Heavy metals in influent and effluent from 146 drinking water treatment plants across China: Occurrence, explanatory factors, probabilistic health risk, and removal efficiency

Natural mackinawite-based elimination of vanadium and ammonium from wastewater in autotrophic biosystem

Vanadium (V) production results in significant amounts of wastewater, which often co-contains considerable ammonium (NH4+) after being used as precipitants. Both pentavalent V [V(V)] and NH4+ can be removed independently through biological process. However, internal interactive biotechnology for one-step elimination of V(V) and NH4+ remains an enigma. In this study, we proposed biologically removing V(V) and NH4+ simultaneously with natural mineral mackinawite as electron donor and its oxidation products as electron acceptors. Our bioreactor achieved a V(V) removal efficiency of 99.5 ± 0.22 % and an NH4+-N removal capacity of 49.5 ± 0.40 g/m3·d. V(V) was reduced to tetravalent V precipitates, while mackinawite was bio-oxidized to Fe(III) and sulfate. Metagenomic binning analysis indicated Sulfurivermis sp. mediated mackinawite oxidation and V(V) reduction. Putative Pseudomonas sp. conducted NH4+ assimilation, anaerobic ammonium oxidation coupled to Fe(III) reduction (Feammox), and denitrification, achieving complete NH4+-N removal. Real-time qPCR validated the upregulation of functional genes involved in V(V) reduction and nitrogen metabolisms, with improved functional enzyme activities. Cytochrome c, nicotinamide adenine dinucleotide, and extracellular polymeric substances promoted electron transfer, facilitating the elimination of both V(V) and NH4+-N from wastewater. This study offers a novel and sustainable biological strategy for one-step treating V industrial wastewater.

Occurrence, sampling, identification and characterization of microplastics in tap water: A systematic review and meta-analysis

Identifying microplastics (MPs) in tap water has recently attracted considerable attention. The present study aimed to systematically review MPs contamination and characteristics in tap water. All techniques used for sampling, processing, and analyzing MPs in tap water were also assessed. Furthermore, the characteristics of MPs, including abundance, type, color, and shape, were summarized. Various databases, including Web of Science, PubMed, ScienceDirect, Scopus, Springer, and MDPI, were searched to find published articles up to January 2025. The occurrence of MPs in tap water was meta-analyzed using a random-effects model. A total of 6100 articles were found, of which 43 were included in the systematic review. The results indicated that the pooled mean concentration of MPs in tap water was 56.98 particles per liter (P/L). Manual sampling with a sample volume of less than 1 liter was most commonly used, and microscopic, Raman, and Fourier-transform infrared spectroscopy (FTIR) methods were frequently applied for extracting and identifying MPs. The most abundant polymer identified was polyethylene (PE), followed by polyethylene terephthalate (PET) and polypropylene (PP). Fibers and fragments were the dominant forms of MPs found in water. The lack of a harmonized protocol and the difficulty in validating MP analysis methods in tap water have led to inconsistent and sometimes contradictory results, making comparisons unreliable. The findings of this systematic review can support the development of a comprehensive protocol and promote standardized, harmonized methods for MP analysis in tap water.

Hydrothermal carbonisation of waste-activated sludge: Possible route to improve sludge management in municipal wastewater treatment facilities

This study investigated the integration of hydrothermal carbonisation (HTC) and anaerobic digestion (AD) of waste-activated sludge (WAS) for sustainable sludge management. HTC were performed at 180 °C, 210 °C, and 260 °C for 30, 60, and 120 min. Hydrochar and aqueous hydrothermal liquor (AHL) were tested for biochemical methane potential. Increasing HTC severity reduced solids and carbon content, altered H/C and O/C ratios and lowered hydrochar yield while increased its stability. Under the mildest condition (180 °C for 30  min), AHL achieved the highest methane yield (387 NmL CH4 g-1 VS), 33 % higher than raw WAS, while hydrochar produced lower yields. Heavy metals were mainly retained in hydrochar with most within regulatory limits except cadmium, leaving AHL relatively clean. Although total biogas production output decreased due to carbon partitioning into hydrochar, AHL required only 86 % of WAS digestion capacity. HTC improves methane yield per unit of AHL, enables better use of existing plant capacity, and generates value-added byproducts.

