Industrial dye effluents, which are a major wastage component that enter the natural environment, pose a significant health risk to human and aquatic life. Therefore, the effective removal of dye effluents is a major concern. Against this backdrop, in this study, a low-cost, earth-abundant, and ecofriendly ɤ-Fe₂O₃–PPy nanocomposite was prepared employing the conventional hydrothermal method. The morphology, functional groups, and elemental composition of ɤ-Fe₂O₃–PPy were characterized by XRD, SEM, XPS, and FTIR studies. Under optimized conditions, the prepared novel ɤ-Fe₂O₃–PPy nanocomposite showed a high methylene blue (MB) adsorption capacity of 464 mg/g, which is significantly higher than that of existing adsorbents such as CNTs and polymer-modified CNTs. The adsorption parameters such as pH, adsorbent dosage, and ionic strength were optimized to enhance the MB adsorption capacity. The adsorption results revealed that MB is adsorbed onto the adsorbent surface via electrostatic interactions, hydrogen bonding, and chemical binding interactions. In terms of practical application, the adsorbent’s adsorption–desorption ability in conjunction with magnetic separation was investigated; the prepared ɤ-Fe₂O₃–PPy nanocomposite exhibited excellent adsorption and desorption efficiencies over more than seven adsorption–desorption cycles.

Potential toxic metal(loid)s (PTMs) in road dust are a major concern in relation to urban environmental quality. Identifying pollution hotspots and sources of PTMs is an essential prerequisite for pollution control and management. Herein, the concentrations, pollution and potential health risks of 8 PTMs (As, Cd, Co, Cu, Hg, Mo, Pb and Zn) in road dust from the highly urbanized areas of Nanjing were studied. Spatial occurrences and sources of PTMs were explored using geostatistics, principal component analysis (PCA) and local Moran’s index. The contamination factor (CF) results showed that Co was mainly natural in origin, while the other PTMs were polluted, with average CFs ranging from 1.4 to 11.0 as follows: Hg > Mo > Cd > Cu > Pb > Zn > As, indicating moderate to very high contamination. Except for Co and Hg, the other PTMs were heavily loaded on PC1, which explained 44.72% of the total variance. Combining the statistical results and distributions of potential sources, we deduced that industrial emissions dominated the spatial patterns of all polluted PTMs in road dust, which showed high levels in the northern parts of the study region and generally decreasing levels southwards. Moreover, Pb and Zn in the south-central area and Cd in the north-central area displayed hotspots, with maximum CFs of 5.5 (Pb), 4.2 (Zn) and 16.2 (Cd), which were related to additional automotive and railway braking emissions, respectively. The resuspension of legacy pesticides in soil is likely responsible for the As pollution hotspot in the southwestern part. Despite the high anthropogenic contributions (27% for As and 68–88% for the other metals) to the PTMs in road dust, their noncarcinogenic and carcinogenic health risks were rarely found for children and adults based on the values of the hazard index and carcinogenic risk index. However, attention still should be paid to the pollution hotspots in the northern region.

Riparian areas are widely recognized as the main areas for carbon sequestration and nitrogen pollution removal, while little is known about the effects of the respective sand mining activities on riparian zones. In this study, the effects of sand mining activities on the soil organic carbon (SOC) storage, different N-removal processes (Feammox, anammox, and denitrification), and composition of the relative bacterial community at a depth of 0–40 cm were determined based on investigations in riparian sand mining areas and adjacent forestlands. The SOC density of the sand mining areas (2.59 t ha⁻¹, depth of 0–40 cm) was lower than that of the riparian forestlands (80.42 t ha⁻¹). Compared with those of the riparian forestland, the sand mining area exhibited a dramatic reduction in the CO₂-fixed gene abundances (cbbL) and a significant change in the composition of cbbL-containing bacteria. The rates of the Feammox (0.038 ± 0.014 mg N kg⁻¹ d⁻¹), anammox (0.017 ± 0.017 mg N kg⁻¹ d⁻¹), and denitrification (0.090 ± 0.1 mg N kg⁻¹ d⁻¹) processes at a depth of 0–20 cm in the soil layer of the sand mining area were reduced by 70.17%, 91.5%, and 93.62% compared with those of the riparian forestland, respectively. The riparian areas in the study area (approximately 12 ha, depth of 0–40 cm) destroyed by sand mining activities released approximately 933.96 t stored soil carbon, which reduce the annual carbon sequestration potential by 28.8–40.8 t. Moreover, the potential N-removal rates in the riparian forestlands (depth of 0–20 cm) by the Feammox, anammox, and denitrification processes were 1514.21–1530.95 kg N ha⁻¹ year⁻¹, whereas the potential N-removal rates in the sand mining area were only 121.2–126.19 kg N ha⁻¹ year⁻¹. Therefore, more investigations are necessary for comparing the benefits and damage of sand mining activities in riparian areas before more sand mining activities are approved.

