Influence of microplastics on the availability of antibiotics in soils.

Microplastics (MPs) and antibiotics, as two major types of emerging pollutants, inevitably coexist in the soil environment due to agricultural film residue, sewage irrigation and sludge application. However, the impact of MPs on antibiotic availability in soils with varying characteristics has not been extensively studied. Therefore, in this study, an interference experiment was conducted using three types of MPs (polyethylene (PE), polyvinyl chloride (PVC) and polypropylene (PP)) in red soil, paddy soil and cinnamon soil. The available antibiotics in soils were evaluated using diffusive gradients in thin-films (DGT). Results showed that MPs had a significant impact on the amount of antibiotics adsorbed on soil solid (Cs) by providing additional binding sites or altering soil characteristics (e.g., pH and dissolved organic carbon). The most significant effects on Cs were observed in cinnamon soil, and the Cs values were dependent on concentration of MPs. The available antibiotics, as measured by DGT significantly decreased after the addition of MPs. This decrease was influenced by the soil characteristics. However, the concentration of antibiotics in soil solutions (Cd) was only slightly impacted by MPs. Therefore, the influence of MPs on the migration of antibiotics was reflected by their impact on the soil/water partition coefficient (Kd), while the resupply ability (R) from the soil solid phase was less influential. Moreover, the dosage of MPs had a significant effect on the availability of antibiotics in CS by promoting the adsorption of antibiotics on the solid phase, while in RS and PS, the soil properties played a dominate role in the changes in antibiotic availability after MP addition. These results indicate that the impact of MPs on available antibiotics mainly depends on soil properties. In addition, DGT measurement is more sensitive than soil solution to investigate the effects of coexisting pollutants on the behavior of antibiotics in soil.

Biodegradation of phenolic pollutants and bioaugmentation strategies: A review of current knowledge and future perspectives.

The widespread use of phenolic compounds renders their occurrence in various environmental matrices, posing ecological risks especially the endocrine disruption effects. Biodegradation-based techniques are efficient and cost-effective in degrading phenolic pollutants with less production of secondary pollution. This review focuses on phenol, 4-nonylphenol, 4-nitrophenol, bisphenol A and tetrabromobisphenol A as the representatives, and summarizes the current knowledge and future perspectives of their biodegradation and the enhancement strategy of bioaugmentation. Biodegradation and isolation of degrading microorganisms were mainly investigated under oxic conditions, where phenolic pollutants are typically hydroxylated to 4-hydroxybenzoate or hydroquinone prior to ring opening. Bioaugmentation efficiencies of phenolic pollutants significantly vary under different application conditions (e.g., increased degradation by 10-95% in soil and sediment). To optimize degradation of phenolic pollutants in different matrices, the factors that influence biodegradation capacity of microorganisms and performance of bioaugmentation are discussed. The use of immobilization strategy, indigenous degrading bacteria, and highly competent exogenous bacteria are proposed to facilitate the bioaugmentation process. Further studies are suggested to illustrate 1) biodegradation of phenolic pollutants under anoxic conditions, 2) application of microbial consortia with synergistic effects for phenolic pollutant degradation, and 3) assessment on the uncertain ecological risks associated with bioaugmentation, resulting from changes in degradation pathway of phenolic pollutants and alterations in structure and function of indigenous microbial community.

Nickel sources affect soil biological properties but do not affect sorghum growth.

Nickel (Ni) is an essential element, but it can be phytotoxic in high concentration, which may be caused by high availability in soil solution. The objective of this study was to evaluate the effect of sources and doses of Ni applied to a dystrophic Red Latosol cultivated with sorghum on i) the availability of the metal in the soil; ii) the impact on biological and biochemical properties of the soil; iii) the absorption and distribution in sorghum plants; and iv) crop productivity. The experiment was carried out within a completely randomized design with two nickel sources [nickel(II) nitrate, Ni(NO3)2 and nickel(III) oxide, Ni2O3], three doses (35, 70, and 140 mg Ni kg-1 soil), plus controls without Ni, with 3 replications. The concentrations of Ni in the soil, soil microbial biomass (SMB), basal soil respiration (BSR), metabolic quotient (qCO2), fluorescein diacetate (FDA) hydrolysis, and urease activity were determined. The concentrations of Ni in the leaf diagnostic and in the plant (shoot, root, and grains) were also measured. In the soil, the concentrations of available Ni remained between 0.21 and 54.01 mg Ni kg-1. Ni2O3 contributed very little to the increase in available Ni. SMB and the FDA hydrolysis were not affected by the Ni source or Ni dose, but BSR and qCO2 had significant increase with Ni application rates, suggesting the soil microorganisms faced stress. Soil urease activity was affected by Ni dose but not by Ni source. The dose of Ni as Ni(NO3)2 decreased the metal concentration in the plant, while that of Ni2O3 increased it. Nickel source did not affect dry mass production of the plants, but grain yield was affected in a dose-dependent manner when Ni2O3 was the source of Ni.

