Ultraviolet (UV) radiation was selected in this study to evaluate its assistant remediation effects on Cr-contaminated soil. Various remediation materials, including corn stover (CS), corn stover biochar (CSB), polypyrrole-modified 44 corn stover (PPy-CS), and polypyrrole-modified corn stover biochar (PPy-CSB), were employed to evaluate their synergistic effects with UV radiation. The results showed that UV radiation increased the toxicity characteristic leaching procedure (TCLP) Cr(VI) when no other remediation was added to the contaminated soil. However, when the remediation materials were added, with UV radiation, the contents of TCLP-Cr(VI) decreased, while the contents of Cr(III) increased, and the removal rates of TCLP-Cr(VI) in contaminated soil treated by CSB, PPy-CSB, CS, and PPy-CS were 18.7%, 7.6%, 11.0%, and 8.2% higher than those of the non-irradiated groups, respectively. Notably, the CS group demonstrated superior efficacy in Cr(VI) removal compared with CSB under UV irradiation. Meanwhile, characteristic analysis including electron paramagnetic resonance (EPR), Fourier-transform infrared spectroscopy(FTIR) and X-ray photoelectron spectroscopy(XPS) assisted us in finding reaction mechanisms, which implied that UV irradiation could enhance the content of oxygen free radicals on the material surface and effectively activate the reactions between Cr(VI) and remediation materials. This study verified that UV irradiation could also be a promising tool in the remediation of heavy-metal-contaminated soil.

Reactive oxygen species (ROS) hotspots formation is initiated by the redox fluctuation in soil, primarily arising from the input of exogenous organic carbon. However, how different mobile fractions derived from biochar regulate ROS generation in the charosphere soil (microzone surrounding biochar) remains poorly understood. Our study found that, for biochar pyrolyzed at 300 °C, the < 0.45 µm (dissolved black carbon, DBC) fractions released from biochar dominated ROS generation in the charosphere via the indirect pathway. This can be attributed to their higher content of water-solublephenols, which increased Fe(II) accumulation by 68.4

The interactions between microplastic-derived dissolved organic matter (MPs-DOM) and heavy metals (Cu, Pb, and Cd) regulate the complex environmental transport behavior of pollutants in terrestrial and aquatic environments. In this study, fluorescence excited emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC) and electrospray ionization coupled Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) were employed to investigate the complexation mechanism of MPs-DOM with heavy metals, as well as the effects of different environmental occurrences of MPs-DOM on the transport behaviors of heavy metals in saturated porous medium. The findings demonstrated that MPs-DOM, particularly humic-like substances containing aromatic structures and various oxygen functional groups, could form stable complexes with heavy metals. This interaction significantly altered the transport capacity of Pb and Cu in saturated porous media. It is noteworthy that MPs-DOM in the free and deposited states in the environment may have markedly disparate effects on heavy metal transport. MPs-DOM in the free state may facilitate the co-migration of heavy metal ions in porous media, thereby enhancing the mobility of heavy metals. In contrast, sedimentary-state MPs-DOM can retain heavy metals in porous media and inhibit their migration through complexation with them.

Pteris vittata, a typical arsenic hyperaccumulator widely used in remediation, has an incompletely understood relationship with microbial arsenic reduction in terms of its arsenic enrichment efficiency. The wild-type and mutant strains without the arsenic-reducing gene were employed to investigate the growth and arsenic enrichment of P. vittata in Yunnan (YN) and Guangxi (GX) soils by a pot experiment. After 60 days of cultivation, compared with the control group, the total biomass of plants treated with wild-type strains and mutant strains increased by 113.81 % and 59.50 % in YN soil, and by 141.86 % and 118.96 % in GX soil, respectively. The arsenic concentration in leaves treated with wild-type strains was 1.29 times (YN) and 1.17 times (GX) higher than that treated with mutant strains. The calculated arsenic enrichment coefficient was 8.07 and 5.18, respectively, under wild-type strain and mutant strain addition. The contribution rate of the arsenic-reducing capacity of bacteria to the promoting effect of wild-type strain on arsenic removal by P. vittata can reach 15.56 %. Arsenic reduction promoted P. vittata's arsenic uptake and contributed to improving its arsenic enrichment efficiency. Above all, microbial arsenic reduction can not only increase the biomass of P. vittata and affect the activity of its antioxidant enzymes but also significantly enhance the arsenic enrichment efficiency of P. vittata. This finding highlights microbial arsenic reduction's important role in enhancing P. vittata's arsenic uptake efficiency and provides a new theoretical foundation for arsenic-contaminated soil microbial remediation.

