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.

In this work, we prepared nanocomposites of nickel-decorated manganese oxynitride on graphene nanosheets and demonstrated them as photocatalysts for degradation of acetylsalicylic acid (ASA). The catalyst exhibited a high degradation efficiency over ASA under visible light irradiation and an excellent structural stability after multiple uses. Compared to manganese oxide (MnO) and manganese oxynitride (MnON) nanoparticles, larger specific surface area and smaller band gap were observed for the nanocomposite accounting for the enhanced photocatalytic efficiency. Besides the compositional effect of the catalyst, we also examined the influence of various experimental parameters on the degradation of ASA such as initial concentration, catalyst dose, initial pH and additives. The best performance was obtained for the nanocomposite when the catalyst dose was 10 mg/mL and the initial pH 3. Detection of intermediates during photocatalysis showed that ASA undergoes hydroxylation, demethylation, aromatization, ring opening, and finally complete mineralization into CO₂ and H₂O by reactive species. For practical applications as a photocatalyst, cytotoxicity of the nanocomposite was also evaluated, which revealed its insignificant impact on the cell viability. These results suggest the nanocomposite of nickel-decorated manganese oxynitride on graphene nanosheets as a promising photocatalyst for the remediation of ASA-contaminated water.

Fuel additive methylcyclopentadienyl manganese tricarbonyl (MMT) is counted as an organic manganese (Mn)-derived compound. The toxic effects of Mn (alone and complexed) on dopaminergic (DA) neurotransmission have been investigated in both cellular and animal models. However, the impact of environmentally relevant Mn exposure on DA neurodevelopment is rather poorly understood. In the present study, the MMT dose of 100 μM (about 5 mg Mn/L) caused up-regulation of DA-related genes in association with cell body swelling and increase in the number of DA neurons of the ventral diencephalon subpopulation DC2. Furthermore, our analysis identified significant brain Mn bioaccumulation and enhancement of total dopamine levels in association with locomotor hyperactivity. Although DA levels were restored at adulthood, we observed a deficit in the acquisition and consolidation of memory. Collectively, these findings suggest that developmental exposure to low-level MMT-derived Mn is responsible for the selective alteration of diencephalic DA neurons and with long-lasting effects on fish explorative behaviour in adulthood.

The widespread decline in oceanic dissolved oxygen (DO), known as deoxygenation, is a threat to many marine ecosystems, and fish are considered one of the more vulnerable marine organisms. While food intake and growth rates in some fish can be reduced under hypoxic conditions (DO ~ 60 μmol kg⁻¹), the dietary transfer of essential metals remains unclear. In this context, we investigated the influence of DO on the dietary acquisition of two essential metals (Zn and Mn) in the commercially important gilthead seabream (Sparus aurata) using radiotracer techniques. Fish were exposed to variable DO conditions (normoxia 100% DO, mild-hypoxia 60% DO, and hypoxia 30% DO), and fed a single radiolabeled food ration containing known activities of ⁵⁴Mn and ⁶⁵Zn. Depuration and assimilation mechanisms under these conditions were followed for 19 d. Based on whole body activity after the radio-feeding, food consumption tended to decrease with decreasing oxygen, which likely caused the significantly reduced growth (- 25%) observed at 30% DO after 19 d. While there was an apparent reduction in food consumption with decreasing DO, there was also significantly higher essential metal assimilation with hypoxic conditions. The proportion of ⁶⁵Zn remaining was significantly higher (~60%) at both low DO levels after 24 h and 19 d while ⁵⁴Mn was only significantly higher (27%) at the lowest DO after 19 d, revealing element specific effects. These results suggest that under hypoxic conditions, stressed teleost fish may allocate energy away from growth and towards other strategic processes that involve assimilation of essential metals.