Influence of elevated temperature on the species and mobility of chromium in ferrous sulfate-amended contaminated soil.

Ferrous sulfate (FeSO4) combined with acid pretreatment is usually employed to remediate contaminated soils containing Cr(VI). However, the long-term efficiency of this stabilization method is important for its sustainability. In this study, a gradient temperature-elevating exposure test was employed to investigate the stability of Cr in FeSO4-remediated soil when exposed to elevated temperatures (40 °C, 120 °C, and 500 °C), possibly caused by hot weather and/or wildfires. The results of chemical extraction and X-ray absorption near edge structure spectroscopy (XANES) showed that the Cr(VI) in contaminated soil was successfully transformed to Cr(III) after stabilization, resulting in the dramatic decrease of water-leachable Cr(VI). The stabilization efficiency was further improved under 40 °C treatment after 30 days. Subsequently, the 120 °C treatment (7 days) had relatively little effect on the Cr speciation and mobility in soils. However, even one day of 500 °C calcination resulted in the deterioration of stabilization efficiency, and the water-leachable Cr(VI) re-increased and became higher than the Chinese environmental standards (total Cr 15 mg/L, Cr(VI) 5 mg/L) for the classification of hazardous solid wastes. XANES results reflected that heating at 500 °C facilitate the formation of Cr2O3, which was mainly caused by thermal decomposition and dehydration of Cr(OH)3 in the soil. Besides, the transformation of Cr species resulted in the enhanced association of Cr with the most stable residual fraction (88.3%-91.6%) in soil. Based on chemical extraction results, it was suggested that the oxidation of Cr(III) to Cr(VI) contributed to the re-increased mobility of Cr(VI) in soil. However, the XANES results showed that almost no significant re-oxidization of Cr(III) to Cr(VI) happened after heating at 500 °C, which was probably caused by XANES linear combination fits (LCF) uncertainties. Moreover, the changes in soil properties, including a rise in pH to a slightly alkaline range and/or the decomposition of organic matter, possibly contributed to the enhanced mobility of Cr(VI) in soil. This study contributes to clarifying the mobility and transformation of Cr in contaminated soils and provides a support for the sustainable management of remediated soils.

Bacterial crude oil and polyaromatic hydrocarbon degraders from Kazakh oil fields as barley growth support.

Bacterial strains of the genera Arthrobacter, Bacillus, Dietzia, Kocuria, and Micrococcus were isolated from oil-contaminated soils of the Balgimbaev, Dossor, and Zaburunye oil fields in Kazakhstan. They were selected from 1376 isolated strains based on their unique ability to use crude oil and polyaromatic hydrocarbons (PAHs) as sole source of carbon and energy in growth experiments. The isolated strains degraded a wide range of aliphatic and aromatic components from crude oil to generate a total of 170 acid metabolites. Eight metabolites were detected during the degradation of anthracene and of phenanthrene, two of which led to the description of a new degradation pathway. The selected bacterial strains Arthrobacter bussei/agilis SBUG 2290, Bacillus atrophaeus SBUG 2291, Bacillus subtilis SBUG 2285, Dietzia kunjamensis SBUG 2289, Kocuria rosea SBUG 2287, Kocuria polaris SBUG 2288, and Micrococcus luteus SBUG 2286 promoted the growth of barley shoots and roots in oil-contaminated soil, demonstrating the enormous potential of isolatable and cultivable soil bacteria in soil remediation. KEY POINTS: • Special powerful bacterial strains as potential crude oil and PAH degraders. • Growth on crude oil or PAHs as sole source of carbon and energy. • Bacterial support of barley growth as resource for soil remediation.

