Knowledge of the influence of microplastics on soil microbiome and nutrients is important for understanding the ecological consequences of microplastic pollution in terrestrial ecosystems. In this ...study, we investigated whether polyvinyl chloride (PVC) microplastic pollution at environmentally relevant concentrations would affect soil bacterial community and available nitrogen/phosphorus content. The results showed that although PVC microplastics at 0.1% and 1% levels did not have a significant effect on overall bacterial community diversity and composition in soil over the course of 35 days, a number of bacterial genera were significantly reduced or enriched by the presence of microplastics. Potentially due to their effect on certain functional groups, microplastics caused a significant change in soil available P content. It is noteworthy that, depending on soil type, pollution level and plasticizer presence, contrasting effects of microplastics may be observed. Further research is definitely warranted to gain a clearer picture of the threats posed by microplastic pollution in soil environments.
•Factors affecting DnBP release from PVC microplastics were systematically studied.•More phthalate was released from microplastics with higher phthalate content.•Natural aging of plastics led to ...changed phthalate release.•Coexistence of fulvic acid and NaCl had a greater effect on phthalate release than fulvic acid alone.•Leaching of surface-active DOC from plastics could promote the release of phthalate plasticizer.
In recent years, great efforts have been made to understand the capacity of microplastics to adsorb environmental pollutants; however, relatively little is known about the ability of microplastics to release inherent additives into peripheral environments. In this study, we investigated the leaching behavior of phthalate plasticizer from polyvinyl chloride (PVC) microplastics, in aqueous solutions relevant to aquatic and soil environments. It was found that plastic properties, such as particle size, plasticizer content and aging of plastics had a great effect on the leaching of dibutyl phthalate (DnBP). Phthalate release was generally higher in smaller particles and particles with higher phthalate content. Whereas, plastic aging caused by solar irradiation could either enhance phthalate release by increasing plastic hydrophilicity or decrease the leaching by reducing readily available fractions of phthalate. Regarding environmental factors, solution pH (3–9) and ionic strength (0–0.2 M NaCl) were found to have minor effect on phthalate release, while fulvic acid (0–200 mg/L) greatly promoted the release by improving phthalate solubility and solution-plastic affinity. Interestingly, we found that more DnBP was leached out when fulvic acid and NaCl coexisted, and the results from dissolved organic carbon (DOC) and three-dimensional fluorescence spectroscopy analyzes suggested that the leaching of other fulvic acid-like additives might have played a role. These findings would be helpful for predicting the potential of microplastics to release toxic additives under different environmental conditions.
Display omitted
Straw return, as an important agricultural management measure, is receiving growing attention. Hydroxyl radical (
•
OH) can be produced when subsurface soil interacts with oxygen, but the effects of ...straw incorporation on
•
OH formation have rarely been evaluated. In this study, we found that straw return had a significant effect on soil properties. Soil pH and redox potential (Eh) decreased while electronic conductivity (EC) showed an increment. Dissolved organic carbon content of soil initially increased and then decreased to the same level as the control by the end of the experiment of 120 days. Moreover, Fe(II) formation was promoted by straw return under anaerobic conditions.
•
OH was produced in the flooded paddy soil when exposed to oxygen, which correlated well with Fe(II) content. The effect of rape (
Brassica campestris L.
) straw on
•
OH formation rate was more evident as compared to wheat (
Triticum aestivum L.
) straw, suggesting a potentially more profound influence of rape straw return on pollutant transformation in paddy soils.