Chromium has been proven to be extremely phytotoxic. This study explored the impacts of increasing Cr(VI) exposure (up to 10 mg L⁻¹ K₂Cr₂O₇) on the growth and development of alfalfa plants and adaptation responses employed, in an environmentally relevant context. The threshold concentration of K₂Cr₂O₇ in irrigation water beyond which stress responses are initiated is 1 mg L⁻¹. Lower Cr(VI) exposure (0.5 mg L⁻¹ K₂Cr₂O₇) induced hormesis, evident through increased biomass and larger leaves, likely mediated by increased NO content (supported by elevated NR enzymatic activity and overexpression of NR and ndh genes). Elevated Cr(VI) exposure (5 and 10 mg L⁻¹ K₂Cr₂O₇) resulted in reduced biomass and smaller leaves, and lower levels of photosynthetic pigment (10 mg L⁻¹ K₂Cr₂O₇). Higher levels of lipid peroxidation, H₂O₂ and NO contents in these plants suggested nitro-oxidative stress. Stress responses included increased SOD and CAT enzymatic activities, further supported to some extent by MnSOD, FeSOD, Cu/ZnSOD and CAT transcripts levels. GST7 and GST17 gene expression patterns, as well as proline content, P5CS enzymatic activity and corresponding P5CS and P5CR gene expression levels emphasized the role of proline and GSTs in the adaptation responses. Results highlight the importance of managing Cr(VI) levels in irrigation water.

Many remote montane ecosystems are experiencing biogeochemical changes driven by warming climate and atmospheric pollution. Compared with circumpolar and temperate lakes, the responses of subtropical montane lakes to these external stressors have been less investigated. Here we present sedimentary multi-proxies records (i.e. chironomids, elements and stable isotope of carbon and nitrogen) in ²¹⁰Pb-dated cores from two montane ponds (central China). Before the 1900s, low biomass and the dominance of opportunistic species (e.g. Chironomus anthracinus-type) in both ponds might be in response to cold and harsh condition. Thereafter, chironomid communities in both ponds experienced pronounced shifts. Nutrient-tolerant/warm-adapted species (e.g. Chironomus sp., Polypedilum nubeculosum-type and Endochironomus impar-type) proliferated and biomass increased synchronously after the 1900s, suggestive of favorable condition for chironomid growth. Redundancy analyses revealed that changes in chironomid communities in both ponds were significantly correlated with rising temperature and δ¹⁵N depletion. Prolonged growing season and nitrogen subsidy would increase primary productivity, and hence enhancing food availability for chironomids. Catchment-mediated indirect effects of warming and nitrogen deposition, such as hydrological changes and terrestrial organic matter inputs, would impose further influences on chironomid communities. Taken together, the combined effects of climate warming and nitrogen deposition have caused significant shifts in primary consumers of these montane ponds, and imposed cascading effects on structure and function of subtropical montane aquatic ecosystems.

