New insight into the functional group mechanism and structure-activity relationship of the complexation between DOM and Cr(III) in landfill leachate.

Widespread landfills represent a significant source of groundwater contamination. Due to the unique and diverse nature of dissolved organic matter (DOM) in landfill leachate, the interaction between DOM and heavy metals, along with its quantitative evaluation, remains unknown. Consequently, we collected ten samples from various landfill types to serve as representatives for a comprehensive investigation of the mechanism involving functional groups and Cr(III) through the establishment of a quantitative structure-activity relationship (QSAR). We employed ESI FT-ICR MS, (MW) 2D-COS, and DFT calculations for this purpose. Our findings indicate that DOM from landfill leachate contains a higher proportion of CHON molecules on intensity compared to those from natural sources. The maximum complexation capacity was determined by the proportion of proteins (69%), normalized carbon average oxidation state (16%), double bond equivalence (8%), and the number of oxygen atoms (7%) in landfill leachate DOM. Besides, N-containing groups such as N = O and C-N in landfill leachate DOM with lower humification, can exhibit stronger affinities than COOH, ArOH, CO, and polysaccharide C-O groups, which are typically identified as dominant sites in natural DOM. A QSAR model incorporating four parameters demonstrated an impressive accuracy rate of 98.8%, underscoring its reliability in predicting the complexation potential of different landfill leachate DOM with Cr(III).

Antibiotic resistance genes and heavy metals in landfill: A review.

Landfill is reservoir containing antibiotic resistance genes (ARGs) that pose a threat to human life and health. Heavy metals impose lasting effects on ARGs. This review investigated and analyzed the distribution, composition, and abundance of heavy metals and ARGs in landfill. The abundance ranges of ARGs detected in refuse and leachate were similar. The composition of ARG varied with sampling depth in refuse. ARG in leachate varies with the distribution of ARG in the refuse. The ARG of sulI was associated with 11 metals (Co, Pb, Mn, Zn, Cu, Cr, Ni, Sb, As, Cd, and Al). The effects of the total metal concentration on ARG abundance were masked by many factors. Low heavy metal concentrations showed positive effects on ARG diffusion; conversely, high heavy metal concentrations showed negative effects. Organic matter had a selective pressure effect on microorganisms and could provide energy for the diffusion of ARGs. Complexes of heavy metals and organic matter were common in landfill. Therefore, the hypothesis was proposed that organic matter and heavy metals have combined effects on the horizontal gene transfer (HGT) of ARGs during landfill stabilization. This work provides a new basis to better understand the HGT of ARGs in landfill.

Specific response of soil properties to microplastics pollution: A review.

The soil environment is a critical component of the global ecosystem and is essential for nutrient cycling and energy flow. Various physical, chemical, and biological processes occur in the soil and are affected by environmental factors. Soil is vulnerable to pollutants, especially emerging pollutants, such as microplastics (MPs). MPs pollution has become a significant environmental problem, and its harm to human health and the environment cannot be underestimated. However, most studies on MPs pollution have focused on marine ecosystems, estuaries, lakes, rivers, and other aquatic environments, whereas few considered the effects and hazards of MPs pollution of the soil, especially the responses of different environmental factors to MPs. In addition, when many MPs pollutants produced by agricultural activities (mulching film, organic fertilizer) and atmospheric sedimentation enter the soil environment, it will cause changes in soil pH, organic matter composition, microbial community, enzyme activity, animals and plants and other environmental factors. However, due to the complex and changeable soil environment, the heterogeneity is very strong. The changes of environmental factors may react on the migration, transformation and degradation of MPs, and there are synergistic or antagonistic interactions among different factors. Therefore, it is very important to analyze the specific effects of MPs pollution on soil properties to clarify the environmental behavior and effects of MPs. This review focuses on the source, formation, and influencing factors of MPs pollution in soil and summarizes its effect and influence degree on various soil environmental factors. The results provide research suggestions and theoretical support for preventing or controlling MPs soil pollution.

A review of the factors affecting the emission of the ozone chemical precursors VOCs and NOx from the soil.

The soil environment is one of the main places for the generation, emission, and absorption of various atmospheric pollutants, including nitrogen oxides (NOx) and volatile organic compounds (VOCs), which are the main chemical precursors for the formation of ground-level ozone. Ground-level ozone pollution has become a concerning environmental problem because of the harm it poses to human health and the surrounding ecological environment. However, current studies on chemical precursors of ozone mainly focus on emissions from industrial sources, forest vegetation, and urban vehicle exhaust; by contrast, few studies have examined the role of the soil environment on NOx and VOCs emissions. In addition, the soil environment is complex and heterogeneous. Agricultural activities (fertilization) and atmospheric deposition provide nutrients for the soil environment, with a significant effect on NOx and VOCs emissions. There is thus a need to study the environmental factors related to the release of NOx and VOCs in the soil to enhance our understanding of emission fluxes and the types of NOx and VOCs in the soil environment and aid efforts to control ground-level ozone pollution through appropriate measures such as management of agricultural activities. This paper reviews the generation of NOx and VOCs in the soil environment and the effects of various environmental factors on this process. Some suggestions are provided for future research on the regulation of NOx and VOCs emissions in the soil environment and the ability of the soil environment to contribute to ground-level ozone pollution.