Combining hydrothermal treatment and composting is an effective method to dispose of penicillin fermentation residue (PFR), but the safety and related mechanism are still unclear. In this study, penicillin solution was hydrothermally treated to decipher its degradation mechanism, and then hydrothermally treated PFR (HT-PFR) was mixed with bulking agents at ratios of 2:0 (CK), 2:1.5 (T1), and 2:5 (T2) to determine the absolute abundance of antibiotic resistance genes (ARGs) and the succession of bacterial community. Results showed that penicillin was degraded to several new compounds without the initial lactam structure after hydrothermal treatment. During composting, temperature and pH of the composts increased with the raising of HT-PFR proportion, except the pH at days 2. After 52 days of composting, the absolute copies of ARGs (blaTEM, blaCMY2, and blaSFO) and the relative abundance of bacteria related to pathogens were reduced significantly (P < 0.05). Especially, the total amount of ARGs in the samples of CK and T1 were decreased to equal level (around 5 log₁₀ copies/g), which indicated that more ARGs were degraded in the latter by the composting process. In the CK samples, Bacteroidetes and Proteobacteria accounted for ~69.8% of the total bacteria, but they were gradually replaced by Firmicutes with increasing proportions of HT-PFR, which can be caused by the high protein content in PFR. Consisting with bacterial community, more gram-positive bacteria were observed in T1 and T2, and most of them are related to manganese oxidation and chitinolysis. As composting proceeded, bacteria having symbiotic or pathogenic relationships with animals and plants were reduced, but those related to ureolysis and cellulolysis were enriched. Above all, hydrothermal treatment is effective in destroying the lactam structure of penicillin, which makes that most ARGs and pathogenic bacteria are eliminated in the subsequent composting.

The present research used zebrafish (5–28 days post-fertilization; dpf) as a model organism to investigate the effects of chronic exposure to environmentally relevant sub-lethal concentrations of waterborne (261 μg/L) and dietary zinc (Zn) (1500 mg Zn/kg dw), either independently or simultaneously, during development. The results showed that whole body contents of Zn were increased in all Zn treatment groups, with the highest accumulation of Zn observed in larvae simultaneously exposed to elevated waterborne and dietary Zn. In addition, exposure to elevated levels of Zn, either through the water or the diet, led to a decrease in whole body calcium (Ca) contents at 28 dpf. The findings also suggested that exposure to elevated levels of Zn resulted in a significant reduction in whole body manganese (Mn) contents. More importantly, the magnitude of decrease in Mn contents by Zn exposure was markedly higher than that in Ca and appeared to mirror the increases in whole body Zn accumulation. These results indicate that Mn regulation is more sensitive than Ca to disruption by Zn exposure in developing fish. Further examination of the Zrt-Irt-Like Protein (ZIP) family of transporters using droplet digital PCR technologies revealed that several zip transporters exhibited temporal and exposure route-specific changes following Zn exposure. In particular, the level of zip4 was influenced by Zn exposure regardless of the exposure routes, while changes in zip7 and zip8 levels were predominantly driven by waterborne exposure. Overall, our findings demonstrated that zebrafish during the developmental periods are sensitive to elevated levels of Zn seen in the environment, particularly following co-exposures to waterborne and dietary Zn. Future toxicological assessment of elevated Zn exposure should consider both the exposure routes and the life stages of fish.

Representing the staple crop for half of the world population, rice can accumulate high levels of cadmium (Cd) in its grain, posing concerns on food safety. Different soil amendments have been proposed to decrease Cd accumulation in rice grain by either decreasing soil Cd availability, introducing competitive ions on Cd uptake, or down-regulating the expression of transporters for Cd uptake. However, the effectiveness of soil amendments applied alone or in combinations needs to be tested under field conditions. Here, we present results of field trials with two rice cultivars differing in Cd accumulation grown at three field sites in southern China in two years, to investigate the effects of two Mn-containing soil amendments (MnO₂, Mn-loaded biochar (MB)), Si fertilizer (Si), limestone, and K₂SO₄, as well as interactions among MnO₂, Si, and limestone on decreasing Cd accumulation in rice grain. We found that single applications of MnO₂ or MB to acidic soils low in Mn decreased grain Cd concentrations by 44–53 % or 78–82 %, respectively, over two years without decrease in performance. These effects were comparable to or greater than those induced by limestone liming alone (45–62 %). Strong interactions between MnO₂ and limestone resulting from their influence on soil extractable Cd and Mn led to non-additive effects on lowering grain Cd. MB addition minimized grain Cd concentrations, primarily by increasing extractable and dissolved Mn concentrations, but also by decreasing Cd extractability in soil. In comparison, Si and K₂SO₄ amendments affected grain Cd levels only weakly. We conclude that the amendments that decrease labile Cd and increase labile Mn in soils are most effective at reducing Cd accumulation in rice grain, thus contributing to food safety.