Combined pollution of heavy metals and polycyclic aromatic hydrocarbons in non-ferrous metal smelting wastewater treatment plant: Distribution profiles, removal efficiency, and ecological risks to receiving river

Combined pollution status of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) from non-ferrous metal smelting (NFMS) industry is crucial but has not been explored. Herein, the co-distribution of HMs and PAHs in a NFMS wastewater treatment plant and the impacts on the receiving river were investigated. Cu, As, and Ni were found to be the characteristic HMs, while Acenaphthylene was the characteristic PAHs in the NFMS wastewater. The removal of HMs and PAHs in wastewater showed a strong positive correlation (R2 > 0.84, p < 0.05) with removal efficiency of 90.7 % and 94.1 %, respectively. It was estimated 547.5 kg HMs and 13.3 kg PAHs were discharged into the receiving river annually. The average concentration of HMs and PAHs in downstream was respective 1.6 and 2.7 times higher than that in upstream, and the sites near discharge outlet had significant spatial autocorrelation (p < 0.05), suggesting the discharge of NFMS wastewater had significantly influenced the receiving river. Aquatic organisms were posed to moderate chronic ecological risk (RQC > 0.1) and surrounding residents were posed to probable carcinogenic risk (TCR > 10-5). This work provides new insights into understanding the combined pollution and corresponding ecological risks from key industrial sectors globally.

Occurrence, distribution, and prioritization of unregulated emerging contaminants including battery-related chemicals in drinking water systems across South Korea

This study investigated the presence of 95 emerging contaminants comprising pharmaceuticals, stimulants, artificial sweeteners, nicotine metabolites, corrosion inhibitors, battery-related pollutants, and pesticides across 70 drinking water treatment plants. Battery-related contaminants (lithium, nickel, and cobalt), with total concentrations raging from 424 to 38,500 ng/L (median 2560 ng/L) in the raw water and from 596 to 34,300 ng/L (median 2510 ng/L) in the treated water, showed the highest detection frequencies (≥99 %). The median levels of nickel (1440 ng/L in raw water and 1620 ng/L in treated water) were higher than those of lithium (591 ng/L in raw water and 445 ng/L in treated water) and cobalt (233 ng/L in raw water and 95.3 ng/L in treated water). Organic contaminants (raw water: 33.6-6540 ng/L, median 827 ng/L; treated water: not detected-1900 ng/L, median 121 ng/L) mostly had lower total levels than battery-related chemicals. Telmisartan (median 36.6 ng/L in raw water and median 7.47 ng/L in treated water) and valsartan acid (median 26.3 ng/L in raw water and median 6.61 ng/L in treated water) were the predominant pharmaceuticals. For corrosion inhibitors, benzothiazole (29.0 ng/L in raw water and 7.21 ng/L in treated water) displayed the highest median concentrations. Bentazone (median 119 ng/L) was the most predominant pesticide in raw water. The distribution patterns of contaminants in raw water were related to various pollution sources in industries, agricultural zones, and daily life. Additionally, rainfall increased the inflow of lithium, nickel, cobalt, and benzothiazole into public waterways. According to the human health risk assessment using the maximum levels of contaminants, lithium, nickel, cobalt, and valsartan acid were the priority contaminants in treated water, indicating potential risks or need for further evaluation. The priority contaminants with high or moderate risks to aquatic ecosystems in raw water were three battery-related chemicals, six pharmaceuticals, and five pesticides.

