The COVID-19 pandemic has resulted in an unprecedented surge of production, consumption, and disposal of personal protective equipment (PPE) including face masks, disposable gloves, and disinfectant wipes, which are often made of single use plastic. Widespread public use of these items has imposed pressure on municipalities to properly collect and dispose of potentially infectious PPE. There has been a lack of structured monitoring efforts to quantify the emerging trend of improperly disposed of PPE debris. In this study, we present a baseline monitoring survey to describe the spatial distribution of PPE debris during the COVID-19 pandemic from the metropolitan city of Toronto, Canada. Our objectives were to: (1) quantify PPE debris types among surveyed areas and; (2) identify PPE debris densities and accumulation of surveyed areas. A total of 1306 PPE debris items were documented, with the majority being disposable gloves (44%), followed by face masks (31%), and disinfecting wipes (25%). Of the face masks, 97% were designed for single use while only 3% were reusable. Of the surveyed locations, the highest daily average densities of PPE debris were recorded in the large and medium-sized grocery store parking lots and the hospital district (0.00475 items/m², 0.00160 items/m², and 0.00133 items/m² respectively). The two surveyed residential areas had the following highest PPE densities (0.00029 items/m² and 0.00027 items/m²), while the recreational trail had the lowest densities (0.00020 items/m²). Assuming a business-as-usual accumulation, an estimated 14,298 PPE items will be leaked as debris in just the surveyed areas annually. To facilitate proper disposal of PPE debris by the public we recommend development of municipal efforts to improve PPE collection methods that are informed by the described PPE waste pathways.

Perfluorobutanesulfonate (PFBS) is an emerging pollutant in aquatic environments and potently disrupts the early developmental trajectory of teleosts. Considering the persistent and toxic nature of PFBS, it is necessary to develop in situ protective measures to ameliorate the toxic damage of PFBS. Probiotic supplements are able to mitigate the growth retardation defects of PFBS. However, the interactive mechanisms remain elusive. To this end, this study acutely exposed zebrafish larvae to a concentration gradient of PFBS (0, 1, 3.3 and 10 mg/L) for 4 days, during which probiotic bacteria Lactobacillus rhamnosus were added in the rearing water. After exposure, alterations in gene transcriptions and key hormones along the hypothalamus–pituitary–interrenal (HPI), growth hormone/insulin–like growth factor (GH/IGF) and hypothalamus–pituitary–thyroid (HPT) axes were examined. The results showed that PFBS single exposure significantly increased the cortisol concentrations, suggesting the induction of stress response, while probiotic supplementation effectively decreased the cortisol levels in coexposed larvae in an attempt to relieve the stress of PFBS toxicant. It was unexpected that probiotic additive significantly decreased the larval GH concentrations independent of PFBS, thereby eliminating the contribution of GH/IGF axis to the growth improvement of probiotics. In contrast, probiotic bacteria remarkably increased the concentration of thyroid hormones, particularly the thyroxine (T4), in zebrafish larvae. The pronounced down-regulation of uridinediphosphate glucoronosyltransferases (UDPGT) gene pointed to the blocked elimination process of T4 by probiotics. Furthermore, proteomic fingerprinting found that probiotics were potent to shape the protein expression pattern in PFBS-exposed zebrafish larvae and modulated multiple biological processes that are essential for the growth. In summary, the present findings suggest that HPI and HPT axes may cooperate to enhance the growth of fish larvae under PFBS and probiotic coexposures.

