The ionic strength of infiltration water changes with the seasonal alternation of irrigation sources. In this study, reactivity changes of birnessite-coated sand with the fluctuations of ionic strength of infiltration water (i.e. from groundwater to rainwater) and the involved mechanism were investigated through column experiments. Birnessite-coated sand was less reactive in groundwater than in rainwater because of the higher cation content and higher pH of groundwater. The cations in the groundwater were adsorbed on birnessite-coated sand and then desorbed in presence of a dilute aqueous solution represented by rainwater. The reactivity of the passivated birnessite-coated sand was recovered instantaneously, and approximately one-third of the pristine reactivity was restored. During recovery, Na⁺ desorption and lincomycin (LIN) removal both exhibited a two-stage reaction pattern. The LIN removal correlated with Na⁺ desorption (r = 0.99) so that the reactive sites that were binding 5.602 μmol of Na⁺ became available for 1 μmol of LIN removal. These results suggest that the reactivity of manganese oxides toward organic contaminant is associated with the ionic strength of infiltration water and indicate that the partial reactivity can be naturally restored.

Considerable investigations have been carried out to address the relationship between ambient fine particulate matter (PM₂.₅) and blood pressure (BP) in patients with hypertension. However, few studies have explored the influence of PM₂.₅ and its constituents on Trimethylamine N-oxide (TMAO), an established risk factor for hypertension and cardiovascular disease (CVD), particularly in severely air-polluted areas. To explore the potential impact of PM₂.₅ constituents on BP, plasma hormones, and TMAO, a panel study was conducted to investigate changes in BP, plasma hormones, and TMAO in response to ambient air pollution exposure in stage 1 hypertensive young adults. Linear mixed effect models were used to estimate the cumulative effects of fine particulate matters (PM₂.₅) and its constituents on BP, plasma hormones and TMAO. We found that one interquartile range (IQR) (35 μg/m³) increase in 0–1 day moving-average PM₂.₅ concentrations was statistically significantly associated with elevated systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) with estimated values of 0.13 (95% confidence interval (CI): 0.03 to 0.23) mmHg, 0.18 (95% CI: 0.08 to 0.28) mmHg, and 0.17 (95% CI: 0.09 to 0.26) mmHg, respectively. Hormone disturbance in the renin-angiotensin-aldosterone system was also associated with PM₂.₅ exposure. Elevated TMAO levels with an IQR increase for 0–4, 0–5, 0–6 moving-average concentrations of PM₂.₅ were found, and the increased values ranged from 26.28 (95% CI: 2.92 to 49.64) to 60.78 (31.95–89.61) ng/ml. More importantly, the PM₂.₅-bound metal constituents, such as manganese (Mn), titanium (Ti), and selenium (Se) showed robust associations with elevated BP and plasma TMAO levels. This study demonstrates associations between PM₂.₅ metal constituents and increased BP, changes in plasma hormones and TMAO, in stage 1 hypertensive young adults. Source control, aiming to reduce the emission of PM₂.₅-bound metals should be implemented to reduce the risk of hypertension and CVD.

We aimed to explore the effects of mixtures of lead and various metals on blood pressure (BP) and the odds of pre-hypertension (systolic blood pressure (SBP) 120–139 mmHg, and/or diastolic blood pressure (DBP) 80–89 mmHg) and hypertension (SBP/DBP ≥140/90 mmHg) among Chinese adults in a cross-sectional study. This study included 11,037 adults aged 18 years or older from the 2017–2018 China National Human Biomonitoring. Average BP and 13 metals (lead, antimony, arsenic, cadmium, mercury, thallium, chromium, cobalt, molybdenum, manganese, nickel, selenium, and tin) in blood and urine were measured and lifestyle and demographic data were collected. Weighted multiple linear regressions were used to estimate associations of metals with BP in both single and multiple metal models. Weighted quantile sum (WQS) regression was performed to assess the relationship between metal mixture levels and BP. In the single metal model, after adjusting for potential confounding factors, the blood lead levels in the highest quartile were associated with the greater odds of both pre-hypertension (odds ratio (OR): 1.56, 95% CI: 1.22–1.99) and hypertension (OR:1.75, 95% CI: 1.28–2.40) when compared with the lowest quartile. We also found that blood arsenic levels were associated with increased odds of pre-hypertension (OR:1.31, 95% CI:1.00–1.74), while urinary molybdenum levels were associated with lower odds of hypertension (OR:0.68, 95% CI:0.50–0.93). No significant associations were found for the other 10 metals. WQS regression analysis showed that metal mixture levels in blood were significantly associated with higher SBP (β = 1.56, P < 0.05) and DBP (β = 1.56, P < 0.05), with the largest contributor being lead (49.9% and 66.8%, respectively). The finding suggests that exposure to mixtures of metals as measured in blood were positively associated with BP, and that lead exposure may play a critical role in hypertension development.