Organophosphorus pesticides （OPs） are one of the most regular pollutants and frequently detected in the contaminated sites, so developing an efficient method for the treatment of OPs is highly ...required. The aim of the present study was to compare the effectiveness of persulfate （PS） activation and Fenton reaction in remediating the soil polluted with OPs. The polluted soil used in this study was sampled from an abandoned insecticide factory in Nantong, Jiangsu Province of China, mainly containing chloropyrifos （CP） and 4-bromo-2-chlorophenol （BCP, the raw material of profenofos） with total concentration of about 30 000 mg kg- 1. The results showed that both BCP and CP were efficiently degraded by base activation of PS, and increasing the ratio of NaOH/PS enhanced CP degradation, but slightly decreased BCP degradation. The greatest degradation rates for CP and BCP were 92% and 97%, respectively, with 7.0 tool L-1 NaOH and 0.21 tool L-1 PS and a soil-to-liquid ratio of 1：1. Furthermore, ferrous iron activation of PS also degraded BCP efficiently, but only 60% of CP was degraded under the same reaction conditions. These results indicated that base activation of PS was more feasible than Fe2＋ activation and Fenton reaction in remediating the soil polluted with OPs. The high degradation rate for CP may be linked to the initial hydrolyzation of CP by base to 3,5,6-trichloro-2-pyridinol, which can be further rapidly degraded by free radicals generated from base activation of PS.
The original version of the article unfortunately contained a mistake in Fig. 3. In this figure, norank_o_DS-100 and
Niastella
were mistakenly labelled with
α
-
Proteobacteria
and
Firmicutes
, ...respectively. The correct lineage is given below.
Both biotic and abiotic mechanisms play a role in soil CO2 emission processes. However, abiotically mediated CO2 emission and the role of reactive oxygen species are still poorly understood in paddy ...soil. This study revealed that OH promoted CO2 emission in paddy soil slurries during short-term oxidation (4 h). OH generation was highly hinged on active Fe(II) content, and the OH contribution to CO2 efflux was 10%–33% in topsoil and 40%–77% in deep-soil slurries. Net CO2 efflux was higher in topsoil slurries, which contained more dissolved organic carbon (DOC). CO2 efflux correlated well with DOC contents, suggesting the critical role of DOC. Microbial mechanisms contributed 9%–45% to CO2 production, as estimated by γ-ray sterilization experiments in the short-term reoxidation process. Solid-aqueous separation experiments showed a significant reduction in net CO2 efflux across all soil slurries after the removal of the original aqueous phase, indicating that the water phase was the main source of CO2 emission (>50%). Besides, C emission was greatly affected by pH fluctuation in acidic soil but not in neutral/alkaline soils. Fourier transform ion cyclotron resonance mass spectrometry and excitation-emission matrix results indicated that recalcitrant and macromolecular dissolved organic matter (DOM) components were more easily removed or attacked by OH. The decrease in DOM content during the short-term reoxidation was the combined result of OH oxidation, co-precipitation, and soil organic matter release. This study emphasizes the significance of the generally overlooked nonmicrobial mechanisms in promoting CO2 emission in the global C cycle, and the critical influence of the aqueous phase on C loss in paddy environments.
Display omitted
●CO2 efflux pulse event explained by nonmicrobial mechanisms mediated by O2.●OH promoted CO2 emission in paddy soil slurries during short-term oxidation.●Aqueous phase was the main sources of CO2 emission during short-term oxidation process.●For the DOM, easily biodegradable favors retention after the short-term oxidation.
Carbon materials (e.g., pyrogenic carbon (PyC)) are widely used in agricultural soils and can participate in various biogeochemical processes, including iron (Fe) cycling. In soils, Fe(II) species ...have been proposed as the main active contributor to produce reactive oxygen species (ROS), which are involved in various biogeochemical processes. However, the effects of PyC on the transformation of different Fe species in soils and the associated production of ROS are rarely investigated. This study examined the influence of PyC (pyrolyzed at 300–700 °C) on Fe(II)/Fe(III) cycling and hydroxyl radical (·OH) production during redox fluctuations of paddy soils. Results showed that the reduction of Fe(III) in soils was facilitated by PyC during anoxic incubation, which was ascribed to the increased abundance of dissimilatory Fe(III)-reducing microorganisms (biotic reduction) and the electron exchange capacity of PyC (abiotic reduction). During oxygenation, PyC and higher soil pH promoted the oxidation of active Fe(II) species (e.g., exchangeable and low-crystalline Fe(II)), which consequently induced higher yield of ·OH and further led to degradation of imidacloprid and inactivation of soil microorganisms. Our results demonstrated that PyC accelerated Fe(II)/Fe(III) cycling and ·OH production during redox fluctuations of paddy soils (especially those with low content of soil organic carbon), providing a new insight for remediation strategies in agricultural fields contaminated with organic pollutants.
