Journal of Environmental Sciences-china最新文献

Several studies have demonstrated that reintroducing crop straw to fields may intensify cadmium (Cd) contamination in agricultural soils. However, the specific effects of long-term straw management practices on Cd concentration and its bioavailability in soil-rice ecosystems remain unclear. In this context, to explore the influence of straw return (SR) and straw removal (NSR) on Cd accumulation in both soil and rice within a double-cropping system, we conducted a four-year field study. Our research study unveiled that NSR consistently decreased soil Cd concentration and its bioavailability by approximately 16.93%–27.30% and 8.23%–21.05% respectively across both study sites. Conversely, SR resulted in a substantial increase in soil Cd bioavailability, ranging from 38.64%–53.95%. Notably, compared to NSR, SR significantly increased total soil Cd by 5.47%–36.58% and increased Cd content in brown rice by 8.00%–100.24%. Remarkably, after four consecutive years of NSR, brown rice Cd concentration at the Changfeng site compiled with national safety standards (GB 2762–2022). Additionally, returning early rice straw significantly raised soil Cd bioavailability for the subsequent crop, more so than late rice straw did for the early rice the following year. The findings suggest that traditional double-cropping cultivation with straw removal can effectively mitigate Cd contamination risks in crops and farmland in Hunan Province.

The kitchen-oil wastewater is characterized by a high concentration of organic matter, complex composition and refractory pollutants, which make wastewater treatment more difficult. Based on the study of using micro-electric field characteristic catalyst HCLL-S8-M to enhance the electron transfer between microorganisms in kitchen-oil wastewater which further improved the COD removal rate, we focus on the microbial community, intracellular metabolism and extracellular respiration, and make an in-depth analysis of the molecular biological mechanisms to microbial treatment in wastewater. It is found that electroactive microorganisms are enriched on the material surface, and the expression levels of cytochrome c and riboflavin genes related to electron transfer are up-regulated, confirming that the surface micro-electric field structure could enhance the electron transfer between microbial species and improve the efficiency of wastewater degradation. This study provides a new idea for the treatment of refractory organic wastewater.

Two anaerobic ammonia oxidation (anammox) systems, one with adding nano-scale zero-valent iron modified biochar (nZVI@BC) and the other with adding biochar, were constructed to explore the feasibility of nZVI@BC for enhancing the resistance of low-nitrogen anammox processes to low temperatures. The results showed that the average nitrogen removal efficiency with nZVI@BC addition at low temperatures was maintained at about 80%, while that with biochar addition gradually decreased to 69.49%. The heme-c content of biomass with nZVI@BC was significantly higher by 36.60%-91.45%. Additional, nZVI@BC addition resulted in more extracellular polymeric substances, better biomass granulation, and a higher abundance of anammox bacteria. In particularly, anammox genes hzsA/B/C, hzo and hdh played a pivotal role in maintaining nitrogen removal performance at 15°C. These findings suggest that nZVI@BC has the potential to enhance the resistance of low-nitrogen anammox processes to low temperatures, making it a valuable approach for practical applications in low-nitrogen and low-temperature wastewater treatment.

Considerable levels of methylmercury (MeHg) have been found rice-based infant cereals as a result of MeHg transfer from the rice as a raw material to the products, hence consumption of rice products may pose a potential health risk to infants who may receive cereals as the major diets and are susceptible to toxicity of MeHg. Determination of bioaccessibility of MeHg would provide a more accurate assessment of MeHg exposure through consumption of rice-based cereals, yet this information remains lacking. Further, the re-adsorption of methylmercury on the residual food will affect the accurate assessment of its bioaccessibility. Our goals in this work were 1) to determine the bioaccessibility of MeHg in infant rice cereals commonly available on the market by using a typical in vitro artificial gastrointestinal digestion model and 2) to evaluate the effects of MeHg re-adsorption on the in vitro assessment of MeHg bioaccessibility. The determined bioaccessibility of MeHg in the studied rice cereals after the standard dual-step (using gastric followed by intestinal juice) protocol ranged from 25% to 74%, a wide range comparable to that of fish samples observed here and in previous studies. The surprisingly higher bioaccessibility of MeHg in fish and rice cereals after the gastric step only, in comparison to after the complete two-step gastrointestinal digestion, suggests the re-adsorption of MeHg on the residual food. Separate experiments with spiked MeHg standards confirmed that the MeHg released by the acetic gastric juice was re-adsorbed on the residues during the intestinal step at neutral pH. This study provided first-hand data on the bioaccessibility of MeHg in infant rice cereals and methodological implications on using in vitro digestion to evaluate the bioaccessibility of MeHg and metal contaminants in general.