Concentrations and human health risks attributed to potentially toxic elements (PTEs) in water resources in China: Systematic review and meta-analysis

Long-term exposure to potentially toxic elements (PTEs) increases carcinogenic and non-carcinogenic risks in the exposed population. The current study was conducted with the aims of meta-analysis concentrations of PTEs including Arsenic (As), Cadmium (Cd), Lead (Pb), Mercury (Hg), Nickel (Ni) and Copper (Cu) in the water resources and human health risk assessment for adult males and female consumers in China. Search was performed in international databases including Web of Science, Scopus, PubMed, Embase and Google Scholar (gery literature) from January 1, 2005 to April 1, 2024. The concentration of PTEs was meta-analyzed using random effects model in water resources (surface water and groundwater) and location of study (urban and rural locations) subgroups. Human health risk assessment due to PTEs in water from ingestion and dermal contact pathways was estimated using target hazard quintet (THQ) and carcinogenic (CR) in adult males and female consumers in China. One hundred and twenty-six papers with 237 data-reports (n = 13,083) were included in this study. The rank order of PTEs based on pooled concentration was As (12.6530 µg/l) > Cu (11.1810 µg/l)> Ni (2.4950 µg/l) > Pb (2.0660 µg/l) > Cd (0.5370 µg/l) > Hg (0.3600 µg/l). The rank order of PTEs based on percentage studies higher than standard limits was As (28.37 %) > Pb (16.67 %) > Hg (11.86 %) > Ni (9.91 %) > Cd (7.48 %) > Cu (2.38 %). The pooled concentration of Pb, Ni, Hg and Cu in surface water resources was higher than groundwater but concentration of As and Cd in groundwater water was higher than surface water. The rank order of PTEs based on percentage studies with the high non-carcinogenic risk (THQ ≥ 1) for male was As (30.49 %) > Cd (8.09 %)> Hg (6.90 %) > Ni (3.60 %)> Cu (3.39 %) > Pb (2.50 %) and for female, As (29.78 %) > Cd (8.09 %)> Hg (6.90 %) > Cu (3.39 %) > Ni (2.70 %)> Pb (1.25 %). The rank order of PTEs based on percentage studies with high carcinogenic risk (TCR ≥ 1E-4) for male was As (60.28 %) > Cd (33.33 %) and for female, As (56.73 %) > Cd (29.93 %). Therefore, to reduce the carcinogenic and non-carcinogenic risks of PTEs especially As, continuous monitoring and control release of As into water resources through novel approaches is recommended.

Predicting bioavailable barium transfer in soil-bok choy systems: A study induced by shale gas extraction in Chongqing, China

Barium (Ba) is a significant contaminant from shale gas extraction and is also used in various other industries. However, there has been very limited attention paid to Ba. Elucidating the Ba in soil-crop system are of great significance for both human health risk assessment and pollution control. In this study, the bioavailability of Ba in soils was studied by using various characterization methods. Then the major factors dominating the transfer of Ba in soil-bok choy system and a suitable predicted model was derived. The results showed that Ba was mainly accumulated in the roots (transfer factor < 0.3). The relationships between Ba in shoots and the bioavailability of Ba characterizing with different methods increased in the order of CH3COOH (R2 = 0.81) < ethylenediamine tetraacetic acid (R2 = 0.87) < pore water (R2 = 0.89) < diffusive gradients in thin film (R2 = 0.90) < CaCl2 (R2 = 0.91). The major soil properties affecting Ba in shoots were pH (r = -0.32, P > 0.05), cation exchange capacity (r = -0.43, P < 0.01) and labile Al (r = 0.38, P < 0.05). Bioavailability of Ba can preferably model the Ba transfer in soil-bok choy system. The best reliable model was LogBa[shoot] = 0.591LogBa[soil-Pore water] + 1.749 (R2 = 0.963, P < 0.001). This model without measuring soil physicochemical properties, making it easier and more convenient to use in practice. Overall, these results highlight the role of metal bioavailability in predicting their transfer in soil-plant systems.

