Reduction strategies of polycyclic aromatic hydrocarbons in farmland soils: Microbial degradation, plant transport inhibition, and their mechanistic analysis

Foliar exposure to microplastics disrupts lettuce metabolism and negatively interferes with symbiotic microbial communities

Plant leaves are considered an important sink for atmospheric microplastics (MPs) because they serve as a vital interface between the atmosphere and terrestrial ecosystems. However, there is still a dearth of information regarding how plant-symbiotic microbe-soil systems are affected by foliar exposure to MPs. In this study, MPs (polystyrene (PS), polyethylene (PE), and polypropylene (PP)) were sprayed over soil-cultivated lettuce (Lactuca sativa L.) four occasions, with final sprays containing 0.4 and 4 μg of MPs per plant. MPs had no discernible impact on lettuce growth as compared to the control group. However, MPs led to reductions in relative chlorophyll content from 16.91 to 30.64 % and net photosynthetic rate from 6.64 to 81.41 %. These results validate the phytotoxicity linked to MP exposure through foliar application. The presence of MPs triggered interspecific competition among phyllosphere microbial species and reduced microbial network complexity by forming ecological niches and regulating carbon- and nitrogen-related metabolic pathways. Furthermore, MPs inhibited the growth of beneficial bacteria in the rhizosphere soil, including a variety of plant growth-promoting bacteria (PGPR) such as Rhizobiales, Pseudomonadales, and Bacillales. This study identifies the ecological health risks associated with atmospheric MPs, which may have a detrimental impact on crop production and further compromise soil ecosystem security.

Vehicular mediated emissions of polycyclic aromatic hydrocarbons in roadside soils of Shanghai

This study evaluates the impact of vehicular emissions on polycyclic aromatic hydrocarbons (PAHs) in roadside soils in Shanghai during the COVID-19 lockdown period. Soil samples from roadside lawns were collected, with PAH concentrations ranging from 153 to 5639 ng g-1. A significant reduction in PAH levels compared to their pre-COVID-19 levels (Kruskal-Wallis H test, p < 0.05) was observed in surface soil samples, highlighting the contribution of traffic and coal combustion to urban pollution. Source identification, using molecular diagnostic ratios and principal component analysis, revealed that vehicular emissions were the primary contributors to PAHs in Shanghai's roadside soils. The toxic equivalent quantity for benzo[a]pyrene concentrations in the soil samples was associated with these sources. The incremental lifetime cancer risk model indicated that adult exposure to PAHs in the soil posed health risks greater than 10-6 but lower than 10-4, suggesting a low-risk level. These findings suggest that targeted measures in the transportation sector could improve urban soil quality and reduce associated health risks.

Degradation and mechanism of PAHs by Fe-based activated persulfate: Effect of temperature and noble metal

The accumulation of contaminants like PAHs in soil due to industrialization, urbanization, and intensified agriculture poses environmental challenges, owing to their persistence, hydrophobic nature, and toxicity. Thus, the degradation of PAHs has attracted worldwide attention in soil remediation. This study explored the effect of noble metal and temperature on the degradation of various polycyclic aromatic hydrocarbons (PAHs) in soil, as well as the types of reactive radicals generated and mechanism. The Fe-Pd/AC and Fe-Pt/AC activated persulfate exhibited high removal efficiency of 19 kinds of PAHs, about 79.95 % and 83.36 %, respectively. Fe-Pt/AC-activated persulfate exhibits superior degradation efficiency than that on Fe-Pd/AC-activated persulfate, due to the higher specific surface area and dispersity of Pt particles, thereby resulting in increased reactive radicals (·OH, SO4-· and ·OOH). Additionally, thermal activation enhances the degradation of PAHs, with initial efficiencies of 64.20 % and 55.49 % on Fe-Pd/AC- and Fe-Pt/AC-activated persulfate systems respectively, increasing to 76.05 % and 73.14 % with elevated temperatures from 21.5 to 50 °C. Metal and thermal activation facilitate S2O82- activation, generating reactive radicals, crucial for the degradation of PAHs via ring opening and oxygen hydrogenation reactions, yielding low-ring oxygen-containing derivatives such as organic acids, keto compounds, ethers, and esters. Furthermore, understanding the impact of parameters such as activation temperature and the types of noble metals on the degradation of PAHs within the activated persulfate system provides a theoretical foundation for the remediation of PAH-contaminated soil.

