Iron-bearing nanoparticles (IBNPs) were abundant in particulate matter (PM). Due to their high reactivity, IBNPs were considered hazardous to human health, however, their toxic mode-of-action(s) are highly unclear. Ferroptosis is a novel programmed cell death (PCD) that highly associated with intracellular iron. However, the pro-ferroptotic effect of IBNPs has not been characterized. To this end, we ought to investigate whether and how IBNPs (synthetic γ-Fe₂O₃ and Fe₃O₄ NPs were selected as the model compounds) are involved in ferroptosis. We found that human umbilical vein endothelial cells (HUVECs) phagocytized large qualities of γ-Fe₂O₃ and Fe₃O₄ NPs, resulting in increased intracellular iron level. We further observed the disrupted cystine/glutamate reverse transporter (System Xc⁻) and glutathione peroxidase 4 (GPX4) signaling in γ-Fe₂O₃ and Fe₃O₄ NPs-challenged HUVECs. γ-Fe₂O₃ and Fe₃O₄ NPs could also cause mitochondrial fusion and fission dysregulation, activate lipid peroxidation and iron metabolism-related genes in a P53-dependent manner. Together, the ferroptotic activity of IBNPs should be acknowledged for the risk assessment of PM associated health effects.

Phosphorus (P) cycling present in sediments associated with iron (Fe), manganese (Mn) and sulfur (S) geochemical processes may cause secondary pollution in overlying water. Understanding the mechanisms of P release from sediments should help to restore water quality. This study used the diffusive gradients in thin film (DGT) technique to investigate the seasonal variation in the lability, remobilization mechanisms, and release characteristics of sediment P in the uncontaminated Xizhi River and the severely contaminated Danshui River, South China. P accumulation in sediments contributed to higher DGT-labile P concentrations in contaminated reaches, and the highest labile P concentrations were generally observed in summer season at each site. The significant positive relationships (p < 0.05) between labile Fe and P confirmed the Fe–P coupling release mechanism in uncontaminated sediments. Stronger relationships between labile Mn and P at contaminated sites indicated that Mn oxides played an important role in P remobilization. However, sulfate reduction associated with microbial activities (crucial genera: Desulfobulbus, Desulfomicrobium and Desulforhabdus) was considered to decouple the Fe & Mn–P cycling relationship, promoting P release at contaminated sites. The effluxes of sediment P were much higher in the Danshui River (mean 0.132 mg cm⁻²·d⁻¹) than in the Xizhi River (mean 0.038 mg cm⁻²·d⁻¹). And hot season led to growth in P effluxes that was much greater in contaminated river.

Populations of plants and animals, including humans, living in close proximity to abandoned uranium mine sites are vulnerable to uranium exposure through drainage into nearby waterways, soil accumulation, and blowing dust from surface soils. Little is known about how the environmental impact of uranium exposure alters the health of human populations in proximity to mine sites, so we used developmental zebrafish (Danio rerio) to investigate uranium toxicity. Fish are a sensitive target for modeling uranium toxicity, and previous studies report altered reproductive capacity, enhanced DNA damage, and gene expression changes in fish exposed to uranium. In our study, dechorionated zebrafish embryos were exposed to a concentration range of uranyl acetate (UA) from 0 to 3000 μg/L for body burden measurements and developmental toxicity assessments. Uranium was taken up in a concentration-dependent manner by 48 and 120 h post fertilization (hpf)-zebrafish without evidence of bioaccumulation. Exposure to UA was not associated with teratogenic outcomes or 24 hpf behavioral effects, but larvae at 120 hpf exhibited a significant hypoactive photomotor response associated with exposure to 3 μg/L UA which suggested potential neurotoxicity. To our knowledge, this is the first time that uranium has been associated with behavioral effects in an aquatic organism. These results were compared to potential metal co-contaminants using the same exposure paradigm. Similar to uranium exposure, lead, cadmium, and iron significantly altered neurobehavioral outcomes in 120-hpf zebrafish without inducing significant teratogenicity. Our study informs concerns about the potential impacts of developmental exposure to uranium on childhood neurobehavioral outcomes. This work also sets the stage for future, environmentally relevant metal mixture studies. Summary Uranium exposure to developing zebrafish causes hypoactive larval swimming behavior similar to the effect of other commonly occurring metals in uranium mine sites. This is the first time that uranium exposure has been associated with altered neurobehavioral effects in any aquatic organism.

