Assessment of antibiotic resistance genes in soils polluted by chemical and technogenic ways with poly-aromatic hydrocarbons and heavy metals.

Anthropogenic activities are leaving lots of chemical footprints on the soil. It alters the physiochemical characteristics of the soil thereby modifying the natural soil microbiome. The prevalence of antimicrobial-resistance microbes in polluted soil has gained attention due to its obvious public health risks. This study focused on assessing the prevalence and distribution of antibiotic-resistance genes in polluted soil ecosystems impacted by industrial enterprises in southern Russia. Metagenomic analysis was conducted on soil samples collected from polluted sites using various approaches, and the prevalence of antibiotic-resistance genes was investigated. The results revealed that efflux-encoding pump sequences were the most widely represented group of genes, while genes whose products replaced antibiotic targets were less represented. The level of soil contamination increased, and there was an increase in the total number of antibiotic-resistance genes in proteobacteria, but a decrease in actinobacteria. The study proposed an optimal mechanism for processing metagenomic data in polluted soil ecosystems, which involves mapping raw reads by the KMA method, followed by a detailed study of specific genes. The study's conclusions provide valuable insights into the prevalence and distribution of antibiotic-resistance genes in polluted soils and have been illustrated in heat maps.

Transfer and Degradation of PAHs in the Soil-Plant System: A Review.

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic, persistent organic pollutants that threaten ecosystems and human health. Consistent monitoring is essential to minimize the entry of PAHs into plants and reduce food chain contamination. PAHs infiltrate plants through multiple pathways, causing detrimental effects and triggering diverse plant responses, ultimately increasing either toxicity or tolerance. Primary plant detoxification processes include enzymatic transformation, conjugation, and accumulation of contaminants in cell walls/vacuoles. Plants also play a crucial role in stimulating microbial PAHs degradation by producing root exudates, enhancing bioavailability, supplying nutrients, and promoting soil microbial diversity and activity. Thus, synergistic plant-microbe interactions efficiently decrease PAHs uptake by plants and, thereby, their accumulation along the food chain. This review highlights PAHs uptake pathways and their overall fate as contaminants of emerging concern (CEC). Understanding plant uptake mechanisms, responses to contaminants, and interactions with rhizosphere microbiota is vital for addressing PAH pollution in soil and ensuring food safety and quality.

Physiological and Biochemical Responses of Solanum lycopersicum L. to Benzo[a]pyrene Contaminated Soils.

Benzo[a]pyrene (BaP) is noted as one of the main cancer-causing pollutants in human beings and may damage the development of crop plants. The present work was designed to explore more insights into the toxic effects of BaP on Solanum lycopersicum L. at various doses (20, 40, and 60 MPC) spiked in Haplic Chernozem. A dose-dependent response in phytotoxicity were noted, especially in the biomass of the roots and shoots, at doses of 40 and 60 MPC BaP and the accumulation of BaP in S. lycopersicum tissues. Physiological and biochemical response indices were severely damaged based on applied doses of BaP. During the histochemical analysis of the localization of superoxide in the leaves of S. lycopersicum, formazan spots were detected in the area near the leaf's veins. The results of a significant increase in malondialdehyde (MDA) from 2.7 to 5.1 times, proline 1.12- to 2.62-folds, however, a decrease in catalase (CAT) activity was recorded by 1.8 to 1.1 times. The activity of superoxide dismutase (SOD) increased from 1.4 to 2, peroxidase (PRX) from 2.3 to 5.25, ascorbate peroxidase (APOX) by 5.8 to 11.5, glutathione peroxidase (GP) from 3.8 to 7 times, respectively. The structure of the tissues of the roots and leaves of S. lycopersicum in the variants with BaP changed depending on the dose: it increased the intercellular space, cortical layer, and the epidermis, and the structure of the leaf tissues became looser.

Microbiological status of natural and anthropogenic soils of the Taganrog Bay coast at different levels of combined pollution with heavy metals and PAHs.