As a redox-sensitive element, manganese (Mn) plays a critical role in Cd mobilization, especially in paddy soil. In an anoxic environment, the precipitation of Mn(II)-hydroxides specifically favors Cd retention, while draining the paddy fields results in substantial remobilization of Cd. However, how the change in Mn redox states during the periodical transit of anoxic to oxic systems affects Cd mobility remains unclear. In this study, we demonstrate that the radical effect generated during the oxidation of Mn(II)-hydroxides exerts a significant effect on the oxidative dissolution of Cd during the aeration of paddy soils. The extractable Cd concentration decreased rapidly during the reduction phases but increased upon oxidation, while Cd availability produced the opposite effect with soil pe + pH and the extractable Mn concentration. Inhibiting the oxidation of Mn(II)-containing phases by microbes suppressed the production of hydroxyl free radicals (•OH) and Cd mobilization in the drainage phase. Analysis of X-ray absorption spectroscopy and sequential extraction demonstrated that the transformation from the Mn phase of Mn(II) to Mn(III/IV) determines Cd solubility. Altogether, the oxidization of Mn(II)-hydroxides was associated with the generation of significant amounts of •OH. The dissolution of Mn(II)- incorporating phases lead to a net release of Cd into soils during soil aeration.

The treatment of contaminants from lignocellulosic biorefinery effluent has recently been identified as a unique challenge. This study focuses on removing phenolic contaminants and polycyclic aromatic hydrocarbons (PAHs) from lignocellulosic biorefinery wastewater (BRW) applying a laccase-assisted approach. Cassava waste was used as a substrate to produce the maximum yield of laccase enzyme (3.9 U/g) from Pleurotus ostreatus. Among the different inducers supplemented, CuSO₄ (0.5 mM) showed an eight-fold increase in enzyme production (30.8 U/g) after 240 h of incubation. The catalytic efficiency of laccase was observed as 128.7 ± 8.47 S⁻¹mM⁻¹ for syringaldazine oxidation at optimum pH 4.0 and 40 °C. Laccase activity was completely inhibited by lead (II) ion, mercury (II) ion, sodium dodecyl sulphate, sodium azide and 1,4 dithiothretiol and induced significantly by manganese (II) ion and rhamnolipid. After treating BRW with laccase, the concentrations of PAHs and phenolic contaminants of 1144 μg/L and 46160 μg/L were reduced to 96 μg/L and 16100 μg/L, respectively. The ability of laccase to effectively degrade PAHs in the presence of different phenolic compounds implies that phenolic contaminants may play a role in PAHs degradation. After 240 h, organic contaminants were removed from BRW in the following order: phenol >2,4-dinitrophenol > 2-methyl-4,6-dinitrophenol > 2,3,4,6-tetrachlorophenol > acenaphthene > fluorine > phenanthrene > fluoranthene > pyrene > anthracene > chrysene > naphthalene > benzo(a)anthracene > benzo(a)pyrene > benzo(b)fluoranthene > pentachlorophenol > indeno(1,2,3-cd)pyrene > benzo(j) fluoranthene > benzo[k]fluoranthène. The multiple contaminant remediation from the BRW by enzymatic method, clearly suggests that the laccase can be used as a bioremediation tool for the treatment of wastewater from various industries.

Nickel (Ni) and manganese (Mn) are well known for the production of steel and alloys and are commonly found co-occurring in Ni ores. They are metals of environmental concern and contamination in the marine environment is problematic single exposures and in combination. Several studies have documented the effects of single metal exposure on the model anemone E. pallida, but research on the effects of metal mixtures is far less common. This novel study assesses the accumulation and stress effects of Ni and Mn over a 12-d exposure period. E. pallida were exposed in two separate experiments; Ni alone and Ni in combination with Mn, to assess accumulation, along with any effect on the density of symbionts and anemone tentacle length. Anemones were transferred to ambient seawater to assess depuration and recovery over 6 d. Anemone tissue accumulated Ni at a magnitude of five times higher in a mixture of 0.5 mg Ni/L with 2.5 mg Mn/L compared to the same concentration in a single Ni exposure experiment. In both experiments, Ni and Mn preferentially accumulated in the Symbiodinium spp. compared to the anemone tissue, but Ni depuration was more rapid in the mixture than Ni alone exposure. This study reveals a significant reduction in anemone Symbiodinium spp. density after exposure to Ni and Mn mixtures, but not with Ni exposure alone. A significant dose-dependent reduction in tentacle length was observed in anemones after 12 d of the Ni exposure both with and without Mn. The estimated sublethal concentration that causes tentacle retraction in 50% of test anemones (EC50) by Ni was 0.51 (0.25–0.73) mg/L, while in combination with Mn the EC50 was 0.30 mg Ni/L (confidence limits not calculatable). The present data reveals the importance of testing metal effects in combination before establishing safe limits for marine invertebrates.