PM₂.₅ (particulate matter ≤2.5 μm in aerodynamic diameter) is a major urban air pollutant worldwide. Its effects on the respiratory system of the susceptible population have been less characterized. This study aimed to estimate the association of short-term PM₂.₅ exposure with respiratory outcomes of the retired adults, and to examine whether these associations were stronger among the subjects with GSTT-null genotype. 32 healthy subjects (55–77 years) were recruited for five follow-up examinations. Ambient concentrations of PM₂.₅ were monitored consecutively for 7 days prior to physical examination. Pulmonary outcomes including forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), peak expiratory flow (PEF), and fractional exhaled nitric oxide (FeNO), and nasal fluid concentrations of 8-epi-prostaglandin F2 alpha (8-epi-PGF2α), tumor necrosis factor-α (TNF-α), interleukin-8 (IL-8) and IL-1β were measured. A linear mixed-effect model was introduced to evaluate the associations of PM₂.₅ concentrations with respiratory outcomes. Additionally, GSTT1 genotype-based stratification was performed to characterize modification on PM₂.₅-related respiratory outcomes. We found that a 10 μg/m³ increase in PM₂.₅ was associated with decreases of 0.52 L (95% confidence interval [CI]: -1.04, -0.002), 0.64 L (95% CI: -1.13, -0.16), 0.1 (95% CI: -0.23, 0.04) and 2.87 L/s (95% CI: -5.09, -0.64) in FVC, FEV₁, FEV₁/FVC ratio and PEF at lag 2, respectively. Meanwhile, marked increases of 80.82% (95% CI: 5.13%, 156.50%) in IL-8, 77.14% (95% CI: 1.88%, 152.40%) in IL-1β and 67.87% (95% CI: 14.85%, 120.88%) in 8-epi-PGF2α were observed as PM₂.₅ concentration increased by 10 μg/m³ at lag 2. Notably, PM₂.₅-associated decreases in FVC and PEF and increase in FeNO were stronger among the subjects with GSTT1-null genotype. In summary, short-term exposure to PM₂.₅ is associated with nasal inflammation, oxidative stress and lung function reduction in the retired subjects. Lung function reduction and inflammation are stronger among the subjects with GSTT1-null genotype.

Excess of water irrigation and fertilizer consumption by crops has resulted in high soil nitrogen (N) losses and underground water contamination not only in China but worldwide. This study explored the effects of soil N input, soil N output, as well as the effect of different irrigation and N- fertilizer managements on residual N. For this, two consecutive years of winter wheat (Triticum aestivum L.) –summer maize (Zea mays L.) rotation was conducted with: N applied at 0 kg N ha⁻¹ yr⁻¹, 420 kg N ha⁻¹ yr⁻¹ and 600 kg N ha⁻¹ yr⁻¹ under fertigation (DN0, DN420, DN600), and N applied at 0 kg N ha⁻¹ yr⁻¹ and 600 kg N ha⁻¹ yr⁻¹ under flood irrigation (FN0, FN600). The results demonstrated that low irrigation water consumption resulted in a 57.2% lower of irrigation-N input (p < 0.05) in DN600 when compared to FN600, especially in a rainy year like 2015–2016. For N output, no significant difference was found with all N treatments. Soil gaseous N losses were highly correlated with fertilization (p < 0.001) and were reduced by 23.6%–41.7% when fertilizer N was decreased by 30%. Soil N leaching was highly affected by irrigation and a higher reduction was observed under saving irrigation (reduced by 33.9%–57.3%) than under optimized fertilization (reduced by 23.6%–50.7%). The net N surplus was significantly increased with N application rate but was not affected by irrigation treatments. Under the same N level (600 kg N ha⁻¹ yr⁻¹), fertigation increased the Total Nitrogen (TN) stock by 17.5% (0–100 cm) as compared to flood irrigation. These results highlighted the importance to further reduction of soil N losses under optimized fertilization and irrigation combined with N stabilizers or balanced- N fertilization for future agriculture development.

Oral bioaccessibility (BAc) is a surrogate for the bioavailability (BAv) of a broad range of substances, reflecting the value that the approach offers for assessing oral exposure and risk. BAc is generally considered to have been validated as a proxy for oral BAv for the important soil contaminants Pb, Cd, and As. Here, using literature data for Ni BAc and BAv, we confirmed that Ni BAc (gastric only, with HCl mimicking stomach conditions) is a conservative measure of BAv for the oral exposure pathway. Measured oral BAv of Ni in soil was shown to be 50–100 times less than the simplest oral BAc estimates (%BAv = 0.012(%BAc) - 0.023 (r = 0.701, 95%CI [0.456, 0.847], n = 30)) in rats, demonstrating a significant conservatism for exposure assessment. The relationship between the oral BAv and BAc of nickel sulfate hexahydrate (NSHH) was comparable to that of soil, with measured oral BAv of NSHH (1.94%) being a small fraction of NSHH gastric BAc (91.1%). BAc and BAv reflect the underlying Ni speciation of the sample, with the bioaccessible leaching limits being represented by the highly soluble Ni salts and the poorly soluble Ni monoxide, and the environmental (e.g. soil properties) or gastric (e.g. food present) conditions. BAc has potential utility for chemical classification purposes because pure Ni substances can be grouped by %BAc values(using standardized methodologies for the relevant exposure routes), these groupings reflecting the underlying chemistry and speciation of the samples of substances tested here, with 0.008% %BAc for alloys (SS304, SS316, Inconel, Monel), <1% in green NiO and Ni metal massives, 0.9–23.6% for Ni powders, 9.8–22.7% for Ni sulfides, 26.3–29.6% for black oxidic Ni, and 82–91% for the soluble Ni salts. Oral BAc provides realistic yet conservative estimates of BAv for the hazard classification and risk assessment of Ni substances.