Metal(loid)-gut microbiota interactions and microbiota-related protective strategies: A review

Human exposure to metal(loid)s has dramatically increased over the past five decades, which has triggered public concern worldwide. Recently, gut microbiota has been considered a target for metal(loid)s, and some literature has reviewed the interactions between gut microbiota and heavy metal(loid)s (HMs) with high toxicity. However, whether there is an interaction between gut microbiota and metal(loid)s with essential roles or some normal functions are far from clear to date. Importantly, in addition to traditional probiotics that have been clarified to alleviate the adverse effect of HMs on the body, some novel probiotics, prebiotics, synbiotics, and postbiotics may also exhibit comparable or even better abilities of metal(loid) remediation. In this review, we mainly outline and discuss recent research findings on the metal(loid)-gut microbiota interactions and microbiota-related protective strategies.

Suitability of inorganic coagulants for algae-laden water treatment: Trade-off between algae removal and cell viability, aggregate properties and coagulant residue

Inorganic coagulants could effectively precipitate algae cells but might increase the potential risks of cell damage and coagulant residue. This study was conducted to critically investigate the suitability of polyaluminum (PAC), FeCl3 and TiCl4 for algae-laden water treatment in terms of the trade-off between algal substance removal, cell viability, and coagulant residue. The results showed that an appropriate increase in coagulant dosage contributed to better coagulation performance but severe cell damage and a higher risk of intracellular organic matter (IOM) release. TiCl4 was the most destructive, resulting in 60.85% of the algal cells presenting membrane damage after coagulation. Intense hydrolysis reaction of Ti salts was favorable for the formation of larger and more elongated, dendritic structured flocs than Al and Fe coagulants. TiCl4 exhibited the lowest residue level and remained in the effluents mainly in colloidal form. The study also identified charge neutralization, chemisorption, enmeshment, and complexation as the dominant mechanisms for algae water coagulation by metal coagulants. Overall, this study provides the trade-off analyses between maximizing algae substance removal and minimizing potential damage to cell integrity and is practically valuable to develop the most suitable and feasible technique for algae-laden water treatment.

Comprehensive assessment of exposure and environmental risk of potentially toxic elements in surface water and sediment across China: A synthesis study

China faces a serious challenge with water pollution posed by potentially toxic elements (PTEs). Comprehensive and reliable environmental risk assessment is paramount for precise pollution prevention and control. Previous studies generally focused on a single environmental compartment within small regions, and the uncertainty in risk calculation is not fully considered. This study revealed the current exposure status of 11 PTEs in surface water and sediment across China using previously reported concentration data in 301 well-screened articles. Ecological and human health risks were evaluated and the uncertainty related to calculation parameters and exposure dataset were quantified. PTEs of high concern were further identified. Results showed Mn and Zn had the highest concentration levels, while Hg and Cd had the lowest concentrations in both surface water and sediment. Risk assessment of individual PTE showed that high-risk PTEs varied by risk receptors and environmental compartments. Nationwide, the probability of aquatic organisms being affected by Mn, Zn, Cu, and As in surface water exceeded 10 %. In sediment, Cd and Hg exhibited high and considerable risk, respectively. As was identified as the major PTE threatening human health as its carcinogenic risk was 1.45 × 10-4 through direct ingestion. Combined risk assessment showed the PTE mixture in surface water and sediment posed medium and high ecological risk with the risk quotient and potential ecological risk index of 1.76 and 558.36, respectively. Adverse health effects through incidental ingestion and dermal contact during swimming were negligible. This study provides a nationwide risk assessment of PTEs in China's aquatic environment and the robustness is verified, which can serve as a practical basis for policymakers to guide the early warning and precise management of water pollution.