The geochemistry of iron (Fe), manganese (Mn) and sulfur (S) and their effects on arsenic (As) mobility in the mudflats of small river estuaries remain unclear. Here, diffusive gradient in thin films (DGT) and high-resolution dialysis (HR-Peeper) techniques combined with a sequential extraction procedure (BCR) were employed to investigate As, Fe, Mn and S geochemistry in the mudflat of the Jiuxi River estuary, Southeast China. Grain size analysis indicated that fine-grained particles were likely to be deposited in the estuarine intertidal zone and coastal area. DGT and HR-Peeper results revealed that in the estuary and coastal area, the dissolved As in sediment in summer was controlled by Mn geochemistry, which includes not only the release of As through Mn/Fe reduction but also the stabilization of dissolved As in pore water. This stabilization of dissolved As may due to the formation of As–Mn-OM complexes. In winter, the significant positive correlations between DGT-Fe, DGT-Mn, DGT-As and DGT-S indicated that sulfate reduction was the start of As mobilization in sediment in winter. In both the estuary and the coastal area, the easily reducible Fe, Mn and As contents in intertidal sediment were higher than those in the subtidal zone. Combined with the As flux across the sediment-overlying water interface (SWI), these phenomena suggested that As in subtidal sediment diffused into overlying water and that As in overlying water tended to accumulate in the intertidal sediment. The total organic carbon content (TOC) and DGT results in the lower reach, estuary and coastal areas indicated that organic matter is the controlling factor of Fe/Mn reduction, sulfate reduction and As mobilization. The BCR test results showed higher reactive fraction contents of Fe, Mn and As in winter sediment, which threaten the overlying water quality.

Air in subway stations is typically more polluted than ambient air, and particulate matter concentrations and compositions can vary greatly by location, even within a subway station. However, it is not known how the sources of particulate matter vary between different areas within subway stations, and source-specific health risks in subway stations are unclear. We analyzed the spatial characteristics of particulate matter by source and calculated source-specific health risks on subway platforms and concourses and in station offices by integrating source apportionment with health risk assessments. A total of 182 samples were collected in three areas in six subway stations in Nanjing, China. Enrichment factors and the positive matrix factorization receptor model were used to identify major sources. The carcinogenic and non-carcinogenic health risks to subway workers and passengers were evaluated to determine control priorities. Seven sources of particulate matter were identified in each area, with a total of four subway sources and six outdoor sources over all the areas. The source contributions to total element mass differed significantly from the source contributions to human health risks. Overall, subway sources contributed 48% of total element mass in the station office and 75% and 60% on the concourse and platform, respectively. Subway-derived sources accounted for 54%, 81%, and 71% of non-carcinogenic health risks on station platforms, concourses, and office areas, respectively. The corresponding values for carcinogenic risks were 51%, 86%, and 86%. Among the elements, cobalt had the largest contributions to carcinogenic and non-carcinogenic risks, followed by manganese for non-carcinogenic risks and hexavalent chromium for carcinogenic risks. Reducing emissions from subway sources could effectively protect the health of subway workers and passengers.

Metal oxide-modified biochar showed excellent adsorption performance in wastewater treatment. Iron nitrate and potassium permanganate were oxidative modifiers through which oxygen-containing groups and iron–manganese oxides could be introduced into biochar. In this study, iron–manganese (Fe–Mn) oxide-modified biochar (BC-FM) was synthesized using rice straw biochar, and the adsorption process, removal effect, and the mechanism of cadmium (Cd) adsorption on BC-FM in wastewater treatment were explored through batch adsorption experiments and characterization (SEM, BET, FTIR, XRD, and XPS). Adsorption kinetics showed that the maximum adsorption capacity of BC-FM for Cd(II) was 120.77 mg/g at 298 K, which was approximately 1.5–10 times the amount of adsorption capacity for Cd(II) by potassium-modified or manganese-modified biochar as mentioned in the literature. The Cd(II) adsorption of BC-FM was well fit by the pseudo-second-order adsorption and Langmuir models, and it was a spontaneous and endothermic process. Adsorption was mainly controlled via a chemical adsorption mechanism. Moreover, BC-FM could maintain a Cd removal rate of approximately 50% even when reused three times. Cd(II) capture by BC-FM was facilitated by coprecipitation, surface complexation, electrostatic attraction, and cation-π interaction. Additionally, the loaded Fe–Mn oxides also played an important role in the removal of Cd(II) by redox reaction and ion exchange in BC-FM. The results suggested that BC-FM could be used as an efficient adsorbent for treating Cd-contaminated wastewater.

Developing efficient catalysts for oxytetracycline (OTC) degradation is an ideal strategy to tackle environmental pollution, and advanced oxidation processes (AOPs) have been widely used for its degradation. However, the studies on the activation of periodate (PI) by biochar and its composites in recent years have been scarcely reported. In this study, we focused on the degradation of OTC by PI activation with manganese oxide/biochar composites (MnₓOy@BC). Experimental results showed that the OTC degradation rate of MnₓOy@BC/PI system reached almost 98%, and the TOC removal efficiency reached 75%. Various characteristic analysis proved that PI could be activated efficiently by surface functional groups and manganese-active species (Mn(II), Mn(III), and Mn(IV)) on biochar, and various reactive species such as singlet oxygen (¹O₂), hydroxyl radical (∙OH), and superoxide radical (O₂∙⁻) can be observed via radical quenching experiments. Based on this, three degradation pathways were proposed. Furthermore, MnₓOy@BC and PI were combined to degrade environmental pollutants, which achieved excellent practical benefits and had great practical application potential. We hope that it can provide new ideas for advanced oxidation processes (AOPs) applying for wastewater treatment in the future.