Long-term application of nitrogen fertilizer alters the properties of dissolved soil organic matter and increases the accumulation of polycyclic aromatic hydrocarbons.

Soil is a key component of terrestrial ecosystems, as it provides nutrients and energy for all terrestrial organisms and is the site of various physical, chemical, and biological processes. Soil organic matter is particularly important for the role that it plays in element cycling, as well as the adsorption and degradation of soil pollutants. Nitrogen (N) fertilizer is an important nutrient element in the soil microenvironment. Applications of N fertilizer can improve soil quality, but the long-term excessive application of N fertilizer can lead to the deterioration of the soil environment, alter the properties of organic matter, and affect the adsorption and accumulation of soil pollutants. In recent years, several pollutants, especially polycyclic aromatic hydrocarbons (PAHs), have accumulated in farmland soil due to long-term sewage irrigation. However, few studies have examined the response of soil PAHs accumulation to long-term N application, as well as the relationship between this response and changes in soil microenvironmental indicators caused by N application. Here, we conducted field experiments to study changes in soil pH, total organic carbon, and dissolved organic matter (DOM) under long-term N application, as well as their effects on PAHs accumulation. The application of N fertilizer resulted in the aromatization and humification of soil DOM, enhanced the accumulation response ratio (-0.05-0.32) and the amount of PAHs accumulated in soil (more than 30%), and exacerbated the environmental risks of PAHs. Our findings provide new insights that could aid the management and control of PAHs pollution of soil in sewage-irrigated areas.

Differential responses of the properties of soil humic acid and fulvic acid to nitrogen addition in the North China Plain.

Humus (HS) is an important component of soil organic matter. Humic acid (HA) and fulvic acid (FA) are two of the most important components of HS, as they substantially affect biogeochemical processes and the migration and transformation of pollutants in soil. Long-term nitrogen (N) addition can lead to changes in soil physical and chemical properties, affect the structural characteristics of soil HS (HA and FA), cause changes in the adsorption and migration of pollutants, and ultimately result in the continuous deterioration of the soil ecological environment. However, few studies have examined the effects of N addition on the structural characteristics of soil HS, including the responses of soil HA and FA to N addition. Here, we conducted a long-term positioning experiment with different levels of N addition (CK: 0 kg N ha-1 yr-1, LN: 100 kg N ha-1 yr-1, and HN: 300 kg N ha-1 yr-1) in typical farmland soils of the North China Plain to study the response of soil HA and FA to N addition. N addition altered the physical and chemical properties of soil (e.g., pH, SOC, TN, and enzyme activity), which affected the responses of the chemical structure, quality indexes, and composition distribution of soil HA and FA to N addition. Differences in the response to N addition between HA and FA were observed. The structural characteristics of FA were stronger in response to HN compared with those of soil HA. As the level of N added increased, soil FA degradation increased, the composition distribution changed, the aromatization degree and molecular weight decreased, and the molecular structure became simpler. The properties of soil HA did not significantly respond to N addition. Given increases in the global N input (N addition and N deposition), our results have implications for agricultural fertilization, soil management, and other activities.

Electron transfer capacity of humic acid in soil micro and macro aggregates in response to mulching years.

Plastic film mulching can help farmers meet food production requirements and even increase output. Although the environmental impact of this mulch has received attention, uncertainty remains about certain soil components and the course of its long-term effects. In particular, it is not clear whether the long-term use of mulching film will affect the electron transfer capacity (ETC) of natural organic matter in the soil. This study evaluated the electron-accepting capacity (EAC) and electron-donating capacity (EDC) of soil humic acid (HA) in different-size aggregates in response to different film mulching years (0-6 years). The EAC of HA in the soil showed a downward trend as mulching years increased, while the EDC fluctuated. EAC decline in microaggregates (MIA) was more significant than that of macroaggregates (MAA). Film mulching changes the physical and chemical properties of soil and the activity of enzymes, changes the chemical structure of HA, and ultimately affects HA electron transfer. In addition, compared with that in MAA, the chemical structure of soil HA in MIA has a stronger correlation with enzyme activity and ETC and thus is more significantly affected by mulching. These results provide an in-depth understanding of the role of HA in soil aggregates of different sizes in processes related to the agricultural soil environment under mulching conditions.