2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) was difficult to degrade in sediments. In this study, the environmental behavior of BDE-47 with/without the effect of benthos (Tubificidae Limnodrilus) and electron acceptors in sediments was investigated using C-14 tracer. Generally, extractable residues of BDE-47 were dominant in sediment and posed high environment risk. The amount of non-extractable residues (NERs) accounted for 39.0% of initial radioactivity in oxic sediments was significantly higher than those in anoxic sediments (17.6%). Most of NERs were localized in the humin fraction and presented as sequestrated forms. Under oxic conditions, the present of Limnodrilus significantly increased the proportion of NERs in sediment. Limnodrilus accumulated 34.2% of initial radioactivity. Under anoxic conditions, the addition of iron (Ⅲ) [Fe(III)], sulfate and nitrate reduced the environmental risk of BDE-47 with the increase of NERs formation, while manganese (IV) [Mn(IV)] addition had no effect on the formation of NERs. The present of Limnodrilus and electron acceptors promoted the production of metabolites. Meanwhile, BDE-47 changed the microbial community structure of sediments. These findings indicated that the environmental behavior and risk of BDE-47 was affected by benthos and electron acceptors, and the high proportion of sequestrated NERs posed high bioactivity and toxic threat to ecological environment.

Industrial metalworking facilities emit a variety of air toxics including volatile organic compounds, polycyclic aromatic hydrocarbons (PAHs) and heavy metals. In order to investigate these emissions, a 1-month multi-instrument field campaign was undertaken at an industrial site in Grande-Synthe, Dunkirk (France), in May and June 2012. One of the main objectives of the study was to provide new information on the chemical composition of particulate matter with aerodynamic diameters smaller than 2.5 μm (PM₂.₅) in the vicinity of metalworking facilities. An aerosol time-of-flight mass spectrometer (ATOFMS) was deployed to provide size-resolved chemical mixing state measurements of ambient single particles at high temporal resolution. This mixing state information was then used to apportion PM₂.₅ to local metalworking facilities influencing the receptor site. Periods when the site was influenced by metalworking sources were characterised by a pronounced increase in particles containing toxic metals (manganese, iron, lead) and polycyclic aromatic hydrocarbons (PAHs) with a variety of chemical mixing states. The association of specific particle classes with a nearby ferromanganese alloy manufacturing plant was confirmed through comparison with previous analysis of raw materials (ores) and chimney filter particle samples collected at the facility. Particles associated with emissions from a nearby steelworks were also identified. The contribution of local metalworking activities to PM₂.₅ at the receptor site for the period when the ATOFMS was deployed ranged from 1 to 65% with an average contribution of 17%, while the remaining mass was attributed to other local and regional sources. These findings demonstrate the impact of metalworking facilities on air quality downwind and provide useful single particle signatures for future source apportionment studies in communities impacted by metalworking emissions.

Sedum alfredii is a Cd/Zn hyperaccumulator native to China, which was collected from a mined area where Mn content in soil was extremely high, together with Zn and Cd content. We investigated the tolerance and accumulation ability of Mn and its possible association with Cd hyperaccumulation in this plant species by using MP-AES, SR-μ-XRF, and RT-PCR. The results showed that the hyperaccumulating ecotype (HE) S. alfredii exhibited high tolerance to Mn and accumulating around 10,000 and 12,000 mg kg⁻¹ Mn in roots and shoots, respectively, without exhibiting toxicity under 5000 mg kg⁻¹ Mn treatment for 4 weeks. Exposure to Cd significantly reduced plant uptake of Mn. In contrast, exogenous Mn application significantly improved root uptake and root-to-shoot translocation of Cd, resulting in the increased Cd accumulation in the shoots of HE S. alfredii. SR-μ-XRF analysis demonstrated that high Mn (20 μM) exposure resulted in higher intensities of Cd localized in both stem vascular bundles and cortex, as well as leaf mesophyll cells, than in those treated with low Mn levels (0.2 μM or 2.0 μM). RT-PCR analysis of several genes possibly involved in Mn/Cd transportation showed that expression of SaNramp3 in roots was significantly reduced under high Mn exposure. These results suggested a significant interaction between Cd and Mn in the HE S. alfredii plants, possibly through their competition for transporters and theoretically provided a strategy to improve the efficiency of Cd extraction from polluted soils by this plant species, after using appropriate nutrient management of Mn.