AI-assisted systematic review on remediation of contaminated soils with PAHs and heavy metals.

This systematic review addresses soil contamination by crude oil, a pressing global environmental issue, by exploring effective treatment strategies for sites co-contaminated with heavy metals and polycyclic aromatic hydrocarbons (PAHs). Our study aims to answer pivotal research questions: (1) What are the interaction mechanisms between heavy metals and PAHs in contaminated soils, and how do these affect the efficacy of different remediation methods? (2) What are the challenges and limitations of combined remediation techniques for co-contaminated soils compared to single-treatment methods in terms of efficiency, stability, and specificity? (3) How do various factors influence the effectiveness of biological, chemical, and physical remediation methods, both individually and combined, in co-contaminated soils, and what role do specific agents play in the degradation, immobilization, or removal of heavy metals and PAHs under diverse environmental conditions? (4) Do AI-powered search tools offer a superior alternative to conventional search methodologies for executing an exhaustive systematic review? Utilizing big-data analytics and AI tools such as Litmaps.co, ResearchRabbit, and MAXQDA, this study conducts a thorough analysis of remediation techniques for soils co-contaminated with heavy metals and PAHs. It emphasizes the significance of cation-π interactions and soil composition in dictating the solubility and behavior of these pollutants. The study pays particular attention to the interplay between heavy metals and PAH solubility, as well as the impact of soil properties like clay type and organic matter on heavy metal adsorption, which results in nonlinear sorption patterns. The research identifies a growing trend towards employing combined remediation techniques, especially biological strategies like biostimulation-bioaugmentation, noting their effectiveness in laboratory settings, albeit with potentially higher costs in field applications. Plants such as Medicago sativa L. and Solanum nigrum L. are highlighted for their effectiveness in phytoremediation, working synergistically with beneficial microbes to decompose contaminants. Furthermore, the study illustrates that the incorporation of biochar and surfactants, along with chelating agents like EDTA, can significantly enhance treatment efficiency. However, the research acknowledges that varying environmental conditions necessitate site-specific adaptations in remediation strategies. Life Cycle Assessment (LCA) findings indicate that while high-energy methods like Steam Enhanced Extraction and Thermal Resistivity - ERH are effective, they also entail substantial environmental and financial costs. Conversely, Natural Attenuation, despite being a low-impact and cost-effective option, may require prolonged monitoring. The study advocates for an integrative approach to soil remediation, one that harmoniously balances environmental sustainability, cost-effectiveness, and the specific requirements of contaminated sites. It underscores the necessity of a holistic strategy that combines various remediation methods, tailored to meet both regulatory compliance and the long-term sustainability of decontamination efforts.

Spatial distribution of Pb and Zn in soils under native vegetation in Southeast Brazil.

Heavy metals can play an important biological role as micronutrients but also as potentially toxic elements (PTEs). Understanding the natural concentrations of PTEs-Pb and Zn included-in soils allows for the identification and monitoring of contaminated areas and their role in environmental risk assessment. In this study, we aim to determine semi-total or natural and available concentrations of Pb and Zn in topsoils (0-20 cm depth) from 337 samples under native vegetation in the State of Minas Gerais, Brazil. Additionally, we sought to interpret the spatial geochemical variability using geostatistical techniques and quality reference values for these elements in soils were established. The semi-total concentrations were determined by flame and graphite furnace atomic absorption after microwave-assisted nitric acid digestion method. The available concentrations were extracted using the Mehlich-I extractor and determined by atomic absorption spectrometer. Spatial variability was modeled using semivariance estimators: Matheron's classic, Cressie and Hawkins' robust, and Cressie median estimators, the last two being less sensitive to extreme values. This allowed the construction of digital maps through kriging of semi-total Pb and Zn contents using the median estimator, as well as other soil properties by the robust estimator. The dominance of acidic pH and low CEC values reflects highly weathered low-fertility soils. Semi-total Pb contents ranged from 2.1 to 278 mg kg-1 (median: 9.35 mg kg-1) whereas semi-total Zn contents ranged from 2.7 to 495 mg kg-1 (median: 7.7 mg kg-1). The available Pb contents ranged from 0.1 to 6.92 mg kg-1 (median: 0.54 mg kg-1) whereas available Zn contents ranged from 0.1 to 78.2 mg kg-1 (median: 0.32 mg kg-1). The highest Pb and Zn concentrations were observed near Januária, in the northern part of the territory, probably on limestone rocks from the Bambuí group. Finally, the QRVs for Pb and Zn in natural soils were lower than their background values from other Brazilian region and below the prevention values suggested by Brazilian environmental regulations.