Rhizosphere microorganisms play a pivotal role in enhancing the arsenic (As) remediation efficiency of Pteris vittata. However, the interactions among rhizosphere microorganisms, root exudates, and As, as well as their influence on As uptake by Pteris vittata at different As concentrations, remain poorly understood. This study systematically elucidates the molecular-ecological mechanisms through which Pteris vittata facilitates arsenic (As) remediation within a multidimensional interaction network. It was found that the rhizosphere microbial community was dominated by Proteobacteria, Acidobacteriota, and Ascomycota, with 44 bacterial and 10 fungal genera identified as genetically conserved core microorganisms. Microbial-mediated arsenic (As) methylation and reduction processes, coupled with metabolic pathways such as carbon fixation, sulfur oxidation, and phosphorus mineralization, contribute to the formation of an "As-multielement cycling" synergy. This synergy drives As speciation transformation and enhances plant uptake. Root exudates, such as L-phenylalanine and citric acid, enhance arsenic (As) activation and detoxification by selectively recruiting functional microbes, including Sphingomonas carrying arsC. The resulting metabolite profiles exhibit soil-specific response patterns. High As stress shifted microbial community assembly from stochastic to deterministic processes while maintaining remediation efficiency through enhanced fungal network stability (increased average connectivity). These findings reveal the dual "genetic conservation-environmental adaptation" regulatory strategy of Pteris vittata, providing both theoretical and practical foundations for designing targeted rhizosphere microecological technologies to enhance the phytoremediation of arsenic (As)-contaminated soils.

Humin (HM), as the main component of soil organic matter, carries various reactive groups and plays a crucial regulatory role in the transformation of arsenic (As). However, current research on the redox pathway of As and its interactions with HM is relatively limited. This study aimed to explore the impact of different HM samples on the redox characteristics of As. The results showed that HM can not only adsorb arsenite [As(III)] but also oxidize As(III) into arsenate [As(V)]. However, once As(III) is adsorbed on the HM, it cannot undergo further oxidation. HMNM (extracted from peat soil) exhibited the highest adsorption capacity of As(III), with a maximum amount of 1.95 mg/kg. The functional groups of HM involved in As complexation were primarily phenolic hydroxyl and carboxyl groups. The adsorption capacity of HM samples for As(III) was consistent with their carboxyl group contents. The oxygen-containing functional groups and environmentally persistent free radicals (EPFRs) on HM can directly oxidize As(Ⅲ) through electron transfer, or indirectly induce the production of reactive oxygen species (ROS), such as hydroxyl radicals, to further oxidize As(Ⅲ). This study provides new insight into the transport and transformation process of As mediated by soil HM, and establishes a theoretical basis for As remediation.

In order to study the safe utilization of acid cadmium （Cd） contaminated soil， light and moderate Cd-contaminated farmland in Shangluo， Shaanxi Province was taken as the research object， and lime， biochar， and calcium magnesium phosphate fertilizer were applied. Through the wheat-maize rotation experiment， the safe utilization effect of different amounts of passivator on Cd-contaminated soil was explored， and the best ratio of passivator was selected. The results showed that： ① the soil quality could be improved to varying degrees by applying the passivator. ② After the application of amendments， the grain yield of wheat and maize increased to different degrees. ③ The lime 2 340 kg·hm-2 （C3） treatment had the best effect， which increased the soil pH of wheat and corn by 1.453 and 1.717 units， respectively， and reduced the available Cd content by 34.38% and 30.20%， respectively. ④ The application of biochar 1 800 kg·hm-2 （B2） treatment had the best effect on reducing the Cd contents in wheat roots， straws， and grains， which were significantly reduced by 53.60%， 38.86%， and 52.96%， respectively， compared with that in CK. The Cd content in wheat grains was reduced to 0.09 mg·kg-1， which was lower than the limit value of wheat Cd （0.1 mg·kg-1） specified in the "National food safety standard food pollutant limit" （GB 2762-2017）. The application of the biochar 1 260 kg·hm-2 （B1） treatment had the best comprehensive effect on reducing the Cd contents of maize roots， straws， and grains， which were significantly reduced by 43.74%， 53.20%， and 94.57%， respectively， compared with that in CK. The Cd content of maize grains was reduced to 0.001 9 mg·kg-1， which was far lower than the limit value of maize Cd （0.1 mg·kg-1） specified in the "National food safety standard food pollutant limit" （GB 2762-2017）. Therefore， under the conditions of the field experiment， considering the influence of various indexes， biochar had the best effect on farmland soil in the wheat-maize rotation area with mild to moderate Cd pollution.