Anthropogenic noise is an emergent ecological pollutant in both terrestrial and aquatic habitats. Human population growth, urbanisation, resource extraction, transport and motorised recreation lead to elevated noise that affects animal behaviour and physiology, impacting individual fitness. Currently, we have a poor mechanistic understanding of the effects of anthropogenic noise, but a likely candidate is the neuroendocrine system that integrates information about environmental stressors to produce regulatory hormones; glucocorticoids (GCs) and androgens enable rapid individual phenotypic adjustments that can increase survival. Here, we carried out two field-based experiments to investigate the effects of short-term (30 min) and longer-term (48 h) motorboat-noise playback on the behaviour, GCs (cortisol) and androgens of site-attached free-living orange-fin anemonefish (Amphiprion chrysopterus). In the short-term, anemonefish exposed to motorboat-noise playback showed both behavioural and hormonal responses: hiding and aggression increased, and distance moved out of the anemone decreased in both sexes; there were no effects on cortisol levels, but male androgen levels (11-ketotestosterone and testosterone) increased. Some behaviours showed carry-over effects from motorboat noise after it had ceased, and there was no evidence for a short-term change in response to subsequent motorboat-noise playback. Similarly, there was no evidence that longer-term exposure led to changes in response: motorboat noise had an equivalent effect on anemonefish behaviour and hormones after 48 h as on first exposure. Longer-term noise exposure led to higher levels of cortisol in both sexes and higher testosterone levels in males, and stress-responses to an additional environmental challenge in both sexes were impaired. Circulating androgen levels correlated with aggression, while cortisol levels correlated with hiding, demonstrating in a wild population that androgen/glucocorticoid pathways are plausible proximate mechanisms driving behavioural responses to anthropogenic noise. Combining functional and mechanistic studies are crucial for a full understanding of this global pollutant.

Most of the previous researches estimate influencing factors impact on air quality average without considering the heterogeneity of influential factors on different levels of air quality. In order to detect the different effects of influencing factors on air quality index (AQI) between lower-AQI and higher-AQI cities, this study applies a spatial quantile regression model (SQRM) to investigate heterogeneity of influential factors on AQI, while accounting for spatial autocorrelation of AQI. The results show that heterogeneity effects of windspeed, terrain slope, urbanization sprawl and spatial autocorrelation on AQI are large across the entire AQI spectrum, while heterogeneity effects of precipitation, temperature, relative humidity, terrain fluctuation and urbanization intensity on AQI are not obvious. The spatial positive autocorrelation of AQI in higher-AQI cities is greater than that in lower-AQI cities. Compared with higher-AQI cities, the negative impact of terrain slope on AQI is lager in lower-AQI cities. One unit increase in wind speed contributes AQI to decrease 9.31 to 5.64 then to 5.39 for lower, medium and higher-AQI cities. One unit increase in urbanization sprawl would lead AQI increase 25.6 to 15.6 then to 10.5 for lower, medium and higher-AQI cities. The heterogeneity analysis of meteorological, topographic and socioeconomic factors effects on air quality are of guiding significance for realizing the differentiation of policy measures for air pollution prevention and control.

NO₂ oxidation of soot exhausted from engines is more efficient than O₂ under low-temperature conditions, and is crucial for diesel particulate filter to control soot pollution. To explore the principle behind accelerating soot oxidation by NO₂, this paper uses density functional theory to reveal soot oxidation process by NO₂. This study contributes to understanding rules of soot oxidation by NO₂ and perfecting soot oxidation models to develop soot emission control technologies. Results show that NO₂ oxidation of pyrene radical involves three steps. Firstly, NO₂ attacks the C∗ atom to form –C (NO₂) with reaction energy of 306.3 kJ/mol, which decomposes to produce a –C (O) compound. Secondly, another NO₂ molecule climbs over an energy barrier of 8.8 kJ/mol, and changes into a –C (ONO₂) intermediate on –C (O). Finally, the N or O atom of NO₂ attacks –C (O) for a second time to help open aromatic ring for releasing CO or CO₂. Further decomposition of –C (NO₂) and –C (ONO₂) requires activation energies of 81.6 kJ/mol, 75.7 kJ/mol, and 53.5 kJ/mol, respectively, on preferential pathways. Calculations prove that attacks of O atom from NO₂ on C∗ help open the aromatic ring more efficiently than N atom.