Examining diverse remediation mechanisms of biochar in soil contaminated with polycyclic aromatic hydrocarbon (PAH) of various ring structures: A global meta-analysis.

Biochar is a widely recognized solution for addressing polycyclic aromatic hydrocarbon (PAH) contamination. However, it is unclear how the different physicochemical properties of PAHs affect remediation mechanisms, thereby affecting the remediation efficiency of biochar. In this study, a meta-analysis of 56 studies with 2236 observations was conducted to quantify the contributions of the preparation parameters and physicochemical properties of biochar, soil properties, and application measures to remediation efficiency. The research results revealed that PAH contents in the contaminated soil were significantly reduced by an average of 24.99 % after the application of biochar. Random Forest analysis identified feedstock, biochar SSA, soil pH, and rate of biochar application to be the most critical factors among the four categories. The reduction of PAH contents in the contaminated soil first decreased from 37.61 % to 17.44 % and then increased to 40.29 % with an increase in the number of aromatic rings from 2 to 6. Our study results suggest that biochar prepared from bio-waste at low temperatures could be favorable for reducing the content of NAP in soil. Wood-derived biochar pyrolyzed at a relatively high temperature is recommended for remediation of soil contaminated with PAHs with 5 or 6 aromatic rings. Our study provides a new perspective and an optimized strategy for the remediation of PAH-contaminated soils with biochar.

Role of keystone drives polycyclic aromatic hydrocarbons degradation and humification especially combined with aged contaminated soil in co-composting.

Accumulation of persistent organic pollutants polycyclic aromatic hydrocarbons (PAHs) in soil has become a global problem. Composting is considered one of the more economical methods of soil remediation and is important for the resourceful use of wastes. Agroforestry waste is produced in huge amounts and is utilized at low rates, hence there is an urgent need to manage it. Here, leaf (LVS) or rice straw (SVS) was co-composting with aged contaminated soil to investigate bacteria interaction to PAHs degradation and humus formation. The degradation rate of high molecular weight PAHs (HMW-PAHs) in LVS and SVS reached 58.9% and 52.5%, and the low molecular weight PAHs (LMW-PAHs) were 77.5% and 65%. Meanwhile, the humus increased by 44.8% and 60.5% in LVS and SVS at the end of co-composting. The topological characteristics and community assembly of the bacterial community showed that LVS had higher complexity and more keystones than SVS, suggesting that LVS might more beneficial for the degradation of PAHs. The stability of the co-occurrence network and stochastic processes (dispersal limitation) dominated community assembly made SVS beneficial for humus formation. Mantel test and structural equation models indicated that the transformation of organic matter was important for PAHs degradation and humus formation. Degradation of HMW-PAHs led to bacterial succession, which affected the formation of precursors and ultimately increased the humus content. This study provided potential technology support for improving the quality of agroforestry organic waste composting and degrading PAHs in aged contaminated soil.

Spatial differentiation of soil nutrients and their ecological chemometrics based on geographic detector in National Agricultural Park of Tangchang, Southwest China.

In order to analyze the spatial variability of soil nutrients and their ecological chemometrics in Tangchang Town, National Agricultural Park, 20 influencing factors were selected: soil pH, Cd, Hg, As, Cu, Pb, Cr, Zn, Ni, Se, elevation, slope, aspect, land use type, distance from industrial land, distance from commercial land, distance from railway, distance from residential area, distance from highway and distance from river. The effects of various influencing factors on the spatial variability of total organic carbon (TOC), total nitrogen (N), total phosphorus (P), total potassium (K) and ecological stoichiometry were analyzed by means of geographic detector. The results showed that average contents of soil TOC, N, P and K in the study area are 10.24 g kg-1, 1.33 g kg-1, 1.14 g kg-1 and 23.60 g kg-1, respectively, and there were significant differences in the spatial distribution of soil nutrients and their eco-stoichiometry in the study area, and TOC, N, P, K, C/N, C/P, C/K, N/P, N/K and P/K has a significant correlation with each other and most correlation coefficients are above 0.5 or below -0.5. Factor detection showed that soil properties, distance from railway and distance from residential area had the most significant explanatory power to the spatial heterogeneity of soil nutrients and eco-stoichiometry. Interaction detection showed that the interaction between soil properties with other factors was the most important factor affecting the spatial differentiation of soil nutrients and their ecological chemometrics, and elevation, distance from railway and distance from residential area were also important factors. Risk detection showed that the differences of soil nutrients and their ecological stoichiometry were most significant in the subregions of soil properties (pH, Cd, Hg, As, Cu, Pb, Cr, Zn, Ni and Se).