The effect of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) pollution on the microbiological status of soils on the coast of the Taganrog Bay and adjacent areas was studied. The content of total and exchangeable forms of HMs, the content of 16 priority PAHs and the abundance of several groups of culturable microorganisms was determined, namely copiotrophic, prototrophic, aerobic spore-forming bacteria, actinomycetes, molds and yeasts. The content of total and exchangeable forms of HMs in urban coastal soils in industrial zone significantly exceeded that in non-urban soils. The maximum concentrations of total forms of Mn, Cr, Ni, Cu, Zn, Pb and Cd are 1821, 871, 143, 89, 1390, 317 and 10 mg/kg, respectively. The median value of the total content of 16 PAHs in urban soils is 3 times higher than in the soils of natural areas and reached 4309 ng/g. The lowest numbers of copiotrophic bacteria, prototrophic bacteria and aerobic spore-forming bacteria were found in the soils of industrial zone: 6.8, 13.8 and 0.63 million CFU g-1 dry soil, respectively. The largest numbers of copiotrophic bacteria, prototrophic bacteria and aerobic spore-forming bacteria were recorded in the soils of natural areas-72.5, 136 and 5.73 million CFU g-1 dry soil, respectively. It was found that the abundance of copiotrophs, prototrophs, and aerobic spore-forming bacteria is more affected by the urbanization of coastal soils including the pollution of HMs and PAHs. Other groups of microorganisms (actinomycetes, molds and yeasts) turned out to be more resistant to anthropogenic factors.

Hyperspectral imaging for small-scale analysis of Hordeum vulgare L. leaves under the benzo[a]pyrene effect.

Hyperspectral imaging is a newly developed approach to estimate the current state of the plants and to develop the methods of soil and plant ecological state improvement under the effect of different sources. The study was devoted to the novel approach of hyperspectral imaging application in the case of persistent organic pollutants (POP) uptake by plants. Hordeum vulgare L. was used as a test plant and grown on the soil artificially contaminated by benzo[a]pyrene (BaP) in the doses of 20, 100, 200, 400, and 800 ng g-1, which corresponds to 1, 5, 10, 20, and 40 maximum permissible concentrations (MPC) and correlates with the level of soil pollution near industrial facilities in the Rostov Region (Russian Federation). It was analyzed a group of indexes responsible for plants stress, consists of broadband greenness group, narrowband greenness group, light use efficiency group, and leaf pigments group. Benzo[a]pyrene had a stronger effect on the efficiency of the photosynthesis process than on the content of chlorophylls. In the phase of active adaptation to stress in H. vulgare, the content of photosynthetic pigments was increased. The proposed method for selecting spectral profiles by cutting off profiles that do not belong to a plant, based on the NDVI value can be effectively used for the estimation of the plants stress under the BaP contamination and for future perspectives in the most suitable way for the application of the plant's growth stimulants.

Features of the polycyclic aromatic hydrocarbon's spatial distribution in the soils of the Don River delta.

PAHs are one of the most toxic organic compounds classes which is obligatory controlled all over the world. There is a luck of studies devoted to the PAHs levels and sources identification in the south of Russia. The features of the PAHs accumulation and spatial distribution in hydromorphic soils (Fluvisol) were studied on the example of the soils of the Don River delta floodplain landscapes. It has been shown that changes in the PAHs content in soils depended on the type and intensity of the emission source. A factor analysis and multivariate linear regression analysis were carried out to determine the features of the spatial distribution for individual PAH compounds, considering the properties of soils and typical differences in the emission source. The most polluted areas in the studied area located along the transit line of the long-distance tankers, where the content of the most toxic high molecular PAHs compounds reached 8862 ng g-1. As a result of regression analysis, a relationship was established between the PAHs accumulation rate with the content of silt (particles less than 0.001 mm in size) and Ca2+ and Mg2+ exchangeable cations in the soil (at p-level < 0.0001). Differences in individual PAH content for medium and heavy loamy Fluvisol and depend on the influence of different types of pollution sources.

Phragmites australis cav. As a bioindicator of hydromorphic soils pollution with heavy metals and polyaromatic hydrocarbons.

