Dissipation of pentachlorophenol in the aerobic-anaerobic interfaces established by the rhizosphere of rice ( Oryza sativa L.) root

Occurrence, fate, and potential impacts of wood preservatives in the environment: Challenges and environmentally friendly solutions

Wood preservation has gained global prevalence in recent years, primarily owing to the renewable nature of wood and its capacity to act as a carbon sink. Wood, in its natural form, lacks intrinsic resilience and is prone to decay if left untreated; hence, wood preservatives (WPs) are used to improve wood's longevity. The fate and potential hazards of wood preservatives to human health, ecosystems, and the environment are complex and depend on various aspects, including the type of the preservative compounds, their physicochemical properties, application methods, exposure pathways, environmental conditions, and safety measures and guidelines. The occurrence and distribution of WPs in environmental matrices such as soil and water can result in hazardous pollutants seeping into surface water, groundwater, and soil, posing health hazards, and polluting the environment. Bioremediation is crucial to safeguarding the environment and effectively removing contaminants through hydrolytic and/or photochemical reactions. Phytoremediation, vermicomposting, and sustainable adsorption have demonstrated significant efficacy in the remediation of WPs in the natural environment. Adsorbents derived from biomass waste have been acknowledged for their ability to effectively remove WPs, while also offering cost-efficiency and environmental sustainability. This paper aims to identify wood preservatives' sources and fate in the environment and present a comprehensive overview of the latest advancements in environmentally friendly methods relevant to the removal of the commonly observed contaminants associated with WPs in environmental matrices.

Co-planting of Salix interior and Trifolium pratense for phytoremediation of trace elements from wood preservative contaminated soil

Phytoextraction potential of a co-planting system was evaluated using a shrub and an herbaceous species and compared with monocultures. A greenhouse experiment with Salix interior and Trifolium pratense grown in combination or alone was conducted for 120 days in soil either uncontaminated or contaminated with wood preservatives containing mixed chromated copper arsenate and pentachlorophenol (PCP). The results showed that the plant species produced similar amounts of dry biomass per pot in monoculture and co-planting, whether growing in contaminated or uncontaminated soil. Arsenic (As), chromium (Cr) and copper (Cu) concentrations in root tissue of S. interior increased 8.6%, 65.9% and 4.5%, respectively, in co-planting compared to its monoculture. T. pratense had superior concentration of As (14% higher) in root tissue when co-planted. However, the higher trace elements concentrations in the plant tissues did not translate into measurable differences in total trace element removal per pot, except for As. The bioconcentration factor for Cu and As was high in the belowground portions of the plants in co-planting. PCP levels in the soil decreased to values near the limit of detection in all treatments. These results suggest that co-planting S. interior with T. pratense could lead to higher phytoextraction potential than monoculture.

Assembly of root-associated microbiomes of typical rice cultivars in response to lindane pollution

Organochlorine pesticides have been extensively used for many years to prevent insect diseases of rice (Oryza sativa L.), but little is known about their residual impacts on the underground micro-ecology in anaerobic environment. In this glasshouse study, we characterized the lindane effects on the assembly of root-associated microbiomes of commonly used indica, japonica and hybrid rice cultivars, and their feedback in turn, in modifying lindane anaerobic dissipation during 60 days' rice production. The results showed that rice growth inhibited the anaerobic dissipation of lindane, but was not affected apparently by lindane at initial spiked concentration of 4.62 and 18.54 mg kg^-1 soil. Suppressed removal of lindane in rice planted treatments as compared with that in unplanted control was likely due to inhibited reductive dechlorination induced by a comprehensive effect of radial O₂ secretion of rice root and co-occurring Fe(III) reduction that consumed electron competitively in rice rhizosphere. However, the hybrid cultivar exhibited a less suppression than the conventional cultivars in high polluted soils. Bacteria was more sensitively responded to lindane pollution than fungal taxa, and Actinobacteria, Chloroflexi, Verrucomicrobia and Proteobacteria were the main different phyla between hybrid and conventional cultivars, with a more stable community structure exhibited in the hybrid rice under lindane stress. Our study highlights the assembly and variation of root-associated microbiomes in responses of lindane pollution, and suggests that hybrid rice cultivar might be most competent for cultivation in paddy fields polluted by lindane and other organochlorine pesticides, especially in the area with high residual levels.