Graphical Abstract
Highlights
Pyrogenic carbon (PyC) with high EEC promoted active Fe(II) formation in anoxic paddy soils through abiotic and biotic mechanisms.
Pyrolysis temperature affected the physiochemical properties of PyC, which regulated Fe cycling and ·OH production in soils.
The enhanced production of ·OH led to microbial inactivation and organic pollutant degradation.
Microplastics, as a group of emerging contaminants, are receiving growing attention. During the last decade, their occurrence and toxicity in aquatic ecosystems have been intensively studied and ...reviewed, but less attention has been paid on soil ecosystems. Given the importance of soil ecosystems and the call for increasing research on soil from scientific communities, it is predicted that relevant studies will boom in the following years. The present review intends to provide a comprehensive overview of current knowledge on microplastic pollution in soil environments. We critically summarize the source, contamination level and fate of microplastics in (industrial and arable) soils. Then, we thoroughly describe what effects have been observed on soil microbes, animals and plants, and analyze what insights we can get from available information. Finally, we identify knowledge gaps that need to be filled and give suggestions for future research.
Alcohols such as ethanol (EtOH) and tert-butanol (TBA) are frequently used as quenching agents to identify the primary radical species in the persulfate (PS)-based oxidation processes. However, the ...contribution of alcohol radicals (ARs) to contaminant degradation in this process has rarely been assessed. In this study, trichloroacetic acid (TCA), phenol, and carbon tetrachloride were selected as probes to test the role of ARs in the thermally activated PS system. It was found that the degradation rates of these compounds were largely depended on their reactivities with ARs and the concentration of dissolved oxygen in the reaction system. In the PS/alcohol system, TCA was degraded efficiently under anaerobic conditions, while it was hardly degraded in the presence of oxygen. The results of electron paramagnetic resonance, reducing radical quenching studies, and the analysis of PS consumption suggested that ARs were the dominant reactive species contributing to TCA degradation in the PS/EtOH system under anaerobic conditions. Further studies indicated that ARs could significantly degrade CCl4 through dechlorination but not phenol. CCl4 was also degraded efficiently by ARs when oxygen in the reaction solution was completely consumed by ARs. This study highlights the important role of alcohol radicals in the degradation of contaminants during quenching studies in PS-activated processes.
Display omitted
•TCA and CCl4 were degraded efficiently in the persulfate/heat/alcohol system.•Alcohol radicals (ARs) were main species accounted for TCA and CCl4 degradation.•The role of ARs was testified with free radical quenching and EPR studies.
In this study, three different structures of MnO2 were synthesized and used to activate peroxymonosulfate (PMS) for the degradation of DDT in aqueous solutions. It was found that DDT was efficiently ...degraded in the MnO2/PMS system and the degradation rate was dependent on the properties of MnO2 including crystal structure (followed the order: α-MnO2 > γ-MnO2 > β-MnO2), surface area and Mn(III) content. Sulfate radicals (SO4−) was primarily responsible for the degradation of DDT based on the results of electron paramagnetic resonance (EPR) and quenching experiments. The degradation of DDT was suppressed at alkaline pH because the formation of SO4− was inhibited. The results of GC–MS indicated that dichlorobenzophenone, 4-chlorobenzoic acid and benzylalcohol were the dominant intermediates for DDT degradation. The possible pathways of DDT degradation were proposed according to the identified products.
Display omitted
•DDT was effectively degraded by MnO2/PMS system.•MnO2 structures affected activation of peroxymonosulfate for DDT degradation.•EPR technique was used to identify the reactive species for DDT degradation.•GC–MS was used to identify the products of DDT degradation.
PDF