Fe-based nanoparticles (Fe-based NPs) have great potential as a substitute for traditional Fe-fertilizer; however, their environmental risk and impact on plant growth are not fully understood. In this study, we compared the physiological impacts of three different Fe-based NP formulations: zero-valent iron (ZVI), Fe₃O₄ and Fe₂O₃ NPs, on hydroponic rice after root exposure for 2 weeks. Fe-normal (Fe(+)) and Fe-deficiency (Fe(−)) conditions were compared. Results showed that low dose (50 mg L⁻¹) of ZVI and Fe₃O₄ NPs improved the rice growth under Fe(−) condition, while Fe₂O₃ NPs did not improve plant growth and caused phytotoxicity at high concentration (500 mg L⁻¹). Under Fe(+) conditions, none of the Fe-based NPs exhibited positive effects on the rice plants with plant growth actually being inhibited at 500 mg L⁻¹ evidenced by reduced root volume and leaf biomass and enhanced oxidative stress in plant. Under Fe(−) condition, low dose (50 mg L⁻¹) of ZVI NPs and Fe₃O₄ NPs increased the chlorophyll content by 30.7% and 26.9%, respectively. They also alleviated plant stress demonstrated by the reduced oxidative stress and decreased concentrations of stress related phytohormones such as gibberellin and indole-3-acetic acid. Low dose of ZVI and Fe₃O₄ NPs treatments resulted in higher Fe accumulation in plants compared to Fe₂O₃ NPs treatment, by down-regulating the expression of IRT1 and YSL15. This study provides significant insights into the physiological impacts of Fe-based NPs in rice plants and their potential application in agriculture. ZVI and Fe₃O₄ NPs can be used as Fe-fertilizers to improve rice growth under Fe-deficient condition, which exist in many rice-growing regions of the world. However, dose should be carefully chosen as high dose (500 mg L⁻¹ in this study) of the Fe-based NPs can impair rice growth.

Twenty-five years after the first look at polycyclic aromatic compounds (PACs) in Canada, this article presents current knowledge on Canadian PAC emission sources. The analysis is based on national inventories (the National Pollutant Release Inventory (NPRI) and the Air Pollutant Emissions Inventory (APEI)), an analysis of Canadian forest fires, and several air quality model-ready emissions inventories. Nationally, forest fires continue to dominate PAC emissions in Canada, however there is uncertainty in these estimates. Though forest fire data show a steady average in the total annual area burned historically, an upward trend has developed recently. Non-industrial sources (home firewood burning, mobile sources) are estimated to be the second largest contributor (∼6-8 times lower than forest fires) and show moderate decreases (25%–65%) in the last decades. Industrial point sources (aluminum production, iron/steel manufacturing) are yet a smaller contributor and have seen considerable reductions (90% +) in recent decades. Fugitive emissions from other industrial sources (e.g. disposals by the non-conventional oil extraction and wastewater sectors, respectively) remain a gap in our understanding of total PAC emissions in Canada. Emerging concerns about previously unrecognized sources such as coal tar-sealed pavement run-off, climate change are discussed elsewhere in this special issue. Results affirm that observations at the annual/national scale are not always reflective of regional/local or finer temporal scales. When determining which sources contribute most to human and ecosystem exposure in various contexts, examination at regional and local scales is needed. There is uncertainty overall in emissions data stemming in part from various accuracy issues, limitations in the scope of the various inventories, and inventory gaps, among others.

Selective removal of arsenic (As) is the key challenge for any of As removal mechanisms as this not only increases the efficiency of removal of the main As species (neutral As(III) and As(V) hydroxyl-anions) but also allows for a significant reduction of waste as it does not co-remove other solutes. Selective removal has a number of benefits: it increases the capacity and lifetime of units while lowering the cost of the process. Therefore, a sustainable selective mitigation method should be considered concerning the economic resources available, the ability of infrastructure to sustain water treatment, and the options for reuse and/or safe disposal of treatment residuals. Several methods of selective As removal have been developed, such as precipitation, adsorption and modified iron and ligand exchange. The biggest challenge in selective removal of As is the presence of phosphate in water which is chemically comparable with As(V). There are two types of mechanisms involved with As removal: Coulombic or ion exchange; and Lewis acid-base interaction. Solution pH is one of the major controlling factors limiting removal efficiency since most of the above-mentioned methods depend on complexation through electrostatic effects. The different features of two different As species make the selective removal process more difficult, especially under natural conditions. Most of the selective As removal methods involve hydrated Fe(III) oxides through Lewis acid-base interaction. Microbiological methods have been studied recently for selective removal of As, and although there have been only a small number of studies, the method shows remarkable results and indicates positive prospects for the future.