The dechlorination of pentachlorophenol under a sulfate and iron reduction co-occurring anaerobic environment

An anaerobic soil slurry incubation experiment was conducted by controlling different Fe/S mole ratios (1/3, 1/2, 1/1, 2/1, 3/1, 8/1 and the control without sulfate) through the addition of sodium sulfate, to investigate the effect of sulfate and iron reduction on the reductive dechlorination of pentachlorophenol (PCP). Two sequential incubation periods were carried out with the stage I incubation conducted under a low electron donor concentration (0.5 mM lactate) and stage II incubation conducted under increased electron donor supply with lactate at 20 mM. During stage I, the production of Fe(II) occurred markedly while sulfate reduction and PCP dechlorination rate were low, with the highest dechlorination rates of PCP only 11.0% among all treatments at the end of stage I incubation. During stage II, both PCP dechlorination and sulfate reduction were greatly enhanced in all treatments, while the concentration of Fe(II) changed slightly. The rate of PCP dechlorination decreased (from 87.7% to 34.2%) with the increase of sulfate concentration (from Fe/S mole ratio of 8/1 to 1/3). Our study suggested that the presence of a certain amount of sulfate might facilitate PCP dechlorination in the range of Fe/S mole ratios greater than 1 when compared with the control without SO₄^2-. With the investigation of the dechlorination of PCP under the Fe-S-PCP coexisting condition with different Fe/S mole ratios, our study may provide improved strategy for optimizing the remediation of flooded soils and sediments polluted by PCP.

Enrofloxacin Transformation on Shewanella oneidensis MR-1 Reduced Goethite during Anaerobic-Aerobic Transition

Antibiotics pollution has become a critical environmental issue worldwide due to its high ecological risk. In this study, rapid degradation of enrofloxacin (ENR) was observed on goethite in the presence of Shewanella oneidensis MR-1 during the transition from anaerobic to aerobic conditions. The abiotic reactions also demonstrated that over 70% with initial concentration of 10 mg L^-1 ENR was aerobically removed within 5 min by goethite with adsorbed Fe(II), without especial irradiation and strong oxidants. The results of spin trap electron spin resonance (ESR) experiments provide evidence that Fe(II)/Fe(III) complexes facilitate the generation of •OH. The electrophilic attack by •OH opens the quinolone ring of ENR and initiates further transformation reactions. Five transformation products were identified using high performance liquid chromatography-quadrupole time-of-flight mass spectrometry and the ENR degradation process was proposed accordingly. The identification of ENR transformation products also revealed that both the surface adsorption and the electron density distribution in the molecule determined the reactive site and transformation pathway. This study highlights an important, but often underappreciated, natural process for in situ degradation of antibiotics. With the easy migration of the goethite-MR-1 complex to the anaerobic/aerobic interface, the environmental fates of ENR and other antibiotics need to be seriously reconsidered.

Plant-assisted rhizoremediation of decabromodiphenyl ether for e-waste recycling area soil of Taizhou, China

To develop an effective phytoremediation approach to purify soils polluted by decabromodiphenyl ether (BDE-209) in e-waste recycling area, pot experiments were conducted through greenhouse growth of seven plant species in BDE-209-polluted soils. The hygrocolous rice (Oryza sativa L.) cultivars (XiuS and HuangHZ) and the xerophyte ryegrass (Lolium perenne L.) were found to be as the most effective functional plants for facilitating BDE-209 dissipation, with the removal of 52.9, 41.9, and 38.7% in field-contaminated soils (collected directly from field, with an average pollution concentration of 394.6 μg BDE-209 kg(-1) soil), as well as 21.7, 27.6, and 28.1% in freshly spiked soils (an average pollution concentration of 4413.57 μg BDE-209 kg(-1) soil, with additional BDE-209 added to field-contaminated soils), respectively. Changes in soil phospholipid fatty acid (PLFA) profiles revealed that different selective enrichments of functional microbial groups (e.g., arbuscular mycorrhizal fungi and gram-positive bacteria) were induced due to plant growth under contrasting water management (flooded-drained sequentially, flooded only, and drained only, respectively). The abundance of available electron donors and acceptors and the activities of soil oxido-reductases were also correspondingly modified, with the activity of catalase, and the content of NO3(-) and Fe(3+) increased generally toward most of the xerophyte treatments, while the activity of dehydrogenase and the content of dissolved organic carbon (DOC) and NH4(+) increased toward the hygrophyte treatments. This differentiated dissipation of BDE-209 in soils as function of plant species, pollution doses and time, and water-dependent redox condition. This study illustrates a possibility of phytoremediation for BDE-209-polluted soils by successive cultivation of rice followed by ryegrass coupling with suitable water management, possibly through dissipation pathway of microbial reductive debromination and subsequent aerobic oxidative cleavage of benzene ring.

Dissipation of phenanthrene and pyrene at the aerobic-anaerobic soil interface: differentiation induced by the rhizosphere of PAH-tolerant and PAH-sensitive rice (Oryza sativa L.) cultivars

A pot experiment was conducted to reveal the removal of two polycyclic aromatic hydrocarbons (PAHs) (phenanthrene, PHE, and pyrene, PYR) during rice cultivation in a paddy field. The rhizosphere effect on facilitating dissipation of PAHs varied simultaneously as a function of soil properties, PAH types, cultivation time, and genotypes within rice cultivars, with differences performed for PYR but not PHE. Changes in soil PLFA profiles evidenced that the growth of rice roots modified the dominant species within rhizosphere microbial communities and induced a selective enrichment of Gram-negative aerobic bacteria capable of degrading, thereby resulting in the differentiated dissipation of PYR. While the insignificant differences in PHE dissipation might be attributed to its higher solubility and availability under flooded condition that concealed the differences in improvement of bioavailability for microorganisms between rhizosphere and non-rhizosphere, and between both soils and both rice cultivars. Our findings illustrate that the removal of PAHs in paddy soils was more complex relative to those in dryland soils. This was possibly due to the specialty of rice roots for oxygen secretion that provides development of redox heterogeneous microbial habitats at root-soil interface under flooded condition.

