Quantification of Element Fluxes in Wastewaters: A Nationwide Survey in Switzerland

Mobility of Rare Earth Elements in Coastal Aquifer Materials under Fresh and Brackish Water Conditions

The indispensable role of rare earth elements (REEs) in manufacturing high-tech products and developing various technologies has resulted in a surge in REE extraction and processing. The latter, in turn, intensifies the release of anthropogenic REEs into the environment, particularly in the groundwater system. REE contamination in coastal aquifer systems, which serve as drinking and domestic water sources for large populations, demands a thorough understanding of the mechanisms that govern REE transport and retention in these environments. In this study, we conducted batch and column experiments using five representative coastal aquifer materials and an acid-wash sand sample as a benchmark. These experiments were conducted by adding humic acid (HA) to the REE solution under fresh and brackish water conditions using NaCl, representing different groundwater compositions in coastal aquifers. The REEs were shown to be most mobile in the acid-wash sand and natural sand samples, followed by two types of low-carbonate calcareous sandstone and one type of high-calcareous sandstone and the least mobile in red loamy sand. The mobility of REEs, found in solution primarily as REE-HA complexes, was controlled mainly by the retention of HA, which increases with increasing ionic strength and surface area of the aquifer material. Furthermore, it was found that the presence of carbonate and clay minerals reduces the REE mobility due to enhanced surface interactions. The higher recoveries of middle-REE (MREE) in the column experiment effluents observed for the acid-wash sand and natural sand samples were due to the higher stabilization of MREE-HA complexes compared to light-REE (LREE) and heavy-REE (HREE) HA complexes. Higher HREE recoveries were observed for the calcareous sandstones due to the preferred complexation of HREE with carbonate ions and for the red loamy sand due to the preferred retention of LREE and MREE by clay, iron, and manganese minerals.

Tracing Gadolinium levels throughout wastewater treatment: Insights from a yearly assessment in northern Spain

Gadolinium (Gd) is a rare earth element (REE) used in the formulation of contrast agents for Magnetic Resonance Imaging (MRI) due to its paramagnetic properties. The growth in population and the improved quality of the healthcare systems over the last years, has promoted the use of MRI as an effective diagnostic tool thus increasing the consumption of gadolinium and its release into the wastewater treatment network. Therefore, the tracking and quantification of this metal in sewage treatment plants and water bodies, is of paramount importance since there are currently no specific rare earth treatment technologies installed in WWTPs, and consequently gadolinium is finally discharged into the environment. In this work, the presence of gadolinium and all other rare earth elements was monitored during a year in three WWTPs in northern Spain (Vuelta Ostrera and San Román in Cantabria and Galindo in País Vasco). These WWTPs are located close to urban centres with hospitals where MRI tests are performed. By tracing Gd throughout the wastewater treatment facilities, its presence was confirmed in water streams, in the order of ng per litter, and in sludge and ashes, in the order of mg per kilogram. A significant human influence was observed, with Gd anomaly values between 3.14 and 79.2 and anthropogenic Gd percentages above 90 %. The presence of Gd in water streams is affected by the sampling period due to the variations of the activity periods of the hospitals nearby the treatment plants. On the contrary, its content in sludge and ashes remains almost constant along the year. The concentration of this metal found in the ashes opens the door to its possible recovery together with other critical raw materials in the context of the circular economy.

Sidestream characteristics in water resource recovery facilities: A critical review

This review compiles information on sidestream characteristics that result from anaerobic digestion dewatering (conventional and preceded by a thermal hydrolysis process), biological and primary sludge thickening. The objective is to define a range of concentrations for the different characteristics found in literature and to confront them with the optimal operating conditions of sidestream processes for nutrient treatment or recovery. Each characteristic of sidestream (TSS, VSS, COD, N, P, Al³⁺, Ca²⁺, Cl^-, Fe^2+/3+, Mg²⁺, K⁺, Na⁺, SO₄^2-, heavy metals, micro-pollutants and pathogens) is discussed according to the water resource recovery facility configuration, wastewater characteristics and implications for the recovery of nitrogen and phosphorus based on current published knowledge on the processes implemented at full-scale. The thorough analysis of sidestream characteristics shows that anaerobic digestion sidestreams have the highest ammonium content compared to biological and primary sludge sidestreams. Phosphate content in anaerobic digestion sidestreams depends on the type of applied phosphorus treatment but is also highly dependent on precipitation reactions within the digester. Thermal Hydrolysis Process (THP) mainly impacts COD, N and alkalinity content in anaerobic digestion sidestreams. Surprisingly, the concentration of phosphate is not higher compared to conventional anaerobic digestion, thus offering more attractive recovery possibilities upstream of the digester rather than in sidestreams. All sidestream processes investigated in the present study (struvite, partial nitrification/anammox, ammonia stripping, membranes, bioelectrochemical system, electrodialysis, ion exchange system and algae production) suffer from residual TSS in sidestreams. Above a certain threshold, residual COD and ions can also deteriorate the performance of the process or the purity of the final nutrient-based product. This article also provides a list of characteristics to measure to help in the choice of a specific process.

Investigation of potential anthropogenic pollution of rare metals in Tama River followed by establishment of a comprehensive multielement analysis of major-to-ultratrace elements in river water and sewage treatment effluent

In this study, comprehensive multi-element analysis of at least 53 elements, including 40 rare metals, in river water at all points from upstream to the estuary in urban rivers and sewage treatment effluent was established using three analytical methods of ICP-MS, chelating solid-phase extraction (SPE)/ICP-MS, and reflux-type heating acid decomposition/chelating SPE/ICP-MS. Recoveries of some elements for sewage treatment effluent in chelating SPE were improved by being combined with reflux-type heating acid decomposition, because organic substances, such as EDTA, in sewage treatment effluent could be effectively decomposed. In particular, the reflux-type heating acid decomposition/chelating SPE/ICP-MS method enabled the determination of Co, In, Eu, Pr, Sm, Tb, and Tm, which had been difficult to determine in chelating SPE/ICP-MS without this decomposition procedure. A potential anthropogenic pollution (PAP) of rare metals in Tama River was investigated by the established analytical methods. As a result, 25 elements in river water samples from the inflow area of sewage treatment effluent were several to several dozen times higher than those in the clean area. In particular, the concentrations of Mn, Co, Ni, Ge, Rb, Mo, Cs, Gd, and Pt increased by more than one order of magnitude compared to the river water from clean area. These elements were suggested to be PAP. The concentrations of Gd in the effluents from five sewage treatment plants ranged from 60 to 120 ng L^-1, 40 to 80 times higher than those in clean river water, and all sewage treatment plants effluents showed the definite elevation of Gd concentrations. This indicates that MRI contrast agent leakage is occurring in all sewage treatment effluents. In addition, concentrations of 16 rare metal elements (Li, B, Ti, Cr, Mn, Ni, Ga, Ge, Se, Rb, Mo, In, Cs, Ba, W, and Pt) in all sewage treatment effluents were higher than those in clean river water, suggesting that many rare metal elements may be PAP. In the river water after the merging of sewage treatment effluent, the concentrations of Gd and In were higher than the reported values about 20 years ago.