The work is devoted to evaluation of the ability of Phragmites australis Сav. to indicate the soil pollution with heavy metals (HMs) and priority polycyclic aromatic hydrocarbons (PAHs) by studying changes in the plant's ultrastructure. The concentration of Mn, Cu, Cr, Cd, Pb, Zn, Ni as well as 16 priority PAHs in hydromorphic soils and macrophyte plants (Phragmites australis Cav.) were increasing with distance decreasing to the power station and approaching to the direction of prevailing wind (northwest). The analyze of distribution of the studied pollutants in plants showed that the highest concentration have prevailed in the roots. A decrease in the diameter of the roots, and an increase in the thickness of the leaf blade was established. The transmission electron microscopy analysis showed that the ultrastructure of P. australis chloroplasts changed affected by accumulation of HMs and PAHs: a rise in the number of plastoglobules; a drop in the number of lamellae in granules, as well as changes in the shape, size, and electron density of mitochondria and peroxisomes. The most serious destructive violations of the main cellular organelles were noted for plants from the site within a 2.5 km from the emissions source and located on the predominant wind rose (north-west) direction. These macrophytes reflect spatial variations of pollutants metals in hydromorphic soils, therefore they are of potential use as bioindicators of environmental pollution.

Uptake of potentially toxic elements and polycyclic aromatic hydrocarbons from the hydromorphic soil and their cellular effects on the Phragmites australis.

The current study provides an information on the combined effect of pollution with potentially toxic elements (PTEs) and polycyclic aromatic hydrocarbons (PAHs) in hydromorphic soils on the accumulation, growth, functional and morphological-anatomical changes of macrophyte plant, i.e., Phragmites australis Cav., as well as information about their bioindication status on the example of small rivers of the Azov basin. The territory of the lower reaches of the Kagalnik River is one of the small rivers of the Eastern Azov region was examined with different levels of PTEs contamination in soils, where the excess of the lithosphere clarkes and maximum permissible concentrations (MPC) for Mn, Cr, Zn, Pb, Cu, and Cd were found. The features of the 16 priority PAHs quantitative and qualitative composition in hydromorphic soils and P. australis were revealed. The influence of soil pollution on accumulation in P. australis, as well as changes in the morphological parameters were shown. It has been observed that morphometric changes in P. australis at sites experiencing the сontamination and salinity are reflected with the changes in the ultrastructure of plastids, mitochondria, and EPR elements of plant cells. PTEs accumulated in inactive organs and damaged cell structures. At the same time, PAHs penetrated through the biomembranes and violated their integrity, increased permeability, resulted cell disorganization, meristem, and conductive tissues of roots. The nature and extent of the structural alterations found are dependent on the type and extent of pollution in the examined regions and can be utilized as bioindicators for evaluating the degree of soil phytotoxicity characterized by the accumulation of PTE and PAHs.

Decrypting the synergistic action of the Fenton process and biochar addition for sustainable remediation of real technogenic soil from PAHs and heavy metals.

The objective of this study was to demonstrate the feasibility and the relevance of combining biochar with the Fenton process for the simultaneous improvement of polycyclic aromatic hydrocarbons (PAHs) degradation and immobilization of heavy metals (HMs) in real soil remediation processes at circumneutral pH. The evaluation of PAHs degradation results was performed through multivariate statistical tools, including principal component analysis (PCA) and partial least squares (PLS). PCA showed that the level of biochar amendment decisively affected the degree of degradation of total PAHs, highlighting the role of biochar in catalyzing the Fenton reaction. Moreover, the PLS model was used to interpret the important features of each PAH's physico-chemical properties and its correlation to degradation efficiency. The electron affinity of PAHs correlated positively with the degradation efficiency only if the level of biochar amendment sat at 5%, explained by the ability of biochar to transfer the electrons to PAHs, improving the Fenton-like degradation. Moreover, the addition of biochar reduced the mobilization of HMs by their fixation on their surface, reducing the Fenton-induced metal leaching from the destruction of metal-organic complexes. In overall, these results on the high immobilization rate of HMs accompanied with additional moderate PAHs degradation highlighted the advantages of using a biochar-assisted Fenton-like reaction for sustainable remediation of technogenic soil.