Biosurfactants-based mixed polycyclic aromatic hydrocarbon degradation: From microbial community structure toward non-targeted metabolomic profile determination.

Biosurfactants-based bioremediation is considered an efficient technology to eliminate environmental pollutants including polycyclic aromatic hydrocarbons (PAHs). However, the precise role of rhamnolipids or lipopeptide-biosurfactants in mixed PAH dissipation, shaping microbial community structure, and influencing metabolomic profile remained unclear. In this study, results showed that the maximum PAH degradation was achieved in lipopeptide-assisted treatment (SPS), where the pyrene and phenanthrene were substantially degraded up to 74.28 % and 63.05 % respectively, as compared to rhamnolipids (SPR) and un-aided biosurfactants (SP). Furthermore, the high throughput sequencing analysis revealed a significant change in the PAH-degrading microbial community, with Proteobacteria being the predominant phylum (>98 %) followed by Bacteroidota and Firmicutes in all the treatments. Moreover, Pseudomonas and Pannonibacter were found as highly potent bacterial genera for mixed PAH degradation in SPR, SPS, and SP treatments, nevertheless, the abundance of the genus Pseudomonas was significantly enhanced (>97 %) in SPR treatment groups. On the other hand, the non-targeted metabolomic profile through UHPLC-MS/MS exhibited a remarkable change in the metabolites of amino acids, carbohydrates, and lipid metabolisms by the input of rhamnolipids or lipopeptide-biosurfactants whereas, the maximum intensities of metabolites (more than two-fold) were observed in SPR treatment. The findings of this study suggested that the aforementioned biosurfactants can play an indispensable role in mixed PAH degradation as well as seek to offer new insights into shifts in PAH-degrading microbial communities and their metabolic function, which can guide the development of more efficient and targeted strategies for complete removal of organic pollutants such as PAH from the contaminated environment.

Influences of extracellular polymeric substances (EPS) recovered from waste sludge on the ability of Jiaozhou Bay to self-remediate of diesel-polluted seawater.

The introduction of EPS recovered from waste sludge may have an impact on the process of microbial remediation of oil-contaminated seawater. This study investigated the effect of EPS on the self-remediation capacity of diesel-polluted seawater in Jiaozhou Bay. Hydrocarbon attenuation and microbial activity were monitored in seawater collected from five islands after diesel and N, P addition, with and without EPS, incubated under aerobic conditions. Compared to seawater without EPS, degradation of TPH (total petroleum hydrocarbon) doubled and improved degradation of non-volatile (C16-C24) hydrocarbons to some extent in EPS-added seawater. The introduction of EPS led to changes in microbiota richness and diversity, significantly stimulating the growth of Proteobacteria and Firmicutes phyla or Bacillus and Pseudomonas genera. RT-qPCR analysis indicated EPS caused higher increases in cytochrome P450 gene copies than alkB. Prediction of alkane decay genes from 16S rRNA sequencing data revealed that EPS addition obviously promoted genes related to ethanol dehydrogenation function in the microbial community. Additionally, EPS enhanced the enzymatic activities of alkane hydroxylase, ethanol dehydrogenase, phosphatase and lipase, but increased protease and catalase inconspicuously. The above outlook that environmental sustainability of EPS from waste sludge for diesel-contaminated seawater remediation may provide new perspectives for oil spill bioremediation.

Toxic metal contamination effects mediated by hotspot intensity of soil enzymes and microbial community structure.