Adsorption studies of a multi-metal system within acetate media, with a view to sustainable phosphate recovery from sewage sludge

Phosphate shortages and the ensuing pressures on food security have led to an interest in processed sewage sludge as a substitute for commercial fertilisers. The presence of heavy metals in this nutrient source causes concerns around environmental release and pollution. This work builds towards a resin-in-pulp sludge detoxification process. It showcases the kinetic and thermodynamic adsorption capabilities of the ion-exchange resins C107E (carboxylic acid functionality), MTS9301 (iminodiacetic acid) and TP214 (thiourea), with respect to Cu(II), Fe(II), Pb(II) and Zn(II), within a simulated sewage sludge weak acid (acetate) leachate. The isotherms produced in this complex system were quite different to those generated when single metals were investigated in isolation, with desorption of lower affinity species clearly observed at higher equilibrium concentration values. Mixed-metal isotherm data were fitted to common two-parameter isotherm models and also a novel modified Langmuir model, which better accounted for the effects of desorption and competition. Kinetic data were also fit to common two-parameter models; results suggesting the system was likely film diffusion-controlled and followed pseudo-2nd-order kinetics. C107E displayed rapid adsorption of lead (t_1/2 = 26 ± 3min), and significant uptake of all metals. MTS9301 showed high affinity for copper ions, with concurrent desorption of all the other metals, and also displayed the fastest kinetics (t_1/2 = 14.1 ± 0.9, 130 ± 20, 25 ± 5 and 49 ± 6 min for copper, iron(II), lead and zinc, respectively). C107E and MTS9301 showed far slower adsorption for iron(II) than the other three metals, which invited the possibility of kinetic separations. TP214 had reasonable effectiveness in removal of copper, but poor affinity for all other metals. The greatest difficulty in modelling the multi-metal system was the two-stage trends observed in equilibrium experiments, as metal-proton exchanges become metal-metal exchanges. While not having the highest capacity, MTS9301 was recommended as the most appropriate resin for rapid and efficient removal of Cu, Pb and Zn from the acetate medium.

Introduction to the biogeochemistry of the trace elements themed issue

Guest editors Elsie Sunderland and Lenny Winkel introduce the Environmental Science: Processes & Impacts themed issue on biogeochemistry of the trace elements.

Variation of the element composition of municipal sewage sludges in the context of new regulations on phosphorus recovery in Germany

Phosphorus (P) recovery is obligatory for all sewage sludges with more than 20 g P/kg dry matter (DM) from 2029 in Germany. Nine wastewater treatment plants (WWTPs) were chosen to investigate variations of phosphorus contents and other parameters in sewage sludge over the year. Monthly sewage sludge samples from each WWTP were analyzed for phosphorus and other matrix elements (C, N, H, Ca, Fe, Al, etc.), for several trace elements (As, Cr, Mo, Ni, Pb, Sn) and loss of ignition. Among the nine WWTPs, there are four which have phosphorus contents both above and below the recovery limit of 20 g/kg DM along the year. Considering the average phosphorus content over the year, only one of them is below the limit. Compared to other matrix elements and parameters, phosphorus fluctuations are low with an average of 7% over all nine WWTPs. In total, only hydrogen and carbon are more constant in the sludge. In several WWTPs with chemical phosphorus elimination, phosphorus fluctuations showed similar courses like iron and/or aluminum. WWTPs with chamber filter presses rather showed dilution effects of calcium dosage. As result of this study, monthly phosphorus measurement is highly recommended to determine whether a WWTP is below the 20 g/kg DM limit.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1186/s12302-022-00658-4.

Nationwide review of heavy metals in municipal sludge wastewater treatment plants in China: Sources, composition, accumulation and risk assessment

Systematically analyzing the problem of heavy metals in the municipal sludge, a meta-analysis of nine metals was undertaken to distinguish the sources and sinks of those with the impact of their accumulation on the environment. Municipal sludge was rich in N, P and K nutrients, was found to contain heavy metals comprising the descending order Zn > Mn > Cu > Cr > Pb > Ni > As > Cd > Hg. The forms, in which heavy metals accumulated in geographical regions, were characterized. The geographical distribution of heavy metals in the sludge showed a significant difference, with higher accumulation in Eastern and Southern regions, however, the risk evaluations showed the higher risk of heavy metals accumulation in Eastern and Western regions. Agricultural, industrial and traffic activities, and storm water pipeline sediments were identified as the main sources of heavy metals in the sludge. The correlation analysis elucidated the role of the total organic carbon in the accumulation of heavy metals in sludge. Municipal sludge is endowed with resource properties due to the detection of heavy metal contents thresholds in household products and its own resource-attributable enrichment behavior, which requires deduction of environmental risks.

Ecotoxicity of Concrete Containing Fine-Recycled Aggregate: Effect on Photosynthetic Pigments, Soil Enzymatic Activity and Carbonation Process

Recycling of materials such as masonry or concrete is one of the suitable ways to reduce amount of disposed construction and demolition waste (CDW). However, the environmental safety of products containing recycled materials must be guaranteed. To verify overall environmental benefits of recycled concrete, this work considers ecotoxicity of recycled concrete, as well as potential environmental impacts of their life cycle. Moreover, impacts related with carbonation of concrete is considered in terms of durability and influence of potential CO2 uptake. Concrete containing fine recycled aggregate from two different sources (masonry and concrete) were examined experimentally at the biochemical level and compared with reference samples. Leaching experiments are performed in order to assess physicochemical properties and aquatic ecotoxicity using water flea, freshwater algae and duckweed. The consequences, such as effects of material on soil enzymatic activity (dehydrogenase activity), photosynthetic pigments (chlorophylls and carotenoids), and the carbonation process, are verified in the laboratory and included in the comparison with the theoretical life cycle assessment. As a conclusion, environmental safety of recycled concrete was verified, and its overall potential environmental impact was lower in comparison with reference concrete.

Influence of Water Treatment and Wastewater Treatment on the Changes in Residues of Important Elements in Drinking Water

Drinking water is the essential medium for food production, and is also needed for direct consumption; while it must be free of harmful substances, it also must have a composition that is beneficial to health. The aim of this study was to evaluate the influence of water and wastewater treatment on reducing the concentrations of zinc (Zn), nickel (Ni), iron (Fe), manganese (Mn), copper (Cu), lead (Pb), and arsenic (As) in the Western Pomerania Voivodeship in Poland. The research was carried out in 2017–2019. The analysis was performed with inductively coupled plasma atomic emission spectrophotometry (ICP-AES). The concentrations of trace elements in drinking water were below maximum acceptable concentrations (MACs). Reductions in the most dangerous elements during water treatment fluctuated from 48.5% (As) to 97% (Pb). Wastewater treatment reduced the concentrations of analyzed elements by a range of 28.6 to 60.8%, and the most toxic elements (Pb and As) by over 50%. Trace element concentrations in treated wastewater were below MAC values, and ranged from 1.15% (Pb) to 6.23% (As) of MACs for toxic elements. The concentrations of both essential elements (Zn, Ni, Fe, Mn, Cu) and toxic elements (Pb, As) in drinking water were below the MACs. Water treatment had a significant (p < 0.05) effect on decreasing trace element concentrations.