The exponential growth of antibiotic-resistant bacteria and antibiotic-resistant genes (ARGs) in soil-crop systems in recent years has posed a great challenge to ecological security and human health. While many studies have documented the residues of ARGs in soils and crops, but little is known about who drives the proliferation of ARGs in farming systems and what their underlying mechanisms are. Herein, we explored the occurrence and proliferating behavior of ARGs in soil-crop environments in terms of root secretions and plant volatiles. This review highlighted that plant root secretions and volatile organic compounds (VOCs) served as key substances mediating the development of antibiotic resistance in the soil-crop system. Still, there is controversy here as to plant root secretions promote the ARGs proliferation or inhibit. Some studies indicated that root secretions can suppress the colonization of ARGs, mainly attributed by the production of blunted metabolic enzymes and blocking of cellular exocytosis systems. Whereas the others have evidenced that root secretions can promote ARGs proliferation, primarily by altering the structure of microbial communities to influence species interactions and thus indirectly affect the proliferation of ARGs. Also, VOCs can act as molecular signals to convey antibiotic resistance information to their neighbors, which in turn drive the up-regulation of ARGs expression. Even so, the mechanism by which VOC-driven antibiotic resistance acquisition and proliferation need to be further probed. Overall, this review contributed to the development of products and technologies to impede the ARGs proliferation in agricultural environment.

NH₂-MIL-125 and its derivatives are receiving more attention in various aspects of photocatalytic reactions, especially in the photocatalytic hydrogen peroxide (H₂O₂) production from water (H₂O) and oxygen (O₂), which is a promising and sustainable strategy. However, the generation of H₂O₂ from NH₂-MIL-125 is far from satisfactory due to rapid photo-generated carriers recombination and poor surface electron transfer. In the work, the composite photocatalyst CQDs/TiO₂/NH₂-MIL-125 (C/T/NM) was designed for the first time by one-step hydrothermal method. TiO₂ was in situ converted from partial NH₂-MIL-125 (NM) during the successful loaded of Carbon quantum dots (CQDs) by hydrothermal process. The results indicated the type Ⅱ heterojunction was successfully constructed between the NM and TiO₂ interface, which could promote the transmission of photo-generated electrons. In addition, the successful loaded of CQDs could effectively transfer and stored the photo-generated electrons to the photocatalyst surface to participate in the reaction, and further avoiding the recombination of photo-generated carriers. The C/T/NM composite photocatalyst achieved a H₂O₂ generation of 455 µmol/L for 5 hours under visible light without oxygen bubbling, which was 7.1 times superior to that of NM. The H₂O₂ generation rate reached 645.4 µM/(g·h), which was in priority in the reported literature under the same conditions. Finally, based on the active species capture experiments, energy band structure analysis and the photoelectrochemical measurements, a possible mechanism for the efficient H₂O₂ generation through C/T/NM had been proposed. This work provided new ideas for designing NH₂-MIL-125 based composite photocatalysts for the production of H₂O₂.

Due to the discharge of industrial wastewater, urban domestic sewage, and intensive marine aquaculture tailwater, nitrate (NO₃⁻) pollution has emerged as a significant issue in offshore waters. Nitrate pollution affects aquatic life and may interact with other pollutants, leading to comprehensive toxicity. Cadmium (Cd²⁺) is the most widespread metal contaminant, adversely affecting aquatic life in the coastal waters of China. Despite this, few studies have focused on the synergistic toxicity of NO₃⁻ and Cd²⁺ in marine organisms. This study conducted a 30-day exposure experiment on marine Japanese flounder (Paralichthys olivaceus) to explore the synergistic toxicity of NO₃⁻ and Cd²⁺. Our results demonstrated that the exposure to Cd²⁺ alone induced slight histopathological changes in the liver. However, malformations such as hepatic vacuolar degeneration and sinusoid dilatation were exacerbated under co-exposure. Moreover, co-exposure induced the downregulation of antioxidants and the upregulation of the product malonaldehyde (MDA) from lipid peroxidation, indicating potent oxidative stress in the liver. The increased mRNA expression of IL-8, TNF-α, and IL-1β, along with the decreased expression level of TGF-β, indicated a synergistic inflammatory response in the organisms. Furthermore, the co-exposure led to an abnormal expression of P53, caspase-3, caspase-9, Bcl-2, and Bax, and disturbed the apoptosis in the liver through TUNEL staining analysis. Overall, our results imply that co-exposure synergistically affects inflammation, redox status, and apoptosis in flounders. Therefore, the findings from this study provide valuable perspectives on the ecological risk assessment of marine teleosts co-exposure to NO₃⁻ and Cd²⁺.

