of surface water was generally good, more than half of the groundwater samples failed drinking water standards, with NO₃⁻ identified as being the most problematic parameter affecting the water quality evaluation. Risk assessment of high groundwater nitrate concentrations indicated that long-term domestic use of groundwater in the study area can put the health of residents at great risk. Totals of 81% and 75% of the groundwater samples exceeded the acceptable limit for non-carcinogenic risk (HI = 1) to infants during the dry and wet seasons, respectively, whereas 75% and 71.3% of samples exceeded the acceptable limit for children, respectively. Future management of water in the Weibei Plain should prioritize the control groundwater nitrate pollution.

The sulfate pollution in water environment gains more and more concerns in recent years. The discharge of domestic, municipal, and industrial wastewaters increases the riverine sulfate concentrations, which may cause local health and ecological problems. To better understand the sources of sulfate, this study collected water samples in a typical agricultural watershed in East Thailand. The source apportionment of sulfide was conducted by using stable isotopes and receptor models. The δ³⁴SSO₄ value of river water varied from 1.2‰ to 16.4‰, with a median value of 8.9‰. The hydrochemical data indicated that the chemical compositions of Mun river water were affected by the anthropogenic inputs and natural processes such as halite dissolution, carbonate, and silicate weathering. The positive matrix factorization (PMF) model was not suitable to trace source of riverine sulfate, because the meaning of the extracted factors seems to be vague. Based on the elemental ratio and isotopic composition, the inverse model yielded the relative contribution of sulfide oxidation (approximately 46.5%), anthropogenic input (approximately 41.5%), and gypsum dissolution (approximately 12%) to sulfate in Mun river water. This study indicates that the selection of models for source apportionment should be careful. The large contribution of anthropogenic inputs calls an urgent concern of the Thai government to establish effective management strategies in the Mun River basin.

The effects of maifanite on the physiological and phytochemical process of submerged macrophytes Hydrilla verticillate (H.verticillata) were investigated for the first time in the study. The growth index: plant biomass, root length, plant height and leaf spacing, and physiological and phytochemical indexes: chlorophyll, soluble protein, malondialdehyde (MDA), peroxidase (POD), superoxide dismutase (SOD) content and vitality of the roots of H.verticillata were tested. The results found that maifanite can significantly promote the growth of H.verticillata. The modified maifanite were more conducive to plant growth compared with the raw maifanite, and the MM1 group had the best growth promoting effect. The physiological and phytochemical indexes showed that maifanite can delay the aging process of H.verticillata (P < 0.05). The possible reasons for promoting H.verticillata growth were that maifanite can provide excellent propagation conditions for plant rhizosphere microorganisms, contains abundant major and microelements, and improve the sediment microenvironment. This study may provide a technique for the further application of maifanite in the field of ecological restoration.

Elevated inorganic arsenic concentrations in groundwater has become a major public and environmental health concern in different parts of the world. Currently, As-contaminated groundwater issue in many countries and regions is a major topic for publications at global level. However, there are many regions worldwide where the problem has still not been resolved or fully understood due to inadequate hydrogeochemical investigations. Hence, this study evaluates for the first time the hydrogeochemical behavior of the arid and previously unexplored inland basin of Sirjan Plain, south east (SE) Iran, in order to assess the controlling factors which influence arsenic (As) mobility and its distribution through groundwater resources. Total inorganic arsenic concentration was measured using inductive-coupled plasma optical emission spectrometry (ICP-OES). Arsenic content in groundwater of this region ranged between 2.4 and 545.8 μg/L (mean value: 86.6 μg/L) and 50% of the samples exceeded the World Health Organization (WHO) guideline value of 10 μg/L in drinking water. Groundwater was mainly of Na-Cl type and alkaline due to silicate weathering, ion exchange and evaporation in arid conditions. Elevated As concentrations were generally observed under weakly alkaline to alkaline conditions (pH > 7.4). Multivariate statistical analysis including cluster analysis and bi-plot grouped As with pH and HCO3 and demonstrated that the secondary minerals including oxyhydroxides of Fe are the main source of As in groundwater in this region. The desorption of As from these mineral phases occurs under alkaline conditions in oxidizing arid environments thereby leading to high levels of As in groundwater. Moreover, evaporation, ion exchange and saltwater intrusion were the secondary processes accelerating As release and its mobility in groundwater. Based on the results of this study, desorption of As from metal oxy-hydroxides surfaces under alkaline conditions, evaporation and intrusion of As-rich saline water are considered to be the major factors causing As enrichment in arid inland basins such as those in southeast Iran. This study proposes the regular monitoring and proper groundwater management practices to mitigate high levels of arsenic in groundwater and related drinking water wells of Sirjan Plain.

