Soil & Environmental Health最新文献

Mercury (Hg) contamination in soils is of concern because of its known adverse effects on ecosystem functions and human health. Research on how to reduce Hg contamination in soil is still needed, mainly because of the difficulties in remediating Hg-contaminated soils while minimizing adverse effects on treated systems. We investigated the potential of a waste substrate, aluminum (Al)-based drinking water treatment residuals (Al-WTRs), as a low-cost sorbent for immobilizing the mobile fraction of Hg in contaminated soils using column leaching studies. Because of the known role of acidic deposition and dissolved organic matter on the environmental cycling of Hg, columns packed with Hg-contaminated alluvial soils collected from the watershed of Poplar Creek in Tennessee of USA were leached using either the synthetic precipitation leaching procedure (SPLP) to simulate the effects of acid rain or low pH dissolved organic carbon (DOC) rich river water (Suwannee River water, pH 4.20) to mimic soil flooding events with DOC-rich waters. The results show that, for soils with very high mobile Hg fractions, control columns without Al-WTR leached with the SPLP solution retained only 51% of total-Hg, which was significantly less (p ​< ​0.05) than in the Al-WTR treated soil columns (up to 80%). Leaching with DOC-rich river water (53.3 ​mg ​C/L) decreased the sorption capacity of Al-WTR. Using waters with increasing DOC concentrations (from 5.33 to 40 ​mg ​C/L) resulted in the removal of 63% of the initial mass of Hg in the control columns compared to 22–29% in the columns amended with 2 and 5% Al-WTR. Overall, Al-WTR can immobilize Hg under extreme leachability conditions and should be considered as a potential sorbent for in situ remediation of Hg-contaminated soils. However, further studies are needed on the fate of Al-WTR-immobilized Hg.

Struvite crystallization is a viable approach for recovering phosphorus from phosphorus-rich solutions such as urine and wastewater. However, designing seed materials to promote crystal growth and enhance the efficiency of struvite crystallization remains an area of active research. In this study, we investigated the seeding characteristics of biochars on struvite crystallization and the impact of biochar feedstock type and production temperature on the process. Microwave-pyrolyzed biochars produced from different feedstocks and under different temperatures were examined as seeding materials for struvite crystallization from urine and the influence of biochar properties on the overall struvite yield, nutrient recovery and struvite crystal size. Sawdust biochar (lignocellulosic biomass) produced at 500 ​°C had the highest struvite yield (7.91 ​g ​L⁻¹), phosphate (97.9%) and ammonium recovery (87.1%), and relative crystal size (85.2%) compared to the non-seeded treatment due to its higher surface area, pore volume, and hydrophobicity of the biochar. Manure pellet biochar (non-lignocellulosic biomass) produced at 500 ​°C also exhibited performance comparable to sawdust biochar produced at 500 ​°C. Increasing pyrolysis temperature increased biochar's hydrophobicity, zeta potential, electrophoretic mobility and bulk density, irrespective of the feedstock type, thereby improving the seeding process. The ash content of biochar was negatively correlated with its surface area, pore volume, and particle size, but positively correlated with biochar's bulk density and suspension stability. In conclusion, feedstock type and pyrolysis temperature significantly affected biochar properties, which interactively influenced struvite crystallization. Therefore, biochars should be carefully selected to improve their efficiency for phosphorus recovery from phosphorus-containing solutions such as urine and wastewater, with the recovered phosphorus being used for soil applications.

It is not widely known that a handful of soil contains more living creatures of all kinds than there are humans living on the globe. The conditions on which all these creatures (fungi, bacteria, and worms) are able to thrive determine soil health, thereby crop production and food safety. In this contribution, I will present and clarify the concept of the Mission Board on Soil Health and Food, which serves the backgrounds and activities during the past three years. I will also explain the possible consequences for future research funding by the European Union (EU). Essentially, the work of the Mission Board focuses on: 1) the relationship between the well-developed and highly-respected discipline of Soil Science, 2) the vast body of knowledge and vested scientific authority it represents and 3) the relationship with the ongoing process of deterioration of soil health in daily use and exploitation. In other words, soil science versus soil health, is there an issue?