Waste date palm-derived biochar (DPBC) was modified with nano-zerovalent iron (BC-ZVI) and silica (BC-SiO₂) through mechanochemical treatments and evaluated for arsenate (As(V)) removal from water. The feedstock and synthesized adsorbents were characterized through proximate, ultimate, and chemical analyses for structural, surface, and mineralogical compositions. BC-ZVI demonstrated the highest surface area and contents of C, N, and H. A pH range of 2–6 was optimum for BC-ZVI (100% removal), 3–6 for DPBC (89% removal), and 4–6 for BC-SiO₂ (18% removal). Co-occurring PO₄³⁻ and SO₄²⁻ ions showed up to 100% reduction, while NO₃⁻ and Cl⁻ ions resulted in up to 26% reduction in As(V) removal. Fitness of the Langmuir, Freundlich and Redlich-Peterson isotherms to As(V) adsorption data suggested that both mono- and multi-layer adsorption processes occurred. BC-ZVI showed superior performance by demonstrating the highest Langmuir maximum adsorption capacity (26.52 mg g⁻¹), followed by DPBC, BC-SiO₂, and commercial activated carbon (AC) (7.33, 5.22, and 3.28 mg g⁻¹, respectively). Blockage of pores with silica particles in BC-SiO₂ resulted in lower As(V) removal than that of DPBC. Pseudo-second-order kinetic model fitted well with the As(V) adsorption data (R² = 0.99), while the Elovich, intraparticle diffusion, and power function models showed a moderate fitness (R² = 0.53–0.93). The dynamics of As(V) adsorption onto the tested adsorbents exhibited the highest adsorption rates for BC-ZVI. As(V) adsorption onto the tested adsorbents was confirmed through post-adsorption FTIR, SEM-EDS, and XRD analyses. Adsorption of As(V) onto DPBC, BC-SiO₂, and AC followed electrostatic interactions, surface complexation, and intraparticle diffusion, whereas, these mechanisms were further abetted by the higher surface area, nano-sized structure, and redox reactions of BC-ZVI.

Heavy metal accumulation in agricultural land causes crop production losses worldwide. Metal homeostasis within cells is tightly regulated. However, homeostasis breakdown leads to accumulation of reactive oxygen species (ROS). Overall plant fitness under stressful environment is determined by coordination between roots and shoots. But little is known about organ specific responses to heavy metals, whether it depends on the metal category (redox or non-redox reactive) and if these responses are associated with heavy metal accumulation in each organ or there are driven by other signals. Maize seedlings were subjected to sub-lethal concentrations of four metals (Zn, Ni, Cd and Cu) individually, and were quantified for growth, ABA level, and redox alterations in roots, mature leaves (L1,2) and young leaves (L3,4) at 14 and 21 days after sowing (DAS). The treatments caused significant increase in endogenous metal levels in all organs but to different degrees, where roots showed the highest levels. Biomass was significantly reduced under heavy metal stress. Although old leaves accumulated less heavy metal content than root, the reduction in their biomass (FW) was more pronounced. Metal exposure triggered ABA accumulation and stomatal closure mainly in older leaves, which consequently reduced photosynthesis. Heavy metals induced oxidative stress in the maize organs, but to different degrees. Tocopherols, polyphenols and flavonoids increased specifically in the shoot under Zn, Ni and Cu, while under Cd treatment they played a minor role. Under Cu and Cd stress, superoxide dismutase (SOD) and dehydroascorbate reductase (DHAR) activities were induced in the roots, however ascorbate peroxidase (APX) activity was only increased in the older leaves. Overall, it can be concluded that root and shoot organs specific responses to heavy metal toxicity are not only associated with heavy metal accumulation and they are specialized at the level of antioxidants to cope with.