Interfacial electron transport and reactive oxygen species (ROS) generation in the redox action between biochar (BC) and low-molecular-weight organic acids (LMWOAs) have been overlooked during the utilization of BC in soil amelioration/remediation. Herein, BC and N-doped BC (NBC) with various physicochemical properties were prepared at pyrolysis temperatures of 350, 550 and 750 degrees C (namely BC/NBC350, 550 and 750) and their in-teractions with LMWOAs were systematically investigated. Results of ROS quenching and electrochemical cell experiments revealed that BC/NBC could strongly interact with LMWOAs, especially ascorbic acid (AA), and acted as an electron shuttle to mediate one electron transfer from AA to oxygen to generate O-2(center dot-), followed by the robust generation of H2O2 and center dot OH. Interestingly, the generation rates of center dot OH and H2O2 in the NBC-AA system were significantly higher than that in the BC-AA system, of which the NBC550-AA system exhibited the best performance, enabling its superior ability in bisphenol A degradation. Different from conventional wisdom, the electron shuttle capacity depended on a combined aromatization degree and electron-accepting capacity of BC/ NBC. These findings complement the interfacial electron transfer mechanism during the natural BC-LMWOAs interaction and provide new inspiration for the development of green and efficient organic pollutant removal technologies.

This study sought to explore the effects of passivator, leaf inhibitor, and their combination on cadmium （Cd）-contaminated farmland and to realize the safe utilization of cultivated land. Coconut shell biochar and calcium magnesium phosphate fertilizer were selected as soil passivators and foliar selenium fertilizer was used as a foliar inhibitor. The best combination was selected through a wheat-maize rotation experiment. The results showed that： ① The soil pH, organic matter content, and CEC could be improved to varying degrees by the application of passivators. ② The grain yield of wheat and maize increased to different degrees after the application of the passivator and foliar inhibitor. ③ The BFL treatment （biochar 1 800 kg·hm-2 +calcium magnesium phosphate 600 kg hm-2 + foliar inhibitor 3 L·hm-2） during the maize season had the best effect, which was significantly lower than that in CK by 13.85%. The effect of the BF treatment （biochar 1 800 kg·hm-2 + calcium magnesium phosphate 600 kg·hm-2） in wheat season was the best, which was significantly reduced by 11.21% compared with that in CK. ④ The BF treatment （biochar 1 800 kg·hm-2 + calcium magnesium phosphate 600 kg·hm-2） had the best effect on reducing Cd content in roots, straws, and grains of maize and wheat, reducing Cd content in roots of wheat and maize by 20.55% and 27.81%, Cd content in straws by 11.39% and 13.70%, and Cd content in grains by 48.97% and 50.44%, respectively. Therefore, considering all the indexes, the combination of passivators and foliar inhibitor, especially biochar combined with calcium magnesium phosphate fertilizer and biochar and calcium magnesium phosphate fertilizer combined with foliar inhibitor, could more effectively reduce the absorption, transport, and enrichment of Cd in maize and wheat and could be popularized and applied in safe use cultivated land.