Urban street canyons formed by high-rise buildings restrict the dispersion of vehicle emissions, which pose severe health risks to the public by aggravating roadside air quality. However, this issue is often overlooked in city planning. This paper reviews the mechanisms controlling vehicle emission dispersion in urban street canyons and the strategies for managing roadside air pollution. Studies have shown that air pollution hotspots are not all attributed to heavy traffic and proper urban design can mitigate air pollution. The key factors include traffic conditions, canyon geometry, weather conditions and chemical reactions. Two categories of mitigation strategies are identified, namely traffic interventions and city planning. Popular traffic interventions for street canyons include low emission zones and congestion charges which can moderately improve roadside air quality. In comparison, city planning in terms of building geometry can significantly promote pollutant dispersion in street canyons. General design guidelines, such as lower canyon aspect ratio, alignment between streets and prevailing winds, non-uniform building heights and ground-level building porosity, may be encompassed in new development. Concurrently, in-street barriers are widely applicable to rectify the poor roadside air quality in existing street canyons. They are broadly classified into porous (e.g. trees and hedges) and solid (e.g. kerbside parked cars, noise fences and viaducts) barriers that utilize their aerodynamic advantages to ease roadside air pollution. Post-evaluations are needed to review these strategies by real-world field experiments and more detailed modelling in the practical perspective.

We conducted a three-year campaign of atmospheric pollutant measurements exploiting portable instrumentation deployed on a mobile cabin of a public transport system. Size selected particulate matter (PM) and nitrogen monoxide (NO) were measured at high temporal and spatial resolution. The dataset was complemented with measurements of vehicular traffic counts and a comprehensive set of meteorological covariates. Pollutants showed a distinctive spatiotemporal structure in the urban environment. Spatiotemporal autocorrelations were analyzed by a hierarchical spatiotemporal statistical model. Specifically, particles smaller than 1.1 μm exhibited a robust temporal autocorrelation with those at the previous hour and tended to accumulate steadily during the week with a maximum on Fridays. The smallest particles (mean diameter 340 nm) showed a spatial correlation distance of ≈600 m. The spatial correlation distance reduces to ≈ 60 m for particle diameters larger than 1.1 μm, which also showed peaks at the stations correlated with the transport system itself. NO showed a temporal correlation comparable to that of particles of 5.0 μm of diameter and a correlating distance of 155 m. The spatial structure of NO correlated with that of the smallest sized particles. A generalized additive mixed model was employed to disentangle the effects of traffic and other covariates on PM concentrations. A reduction of 50% of the vehicles produces a reduction of the fine particles of −13% and of the coarse particle number of −7.5%. The atmospheric stability was responsible for the most significant effect on fine particle concentration.

Expanding applications of metal-oxide nanoparticles (NPs) and increased environmental deposition of NPs followed by their interactions with edible crops threaten yields. This study demonstrates the effects of aging (45 days in soil) of four NPs (ZnO, CuO, Al₂O₃, TiO₂; 3.9–34 nm) and their corresponding metal oxide bulk particles (BPs; 144–586 nm) on cucumbers (Cucumis sativus L.) cultivated in sandy-clay-loam field soil and compares these with the phytotoxic effects of readily soluble metal salts (Zn²⁺, Cu²⁺, and Al³⁺). Data revealed the cell-to-cell translocations of NPs, their attachments to outer and inner cell surfaces, nuclear membranes, and vacuoles, and their upward movements to aerial parts. Metal bioaccumulations in cucumbers were found in the order: (i) ZnO-NPs > ZnO-BPs > Zn²⁺, (ii) CuO-NPs > CuO-BPs > Cu²⁺, (iii) Al³⁺> Al₂O₃-NPs > Al₂O₃-BPs and (iv) TiO₂-NPs > TiO₂-BPs. Aging of NPs in soil for 45 days significantly enhanced metal uptake (P ≤ 0.05), for instance aged ZnO-NPs at 1 g kg⁻¹ increased the uptake by 20.7 % over non-aged ZnO-NPs. Metal uptakes inhibited root (RDW) and shoot (SDW) dry weight accumulations. For Cu species, maximum negative impact (%) was exhibited by Cu²⁺ (RDW:SDW = 94:65) followed by CuO-NPs (RDW:SDW = 78:34) and CuO-BPs (RDW:SDW = 27:22). Aging of NPs/BPs at 1–4 g kg⁻¹ further enhanced the toxic impact of tested materials on biomass accumulations and chlorophyll formation. NPs also induced membrane damage of root tissues and enhanced levels of antioxidant enzymes. The results of this study suggest that care is required when aged metal-oxide NPs of both essential (Zn and Cu) and non-essential (Al and Ti) metals interact with cucumber plants, especially, when they are used for agricultural purposes.