Natural sulfur (S)-rich biochar (NRB) can be employed as an alternative for traditional S-modified biochar. However, the effect of dissolved organic matter (DOM) on mercury (Hg) speciation in rice rhizosphere soils under natural S-rich biochar application remains unclear. We conducted a pot experiment to study the effects of NRB application on the chemical composition and structure of DOM and the related speciation and availability of Hg in rice rhizosphere. Applying NRB significantly increased the concentration of methylmercury (MeHg) in the rhizosphere soils, which was enhanced with application frequency. This observation can be explained by MeHg immobilization in response to increasing S content in rice rhizosphere soils. We also observed increased molecular weight and functional group complexity of DOM, likely contributing to the decrease in MeHg mobility. Furthermore, the increase in pH and humification of DOM caused by S-rich biochar application generally reduced the concentrations of water-soluble and mercuric-sulfide fraction (easily-available Hg species) and organo-chelated fraction (potentially-available Hg species). Our findings highlight that the application of NRB can reduce the availability of MeHg in rice rhizosphere, thus providing a practical basis for reducing the potential risk of MeHg toxicity.

Soil health is an important aspect for maintaining adequate crop production, but the specifics of what entails a healthy soil can vary from region to region and crop to crop. In highly managed agricultural systems, unhealthy soil can be masked by intensive management practices, yet there must be detrimental cutoff points in various characteristics, such as soil organic matter (SOM) concentrations, where even highly managed systems start to lose productivity. This negative impact was observed in a Florida citrus grove containing Valencia orange trees with observable differences in tree size yet were otherwise managed identically. A soil health index demonstrated that the areas with smaller trees had a significantly lower index score and those soils contained significantly less SOM (average SOM ​= ​0.57%) compared to areas with larger trees (average SOM ​= ​0.94%). The areas of lower crop productivity also had less enzymatic activity of common carbon-cycling enzymes and different microbial populations, which all together negatively affected soil health and corresponding plant productivity. This agricultural region is also known to have a Citrus Greening disease (HLB) infection rate of close to 100%, hence we developed a hypothesis that could explain how progression of this infection could be impacted by SOM concentrations and differences in microbial diversity. We posit that areas of this grove with healthier soil could have more resistance to the onset of fatal HLB symptoms. Consequently, soil organic matter distribution and concentration should be considered when establishing new groves in order to optimize soil and crop productivity.

Large-scale production, rapid consumption, insufficient recovery and management, and slow degradation lead to a large accumulation of plastic waste and microplastics. Microplastics are characterized as stable, small, and having a large specific surface area and strong hydrophobicity. They are carriers of many hydrophobic organic pollutants, heavy metals, pathogenic bacteria and drug resistance genes. Worldwide, microplastic pollution in soils has attracted much attention. The progress and perspectives in the separation and detection of soil microplastics deserve a comprehensive review and discussion. Here, the sources and distributions of microplastics in soil from the use of agricultural plastic film, sludge recycling, long-term application of organic fertilizer, surface runoff, and sewage irrigation are summarized. Physical separation methods such as density separation, electrostatic separation, oil extraction and pressurized liquid extraction, and chemical extraction methods such as acid digestion, alkaline digestion, hydrogen peroxide and Fenton reagent oxidation, and enzymatic hydrolysis for soil microplastics are reviewed. Futhermore, the detection technologies of soil microplastics through microscopy, spectroscopy, mass spectrometry, thermogravimetric analysis, differential scanning calorimetry, X-ray photoelectron spectroscopy and nuclear magnetic resonance are reviewed. Finally, the perspectives are put forward from understanding the impacts of microplastics on soil functions and health, developing source control and environmental remediation technology, investigating low-cost and rapid separation and extraction methods that preserve the characteristics of microplastics, strengthen the degree of automation to avoid artificial operation error, and establish the standard methods for isolating, extracting, identifying, and quantifying microplastics in soils. This review serves as a technical reference for rapid identification of soil microplastics and builds the foundation for scientific assessment of the ecological and human environmental risks of soil microplastics.

Global food crisis makes intense agricultural activity necessary, which accelerates soil degradation and increases pollution risk to nearby catchments. Application of biochar can effectively retain plant-required nutrients in soils. However, the linkage between retention and loss pathways of nutrients is still unclear, particularly at slope lands. Therefore, a simulated rainfall experiment (rainfall intensity ​= ​50 ​mm ​h⁻¹) was conducted in a sandy soil with 10° gradient slope (indoor experiment) to clarify loss pathways of soluble C, N, P and K in biochar-amended soils. Wood biochar pyrolized at 300 ​°C (LWB) or 600 ​°C (HWB) was applied at 1% (LWB1; HWB1) or 2% (LWB2; HWB2). Our results show that the pathways for C, N, P and K loss was percolation ​> ​surface runoff ​> ​soil erosion. Compared to control, HWB2 treatment had a 2–4 times higher infiltration amount but 5–6 times lower surface runoff and soil loss, indicating that this treatment alleviated nutrient loss via erosion and runoff in the sloped soil. Among all treatments, HWB2 treatment was the most effective for retaining organic C, dissolved organic C, total N, and exchangeable K through various pathways. However, a substantial amount of soluble P was lost through percolation. Therefore, the potential pollution of groundwater by P through percolation pathway should be considered during biochar application.