Loads and elimination of trace elements in wastewater in the Great Lakes basin

The growing use of trace elements in industrialized societies is driving an increase in the occurrence of trace elements in anthropogenic waste streams globally. Yet, the large-scale sources of many trace elements to wastewater and their elimination during treatment remain poorly understood and potential environmental impacts on freshwater systems therefore unclear. We screened 42 wastewater treatment facilities in the North American Great Lakes basin and deployed a black-box approach to calculate representative estimates for average per-capita trace element loads and basin-scale effluent discharge rates, as well as trace element removal efficiencies across different treatment technologies. Our results show different removal of specific groups of trace elements during wastewater treatment: average removal efficiencies were 25% for alkali metals, 50% for alkaline earth metals, 74% for transition metals, and 85% for rare earth elements. Higher elimination of the majority of trace elements was generally achieved by more advanced, tertiary treatment types. Elemental loads generally followed natural abundance patterns, but anomalous loading rates were observed for various trace elements across the sampled facilities. By examining geospatial attributes of the sampled sewersheds, trends in select trace element loads were qualitatively tied to possible point sources and diffuse sources. Overall, these results illustrate the potential of wastewater surveillance to inform environmental management of emerging trace element contaminants.

Watershed-Scale Risk to Aquatic Organisms from Complex Chemical Mixtures in the Shenandoah River

River waters contain complex chemical mixtures derived from natural and anthropogenic sources. Aquatic organisms are exposed to the entire chemical composition of the water, resulting in potential effects at the organismal through ecosystem level. This study applied a holistic approach to assess landscape, hydrological, chemical, and biological variables. On-site mobile laboratory experiments were conducted to evaluate biological effects of exposure to chemical mixtures in the Shenandoah River Watershed. A suite of 534 inorganic and organic constituents were analyzed, of which 273 were detected. A watershed-scale accumulated wastewater model was developed to predict environmental concentrations of chemicals derived from wastewater treatment plants (WWTPs) to assess potential aquatic organism exposure for all stream reaches in the watershed. Measured and modeled concentrations generally were within a factor of 2. Ecotoxicological effects from exposure to individual components of the chemical mixture were evaluated using risk quotients (RQs) based on measured or predicted environmental concentrations and no effect concentrations or chronic toxicity threshold values. Seventy-two percent of the compounds had RQ values <0.1, indicating limited risk from individual chemicals. However, when individual RQs were aggregated into a risk index, most stream reaches receiving WWTP effluent posed potential risk to aquatic organisms from exposure to complex chemical mixtures.

Rare earth elements (REE) for the removal and recovery of phosphorus: A review

There is little doubt that 'rock phosphate' reserves are decreasing, with phosphorus (P) peak to be reached in the coming decades. Hence, removal and recovery of phosphorus (P) from alternative nutrient-rich waste streams is critical and of great importance owing to its essential role in agricultural productivity. Adsorption technique is efficient, cost-effective, and sustainable for P recovery from waste streams which otherwise can cause eutrophication in receiving waters. As selective P sorption using rare earth elements (REE) are gaining considerable attention, this review extensively focuses on P recovery by utilising a range of REE-incorporated adsorbents. The review briefly provides existing knowledge of P in various waste streams, and examines the chemistry and behaviour of REE in soil and water in detail. The impact of interfering ions on P removal using REE, adsorbent regeneration for reuse, and life cycle assessment of REE are further explored. While it is clear that REE-sorbents have excellent potential to recover P from wastewaters and to be used as fertilisers, there are gaps to be addressed. Future studies should target recovery and reuse of REE as P fertilisers using real wastewaters. More field trials of synthesized REE-sorbents are highly recommended before practical application.

Release of gold (Au), silver (Ag) and cerium dioxide (CeO2) nanoparticles from sewage sludge incineration ash

Engineered nanoparticles (NPs) that are released into wastewater are retained by wastewater treatment plants (WWTPs) and accumulate in sewage sludge. Increasing shares of sludge are incinerated and landfilled, especially in industrialized countries. It is debated whether certain types of NPs can outlive the incineration process and subsequently be released from sewage sludge ash (SSA) landfills. To investigate the release of different types of NPs from SSA, we spiked gold (Au), silver (Ag) and cerium dioxide (CeO₂) NPs to a pilot WWTP increasing the Au, Ag and Ce concentrations to 30, 43 and 389 mg kg^-1 (dry matter basis) in the digested sludge. The spiked sludge was incinerated in a pilot fluidized bed reactor resulting in SSA with Au, Ag and Ce concentrations of 61, 103 and 854 mg kg^-1. In addition, two sludge samples from a full-scale WWTP with Au concentrations of 5 and 16 mg kg^-1 were incinerated, resulting in SSA with 9 mg kg^-1 and 30 mg kg^-1 Au. The spiked Au-NPs remain largely unaltered during the wastewater treatment and incineration process, whereas Ag-NPs and CeO₂-NPs undergo transformation. During simulated landfill leaching in columns flushed with 400 to 500 pore volumes of artificial rainwater, Ag and Ce were retained in the ash, whereas about 17% of the spiked Au was released, mainly in particulate form. Lower fractions of mostly particulate Au were released from the ashes (3 and 9%) of unspiked SSA. In conclusion, unaltered Au-NPs significantly leach from landfilled SSA, whereas the incorporation of Ag-NPs and CeO₂-NPs as transformed species into the SSA matrix limits the leaching of (nano)particulate and dissolved Ag and Ce compounds.

Extraction of Au(III) by Microbially Reduced Metal-Organic Frameworks

Gold is a critical resource in the jewelry and electronics industries and is facing increased consumer demand. Accordingly, methods for its extraction from waste effluents and environmental water sources have been sought to supplement existing mining infrastructure. Redox-mediated treatments, such as Fe(II)-based platforms, offer promise for precipitating soluble Au(III). We hypothesized that microbial generation of Fe(II) in the presence of sorbent metal-organic frameworks could capitalize on the advantages of both biological- and chemical-driven extraction approaches. Toward this aim, we tested Au(III) removal by Shewanella oneidensis cultured with Fe(III)-based materials (ferrihydrite, Fe-BTC, MIL-100, or MIL-127). Across all tested materials, S. oneidensis generated the highest levels of redox-active Fe(II) (1.99 ± 0.27 mM) when cultured with MIL-127 as a respiratory substrate in a bicarbonate-buffered medium. This translated into superior Au(III) removal performance in terms of both removal rate and capacity (k = 2.55 ± 0.60 h^-1; Q = 183 mg g^-1). Unlike other materials tested, MIL-127 also maintained cell viability following repeated Au(III) challenges, enabling the regeneration of Fe(II) in the framework. Together, these effects facilitated the treatment of multiple cycles of Au(III) by S. oneidensis-reduced MIL-127. Overall, this work demonstrates that microbial generation of Fe(II) can facilitate the removal of Au(III), augmenting purely adsorptive platforms. Given the biological and chemical modularity of our system, our results suggest that future optimizations to microbial Fe(II) generation may offer promise for improving Au(III) extraction processes.