Black bloom has become an increasingly severe environmental and ecological problem in lots of lakes. Ferrous monosulfide (FeS), which is closely related to chemical iron reduction (CIR), is considered the major cause for black water in shallow lakes, but few studies focus on the effect of organic matters (OM) content on iron and sulfate reduction and its contribution to the black bloom in deep lakes. Here, in Lake Fuxian, a Chinese deep lake which has also suffered from black bloom, FeS was identified responsible for the surface water blackness by using multiple microscopy and element analyses. Dissolved oxygen (DO) penetrated 1.6–4.2 mm in all sediment sites, further indicating FeS formed in the sediments instead of the permanently oxic water column. Geochemical characteristics revealed by diffusive gradients in thin films (DGT) showed that DGT-Fe²⁺ concentration was 57.6–1919.4 times higher than the DGT-S²⁻ concentration and both were positively correlated with DGT-PO₄³⁻. Combining DGT profiles and anaerobic OM remineralization rate according to bag incubation, iron reduction is more effective than sulfate reduction although the two processes coexisted. Moreover, correlation of DGT-Fe²⁺ and DGT-PO₄³⁻ was better than that of DGT-PO₄³⁻ and DGT-S²⁻ at OM-depleted sites but opposite at OM-rich sites. In addition, total organic carbon (TOC) was significantly positively related to acid volatile sulfide (AVS). We therefore conclude that abundant OM potentially exacerbate chemical iron reduction and further lead to surface water blackness. Our study revealed the mechanisms behind the black bloom and gives credence to the management strategy of reducing OM loading to protect water quality in deep lakes.

Transition metals (TMs) (e.g. copper (Cu) and iron (Fe)) and certain organic compounds are known active constituents causing oxidative potential (OP) by inhaled ambient fine particulate matter (PM₂.₅) in lung fluid. Humic-like substances (HULIS), isolated from atmospheric PM₂.₅, are largely metal-free and contain mixtures of organics that are capable of complexing TMs. TMs and HULIS co-exist in the water-extractable part of PM₂.₅. In this work, we used a solid phase extraction procedure to isolate the water-soluble TMs in the hydrophilic fraction (HPI) and HULIS in the hydrophobic fraction (HPO) and carried out this isolation procedure to a set of 32 real-world PM₂.₅ samples collected in Beijing and Hong Kong, China. We quantified two OP endpoints, namely hydroxyl radical formation (denoted as OP•OH) and ascorbic acid depletion (denoted as OPAA), by the two fractions separately and combined, as well as by the bulk water-soluble aerosols. OP•OH and OPAA were well-correlated in both separate fractions and their combined mixtures or bulk water-soluble aerosols. OP by HPI far exceeded that by HPO. On a per unit PM₂.₅ mass basis, the Hong Kong samples on average had a higher OPAA and OP•OH than the Beijing samples due to more water-soluble Cu. For HPI, Cu was a dominant OP•OH and OPAA contributor (>80%), although water-soluble Fe was present at a concentration approximately one order of magnitude higher. Suppression effects on OP•OH were observed through comparing the OP of the bulk water-soluble aerosol with that of HPI. Our work reveals the importance of monitoring PM₂.₅ chemical compositions (especially water-soluble redox active metals). Furthermore, we demonstrate the need to consider metal-organic interactions when evaluating the aggregate OP by PM₂.₅ from individual components or apportioning OP by PM₂.₅ to specific chemical components.

Perfluorohexane sulfonate (PFHxS) has been newly recommended to be added into the Stockholm Convention on persistent organic pollutants (POPs). As one of the major perfluoroalkyl pollutants, its long half-time in human serum and neurotoxicity are cause for significant concern. Although mechanochemical degradation has been evaluated as a promising ecofriendly technology to treat pollutants, the extraordinary stability of poly- and perfluoroalkyl substances (PFASs) raises harsh requirements for co-milling reagents. In the present study, zero-valent iron (ZVI) and ferrate(VI) were for the first time used as the co-milling reagents to degrade PFHxS. When ZVI and ferrate(VI) were used alone, both the degradation and defluorination efficiencies were low. However, after milling at the optimum ratio (ferrate(VI):ZVI = 1:2) for 4 h, the synergistic effect of ZVI and ferrate(VI) resulted in almost complete degradation (100%) and defluorination (95%). Two points can account for this excellent performance: (1) the mechanochemical energy input in the system initiates and prominently promotes related reactions; and (2) the active species generated from the reactions among ZVI, ferrate(VI) and other high-valent iron species will accelerate the process of electron transfer. The sulfonate group comprises the favorable attack sites, as corroborated by both the identified intermediates and quantum chemical calculations. The homolysis of the C–S bond is not only the triggering step, but also the rate-limiting step. In summary, the present work confirms the feasibility and underlying mechanism of the ZVI–ferrate(VI) co-milling system to defluorinate PFHxS, which might be a promising technology to treat PFASs in solid wastes.