Precious metal mining activities have left complex environmental legacies in lakes around the world, including some sites in climatically sensitive regions of the Canadian sub-Arctic. Here, we examined the long-term impacts of past regional gold mining activities on sub-Arctic lakes near Con Mine (Yellowknife, Northwest Territories) based on sediment core analysis (paleolimnology). In addition to receiving metal(loid)s from roaster stack emissions, the study lakes were also influenced by salt-rich mine drainage from Con Mine tailings. Water samples from these lakes had some of the highest concentrations for salinity-related variables (e.g. Ca²⁺, Cl⁻, Na⁺) and metal(loid)s (e.g. As, Cu, Ni, Sb) in the Yellowknife area. Furthermore, the presence of halophilic diatom (Bacillariophyceae) taxa (Achnanthes thermalis and Navicula incertata) in the recent sediments of Keg and Peg lakes suggest that the extreme saline conditions are strongly influencing the present biota, more than 10 years after the cessation of gold mining activities at Con Mine. The sedimentary metal(loid) profiles (e.g. As, Cu, Ni) of Kam Lake tracked the influence of regional gold mining activities, particularly those at Con Mine, while the algal assemblages recorded the biological responses to salinization and metal(loid) pollution (e.g. marked decreases in diatom species richness, Hill’s N2 diversity, and chrysophyte cyst:diatom valve ratio). At Kam Lake, the algal assemblage changes in the post-mining era were indicative of climate-mediated changes to lake thermal properties (e.g. rise in planktonic diatoms), nutrient enrichment related to urbanization (e.g. increase in eutrophic Stephanodisucs taxa), and/or a combination of both stressors. The lack of biological recovery (i.e. return to pre-mining assemblages) is consistent with investigations of mine-impacted lakes in temperate regions where elevated contaminant levels and emerging stressors (e.g. climate warming, land-use changes) are influencing lake recovery.

Hydrodynamic conditions often affect the eutrophication process and play a key role in algal growth in reservoirs. A promising approach for controlling algal blooms in reservoirs is to create adverse hydrodynamic conditions by implementing reservoir operation strategies. However, research on this method is still nascent and does not support practical applications due to the lack of quantitative hydrodynamic thresholds. In this paper, field observations of algal growth from April 2015 to August 2016 were conducted, and a three-dimensional (3D) model that couples hydrodynamics and water temperatures for the Zipingpu Reservoir was established. Low flow velocities (V) and low Reynolds numbers (Re) in the Longchi tributary are favorable for dinoflagellate growth and accumulation, which can explain why dinoflagellate blooms are more likely to occur in the tributary. A temperature of 18–22 °C is considered a precondition for Peridiniopsis penardii blooms, suggesting that freshwater dinoflagellate species may prefer lower temperatures than marine dinoflagellate species. Shallow mixing layer depth (Zₘᵢₓ) is conducive to Peridiniopsis penardii gathering in the upper water layers and promotes growth. The shallow euphotic layer depth (Zₑᵤ) was speculated to promote the dominance of this species by stimulating its heterotrophy and inhibiting other algal autotrophy. Furthermore, a boundary line analysis was introduced to characterize the relationships between algal biomass and hydrodynamic indicators. Thus, the thresholds for V, Re, and Zₘᵢₓ/Zₑᵤ were determined to be 0.034 m s⁻¹, 6.7 × 10⁴, and 1.7, respectively. Either accelerating horizontal flow to exceed the thresholds of V and Re or facilitating vertical mixing to exceed the threshold of Zₘᵢₓ/Zₑᵤ can prevent dinoflagellate blooms. Therefore, the summarized hydrodynamic threshold system is suggested to be an effective standard for controlling dinoflagellate blooms in the reservoir. Moreover, this study can provide a useful reference for understanding the mechanism of freshwater dinoflagellate blooms.