Antimony (Sb) contamination in soil has become a growing concern due to its toxic effects on ecological soil functions. Soil enzymes, which are effective biological indicators, play a crucial role in assessing the ecological impact of heavy metals in soil. However, the effects of Sb on soil enzyme activity, particularly during the ageing process, remain poorly understood. This study examines the ageing process of Sb in soil and its biological toxicity on three key soil enzyme activities (arylsulfatase, urease, phosphatase) at different enzyme pool levels (total, intracellular and extracellular). Our findings reveal that the ageing of exogenous Sb in soil follows a heterogeneous dispersion process, with the Sb ageing rate constant (|b|) in acidic soil (S1, red soil, pH 4.90) being 1.21 to 1.90 times higher than in alkaline soil (S2, gray desert soil, pH 8.12). This suggests that Sb stabilizes more rapidly in acidic conditions. Regarding Sb effects on soil enzymes, extracellular urease activity and the total enzyme activity index (TEI) of extracellular enzymes were particularly sensitive to Sb stress. Over the course of the ageing period, extracellular urease activity decreased by 23.46-57.85 % in both soils under Sb stress at 7000 mg·kg-1. The inhibition of TEI by Sb ranged from 29.08 to 42.47 % in S1 soil, and from 12.47 to 20.65 % in S2 soil. Ecological dose (ED10) values indicated that Sb concentrations of 24.86-184.00 mg·kg-1 caused a 10 % reduction in extracellular enzyme TEI, whereas higher Sb concentrations (29.63-1791.86 mg·kg-1) were needed to inhibit 10 % of extracellular urease activity. Overall, TEI of extracellular enzymes emerges as a more sensitive and reliable indicator of long-term Sb contamination. This study provides essential insights for monitoring Sb pollution and provides a basis for establishing a soil Sb pollution assessment and early-warning system.

The elemental composition may affect the persistent free radical (PFR) and reactive species (RS) formation associated with photoaging microplastics; however, a relevant study is still lacking. This study systematically investigated the formation, evolution, and types of PFRs and RS on sulfur-containing microplastics (S-MPs) under simulated sunlight. Electron paramagnetic resonance detection and power saturation curve analysis isolated three different PFRs on each photoaging poly(phenylene sulfide) (PPS) and polysulfone (PSF). Combining the results of characterization and density functional theory calculation, these observed PFRs on the irradiated S-MPs were classified as oxygen-centered radicals with an adjacent S atom (namely, thio-oxygen radicals), oxygen-centered and sulfur-centered radicals, where the thio-oxygen radicals on PPS were benzenethiol-like radicals, and oxygen-centered radicals and sulfur-centered radicals on PSF that were identified as benzenesulfonic-like radicals and phenyl sulfonyl-like radicals, respectively. Moreover, potential precursor molecule fragments of PFRs on the photoaging S-MPs, including p-toluenesulfinic acid and benzenesulfonic acid, were detected by pyrolysis-gas chromatography/mass spectrometry and liquid chromatography-mass spectrometry. Interestingly, reactive sulfur species (SO3•-) was also observed on irradiated S-MPs in addition to reactive oxygen species, which was mainly derived from the reaction of •OH and sulfonyl radicals. These results have implications for assessing the potential risks of atmospheric S-MPs.

为研究施加钝化剂、叶面肥对大田小麦-玉米轮作Cd吸收转运的影响,实现安全利用类耕地农作物的安全生产,通过大田轮作试验的方式,选用小麦秸秆生物炭、钙镁磷肥为土壤钝化剂,叶面硒肥为叶面阻隔剂,在田间共设置6个处理:小麦和玉米常规种植(CK)、基施生物炭(B)、基施钙镁磷肥(P)、叶面喷施硒肥(F)、叶面喷施硒肥的同时基施生物炭(BF)、叶面喷施硒肥的同时基施钙镁磷肥(PF).小麦和玉米成熟后对其籽粒、秸秆、根系3部分的Cd含量进行检测,并对耕地土壤的pH值、有效态Cd、全量Cd进行测定.结果表明:与CK处理相比,小麦和玉米各处理土壤pH值有不同程度的升高,其中B处理和BF处理会显著提升土壤pH值;小麦和玉米各处理土壤中全量Cd无明显变化;P处理和PF处理可显著降低土壤有效态Cd含量.与CK处理相比,各处理农作物籽粒中Cd含量均有不同程度的降低,且叶面阻隔联合土壤钝化技术(BF、PF)的效果更好.较CK处理,PF处理小麦和玉米籽粒Cd含量下降最明显,降幅分别为39.91％、43.51％,BF处理小麦和玉米籽粒Cd含量分别下降了22.58％、33.53％,F、B处理和P处理变化较小,降低效果表现为B处理