Metal contamination from mine waste is a widespread threat to soil health. Understanding of the effects of toxic metals from mine waste on the spatial patterning of rhizosphere enzymes and the rhizosphere microbiome remains elusive. Using zymography and high-throughput sequencing, we conducted a mesocosm experiment with mine-contaminated soil, to compare the effects of different concentrations of toxic metals on exoenzyme kinetics, microbial communities, and maize growth. The negative effects of toxic metals exerted their effects largely on enzymatic hotspots in the rhizosphere zone, affecting both resistance and the area of hotspots. This study thus revealed the key importance of such hotspots in overall changes in soil enzymatic activity under metal toxicity. Statistical and functional guild analysis suggested that these enzymatic changes and associated microbial community changes were involved in the inhibition of maize growth. Keystone species of bacteria displayed negative correlations with toxic metals and positive correlations with the activity of enzymatic hotspots, suggesting a potential role. This study contributes to an emerging paradigm, that changes both in the activity of soil enzymes and soil biota - whether due to substrate addition or in this case toxicity - are largely confined to enzymatic hotspot areas.

Composite biomediated engineering approaches for improving problematic soils: Potentials and opportunities.

Several conventional chemical stabilizers are used for soil stabilization, among which cement is widely adopted. However, the high energy consumption and environmental challenges associated with these stabilizers have necessitated the transition toward the adoption/deployment of eco-friendly approaches for soil stabilization. Biomediated techniques are sustainable soil improvement methods adopting less toxic microorganisms, enzymes, or polymers for cementing soil. However, these processes also have several drawbacks, such as slow hardening, environmental impact, high cost, and lack of compatibility with different types of soils. It is hypothesized that these limitations may be overcome by exploring the prospects and opportunities offered by hybrid technological approaches involving the integration of nontraditional stabilizers and microbial-induced biomineralization processes for improving problematic soils. This paper discusses selected previous studies integrating different technologies and their benefits and challenges. The emerging fungi-based bio-mediation techniques and the possibility of forming sustainable fungal-based biocomposites to improve problematic soils are also highlighted.

Bio-augmentation and bio-stimulation with kenaf core enhanced bacterial enzyme activities during bio-degradation of petroleum hydrocarbon in polluted soil.

Indigenous micro-organisms often possess the ability to degrade petroleum hydrocarbon (PHC) in polluted soil. However, this process can be improved by supplementing with nutrients or the addition of more potent microbes. In this study, the ability of kenaf-core to stimulate the PHC degradation capability of microbial isolates from PHC polluted soil samples was evaluated. The standard experimental methods used in this study include: the digestion and analysis of the physico-chemical properties of petroleum hydrocarbon contaminated and non-contaminated soil samples; evaluation of petroleum hydrocarbon biodegradation using bio-augmentation and bio-stimulation (with kenaf-core) treatments; and, determination of soil microbial enzyme activities. Results from this study show that K, Na, total nitrogen, organic carbon, exchangeable cations, and heavy metals were found to be significantly (P < 0.05) higher in the polluted soil than in the non-polluted soil. Also, the polluted samples had pH values ranging from 5.5 to 6.0 while the non-polluted samples had a pH of 7.6. The microbial enzyme activities were comparatively lower in the polluted soils as compared to the non-polluted soil. The percentage degradation in the kenaf-core treated samples (AZ1T2-78.38; BN3T2-70.69; OL1T2-71.06; OT1T2-70.10) were significantly (P < 0.05) higher than those of the untreated (AZ1T1-13.50; BN3T1-12.50; OL1T1-10.55; OT1T1-9.50). The degradation of petroleum hydrocarbon in the bio-augmented and bio-stimulated treatments increased with increasing time of incubation, and were higher than that of the untreated sample. Comparatively, the treatment with a combination of kenaf-core and rhamnolipid exhibited a significantly (P < 0.05) higher degradation rate than that of the treatment with only kenaf core or rhamnolipid. While, the bio-stimulated and bio-augmented treatments had appreciable microbial counts that are higher than that of the untreated. In conclusion, the nutrient-supplement with kenaf-core significantly enhanced microbial growth and activities in the soil, thus improving their ability to biodegrade petroleum hydrocarbons in the polluted soils. Thus, supplementing with Kenaf core to encourage microbiological degradation of petroleum hydrocarbon is recommended.

[Effects of Polystyrene Microplastics Combined with Cadmium Contamination on Soil Physicochemical Properties and Physiological Ecology of Lactuca sativa].