Intra-soil waste recycling provides safety of environment.

Amelioration and remediation technology was developed for phosphogypsum utilization in Haplic Chernozem of South-European facies (Rostov Region). The technology comprises phosphogypsum dispersed application into the soil layer of 20-45 cm during intra-soil milling. In the model experiment, the phosphogypsum doses 0 (control), 10, 20, and 40 t ha-1 were studied. The Cd thermodynamic forms in soil solution were calculated via the developed mathematical chemical-thermodynamic model and program ION-3. The form of ion in soil solution (or water extract) was considered accounting the calcium-carbonate equilibrium (CCE) and association of ion pairs CaCO30; CaSO40, MgCO30, MgSO40, CaHCO3+, MgHCO3+, NaCO3-, NaSO4-, CaOH+, MgOH+. For calculation of the equilibrium of microelements concentration in soil solution ion including heavy metals (HMs), the coefficient of microelement association kas was proposed. According to calculations, Cd2+ ion in soil solution was mostly bounded to associates CdOH+, partly to associates CdCO30 and CdHCO3+. The calculated kas of Cd was 1.24 units in the control option of experiment and decreased to 0.95 units at phosphogypsum dose 40 t ha-1. The ratio of "active [Cd2+] to total Cd" reduced from 33.5% in control option to 28.0% in the option of phosphogypsum dose 40 t ha-1. The biogeochemical barrier for penetration of HMs from soil to plant roots was high after application of phosphogypsum. According to calculation by ION-3, the standard soil environmental limitations overestimate the toxicity of Cd in soil solution. New decision for intra-soil milling and simultaneous application of phosphogypsum was developed to provide the environmentally safe waste recycling.

Influence of carbon-containing and mineral sorbents on the toxicity of soil contaminated with benzo[a]pyrene during phytotesting.

Benzo[a]pyrene (BaP) is a member of polycyclic aromatic hydrocarbons known for high persistency and toxicity. Technologies of BaP sorption through solid matrixes have received relatively more attention. The present study was devoted to the phytotesting investigations of two different groups of sorbents, such as carbonaceous, including biochar and granulated activated carbon (GAC), and mineral, including tripoli and diatomite. Evaluation of the BaP removing efficiency was carried out using the phytotesting method with spring barley in Haplic Chernozem contaminated with different levels of contamination (200 and 400 µg kg-1 BaP). The sorbents' efficiency for BaP remediation was estimated in the sorbents doses from 0.5 to 2.5% per kg of soil. It was shown that biochar and GAC decreased the soil toxicity class to a greater extent than mineral sorbents ones. The effect intensified with an increase in applying sorbents doses. The optimal dose of carbonaceous sorbents into the soil contaminated with 200 µg kg-1 was 1%, decreasing the BaP content up 57-59% in the soil. Simultaneously, the optimal dose of the mineral sorbents was found to be 1.5%, which decreased the BaP content in the soil up 41-48%. Increasing the BaP contamination level up to 400 µg kg-1 showed the necessity of a sorbent dose increasing. In these conditions, among all applied sorbents, only 2% GAC could reduce the soil toxicity class to the normal level up to 0.91-1.10. It was shown that BaP tended to migrate from the soil to the roots and further into the vegetative part of barley.

Biochar-assisted Fenton-like oxidation of benzo[a]pyrene-contaminated soil.