The biotreatment of mine drainage containing dissolved manganese (Mn) using Mn(II)-oxidizing bacteria is challenging. Sequencing-batch (SBRs) and continuous-flow reactors (CFRs) packed with limestones and inoculated with the mine-drainage microbial community were compared to determine the removal efficiency of Mn(II) from mine drainage. Mn(II) removal in CFRs was 11.4%±0.0% (mean ± standard deviation) in the first two weeks and; it slightly increased to 13.6%±0.0% after four weeks, and more than 94% of Mn(II) was removed under the steady-state treatment phase. The performance of SBRs was more effective, wherein 24.4%±0.1% of Mn was removed in the first two weeks, and in four weeks, surpassed 66.6%±0.2%. Rapid Mn(II) removal observed in the start-up of SBR resulted from higher microbial metabolic activities. The adenosine triphosphate (ATP) content of the microbial community was four-fold more than in CFR, but comparable during the steady-state phase. The Mn-oxide deposits occurring in the SBR and CFR at steady-state were mixed phases of birnessite and woodruffite, and the average Mn oxidation valence in the SBR (+3.73) was slightly higher than that in the CFR (+3.54). During the start-up treatment, the closest relatives of Methyloversatilis, Methylibium, and Curvibacter dominated the SBR, whereas putative Mn oxidizers were associated with Hyphomicrobium, Pedobacter, Pedomicrobium, Terricaulis sp., Sulfuritalea, and Terrimonas organisms. The growth of potential Mn-oxidizing genera, including Mesorhizobium, Rhodococcus, Hydrogenophaga, Terricaulis sp., and ‘Candidatus Manganitrophus-noduliformans’ was observed under the steady state. The SBR operation was effective as a prior start-up treatment for mine drainage-containing Mn(II), through which the CFR performed well as posterior bio-treatment.

Green and atom-economic depolymerization of lignin remains a great challenge due to its complex non-repetitive structure and the inert property for chemo-digestion. A redox-neutral lignin depolymerization system without the use of extra oxidant and/or reductant over a Co-NC catalyst has been developed in this work, providing the first non-noble metal heterogeneous catalytic system for redox-neutral valorization of lignin. Mechanistic studies based on control reactions and deuterium labeling experiments suggest that the reaction proceeds via a metal-catalyzed dehydrogenation of C_α-OH to afford a carbonyl intermediate, followed by C_β-O bond cleavage (via hydrogenolysis) to afford monophenols and aromatic ketone products. The hydrogen used for the cleavage of the C_β-O bond originates from the alcohol moiety in the substrate, and the cascade dehydrogenation and hydrogenolysis steps are highly coupled, rendering it an efficient and atom-economic process.

Currently, ferrate(VI) oxidation technology (FOT) has been regarded as one of the most promising options for the degradation of emerging organic pollutants. However, the role and transformation of chloride ions (Cl⁻) in FOT have not been well explored. The current study aims to investigate the formation of chlorinated phenolic byproducts upon ferrate(VI) oxidation processes. The obtained results indicate that chlorides suffering ferrate(VI) attack will be transformed to active chlorine species (ACS), which will subsequently lead to the formation of highly toxic aromatic chlorinated byproducts. The identified byproducts include common chlorinated phenolic derivatives, as well as complex chlorinated oligomer byproducts with ether structures (mainly dimers and trimers). While the formation of common chlorophenols can be ascribed to the electrophilic substitution reactions mediated by ACS, the oligomer byproducts are generated via coupling reactions between chlorinated phenoxy radicals. ECOSAR software predicts that the generated chlorinated oligomer byproducts exhibit high ecotoxicological effects. As a whole, the above findings shed light on the potential risk of FOT in real practice.