Quantification of individual Rare Earth Elements from industrial sources in sewage sludge

Rare Earth Elements (REEs) are used in increasing amounts in technical applications and consumer products. However, to date, the contribution of industrial sources to the loads of individual REEs in wastewater streams have not been quantified. Here, we determine the REE contents in sludge collected from 63 wastewater treatment plants (WWTPs) across Switzerland. To quantify the industrial fraction of individual REEs in the sewage sludge, we develop two complementary approaches, based on REE ratios and REE pattern fitting. Unspecific (background) inputs, with REE patterns similar to the averaged REE pattern of soils collected across Switzerland, dominate the REE budget of most WWTPs. A few WWTPs receive significant REE inputs from specific industrial sources. Based on population equivalents of Switzerland, we estimate a total annual load of 4200 kg Cerium (Ce, 0.5 g Ce year^-1 capita^-1), with an industrial contribution of 2000 kg year^-1. The latter agrees with estimates of probabilistic mass flow models for engineered nanoscale CeO₂ particles discharged to the sewer network. About 7 kg year^-1 of Samarium (Sm,total for Switzerland: 184 kg year^-1 or 0.02 g Sm year^-1 capita^-1) and 3 kg year^-1 of Europium (Eu,total for Switzerland: 44 kg year^-1 or 0.005 g Eu year^-1 capita^-1) are assigned to industrial inputs from single WWTPs. Gadolinium (Gd) is used in the form of a stable complex as contrast agent in magnetic resonance imaging. Assuming 10% removal of Gd during wastewater treatment, we calculate an annual discharge of 90 kg of Gd from one individual WWTP to surface waters. WWTPs with exceptionally high industrial inputs of specific REEs warrant detailed investigations to identify the respective sources and to assess whether REE concentrations in effluents are elevated to the same degree.

Synchrotron Radiation Spectroscopy and Transmission Electron Microscopy Techniques to Evaluate TiO2 NPs Incorporation, Speciation, and Impact on Root Cells Ultrastructure of Pisum sativum L. Plants

Biosolids (Bs) for use in agriculture are an important way for introducing and transferring TiO₂ nanoparticles (NPs) to plants and food chain. Roots of Pisum sativum L. plants grown in Bs-amended soils spiked with TiO₂ 800 mg/kg as rutile NPs, anatase NPs, mixture of both NPs and submicron particles (SMPs) were investigated by Transmission Electron Microscopy (TEM), synchrotron radiation based micro X-ray Fluorescence and micro X-ray Absorption Near-Edge Structure (µXRF/µXANES) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). TEM analysis showed damages in cells ultrastructure of all treated samples, although a more evident effect was observed with single anatase or rutile NPs treatments. Micro-XRF and TEM evidenced the presence of nano and SMPs mainly in the cortex cells near the rhizodermis. Micro-XRF/micro-XANES analysis revealed anatase, rutile, and ilmenite as the main TiO₂ polymorphs in the original soil and Bs, and the preferential anatase uptake by the roots. For all treatments Ti concentration in the roots increased by 38–56%, however plants translocation factor (TF) increased mostly with NPs treatment (261–315%) and less with SMPs (about 85%), with respect to control. In addition, all samples showed a limited transfer of TiO₂ to the shoots (very low TF value). These findings evidenced a potential toxicity of TiO₂ NPs present in Bs and accumulating in soil, suggesting the necessity of appropriate regulations for the occurrence of NPs in Bs used in agriculture.

Emerging investigator series: automated single-nanoparticle quantification and classification: a holistic study of particles into and out of wastewater treatment plants in Switzerland

Single particle inductively coupled plasma time-of-flight mass spectrometry (sp-ICP-TOFMS), in combination with online microdroplet calibration, allows for the determination of particle number concentrations (PNCs) and the amount (i.e. mass) of ICP-MS-accessible elements in individual particles. Because sp-ICP-TOFMS analyses of environmental samples produce rich datasets composed of both single-metal nanoparticles (smNPs) and many types of multi-metal NPs (mmNPs), interpretation of these data is well suited to automated analysis schemes. Here, we present a new data analysis approach that includes: 1. automatic particle detection and elemental mass determinations based on online microdroplet calibration, 2. correction of false (randomly occurring) multi-metal associations caused by measurement of coincident but distinct NPs, and 3. unsupervised clustering analysis of mmNPs to identify unique classes of NPs based on their element compositions. To demonstrate the potential of our approach, we analyzed water samples collected from the influent and effluent of five wastewater treatment plants (WWTPs) across Switzerland. We determined elemental masses in individual NPs, as well as PNCs, to estimate the NP removal efficiencies of the individual WWTPs. From WWTP samples collected at two points in time, we found an average of 90% and 94% removal efficiencies of single-metal and multi-metal NPs, respectively. Between 5% to 27% of detected NPs were multi-metal; the most abundant particle types were those rich in Ce-La, Fe-Al, Ti-Zr, and Zn-Cu. Through hierarchical clustering, we identified NP classes conserved across all WWTPs, as well as particle types that are unique to one or a few WWTPs. These uniquely occurring particle types may represent point sources of anthropogenic NPs. We describe the utility of clustering analysis of mmNPs for identifying natural, geogenic NPs, and also for the discovery of new, potentially anthropogenic, NP targets.

Plastic in agricultural soils - A global risk for groundwater systems and drinking water supplies? - A review

The global plastic contamination is one of the major challenges facing mankind as plastic is ubiquitously present in all environmental compartments. In contrast to freshwater and marine environments, plastic contamination of agricultural soils was only recently subject to investigations although it represents a significant amount (14%) of the global plastic pollution. Of concern is the vertical migration of plastic particles in agricultural soils and plastic-induced enhancement of pesticide transport towards underlying groundwater systems. To assess the risk of the large plastic inventory in agricultural soils for groundwater systems and drinking water supplies, this review critically synthesizes the current knowledge of the plastic mobility and plastic-pesticide interactions in agricultural soils, identifies future research directions and evaluates associated analytical challenges. The reviewed studies provide consistent evidence for vertical migration of plastic in agricultural soils towards aquifer systems, especially for sub-micrometer sized plastic particles, analogously to the well-known migration of natural particles in the sub-micrometer range (colloids). The reviewed investigations also showed that plastic changes the sorption behavior of pesticides in agricultural soils and enhances their transport towards underlying groundwater systems. Hence, the deposited plastic in agricultural soils likely poses a major risk for underlying aquifers and drinking water supplies that rely on groundwater resources below farmlands to be contaminated by plastic and pesticides. This demonstrates that improved regulatory measures are necessary regarding the general usage of plastic in the farming process to protect aquifers and drinking water supplies from plastic and pesticide contamination and to avoid a potential human health hazard.

Survey of elemental composition in dewatered sludge in Japan

The elemental composition of 120 dewatered sludge samples from 32 wastewater treatment plants in Japan was analyzed, and the influential factors determining sludge elemental composition were clarified. Through Hayashi's quantification method I, the relationship and influence of each element to the dominant categories were confirmed, and the correlation between the elements was also analyzed. The Van Krevelen diagram was used to determine the similarity in organic contents between sludge and biomass/fossil fuels. Principal component and cluster analyses were used to verify the identification of influential factors. Finally, a standard composition of dewatered sludge in Japan was defined based on different sewage collection systems and digestion processes, shown to have the greatest influence on sludge composition. The potential of sludge for agricultural and cement industrial recycling was also assessed.