Stabilizing cadmium by incorporating it into crystalline products is an effective approach to detoxify cadmium-containing wastes. In this study, two Si-rich matrices in amorphous and crystalline forms (i.e., silica fume and α-quartz, respectively) were employed to incorporate Cd. The processing parameters, namely the type of Si-rich matrix, Cd/Si molar ratio (Г) and sintering temperature, were thoroughly investigated using quantitative X-ray diffraction technique. Cd incorporation was more energetically favored when silica fume was used rather than when α-quartz was used because of the lower Gibbs free energy of formation for silica fume. The sintering temperature and Г values substantially affected the formation of three cadmium silicates, namely monoclinic CdSiO₃, orthorhombic Cd₂SiO₄, and tetragonal Cd₃SiO₅. CdSiO₃ formed only in Г = 1.0 systems. Cd₂SiO₄ was dominant in all reactive systems. In Г = 3.0 systems, Cd₃SiO₅ rather than Cd₂SiO₄ was the predominant Cd-hosting product at temperatures above 850 °C. Leaching test results demonstrated that CdSiO₃ possessed the highest acid resistance among the cadmium silicates. The leachability of Cd₂SiO₄ was very similar to that of Cd₃SiO₅. CdSiO₃ preferred incongruent dissolution, whereas Cd₂SiO₄ and Cd₃SiO₅ favored near-congruent dissolution. This study delineated the feasibility of cadmium incorporation by Si-rich matrices, identifying a promising approach for cadmium detoxification.

Packed column experiments were conducted to investigate the transport and blocking behavior of surfactant- and polymer-stabilized engineered silver nanoparticles (Ag-ENPs) in saturated natural aquifer media with varying content of material < 0.063 mm in diameter (silt and clay fraction), background solution chemistry, and flow velocity. Breakthrough curves for Ag-ENPs exhibited blocking behavior that frequently produced a delay in arrival time in comparison to a conservative tracer that was dependent on the physicochemical conditions, and then a rapid increase in the effluent concentration of Ag-ENPs. This breakthrough behavior was accurately described using one or two irreversible retention sites that accounted for Langmuirian blocking on one site. Simulated values for the total retention rate coefficient and the maximum solid phase concentration of Ag-ENPs increased with increasing solution ionic strength, cation valence, clay and silt content, decreasing flow velocity, and for polymer-instead of surfactant-stabilized Ag-ENPs. Increased Ag-ENP retention with ionic strength occurred because of compression of the double layer and lower magnitudes in the zeta potential, whereas lower velocities increased the residence time and decreased the hydrodynamics forces. Enhanced Ag-ENP interactions with cation valence and clay were attributed to the creation of cation bridging in the presence of Ca2+. The delay in breakthrough was always more pronounced for polymer-than surfactant-stabilized Ag-ENPs, because of differences in the properties of the stabilizing agents and the magnitude of their zeta-potential was lower. Our results clearly indicate that the long-term transport behavior of Ag-ENPs in natural, silicate dominated aquifer material will be strongly dependent on blocking behavior that changes with the physicochemical conditions and enhanced Ag-ENP transport may occur when retention sites are filled.