Phytoremediation efficiency of a pcp-contaminated soil using four plant species as mono- and mixed cultures

Bioremediation of soil polluted by pentachlorophenol (PCP) is of great importance due to the persistence and carcinogenic properties of PCP. Phytoremediation has long been recognized as a promising approach for removal of PCP from soil. The present study was conducted to investigate the capability of four plant species; white clover, ryegrass, alfalfa, and rapeseed grown alone and in combination to remediate pentachlorophenol contaminated soil. After 60 days cultivation, white clover, raygrass, alfalfa, and rapeseed all significantly enhanced the degradation of PCP in soils. Alfalfa showed highest efficiency for the removal of PCP in single cropping flowed by rapeseed and ryegrass. Mixed cropping significantly enhanced the remediation efficiencies as compared to single cropping; about 89.84% of PCP was removed by mixed cropping of rapeseed and alfalfa, and 72.01% of PCP by mixed cropping of rape and white clover. Mixed cropping of rapeseed with alfalfa was however far better for the remediation of soil PCP than single cropping. An evaluation of soil biological activities as a monitoring mechanism for the bioremediation process of a PCP-contaminated soil was made using measurements of microbial counts and dehydrogenase activity.

Spatial and temporal variations in pentachlorophenol dissipation at the aerobic--anaerobic interfaces of flooded paddy soils

Pentachlorophenol (PCP) dissipation occurs naturally in flooded soils and although dissipation half-lives vary between soil profiles at the millimeter-scale the reason is poorly understood. Vertical variations of PCP dissipation were investigated in three typical Chinese paddy soils; Soil 1 (Umbraqualf), Soil 2 (Plinthudult) and Soil 3 (Tropudult). The soil depth was divided into a surface and a deep layer based upon different PCP dissipations in the surface layer of 40-93, 42-88 and 16-100% for Soils 1-3 respectively. In the deep layer, PCP was greatly dissipated in Soil 2, but much less in Soil 1 and Soil 3. Correlation analysis indicated that SO4(2-) and Fe(III) were negatively related to PCP dissipation. SO4(2-) and Cl(-) were highly mobile in the flooded soil profiles. Fe(III) reduction increased with increasing soil depth, and was inhibited by high SO4(2-) concentrations.

Changing redox potential by controlling soil moisture and addition of inorganic oxidants to dissipate pentachlorophenol in different soils

The potential for dissipation of pentachlorophenol (PCP) was investigated in soils from four different sites in China. These were an umbraqualf (Soil 1), a Plinthudult (Soil 2), a Haplustalf (Soil 3) and an Argiustoll (Soil 4) which were either flooded, to produce anaerobic conditions, or incubated aerobically at 60% water-holding capacity (WHC). The dissipation of PCP in Soil 1 at 60% WHC was higher than under flooded condition, while the opposite occurred in the other three soils. Under flooded conditions, the redox potential decreased significantly in Soil 1 and Soil 4, where sulphate reduction was occurred and the dissipation of PCP was statistically significant (about 96% and 98%, respectively) at the end of incubation. After addition of inorganic oxidants, dissipation of PCP was significantly inhibited by FeCl(3), while Na(2)SO(4) and NaNO(3) had different effects, depending upon the soil type.

Nonpoint source pollution, environmental quality, and ecosystem health in China: introduction to the special section

The rapid economic and industrial growth of China, exemplified by a 10-fold increase in its gross domestic product in the past 15 years, has lifted millions of its citizens out of poverty but has simultaneously led to severe environmental problems. The World Health Organization estimates that approximately 2.4 million deaths in China per year could be attributed to degraded environmental quality. Much of China's soil, air, and water are polluted by xenobiotic contaminants, such as heavy metals and organic compounds. In addition, soil quality is degraded by erosion, desertification, and nutrient runoff. Air quality is further compromised by particulates, especially in heavily populated areas. Research shows that 80% of urban rivers in China are significantly polluted, and poor water quality is a key contributor to poverty in rural China. Economic and industrial growth has also greatly expanded the demand for water sources of appropriate quality; however, pollution has markedly diminished usable water resource quantity. Desertification and diminishing water resources threaten future food security. In recent years, China's government has increased efforts to reverse these trends and to improve ecosystem health. The Web of Science database showed that the percentage of articles on China devoting to environmental sciences increased dramatically in recent years. In addition, the top 25 institutes publishing the papers in environmental sciences were all in China. This special issue includes seven articles focusing on nonpoint source pollution, environmental quality, and ecosystem health in China. The major issues, and results of these studies, are discussed in this introduction.