为了解微塑料与镉单一及其复合污染对水培小麦发芽和幼苗生长的影响,选取农业土壤中普遍存在的两种微塑料[聚苯乙烯(mPS)和聚氯乙烯(mPVC),0、100、500 mg·L-1和1000 mg·L-1]、重金属镉(Cd,0、2、10 mg·L-1和50 mg·L-1)和小麦种子为试验对象进行种子发芽试验.结果表明:单一微塑料污染下,mPS和mPVC对小麦种子发芽率的影响总体表现为低浓度促进、中高浓度抑制,其中mPVC对小麦种子的发芽指数、发芽势、平均发芽速度均有促进作用,mPS对小麦的生物量有促进作用;单一镉胁迫对小麦种子发芽率的影响基本表现为低浓度(2 mg·L-1)促进发芽,中高浓度(10 mg·L-1和50 mg·L-1)抑制发芽,对小麦芽与根的影响基本表现为低促高抑的规律.微塑料和镉复合污染试验中,与对照组相比,低浓度镉(2 mg·L-1)-微塑料复合污染抑制小麦种子发芽,其余复合污染几乎对小麦种子的发芽无影响;而低浓度的mPVC与镉复合对小麦种子发芽指数、活力指数、平均发芽速度、根芽的生长和含水率等起协同作用.研究表明,与单一污染处理相比,微塑料-镉复合污染对小麦种子发芽势、活力指数、芽长和生物量的影响基本表现为拮抗作用,即两者复合在一定程度上降低了单一污染物的毒性.

Long-term input of agricultural chemicals such as pesticides into the soil can increase soil pollution, thereby affecting the productivity and quality of black soil. Triazine herbicide atrazine has been shown to have long-lasting residual effects in black soil. The atrazine residues affected soil biochemical properties, further leading to microbial metabolism restriction. It is necessary to explore the strategies to mitigate the limitations on microbial metabolism in atrazine-contaminated soils. Here, we evaluated the effect of the atrazine on microbial nutrient acquisition strategies as indicated by extracellular enzyme stoichiometry (EES) in four black soils. Atrazine degradation in soil followed the first-order kinetics model across various concentrations ranging from 10 to 100 mg kg−1. We found that the atrazine was negatively correlated with the EES for C-, N-, and P-acquisition. Vector lengths and angles decreased and increased significantly with an increase of atrazine concentration in tested black soils except for Lishu soils. Moreover, the vector angles were >45° for tested four black soils, indicating that atrazine residue had the greatest P-limitation on soil microorganisms. Interestingly, microbial C- and P-limitations with different atrazine concentrations showed a strong linear relationship, especially in Qiqihar and Nongan soils. Atrazine treatment significantly negatively affected microbial metabolic limitation. Soil properties and EES interaction explained up to 88.2% for microbial C-/P-limitation. In conclusion, this study confirms the EES as a useful method in evaluating the effects of pesticides on microbial metabolic limitations.

Arsenic-related functional genes are ubiquitous in microbes, and their distribution and abundance are influenced by edaphic factors. In arsenic-contaminated soils, soil arsenic content and pH determine the distribution of arsenic metabolizing microorganisms. In the uncontaminated natural ecosystems, however, it remains understudied for the key variable factor in determining the variation of bacterial assembly and mediating the arsenic biogeographical cycles. Here, we selected natural forest soils from southern and northern slopes along the altitudinal gradient of Taibai Mountain, China. The arsenic-related functional genes and soil bacterial community was examined using GeoChip 5.0 and high-throughput sequencing of 16S rRNA genes, respectively. It was found that arsenic-related functional genes were ubiquitous in tested forest soils. The gene arsB has the highest relative abundance, followed by arsC, aoxB, arrA, arsM, and arxA. The arsenic-related functional genes distribution on two slopes were decoupled from their corresponding bacterial community. Though there are higher abundance of bacterial communities on the northern slope than that on the southern slope, for arsenic-related functional genes, the abundance has the contrary trend which showing the more arsenic-related functional genes on the southern slope. In the top ten phyla, Proteobacteria and Actinobacteria were dominant phyla which affected the abundance of arsenic-related functional genes. Redundancy analysis and variance partitioning analysis indicated that soil pH, organic matter and altitude jointly determined the arsenic-related functional genes diversity in the two slopes of Taibai Mountain, and soil pH was a key factor. This indicates that the lower pH may shape more microbes with arsenic metabolic capacity. These findings suggested that soil pH plays a significant role in regulating the distribution of arsenic-related functional microorganisms, even for a forest ecosystem with an altitudinal gradient, and remind us the importance of pH in microbe mediated arsenic transformation.