Heavy metals in centralized drinking water sources of the Yangtze River: A comprehensive study from a basin-wide perspective

Water quality in the Yangtze River Basin (YRB) has received considerable attention because it supplies water to 400 million people. However, the trends, sources, and risks associated with heavy metals (HMs) in water of centralized drinking water sources (CDWSs) in the YRB region are not well understood due to the lack of high-frequency, large-scale monitoring data. Moreover, research on the factors affecting the transportation of HMs in natural water are limited, all of which significantly reduce the effectiveness of CDWSs management. Therefore, this study utilized data on 11 HMs and water quality from 114 CDWSs, covering 71 prefecture-level cities (PLC) in 15 provinces (cities), to map unprecedented geospatial distribution of HMs in the YRB region and examine their concentrations in relation to water chemistry parameters. The findings revealed that the frequency of detection (FOD) of 11 HMs ranged from 28.59% (Hg) to 99.64% (Ba). The mean concentrations are ranked as follows: Ba (40.775 μg/L) > B (21.866 μg/L) > Zn (5.133 μg/L) > V (2.668 μg/L) > Cu (2.049 μg/L) > As (1.989 μg/L) > Mo (1.505 μg/L) > Ni (1.108 μg/L) > Sb (0.613 μg/L) > Pb (0.553 μg/L) > Hg (0.002 μg/L). Concentrations of Zn, As, Hg, Pb, Mo, Sb, Ni, and Ba exhibited decreasing trends from 2018 to 2022. Human activities, including industrial and agricultural production, have led to higher pollution levels in the midstream and downstream of the river than in its upstream. Additionally, the high concentrations of Ba and B are influenced by natural geological factors. Anion concentrations and nutrient levels, play a significant role in the transport of HMs in water. Probabilistic health risk assessment indicates that As, Ba, and Sb pose a potential carcinogenic risk. Additionally, non-carcinogenic risk to children under extreme conditions should also be considered.

Theoretical study of the adsorption capacity of potentially toxic Cd2+, Pb2+, and Hg2+ ions in hemicellulose matrices

Hemicellulose is widely available in nature, is a sustainable resource and has a wide range of applications. Among them, adsorption stands out for the removal of potentially toxic ions. Thus, in the study, the adsorption of Cd2+, Pb2+ and Hg2+ ions in two hemicellulose matrices were elucidated through computational simulations using density functional theory. Molecular electrostatic potential and frontier molecular orbitals demonstrated whether the interactions could happen. Four interaction complexes were highlighted due to the interaction energy criteria, ΔEBind, ΔH and ΔG < 0.00 kcal mol-1, that is: Hm1… Pb (1); Hm2… Pb (3); Hm2…Cd (4) and Hm2…Hg (4) and the results show that they occur through physisorption. In structural parameter studies, interaction distances smaller than 3000 Å were identified, which ranged from 2.253 Å to 2.972 Å. From the analysis of the topological parameters of QTAIM, it was possible to characterize the intensities of the interactions, as well as their nature, which were partially covalent or electrostatic in nature. Finally, based on the theoretical results, it can be affirmed that the hemicellulose can interact with Cd2+, Pb2+ and Hg2+ ions, evidencing that this study can support further experimental essays to remove contaminants from effluents.

Vanadium in the Environment: Biogeochemistry and Bioremediation

Vanadium(V) is a highly toxic multivalent, redox-sensitive element. It is widely distributed in the environment and employed in various industrial applications. Interactions between V and (micro)organisms have recently garnered considerable attention. This Review discusses the biogeochemical cycling of V and its corresponding bioremediation strategies. Anthropogenic activities have resulted in elevated environmental V concentrations compared to natural emissions. The global distributions of V in the atmosphere, soils, water bodies, and sediments are outlined here, with notable prevalence in Europe. Soluble V(V) predominantly exists in the environment and exhibits high mobility and chemical reactivity. The transport of V within environmental media and across food chains is also discussed. Microbially mediated V transformation is evaluated to shed light on the primary mechanisms underlying microbial V(V) reduction, namely electron transfer and enzymatic catalysis. Additionally, this Review highlights bioremediation strategies by exploring their geochemical influences and technical implementation methods. The identified knowledge gaps include the particulate speciation of V and its associated environmental behaviors as well as the biogeochemical processes of V in marine environments. Finally, challenges for future research are reported, including the screening of V hyperaccumulators and V(V)-reducing microbes and field tests for bioremediation approaches.