Nitrogen input leads to the differential accumulation of polycyclic aromatic hydrocarbons in the low- and high-density fractions in sewage-irrigated farmland soil.

Because of a shortage of water resources, sewage irrigation has become a popular management tool for farmland soil in arid areas of China; however, this has led to the accumulation of polycyclic aromatic hydrocarbons (PAHs) in soil. Soil is an important component of ecosystems, and nitrogen is an important nutrient required for plant growth. Nitrogen input can alter the physical, chemical, and biological processes in soil and thus lead to changes in soil organic matter and organic pollutants. However, whether these changes affect the accumulation of PAHs and whether such accumulation differs in the low-density fraction (LF) and high-density fraction (HF) of soil remains unclear. In this study, the response of PAHs in soil to nitrogen input (0, 100, 200, and 300 kg N ha-1 yr-1, respectively), including differences in LF and HF, were investigated through field experiments in a typical sewage-irrigated area. The results showed that nitrogen input could increase the concentrations of PAHs in soil from (7.6 ± 1.1) × 103 to (10.4 ± 0.6) × 103 µg kg-1 and lead to striking differences between the LF ((5.06 ± 0.75) × 103 to (1.89 ± 0.18) × 103 µg kg-1) and HF ((2.54 ± 0.36) × 103 to (8.54 ± 0.44) × 103 µg kg-1). Given the significant increase in global nitrogen input, our findings have implications for the optimization and management of agricultural activities in sewage irrigation areas, such as soil investigation before fertilization, the use of soil improvers, and the improvement of soil planting measures.

Nitrogen addition increases the ecological and human health risks of PAHs in different fractions of soil in sewage-irrigated area.

Nitrogen (N) is one of the most important nutrients required by soil and crops. N addition improves soil quality and fertility. However, long-term N addition changes the soil environment, which may affect the adsorption and accumulation of organic pollutants in soil. The adsorption of pollutants by the light fractions (LF) and heavy fractions (HF) of soil, and their resulting risks, might differ. In addition, several organic pollutants, especially PAHs, accumulate in farmland soil under long-term sewage irrigation. However, few studies have examined the response of PAHs to N addition in soil in sewage-irrigated areas, including whether there is a difference in the response of the LF and HF of soil. Here, a long-term experiment was carried out in farmland soils in typical sewage-irrigated areas to reveal the adsorption and accumulation of PAHs in bulk soil, LF, and HF, and the human health and ecological environment risks posed by PAHs under different levels of N addition. Under long-term N addition, the concentration of PAHs in soil increased and fluctuated from 7598 µg kg-1 to 10,414 µg kg-1. Significant differences in the PAHs concentration in the LF (5048 µg kg-1 to 1889 µg kg-1) and HF (2536 µg kg-1 to 8521 µg kg-1) and the human health and ecological risks of soil with N addition in typical sewage-irrigated areas were observed. The HF of soil was characterized by low carcinogenic and ecological risks. The results of our research provide insight into possible management actions that could be taken to enhance the environmental protection and safety of agricultural production activities, such as sustainability fertilization.

Accumulation of phthalates under high versus low nitrogen addition in a soil-plant system with sludge organic fertilizers instead of chemical fertilizers.

Nitrogen is the main nutrient in soil. The long-term addition of N leads to changes in the soil dissolved organic matter (DOM) and other quality indicators, which affects the adsorption and accumulation of organic pollutants. The use of organic fertilizer is important for the development of green agriculture. However, organic fertilizers (especially sludge organic fertilizers (SOFs) contain phthalates (PAEs) that may accumulate in the soil and result in environmental contamination. How this accumulation response varies with the magnitude of long-term N addition, especially in different soil layer profiles, remains unclear. Here, changes in the content of PAEs in the soil-plant system without and after SOFs application were studied through field experiments in soils with different N addition backgrounds (CK, N1, N3 (0, 100, 300 kg N ha-1 yr-1 respectively)). Our results showed that the application of SOFs increase the accumulation of PAEs in soil profiles and plant systems, increasing human health risks. The content of Σ5PAEs in the topsoil increased from 0.96 ± 0.10 to 1.86 ± 0.09 mg kg-1. Moreover, under a high N addition background and SOFs application, the characteristics of soil DOM change, and the accumulation of PAEs in soil was nearly 30% higher compared with the low N group. Some suggestions such as removing PAEs from SOFs during preparation, conducting soil surveys before applying PAEs, and using soil amendments, which are provided for optimizing the trialability and environmental safety of SOFs application.