Potential Anthropogenic Pollution of High-technology Metals with a Focus on Rare Earth Elements in Environmental Water

In recent years, the utilization of high-technology metals such as rare earth elements (REEs), which exist in extremely low quantities in the Earth, has rapidly increased with the development of new types of industrial materials and pharmaceutical products. This review provides an overview of a new type of potential anthropogenic pollution caused by high-technology metals, with a focus on REEs released into environmental waters from waste treatment plants. In this paper, potential anthropogenic pollution was defined as pollution caused by metals gradually enriched in the environment by human activity, although standard and guideline concentrations of these elements are not regulated by environmental quality standards for water pollution. We review the analytical methods of REEs and the potential anthropogenic pollution of REEs with a focus on Gd, from the viewpoints of a comparison of the degree of Gd anomaly, chemical speciation, ecotoxicology, and bioaccessibility. Moreover, we also highlight the comprehensive analysis based on multielement analysis of high-technology metals as well as REEs for the further screening for potential anthropogenic pollution.

Quantification of anthropogenic and geogenic Ce in sewage sludge based on Ce oxidation state and rare earth element patterns

Emissions of Ce from anthropogenic activities (anthropogenic Ce) into urban wastewater systems and the environment result from its widespread industrial use (abrasives, catalysts, nanotechnology). Because Ce in sewage sludge can also be of geogenic origin, the quantification of anthropogenic Ce in sewage sludge remains elusive. In this study, we evaluated the suitability of Ce oxidation state and rare earth element (REE) patterns for the quantification of anthropogenic Ce fractions in sewage sludge. A diverse set of soil samples served to gain baseline information on geogenic Ce. Geogenic Ce in the soils was characterized by high Ce(III) fractions (≥70%) and their REE patterns were comparable to the REE patterns of the upper continental crust. The sewage sludges contained on average ∼80% Ce(IV) (range 18-108%), pointing to the importance of anthropogenic inputs of Ce(IV). The quantification of the anthropogenic Ce fraction based on Ce oxidation state, however, was associated with considerable uncertainty because geogenic and anthropogenic Ce cannot exclusively be assigned to Ce(III) and Ce(IV), respectively. The REE patterns of most sewage sludges indicated a clear enrichment of Ce compared to heavier REE. Based on the assumption that the industrially used Ce is free of (most) other REE, we estimated the fraction of anthropogenic Ce in the sludges based on individual Ce/REE ratios. For the individual sludges the anthropogenic contributions were very variable (10-100%) but consistent fractions were obtained for individual sludges when calculated based on Ce/Dy (dysprosium), Ce/Er (erbium) and Ce/Eu (europium) ratios. Electron microscopy analysis of sludges dominated by anthropogenic Ce revealed that the Ce was mostly contained in nanoscale particles devoid of elements characteristic of Ce-bearing minerals. Thus, anthropogenic Ce contents derived from REE patterns may be used to validate current mass flow models for engineered CeO2 nanoparticles.

Anthropogenic gadolinium in freshwater and drinking water systems

The increasing use of gadolinium-based contrast agents (GBCAs) for magnetic resonance imaging is leading to widespread contamination of freshwater and drinking water systems. Contrary to previous assumptions that GBCAs are stable throughout the water cycle, they can degrade. The stability of GBCAs depends largely on their organic ligands, but also on the physicochemical conditions. There is specific concern regarding UV end-of-pipe water treatments, which may degrade GBCAs. Degradation products in drinking water supplies can increase the risk of adverse health effects. This is of particular relevance where the raw water for drinking water production has a higher proportion of recycled wastewater. GBCAs concentrations in aquatic systems, often referred to as anthropogenic gadolinium, are determined using a variety of calculation methods. Where anthropogenic gadolinium concentrations are low, the inconsistent use of these methods results in high discrepancies and high levels of uncertainty. The current COVID-19 crisis will, in the short-term, drastically decrease the input of GBCAs to freshwater systems. Temporal variations in anthropogenic gadolinium concentrations in river water can be used to better understand river-aquifer interactions and groundwater flow velocities. Collecting urine from all patients following MRI examinations could be a way forward to halt the generally increasing concentrations of Gd in drinking water systems and recover this technologically critical element.

Biosorption of Rare Earth Elements by Different Microorganisms in Acidic Solutions

Acidic solutions from metal bioleaching processes usually contain mixtures of metals in different concentrations which need to be separated and concentrated in downstream processing. Aim of this study was to explore and compare biosorption of rare earth elements (REE) by different microorganisms in acidic solutions. Biosorption of REE by bacteria and fungi showed element selective biosorption. The gram-positive bacterium Bacillus subtilis showed a higher selectivity to ytterbium (Yb) and lutetium (Lu) than the gram-negative bacteria Leisingera methylohalidivorans and Phaeobacter inhibens. In contrast, the tested fungi (Catenulostroma chromoblastomyces, Pichia sp.) showed a preference for the middle rare earth elements. Algae exhibited a low biosorption performance. Additionally, for B. subtilis and one yeast (Pichia sp.), better results were achieved with living than dead biomass. This study compares for the first time biosorption of different microorganisms at standardized conditions at low pH und application related conditions.

Visualizing the invisible: class excursions to ignite children's enthusiasm for microbes

We have recently argued that, because microbes have pervasive - often vital - influences on our lives, and that therefore their roles must be taken into account in many of the decisions we face, society must become microbiology-literate, through the introduction of relevant microbiology topics in school curricula (Timmis et al. 2019. Environ Microbiol 21: 1513-1528). The current coronavirus pandemic is a stark example of why microbiology literacy is such a crucial enabler of informed policy decisions, particularly those involving preparedness of public-health systems for disease outbreaks and pandemics. However, a significant barrier to attaining widespread appreciation of microbial contributions to our well-being and that of the planet is the fact that microbes are seldom visible: most people are only peripherally aware of them, except when they fall ill with an infection. And it is disease, rather than all of the positive activities mediated by microbes, that colours public perception of 'germs' and endows them with their poor image. It is imperative to render microbes visible, to give them life and form for children (and adults), and to counter prevalent misconceptions, through exposure to imagination-capturing images of microbes and examples of their beneficial outputs, accompanied by a balanced narrative. This will engender automatic mental associations between everyday information inputs, as well as visual, olfactory and tactile experiences, on the one hand, and the responsible microbes/microbial communities, on the other hand. Such associations, in turn, will promote awareness of microbes and of the many positive and vital consequences of their actions, and facilitate and encourage incorporation of such consequences into relevant decision-making processes. While teaching microbiology topics in primary and secondary school is key to this objective, a strategic programme to expose children directly and personally to natural and managed microbial processes, and the results of their actions, through carefully planned class excursions to local venues, can be instrumental in bringing microbes to life for children and, collaterally, their families. In order to encourage the embedding of microbiology-centric class excursions in current curricula, we suggest and illustrate here some possibilities relating to the topics of food (a favourite pre-occupation of most children), agriculture (together with horticulture and aquaculture), health and medicine, the environment and biotechnology. And, although not all of the microbially relevant infrastructure will be within reach of schools, there is usually access to a market, local food store, wastewater treatment plant, farm, surface water body, etc., all of which can provide opportunities to explore microbiology in action. If children sometimes consider the present to be mundane, even boring, they are usually excited with both the past and the future so, where possible, visits to local museums (the past) and research institutions advancing knowledge frontiers (the future) are strongly recommended, as is a tapping into the natural enthusiasm of local researchers to leverage the educational value of excursions and virtual excursions. Children are also fascinated by the unknown, so, paradoxically, the invisibility of microbes makes them especially fascinating objects for visualization and exploration. In outlining some of the options for microbiology excursions, providing suggestions for discussion topics and considering their educational value, we strive to extend the vistas of current class excursions and to: (i) inspire teachers and school managers to incorporate more microbiology excursions into curricula; (ii) encourage microbiologists to support school excursions and generally get involved in bringing microbes to life for children; (iii) urge leaders of organizations (biopharma, food industries, universities, etc.) to give school outreach activities a more prominent place in their mission portfolios, and (iv) convey to policymakers the benefits of providing schools with funds, materials and flexibility for educational endeavours beyond the classroom.