Anaerobically-digested manure is frequently applied to agricultural soil to enhance plant growth and reduce the need for chemical fertilizers. This practice also stimulates microbial nitrogen transformations and often results in N₂O emissions. A single mesophilic anaerobic digestion is insufficient for pathogen removal or inactivation and therefore, a post treatment is required for its stabilization and hygienization. Here, we examined the effects of limed manure-digestate as a nitrogen source for plant growth and on N₂O emission compared with compost. A plant growth experiment was conducted in a sandy soil and N₂O emissions were monitored throughout the experiment. Plants were irrigated with freshwater or liquid-N fertilizer. The combination of compost application and liquid-N fertilizer resulted in surface N₂O fluxes over 0.7 ​mg ​m⁻² d⁻¹, which were correlated with ammonium concentration in the soil. The presence of N₂O in the rhizosphere was only detected in compost-amended soil 2–10 days after plantation. A significantly-lower surface N₂O flux of 0.4 ​mg ​m⁻² d⁻¹ was recorded with application of limed-digestate, probably due to its effects on nitrogen-transforming microorganisms. Both compost and limed-digestate enhanced plant growth, with a more distinct effect in the freshwater treatment. Our observations demonstrate that limed-digestate can be an efficient substitute for compost as it effectively supports plant growth with substantially-lower N₂O emissions.

Per- and polyfluoroalkyl substances (PFAS) are being widely investigated for their distribution and remediation in the environment. It is crucial to consider the interactions of PFAS between soil and the other media in the ecosystem, including air, water, and plants, when studying their fate and transport in soil, while few studies have taken such an integrative approach. This review examined the potential input of PFAS to soil from air, water, and landfill by analyzing both the PFAS concentration in each source and the mechanisms by which a soil is impacted by PFAS from these sources. It was found that PFAS in air (on average 10¹⁻² ​pg/m³) and landfill leachates (on average 10^0-2 ​ng/L) are the main sources of PFAS in soil. Many factors, such as solution pH and cations, influence sorption and desorption of PFAS in the water-soil interface, but no single factor is deterministic. The migration of PFAS from soil to plant through root uptake was found in many plant species, including wheat and maize, and the effects vary with different PFAS and plant species. PFAS levels in soil were associated with land-use type. They were the highest in the primary exposure sites (10⁻¹-10² ​ng/g), followed by secondary exposure sites (10⁻¹-10¹ ​ng/g), and background sites (10⁻²-10¹ ​ng/g), with legacy PFAS- PFOA (10^0-1 ​ng/g) and PFOS (10^0-2 ​ng/g) as the most predominant. There are a few promising destructive technologies targeted at PFAS in soil, such as thermal treatment and ultrasound, but still need to overcome low efficiency and high cost to scale up. In the meantime, PFAS may either be immobilized in soil or be removed for ex-situ treatment.

Hormesis refers to positive biological effects caused by exposure to low doses of a stressor known to be toxic at higher doses. These effects include an enhanced defense system and stimulated plant/microorganism growth and reproduction. Hormesis has emerged as a fundamental concept with broad relevance to the field of soil and environmental health. Its utilization in evaluating environmental effects and ecotoxicity can reduce uncertainties introduced by extrapolating from high to low doses of pollutants. Similarly, its consideration in risk assessment can help tackle toxicity risks imposed by chemical mixtures. Further, it can maximize the effectiveness of novel agrochemicals applied at the lowest possible concentration, thus reducing their ecological and human risks. Hormesis-based interventions, such as plant priming and stimulation of beneficial insects and waste-degrading microbes, can further reduce agrochemical loads into the environment, thereby enhancing plant and soil health. Inclusion of hormesis in strategies to control harmful organisms, such as pests, pathogenic microbes and harmful algal bloom organisms, can aid in combating chemical resistance. Hormesis-inclusive studies also provide useful information regarding suitable pollutant tolerance levels for microorganisms and plants during bioremediation and phytoremediation, thus enhancing environmental remediation. In sum, hormesis is highly relevant and offers numerous potential applications in soil and environmental health research.