Soil phosphatase is considered an indicator to assess soil arsenic (As) pollution. In the phosphatase activity determination, a fixed buffer value (pH 5-10) is commonly used for all soils, ignoring the soil's actual pH. Here, we determined the soil phosphatase activity of 20 soils under As stress at the soils' pH, and the As inhibition mechanism was also explored by the enzyme kinetics. Our results show that soil phosphatase activity was significantly inhibited under As stress. The inhibition rate in acid soils (39.2 %) was considerably higher than in alkaline soils (25.4 %) when As concentration was 600 mg kg-1. For alkaline soils, As inhibited phosphatase by competitive inhibition or linear mixed inhibition, while for acid soils, it was more complex, including linear mixed inhibition, non-competitive inhibition, and anti-competitive inhibition. Simultaneously, our results showed that the ecological dose (ED10) described by the partial inhibition model was far below than the complete inhibition model. According to the partial inhibition model, the ED10 of As ranged from 2.66 to 164.07 mg kg-1 for alkaline soils and 0.11 to 89.95 mg kg-1 for acid soils. Moreover, Vmax/Km of phosphatase is a more sensitive index for evaluating As contamination than Vmax in partial inhibition models. The ED10 obtained based on the relationship between Vmax/Km and As concentration was 0.64-34.75 mg kg-1 for acid soils and 8.48 to 20.16 mg kg-1 for alkaline soils. This also confirms Vmax/Km as a sensitive and ideal index for assessing As pollution under soils' actual pH. Furthermore, soil pH and cation exchange capacity are dominant factors affecting As inhibition on soil phosphatase. The above kinetic studies indicate that performing the assay by adjusting the buffer pH to the soil pH is essential for more accurately evaluating arsenic toxicity.

While pollution of the environment by polycyclic aromatic hydrocarbons has been rather well studied, the fate of substituted polycyclic aromatic hydrocarbons in ecosystems is less understood, notably in soil–plant systems. Here we hypothesized that substituted polycyclic aromatic hydrocarbons could enter wheat and induce phytotoxicity. We studied the accumulation, root-shoot translocation and phytotoxicity of α-tetralone, 1-nitronaphthalene, 1-nitropyrene, and 7,12-dimethylbenz[a]anthracene in wheat using hydroponic experiments. We deciphered the accumulation and translocation mechanisms by inhibition with sodium vanadate, glycerol and silver nitrate. Results show that pollutant concentrations increased rapidly in roots, reaching maximum of 38.3 μg/g for α-tetralone, 268.7 μg/g for 1-nitronaphthalene, 3566.1 μg/g for 1-nitropyrene, and 3632.7 μg/g for 7,12-dimethylbenz[a]anthracene. In contrast, the root-shoot translocation factors of α-tetralone, 1-nitronaphthalene, 1-nitropyrene and 7,12-dimethylbenz[a]anthracene were 2.4, 1.6, 0.1, and 0.1, respectively, thus decreasing significantly with increasing compound hydrophobicity. This could be explained by preferential adsorption for hydrophobic compounds, whereas less hydrophobic compounds could be partly translocated in a soluble form through plant water channels. The accumulated substituted polycyclic aromatic hydrocarbons in wheat induced the decrease of the total chlorophyll contents by 19.0–30.1