Paradigm shifts and current challenges in wastewater management

Wastewater is a significant environmental and public health concern which management is a constant challenge since antiquity. Wastewater research has increased exponentially over the last decades. This paper provides a global overview of the exponentially increasing wastewater research in order to identify current challenges and paradigm shifts. Besides households, hospitals and typical industries, other sources of wastewater appear due to emerging activities like hydraulic fracturing. While the composition of wastewater needs constant reassessment to identify contaminants of interest, the comprehensive chemical and toxicological analysis remains one of the main challenges in wastewater research. Moreover, recent changes in the public perception of wastewater has led to several paradigm shifts: i) water reuse considering wastewater as a water resource rather than a hazardous waste, ii) wastewater-based epidemiology considering wastewater as a source of information regarding the overall health of a population through the analysis of specific biomarkers, iii) circular economy through the implementation of treatment processes aiming at harvesting valuable components such as precious metals or producing valuable goods such as biofuel. However, wastewater research should also address social challenges such as the public acceptance of water reuse or the access to basic sanitation that is not available for nearly a third of the world population.

Mercury loads and fluxes from wastewater: A nationwide survey in Switzerland

Mercury (Hg) pollution threatens ecosystems and human health. Wastewater treatment plants (WWTPs) play a key role in limiting Hg discharges from wastewaters to rivers and lakes, but large-scale studies to estimate Hg loads and discharge at national levels are scarce. We assessed the concentration, flux, speciation, and removal of Hg in municipal wastewater throughout Switzerland by investigating 64 WWTPs in a pre-study and a subset of 28 WWTPs in the main study. We also studied the behavior and pathways of Hg along the various treatment steps in a state-of-the-art WWTP. The resulting dataset, representative of industrialized countries, provides an overview of (i) current Hg concentration ranges, (ii) average per capita loads, and (iii) wastewater Hg inputs into surface waters. The results allowed estimation of a total Hg (THg) load in Swiss wastewater of 130 ± 30 kg THg/year (15.7 mg/capita/y), of which 96 ± 4% is retained in sewage sludge. About 4.7 ± 0.5 kg THg/year (0.57 mg/capita/y) is discharged with the treated wastewater into surface waters. This corresponds to only 1.5-3% of the THg load carried by the major Swiss rivers, indicating that >95% of riverine Hg originates from other sources. Extrapolation to the population of Europe would yield a total amount of 11,700 kg THg/year in raw wastewater, with some 480 kg THg/year discharged to surface waters. Monomethyl mercury on average accounted for 0.23% of THg, and its fraction remained constant along the different treatment steps.

Occurrence and fate of antimony in plastics

Antimony (Sb) is a technology critical element whose presence is ubiquitous in manufactured products, and in particular in plastics where it is used extensively as a flame retardant synergist for brominated compounds, as a catalyst for polyethylene terephthalate production, and as a pigment for colour. This study reviews the usage, regulations and fate of Sb in plastics by examining primary data on its production, applications, contents in and migration from manufactured objects, and presence in and release from waste, including the disposal and recycling routes for this material (i.e., non-controlled disposal, incineration, landfilling and recycling). Consumption of Sb and the relative apportioning of the metalloid between different uses in plastics change continuously and are largely driven by dynamic economic factors; accordingly, reference to secondary data or sources can be misleading. Since Sb is not recovered from plastics, its fate is entirely linked to the fate of plastics themselves which, as far as disposal and recycling are concerned, might be dictated by the presence of co-associated regulated substances such as brominated flame retardants. Significantly, because of the high leachability of Sb from bottom incineration ashes, the EU considers the metalloid as the most problematic substance regarding the potential reuse of this material.

Occurrence, geochemical fractionation, and environmental risk assessment of major and trace elements in sewage sludge

Industrialization and accelerated population growth have created a huge amount of sewage sludge. Many studies have reported the sewage sludge as a sink of major and trace elements, but less is known about their geochemical fractionations. In order to assess the mobility, the distribution, bioavailability, and toxicity of those elements in sludge, we collected the sewage sludge samples from all the seven wastewater treatment plants in Xiamen City, China. Results revealed a strong spatial variation and the occurrence of 48 elements with concentrations ranging from 1.00×10^-2 mg kg^-1 (Re) to 9.03×10¹ g kg^-1 (Fe) on the basis of dry sludge weight. Sequential extraction procedure showed that residual and oxidizable fractions were the main geochemical fractions of most studied elements. However, Ca, Mn, Sr, and Ni were mainly bound to acid-exchangeable fractions, while Fe, Zn, Cd, Cr, Co, and V were mainly distributed in the reducible fractions. The contamination factor and risk assessment code indicated that Ni, Cu, Zn, Cd, Cr, Co, Sr, Ca, Mn, Mo, Re, and W were highly mobile with less retention time and exerted high environmental risks through sludge land application. The sludge disposal strategy should consider not only the total concentrations of a broad range of elements but also their bioavailability.

Transformation of Nanoscale and Ionic Cu and Zn during the Incineration of Digested Sewage Sludge (Biosolids)

Engineered nanoparticles (NP) discharged to sewers are efficiently retained by wastewater treatment plants and accumulate in the sewage sludge, which is commonly digested. The resulting biosolids are either used as fertilizer or incinerated. In this study, we address the transformation of Cu and Zn during sewage sludge incineration and evaluate whether the form of Cu or Zn (nanoparticulate versus dissolved) added to the digested sewage sludge affects the fate of the metals during incineration. We spiked CuO-NP, dissolved CuSO₄, ZnO-NP, or dissolved ZnSO₄ into anaerobically digested sewage sludge to reach Cu and Zn concentrations of ≈2500 and ≈3700 mg/kg and maintained the sludge under mesophilic, anaerobic conditions for 24 h. Subsequently, the sludge was incinerated in a pilot fluidized bed reactor. The speciation of Cu and Zn in the sludge, derived from X-ray absorption spectroscopy measurements, was dominated by sulfidic species, with >90% of Cu and >60% of Zn coordinated to reduced sulfur groups. In the ash, both Cu (>60%) and Zn (≈100%) were coordinated to oxygen. The chemical speciation of Cu and Zn in the ashes was independent of whether they were spiked in the dissolved or nanoparticulate form and closely matched the speciation of Cu and Zn observed in ashes from full-scale incinerators.