Transformation and Degradation of PAH Mixture in Contaminated Sites: Clarifying Their Interactions with Native Soil Organisms

Soil contamination of polycyclic aromatic hydrocarbons (PAHs), especially caused by the mixture of two or more PAHs, raised great environmental concerns. However, research on the migration and transformation processes of PAHs in soils and their interactions with native communities is limited. In this work, soil samples from uncontaminated sites around the industrial parks in Handan, Hengshui, and Shanghai were artificially supplemented with three concentrations of anthracene (Ant), 9-chloroanthracene (9-ClAnt), benzopyrene (BaP), and chrysene (Chr). Ryegrass was planted to investigate the degradation of PAHs and its interaction with native soil organisms in the constructed ryegrass-microbe-soil microcosmic system. The bacterial and fungal communities in soil were affected by PAHs; their species diversity and relative abundance changed after exposure to different concentrations of PAHs, among which Lysobacter, Bacillus, Pseudomonas, and Massilia bacteria were correlated to the degradation of PAHs. On the 56th day, the contents of BaP, Chr, and Ant decreased with the degradation process, while the degradation of 9-ClAnt was limited. Nineteen intermediates, including hydroxylation and carboxylated compounds, were identified. The present research would help clarify the potential interactions between PAHs and native organisms in contaminated sites, providing fundamental information for evaluating the transformation risks of PAHs in the natural environment.

Role of biochar pyrolysis temperature on intracellular and extracellular biodegradation of biochar-adsorbed organic compounds

Immobilizing organic pollutants by adsorption of biochar in farmland soil is a cost-effective remediation method for contaminated soil. As the adsorption capacity of biochar is limited, biodegradation of biochar-adsorbed organic pollutants was a potential way to regenerate biochars and maintain the adsorption performance of biochars to lower the cost. It could be affected by the biochar pyrolysis temperature, but was not evaluated yet. In this study, biodegradation of adsorbed phenanthrene on a series of biochars with pyrolysis temperatures from 150 to 700 °C by Sphingobium yanoikuyae B1 was investigated using batch experiments of biodegradation kinetics at 30 °C, to explore the role of biochar pyrolysis temperature on biodegradation of biochar-adsorbed organic compounds. It was observed that 37.5-47.9% of adsorbed phenanthrene on moderate temperature-pyrolyzed biochars produced at 400 and 500 °C were biodegraded, less than that on high temperature-pyrolyzed biochars produced at ≥600 °C (48.8-60.8%) and low temperature-pyrolyzed biochars produced at ≤300 °C (63.4-92.5%). Phenanthrene adsorbed largely on the low temperature-pyrolyzed biochars by partition mechanism and thus is easily desorbed to water for a dominated intracellular biodegradation. On the high temperature-pyrolyzed biochars, phenanthrene is adsorbed largely by pore-filling mechanism and thus less desorbed to water for intracellular biodegradation. However, high temperature-pyrolyzed biochars can promote microbes to produce siderophore, H2O2 and thus release extracellular •OH for a dominated degradation of adsorbed phenanthrene by Fenton-like reaction. With the increase of biochar pyrolysis temperature, desorption and consequently the intracellular biodegradation of adsorbed phenanthrene on biochars decreased, while the secretion of siderophore and H2O2 by microbes on biochars increased to produce more extracellular •OH for degradation by Fenton-like reaction. The results could provide deep insights into the role of biochar pyrolysis temperature on biodegradation of biochar-adsorbed organic compounds, and optimize the selection of biochar with higher adsorption performance and easier regeneration for soil remediation.