Robinia pseudoacacia is the main non-native tree species that has been widely planted in the Loess Plateau (LP) for revegetation. Most studies focused on its effects on soil and plant properties, but few works investigated biodiversity, especially soil fauna. We investigated soil fauna in areas where R. pseudoacacia was planted 10, 20, 30, and 50 years ago and grassland areas in LP. Results showed that afforestation can significantly increase the soil fauna groups of the litter layer which does not further increase with forest age. However, the number of soil fauna groups, especially the dominant groups (mites and springtails), was not significantly affected by afforestation. After afforestation, soil fauna abundance first increased and then decreased, with a maximum value observed 20 years post-planting. The average abundance of soil fauna in the soil layer of the R. pseudoacacia was 22, 292 individuals m–2, which was 4.91 times more than in the litter layer. However, the number of soil fauna groups in the soil layer (10) was significantly lower than that in the litter layer (17). Litter thickness and soil total nitrogen contributed the most and explained 34.7

Antimony (Sb), a toxic metalloid, is ubiquitous in the environment and threatens human and ecological health. Soil arylsulfatase (ARS) activity indicates heavy metal pollution. However, the enzyme's substrate concentration can affect the toxicity evaluation of heavy metals using enzyme activity. Enzyme kinetic parameters directly reflect the potency of heavy metals, and the magnitude of these parameters does not change with the substrate concentration of soil enzyme. In this work, seventeen soils were exposed to Sb contamination to investigate the change of kinetic parameters of soil arylsulfatase under Sb stress. Results showed that Sb inhibited soil arylsulfatase activity. The maximum reaction rate (Vmax) of soil arylsulfatase was reduced by 11.58-46.72% in 16 tested soils and unchanged in S15 when exposed to Sb. The Michaelis constant (Km) presented three trends: unchanged, increased by 28.46-41.27%, and decreased by 19.71-29.91% under Sb stress. The catalytic efficiency (Ka as the ratio of Vmax to Km) decreased by 12.56-55.17% in all soils except for S12 and S16. Antimony acted as a non-competitive and linear mixed inhibitor by decreasing ARS activity in S1-S12, S14, and S17-S18 soils, as an uncompetitive inhibitor in S13 and S16 soils and as a competitive inhibitor in S15. The competitive and uncompetitive inhibition constants (Kic and Kiu) were 0.058-0.142 mM and 0.075-0.503 mM. The ecological dose values of Sb to catalytic efficiency (Ka) of ARS (ED10-Ka) ranged from 50 to 1315 mg kg-1. Soil pH and total phosphorus (TP) contents were the dominant factors responsible for Sb toxicity on Ka by affecting the interaction of inhibitor (Sb) with enzyme-substrate (ES) complex. The findings of this study advance the current knowledge on Sb toxicity to soil enzymes and have significant implications for the risk assessment of Sb in soils.

The photo-transformation of microplastic (MP) in natural water may involve interactions with various ingredients, but the photoaging kinetics and underlying mechanism are not well understood. This work systematically explored the photoaging process of polystyrene microplastic (PS-MP) in the presence of commonly-found inorganic anions, including NO3?, HCO3?, Br? and Cl?. The addition of these ions led to more obvious changes in the morphology, functional groups and molecular weight of photoaging PS-MP. The evolution of carbonyl index value for the photoaged samples conformed to pseudo-first-order kinetic model, and the photoaging rate constant (k) in the presence of inorganic anions at their environmentally relevant concentrations of 0.6 mM, 1.2 mM, 0.1 M and 0.1 mM was calculated to be k(HCO3-)= 0.0074 d(-1), k(NO3-)= 0.01001 d(-1), k(Cl-)= 0.00783 d(-1), and k(Br-)= 0.00888 d(-1), which was higher than that in ultrapure water (k=0.00705 d(-1)). Electron paramagnetic resonance technique and quenching experiments demonstrated that photo-transformation of PS-MP was mainly mediated by indirect photolysis, i.e., the formation of reactive radical species. The photosensitivity of NO3- promoted more center dot OH production, thereby accelerated the indirect photoaging of PS-MP. Meanwhile, the presence of halide ions promoted the generation of reactive halogen species, which were also involved in the indirect photoaging of PS-MP. Interestingly, as center dot OH scavenger, HCO3- had no inhibitory effect on PS-MP photoaging, attributing to the oxidation of CO3 center dot-. This study provides valuable insights into the understanding of photo-transformation of MPs in natural aquatic environments.