In the present study, the biochar derived from sunflower husks was used as a mediator in the heterogeneous Fenton process. The physical and chemical characteristics were studied in terms of specific surface area, elemental contents, surface morphology, surface functional groups, thermal stability, and X-ray crystallography. The main aim was to evaluate the effectiveness of biochar in a heterogeneous Fenton process catalyzed by hematite toward the degradation of benzo[a]pyrene (BaP) in Haplic Chernozem. The Fenton-like reaction was performed at a pH of 7.8 without pH adjustment in chernozem soil. The effects of operating parameters, such as hematite dosage and H2O2 concentrations, were investigated with respect to the removal efficiency of BaP. The overall degradation of 65% was observed at the optimized conditions where 2 mg g-1 hematite and 1.25 M H2O2 corresponded to the H2O2 to Fe ratio of 22:1. Moreover, the biochar amendment showed an increment in the removal efficiency and promotion in the growth of spring barley (Hordeum sativum distichum). The BaP removal was reached 75 and 95% after 2.5 and 5% w/w addition of biochar, respectively. The results suggested that the Fenton-like reaction's effectiveness would be greatly enhanced by the ability of biochar for activation of H2O2 and ejection of the electron to reduce Fe(III) to Fe(II). Finally, the presence of biochar could enhance the soil physicochemical properties, as evidenced by the better growth of Hordeum sativum distichum compared to the soil without biochar. These promising results open up new opportunities toward the application of a modified Fenton reaction with biochar for remediating BaP-polluted soils.

The effect of combined pollution by PAHs and heavy metals on the topsoil microbial communities of Spolic Technosols of the lake Atamanskoe, Southern Russia.

The contamination with organic and inorganic pollutants changes significantly soil microbial community structure. These shifts indicate anthropogenic pressure and help to discover new possibilities for soil remediation. In this study, the microbial community structure of Spolic Technosols formed at the territory of a former industrial sludge reservoir near the Kamensk-Shakhtinsky (Southern Russia) was studied using a metagenomics approach. The studied soils contain high concentrations of heavy metals (HM) (up to 72,900 mg kg-1) and 16 priority polycyclic aromatic hydrocarbons (PAHs) (up to 6670 mg kg-1). Its microbial communities demonstrate an excellent adaptability level reflected in their complexity and diversity. As shown by the high values of alpha diversity indices (Shannon values up to 10.1, Chao1 values from 1430 to 4273), instead of decreasing quantitatively and qualitatively on the systemic level, microbial communities tend to undergo complex redistribution. Regardless of contamination level, the share of Actinobacteria and Proteobacteria was consistently high and varied from 20 to 50%. Following the results of the Mann-Whitney U test, there were significant changes of less abundant phyla. The abundance of oligotrophic bacteria from Gemmatimonadetes and Verrucomicrobia phyla and autotrophic bacteria (e.g., Nitrospira) decreased due to the high PAH's level. And abundance of Firmicutes and amoebae-associated bacteria such as TM6 and soil Chlamydia increased in highly contaminated plots. In the Spolic Technosols studied, the influence of factors on the microbial community composition decreased from PAHs concentration to soil characteristics (organic carbon content) and phylum-phylum interactions. The high concentrations of HMs influenced weakly on the microbial community composition.

Impact of Metal-Based Nanoparticles on Cambisol Microbial Functionality, Enzyme Activity, and Plant Growth.

An increase in the penetration of metal-based nanoparticles (NPs) into the environment requires an assessment of their ecotoxicity as they impair the critical activity of plants, animals, bacteria, and enzymes. Therefore, the study aimed to observe the effects of metal-based NPs, including copper (Cu), nickel (Ni), and zinc (Zn), on the Cambisols, which cover a significant part of the earth's soil and play an important role in the biosphere. Metal-based NPs were introduced into the soil at concentrations of 100, 1000, and 10,000 mg/kg. The biological properties of the soil are being investigated as the most sensitive to external contamination. The highest ecotoxicity of the studied pollutants introduced into the soil at the same concentrations was shown by Cu (up to 34%) and Zn (up to 30%) NPs, while Ni NPs showed less (up to 22%). Microbiological (total number of bacteria, Azotobacter sp. abundance) and phytotoxic properties (radish seed germination and length of roots) of Cambisols were more sensitive (22-53%) to pollution by NPs of Cu, Zn, and Ni, while enzymatic activity (catalase and dehydrogenases) showed less sensitivity (14-32%). The present results could be useful for biomonitoring the state of contaminated soils, especially by NPs.