Contaminants such as microplastics (MPs) and heavy metals are commonly found in soils, both of which are extremely difficult to degrade and can easily form compound contamination, altering the physicochemical properties of the soil and thus potentially changing the growth and physiological and ecological characteristics of plants. In order to study the effects of the combined contamination of soil MPs and heavy metals on soil properties and plant growth, polystyrene microplastics (PS-MPs) with a particle size of 3 µm and the heavy metal cadmium were selected in the study. The changes in the physicochemical properties of soil and their effects on lettuce (Lactuca sativa) seed germination and seedling growth were studied at various exposure concentrations of PS-MPs (0, 10, 50, 100, 200, and 400 mg·kg-1) and combined with different Cd contamination concentrations (0, 1.2, and 6.0 mg·kg-1), respectively. The results showed that soil organic matter (SOM), available phosphorus (AP), alkali-hydrolysable nitrogen (AHN), and available kalium (AK) showed significant decreases as the intensity of PS-MPs combined with Cd contamination increased. Simultaneously, PS-MPs combined with Cd contamination also significantly reduced the germination rate of lettuce seeds, but low concentrations of PS-MPs slowed down the effect of Cd (6.0 mg·kg-1) contamination on lettuce seeds, and high concentrations of PS-MPs enhanced the effect of Cd (6.0 mg·kg-1). The fresh weight, dry weight, and plant height of lettuce seedlings showed an increasing and then decreasing trend with increasing exposure to PS-MPs. Chlorophyll content, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) showed a decreasing trend, whereas malondialdehyde (MDA) content showed an overall increasing trend under different Cd concentrations. The main physicochemical indicators of the soil were negatively correlated with MDA of lettuce seedlings, whereas other indicators of the seedlings were positively correlated. The combined contamination of PS-MPs and Cd could affect the germination of plant seeds and the physiological and ecological characteristics of seedlings by changing the physicochemical properties of the soil. Both exposure to single PS-MPs contaminants and the combination of PS-MPs with Cd inhibited the germination of lettuce seeds and affected the physiological activities of their seedlings, and the inhibition was significantly increased with increasing exposure. Low exposure to PS-MPs or the combination of PS-MPs with Cd contamination exhibited a promotive effect on lettuce seedling growth. High exposure to PS-MPs combined with Cd contamination exhibited significant ecological effects on lettuce seedlings, and high exposure to PS-MPs exacerbated the ecotoxicological effects of Cd contaminants on lettuce seedlings, and PS-MPs and Cd exhibited synergistic effects. The results can provide some reference for assessing the ecological effects of MPs and heavy metal pollution in soil-plant systems.

[Effect of Microplastics and Phenanthrene on Soil Chemical Properties, Enzymatic Activities, and Microbial Communities].

Microplastic and polycyclic aromatic hydrocarbon (PAHs) pollution have received increasing attention due to their ubiquitous distribution and potential risks in soils. However, the effects of microplastics-PAHs combined pollution on soil ecosystems remain unclear. Polyethylene (PE)/polypropylene (PP) and phenanthrene (PHE) were selected as the representatives of microplastics and PAHs, respectively. A 300-day soil microcosm experiment was conducted to study the single and combined effects of PE/PP and PHE on soil chemical properties, enzymatic activities, and bacterial communities (i.e., quantity, composition, and function), using the soil agricultural chemical analysis method and 16S amplicon sequencing technology. The interactions of soil properties, enzyme activities, and flora in the presence of PE/PP and PHE were analyzed. The results showed that the addition of PE/PP and PHE slightly changed the pH, available phosphorus (AP), and microbial quantity (i.e., bacteria, actinomycetes, and mold) but considerably increased the fluorescein diacetate hydrolase (FDAse) activity. There was a significant enhancement of soil organic matter (SOM) and urease activity in PE, PP, PHE-PE, and PHE-PP amended systems. PHE, PHE-PE, and PHE-PP obviously increased the dehydrogenase/neutral phosphatase activities and available nitrogen (AN) content. PHE had little effect on the microbial community. The PE, PP, PHE-PE, and PHE-PP addition influenced the microbial community to some extent. PE/PP and PHE showed positive effects on the energy production, growth, and reproduction of soil microorganisms and then accelerated the metabolism/degradation of pollutants and membrane transport. The changes in AN and SOM induced by PE/PP and PHE were the key factors affecting soil enzyme activities. Alterations in AN, AP, and pH were mainly responsible for the increase in microbial population. The changes in the microbial community were related to soil chemical properties and enzyme activities, and SOM had a significant effect on the microbial community. The presence of different carbon sources (PE/PP and PHE) in the soil and the microbial interaction also affected the microbiota. In conclusion, the addition of single or combined pollutants of PE/PP and PHE influenced the soil chemical properties, enzymatic activities, bacterial communities, and their interaction processes, thus facilitating the adaptation of the microbial community to pollutant stress.