Ion exchange removal of Cu(II), Fe(II), Pb(II) and Zn(II) from acid extracted sewage sludge - Resin screening in weak acid media

A shortage of phosphate rock resources has led to a focus on the use of sewage sludge as a fertiliser. One factor preventing the unlimited application of sewage sludge in agriculture is the heavy metal content. This work looks at a process where weak acid leaching of sewage sludge would be coupled to ion exchange (IX) for heavy metal ion removal. IX offers an effective method for the recovery of these metals from a leachate. This study presents the pH performance of six selected IX resins in extracting Cu²⁺, Fe²⁺, Pb²⁺ and Zn²⁺ from acetic, lactic and citric acid media simulated weak acid leachate. Acetic acid media displayed limited suppression of metal extraction, whilst lactic and citric acid media rendered MTS9100 ineffective. Lactic acid media when combined with C107E resin allows for the targeted extraction of lead. Both MTS9570 and MTS9501 display high ferrous extraction in all media at all pH values, although citric acid hinders extraction by both resins at higher pH values. TP214 is selective for copper over all other metal ions in all weak acid media. MTS9301 is the most effective at extracting all metals from all media solutions, with separation of copper becoming more apparent when transitioning to citric acid.

Behavior of major and trace elements in a transient surface water/groundwater system following removal of a long-term wastewater treatment facility source

In many aquatic environments, municipal wastewater treatment facility (WWTF) effluent discharges influence local hydrologic and chemical connectivity between the surface-water and adjacent alluvial shallow-groundwater systems. Fourmile Creek located in Polk County, Iowa received effluent from the Ankeny WWTF for nearly forty years before it was shut down in November 2013. The decommissioning of the municipal WWTF provided a unique opportunity to characterize the recovery from impacts of treated wastewater discharge on water quality at the surface-water/groundwater interface in a shallow, unconfined alluvial aquifer. Dissolved major element and trace element concentrations in Fourmile Creek surface water, hyporheic-zone water, and shallow, unconfined groundwater were monitored upstream and downstream from the WWTF discharge before and after the shutdown. Multivariate statistical techniques including principal component analysis (PCA) and agglomerative hierarchical clustering (AHC) were used to differentiate source-water contributions, characterize elemental components, and describe surface-water/groundwater interaction dynamics. During the post-closure assessment, there was subsurface attenuation of wastewater constituents including Al, B, Cu, Gd, K, Mo, Na, P, Pb, Sb, and Zn. During the same time, groundwater concentrations increased for As, Ba, Ca, Fe, Mg, Mn, SiO₂, Sr, and U and represented a profile characteristic of the shallow alluvial aquifer. Hydrologic conditions transitioned from predominantly wastewater infiltration and hyporheic exchange before the WWTF shutdown, to predominantly discharge of native groundwater. Precipitation-driven streamflow events created fluctuations in the groundwater water-table elevations, resulting in variable contact between the saturated and unsaturated zones within the unconfined, alluvial aquifer and intermittent exposure to constituents stored in the sediments. The inorganic fingerprint of municipal wastewater was flushed relatively quickly (≤19 weeks) from the hyporheic zone indicating that processes like diffusion or sorption/desorption that might extend recovery may not be important for many trace elements in this system.

Cryptic footprints of rare earth elements on natural resources and living organisms

BACKGROUND

Rare earth elements (REEs) are gaining attention due to rapid rise of modern industries and technological developments in their usage and residual fingerprinting. Cryptic entry of REEs in the natural resources and environment is significant; therefore, life on earth is prone to their nasty effects. Scientific sectors have expressed concerns over the entry of REEs into food chains, which ultimately influences their intake and metabolism in the living organisms.

OBJECTIVES

Extensive scientific collections and intensive look in to the latest explorations agglomerated in this document aim to depict the distribution of REEs in soil, sediments, surface waters and groundwater possibly around the globe. Furthermore, it draws attention towards potential risks of intensive industrialization and modern agriculture to the exposure of REEs, and their effects on living organisms. It also draws links of REEs usage and their footprints in natural resources with the major food chains involving plants, animals and humans.

METHODS

Scientific literature preferably spanning over the last five years was obtained online from the MEDLINE and other sources publishing the latest studies on REEs distribution, properties, usage, cycling and intrusion in the environment and food-chains. Distribution of REEs in agricultural soils, sediments, surface and ground water was drawn on the global map, together with transport pathways of REEs and their cycling in the natural resources.

RESULTS

Fourteen REEs (Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Tb, Th and Yb) were plighted in this study. Wide range of their concentrations has been detected in agricultural soils (<15.9-249.1 μg g^-1) and in groundwater (<3.1-146.2 μg L^-1) at various sites worldwide. They have strong tendency to accumulate in the human body, and thus associated with kidney stones. The REEs could also perturb the animal physiology, especially affecting the reproductive development in both terrestrial and aquatic animals. In plants, REEs might affect the germination, root and shoot development and flowering at concentration ranging from 0.4 to 150 mg kg^-1.

CONCLUSIONS

This review article precisely narrates the current status, sources, and potential effects of REEs on plants, animals, humans health. There are also a few examples where REEs have been used to benefit human health. However, still there is scarce information about threshold levels of REEs in the soil, aquatic, and terrestrial resources as well as living entities. Therefore, an aggressive effort is required for global action to generate more data on REEs. This implies we prescribe an urgent need for inter-disciplinary studies about REEs in order to identify their toxic effects on both ecosystems and organisms.

Synthesis of metal-doped nanoplastics and their utility to investigate fate and behaviour in complex environmental systems

Research on the distribution and effects of particulate plastic has intensified in recent years and yet, due to analytical challenges, our understanding of nanoplastic occurrence and behaviour has remained comparatively elusive. However, process studies could greatly aid in defining key parameters for nanoplastic interactions within and transfers between technical and environmental compartments. Here we provide a method to synthesize nanoplastic particles doped with a chemically entrapped metal used as a tracer, which provides a robust way to detect nanoplastics more easily, accurately and quantitatively in complex media. We show the utility of this approach in batch studies that simulate the activated sludge process of a municipal waste water treatment plant and so better understand the fate of nanoplastics in urban environments. We found that the majority of particles were associated with the sludge (>98%), with an average recovery of over 93% of the spiked material achieved. We believe that this approach can be developed further to study the fate, transport, mechanistic behaviour and biological uptake of nanoplastics in a variety of systems on different scales.

Natural, incidental, and engineered nanomaterials and their impacts on the Earth system

Nanomaterials are critical components in the Earth system’s past, present, and future characteristics and behavior. They have been present since Earth’s origin in great abundance. Life, from the earliest cells to modern humans, has evolved in intimate association with naturally occurring nanomaterials. This synergy began to shift considerably with human industrialization. Particularly since the Industrial Revolution some two-and-a-half centuries ago, incidental nanomaterials (produced unintentionally by human activity) have been continuously produced and distributed worldwide. In some areas, they now rival the amount of naturally occurring nanomaterials. In the past half-century, engineered nanomaterials have been produced in very small amounts relative to the other two types of nanomaterials, but still in large enough quantities to make them a consequential component of the planet. All nanomaterials, regardless of their origin, have distinct chemical and physical properties throughout their size range, clearly setting them apart from their macroscopic equivalents and necessitating careful study. Following major advances in experimental, computational, analytical, and field approaches, it is becoming possible to better assess and understand all types and origins of nanomaterials in the Earth system. It is also now possible to frame their immediate and long-term impact on environmental and human health at local, regional, and global scales.