Effects of benzo[a]pyrene toxicity on morphology and ultrastructure of Hordeum sativum.

Many studies have been devoted to investigation of toxic benzo(a)pyrene (BaP) compound, but studies involving changes at the cellular level are insufficient to understand the mechanisms of polycyclic aromatic hydrocarbons (PAHs) effect on plants. To study the toxicity of BaP, a model vegetation experiment was conducted on cultivation of spring barley (Hordeum sativum distichum) on artificially polluted BaP soil at different concentrations. The article discusses the intake of BaP from the soil into the plant and its effect on the organismic and cellular levels of plant organization. The BaP content in the organs of spring barley was determined by the method of saponification. With an increase in the concentration of BaP in the soil, its content in plants also rises, which leads to inhibition of growth processes. The BaP content in the green part of Hordeum sativum increased from 0.3 µg kg-1 in control soil up to 2.6 µg kg-1 and 16.8 µg kg-1 under 20 and 400 ng/g BaP applying in soil, as well as in roots: 0.9 µg kg-1, 7.7 µg kg-1, 42.8 µg kg-1, respectively. Using light and electron microscopy, changes in the tissues and cells of plants were found and it was established that accumulation of BaP in plant tissues caused varying degrees of ultrastructural damage depending on the concentration of pollutant. BaP had the greatest effect on the root, significant changes were found in it both at histological and cytological levels, while changes in the leaves were observed only at the cytological level. The results provide significant information about the mechanism of action of BaP on agricultural plants.

Soil PAHs contamination effect on the cellular and subcellular organelle changes of Phragmites australis Cav.

The concentrations of ∑16 priority polycyclic aromatic hydrocarbons (PAHs) for soils, roots, and above-ground parts of reed (Phragmites australis Cav.) were determined on different monitoring plots located near the city of Kamensk-Shakhtinsky, southern Russia, where historically received industrial sewage and sludge. The total PAHs concentration in monitoring soil plots was significantly higher than those in the background site which situated at the distance of 2 km from the contamination source. Accordingly, the maximum accumulation was found for phenanthrene and chrysene among the 16 priority PAHs in most of the plant samples collected in the impact zone. The effects of PAHs' pollution on changes of Phragmites australis Cav. cellular and subcellular organelles in the studied monitoring sites were also determined using optical and electron microscopy, respectively. The obtained data showed that increasing of PAHs contamination negatively affected the ultrastructural changes of the studied plants. Phragmites australis Cav. showed a high level of adaptation to the effect of stressors by using tissue and cell levels. In general, the detected alterations under the PAHs effect were possibly connected to changes in biochemical and histochemical parameters as a response for reactive oxygen species and as a protective response against oxidative stress. The obtained results introduce innovative findings of cellular and subcellular changes in plants exposed to ∑16 priority PAHs as very persistent and toxic contaminants.

Impact of humic acid on degradation of benzo(a)pyrene polluted Haplic Chernozem triggered by modified Fenton-like process.

In this study, the applicability of a modified Fenton reaction for remediation of polycyclic aromatic hydrocarbons (PAHs) was demonstrated in chernozem soil. The main aim was to investigate the impact of variation of humic acid (HA) on the modified Fenton capabilities to degrade of benzo(a)pyrene (BaP). Experimental was designed with two independent variables, including hydrogen peroxide (H2O2) and hematite (α-Fe2O3), to determine the most effective BaP treatment conditions with exploring natural and an extra added amount of HA. For modified Fenton reaction at Haplic Chernozem, the best BaP degradation conditions resulted in an overall degradation of 68% with the following conditions: 0.95 M H2O2; 17.54 mg/g hematite; pH 7.8 without adjustment; 24 h; unsaturated (soil: water ratio 1:0.5). In the soil supplemented with 1% HA, Fenton-like reaction was found to perform better and resulted in 76% BaP degradation with less amount of hematite dosage (16.71 mg). The fact that HA, a significant class of naturally occurring compounds in soil, supports the Fenton reaction has strong relevance in the field of enhancing PAHs degradation field to obtain a more economical route.