Prospects for application of microorganisms in bioremediation of soils contaminated with pesticides.

The contamination of soil with residual amounts of pesticides remains an urgent challenge for human community. The most efficient approach to address this challenge is the direct microbial degradation of a pesticide in agricultural lands. To this end, the selected microorganisms, which quickly and completely utilize pesticides, are employed. In the present work, two herbicides belonging to different classes of chemical compounds, that is, imazamox and chlorsulfuron were used. The screening of promising microorganisms was carried out among different strains of bacteria and fungi in a liquid mineral medium containing a pesticide as the only source of carbon. It was found that the most active microorganisms were capable of utilizing up to 90% of the active substance for a short time. The dynamics of pesticides degradation indicated that the maximum destruction of the studied substances occurred during the first two weeks of cultivation. Further, the rate of degradation dramatically dropped or stopped at all. An increase in the concentration of pesticides in the cultivation medium almost completely suppressed their degradation. It is interesting that the bacteria were more suitable for the degradation of imazamox, while the fungi rendered the destruction of chlorsulfuron.

Mechanisms of microbial-driven changes in soil ecological stoichiometry around gold mines.

In this study, we used soils with different pollution and nutrient levels (non-polluted S1, highly polluted low-nutrient S2, and highly polluted high nutrient S3) around the gold mine tailing ponds, and combined with metabolic limitation modeling and macro-genomics approaches, aiming to investigate the relationship between soil microbial composition and soil eco-chemometrics characteristics under heavy metal stress. The results showed that heavy pollution resulted in reduced SOC, TN, microbial biomass, and with C- and P- acquisition (BG, CBH, ALP) as well as nitrogen limitation of soil microbial metabolism in soils (S2, S3). Further analysis by macrogenomics showed that heavy metal contamination led to an increase in α-microbial diversity and altered the composition of microbial communities in the soil. The cycling of C, N, and P nutrients was altered by affecting the relative abundance of Anaeromyxobacter, Steroidobacter, Bradyrhizobium, Acidobacterium, Limnochorda (predominantly in the Ascomycetes and Acidobacteria phyla), with the most pronounced effect on the composition of microorganisms synthesizing C-acquiring enzymes, and heavy metals and pH were the main influences on ecological stoichiometry. The results of this study are useful for understanding the sustainability of ecological remediation in heavy metal contaminated areas and for developing ecological restoration strategies.

High-resolution chemical imaging to understand Cd activation in rice rhizosphere of karstic soils.

Cadmium (Cd) activation, especially at a high spatial resolution, in paddy soils with a high geogenic Cd background is yet to be understood. To investigate the temporal and spatial patterns of Cd activation in rice rhizosphere, pot and rhizotron experiments were conducted using four paddy soils with high geogenic Cd (0.11-3.70 mg kg-1) from Guangxi, southwestern China. The pot experiment results showed that porewater Cd concentrations initially decreased and then increased over the complete rice growth period, reaching its lowest value during the late-tillering and early-filling stages. Besides, correlation analysis identified organic matter and root manganese (Mn) content as the main factors affecting rice Cd uptake, with Mn having a negative effect and organic matter having a positive effect. Sub-millimeter two-dimensional chemical imaging revealed that the distribution of labile Cd in the rhizosphere (by diffusive gradients in thin-films, or DGT) was influenced by the root system and soil properties, such as pH (by planar optode) and acid phosphatase activity (by soil zymography). Soil acid phosphatase activity increased under Cd stress. The overall pH at rice rhizosphere decreased. Moreover, a close relationship was found between the spatial distributions of soil labile Mn and Cd at the rhizosphere, with higher Mn being associated with lower Cd lability. This study highlights Mn as a key element in regulating rice Cd uptake and enlightens future Mn-based strategies for addressing Cd pollution in rice paddy soils, especially in karst areas with high geochemical background.