Leaching behavior of major and trace elements from sludge deposits of a French vertical flow constructed wetland

Surface sludge deposits were collected from a French Vertical Flow Constructed Wetland (French VFCW) sewage treatment plant. The objectives were to characterize the retention of major elements and trace metals within the sludge deposits particles under regular operating conditions, and the influence of extreme pH conditions on their potential release which may occur in situations when the plant malfunctions or after land application of the dredged sludge. A sequential extraction protocol was first used to assess the distribution of the elements within the sludge deposits. Results showed that most of Cu and Pb were associated to organic matter within the oxidizable fraction. Zn, Ni and Cd were distributed in several fractions, notably bound to Fe-Mn oxides and associated to organic matter. Cr was analyzed mostly in the residual fraction. Aliquot fractions of sludge deposits were also submitted to Acid and Base Neutralization Capacity tests (ANC-BNC) where the samples were suspended into acidic or alkaline aqueous solutions, and the solutions analyzed after 48 h contact time. Results showed a pH-dependent leaching profile for all monitored elements. The role of organic matter was observed for almost all metals. It was particularly dominant for Cu which was leached more extensively under alkaline than acidic conditions. Since Cu is not an amphoteric element, this leaching pattern was attributed to the leaching of organic matter which followed a similar pH-dependent profile than Cu. Spectrometric indices were used to characterize soluble organic compounds. Results showed that complex and humified dissolved organic compounds were mostly released under alkaline conditions.

Comparative characterization of surface sludge deposits from fourteen French Vertical Flow Constructed Wetlands sewage treatment plants using biological, chemical and thermal indices

Due to their design and mode of operation, French Vertical Flow Constructed Wetlands (VFCWs) accumulate suspended solids from the inflow wastewater in the form of a sludge layer at the surface of the first filter. In order to maintain the treatment performance over the long term, the characteristics of the sludge deposits and their evolution have to be well described. In this objective, a panel of sludge deposit samples taken from 14 French VFCW sewage treatment plants was investigated. Elemental composition and organic matter content, nature and reactivity were analyzed. Results clearly revealed two categories of sludge deposits, namely the "young-age plants" type (1 year of operation and less) and the "mature plants" type (3 years of operation and more). Sludge deposits from the "mature plants" exhibited same biological, physical and chemical properties. Their organic matter was globally less abundant, more humified and less biodegradable than in the young-age plants type. Their overall contents in trace metals were also higher, although in a limited manner. The effect of additional treatments, particularly FeCl₃ injection for phosphorus precipitation, was observable in the "young-age plants" group. Finally, the sludge deposits sampled from one particular plant with specific operating conditions were found to exhibit very different characteristics from those of either groups identified. This observation underlined the influence of local conditions on the typology of the sludge deposits.

Sources, behaviour, and environmental and human health risks of high-technology rare earth elements as emerging contaminants

Recent studies show that high-technology rare earth elements (REEs) of anthropogenic origin occur in the environment including in aquatic systems, suggesting REEs are contaminants of emerging concern. However, compared to organic contaminants, there is a lack of comprehensive reviews on the anthropogenic sources, environmental behaviour, and public and ecological health risks of REEs. The current review aims to: (1) identify anthropogenic sources, transfer mechanisms, and environmental behaviour of REEs; (2) highlight the human and ecological health risks of REEs and propose mitigation measures; and (3) identify knowledge gaps and future research directions. Out of the 17 REEs, La, Gd, Ce and Eu are the most studied. The main sources of anthropogenic REE include; medical facilities, petroleum refining, mining and technology industries, fertilizers, livestock feeds, and electronic wastes and recycling plants. REEs are mobilized and transported in the environment by hydrological and wind-driven processes. Ecotoxicological effects include reduced plant growth, function and nutritional quality, genotoxicity and neurotoxicity in animals, trophic bioaccumulation, chronic and acute toxicities in soil organisms. Human exposure to REEs occurs via ingestion of contaminated water and food, inhalation, and direct intake during medical administration. REEs have been detected in human hair, nails, and biofluids. In humans, REEs cause nephrogenic systemic fibrosis and severe damage to nephrological systems associated with Gd-based contrast agents, dysfunctional neurological disorder, fibrotic tissue injury, oxidative stress, pneumoconiosis, cytotoxicity, anti-testicular effects, and male sterility. Barring REEs in medical devices, epidemiological evidence directly linking REEs in the environment to human health conditions remains weak. To minimize health risks, a conceptual framework and possible mitigation measures are highlighted. Future research is needed to better understand sources, environmental behaviour, ecotoxicology, and human epidemiology. Moreover, research on REEs in developing regions, including Africa, is needed given prevailing conditions predisposing humans to health risks (e.g., untreated drinking water).

Ozonation of municipal wastewater effluent containing metal sulfides and metal complexes: Kinetics and mechanisms

Ozonation can be applied to mitigate the discharge of organic micropollutants from municipal wastewater treatment plants (WWTPs) to the aquatic environment. The toxicity of metals also present in WWTP effluents strongly depends on their speciation. Therefore, knowledge on the change of the metal speciation during ozonation of a WWTP effluent is essential to assess possible negative impacts. The kinetics and the stoichiometries of the reactions of ozone with three metal sulfides (ZnS, CuS and CdS) and metal-ethylenediaminetetraacetate (EDTA)/nitriloriacetic acid (NTA) complexes of Cu(II), Cd(II), Ni(II), Zn(II), Mg(II) and Pb(II) were investigated. With a stoichiometric factor of 2.6-3.9 moles of ozone per mole of sulfide and apparent second-order rate constants at pH 8 > 10⁴ M^-1 s^-1, a complete oxidation of the sulfides and a concomitant release of the respective metals is expected during ozonation of a WWTP effluent for enhanced micropollutant abatement. The apparent second-order rate constants at pH 8 for the reactions of metal-EDTA complexes with ozone ranged from 42 M^-1s^-1 to 2.0 × 10⁴ M^-1s^-1 and increased in the order Cd(II) < Cu(II) < Mg(II) < Ni(II) < Zn(II). Approximately 40% of Cd(II)-EDTA spiked to a WWTP effluent was oxidized at typical specific ozone doses of 0.5-0.7 g_O3/g_DOC. For the other metal-EDTA complexes a significantly higher fraction was oxidized. The bioavailable fraction determined by the diffusive-gradient thin films (DGT) method in the WWTP effluent increased during ozonation, due to the oxidative release of the metal ions. Algal toxicity (chlamynomodas reinhardtii) tests with CuS/CdS spiked WWTP effluent revealed a high tolerance toward Cu and Cd in the respective media. A toxic response was only observed at Cu concentrations above 10 μM, which is above typical WWTP effluent concentrations. Biological post-treatment after ozonation generally reduced the bioavailability of the metals, which resulted in a lower toxicity. Therefore, the biological post-treatment serves as an additional barrier to protect the downstream ecology of receiving waters.