Soil Pollution, Control, and Remediation
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    Sana Khalid, Muhammad Shahid, Zeid A. ALOthman, Abdullah A. Al-Kahtani, Behzad Murtaza, Camille Dumat
    Soil Ecology Letters, 2023, 5(3): 220162.

    ● Soil processes affect metal chemical speciation and their biogeochemical activity.

    ● The current study predicted chemical speciation of eight metals in two soil layers.

    ● Divalent forms of metals predominated in both soil layers (79.9%).

    ● Chromium showed a chemical speciation that varied from that of the other metals (95.8% as CrOH+).

    ● Mean percentage ages of all metal ions were similar for all 15 field locations investigated.

    From soil contamination and risk assessment perspectives, it is imperative to understand the ecological processes occurring in soils. Certain soil processes greatly affect chemical speciation of potentially toxic metals (PTMs), and thus also influence their biogeochemical activity. The current study analyzed chemical speciation of eight PTMs (Cd, Cr, Fe, Cu, Mn, Ni, Zn, and Pb) in upper and lower soil layers for 15 agronomic fields of Vehari-Pakistan using Visual Minteq software. The divalent forms of most PTMs (PTM2+) generally predominated in both soil layers (79.9% overall occurrence). However, chromium revealed a different pattern of chemical speciation (95.8% as CrOH+) compared to other PTMs. The mean percentage of all the PTMs2+ was slightly higher for the lower soil layer (81.3%) than in the upper layer (78.4%), the trend being same for all the PTMs, except Cr. This higher PTMs2+ percentage in lower soil layers than upper layers was due to lower content of organic matter and other anions such as Cl and HCO3. The mean percentage ages of all the PTMs2+ was similar among all the 15 agronomic fields, which was confirmed by strong Pearson correlation values (R2 > 0.95). The PCA graph grouped all the agronomic fields and PTM2+ closely, except Cr2+ and Cu2+. This grouping confirmed the similar chemical speciation of PTMs, except Cu and Cr in studied fields.

    Shuyu Hou, Jue Wang, Jun Dai, Mohammed Boussafir, Chi Zhang
    Soil Ecology Letters, 2023, 5(2): 220158.

    ● Earthworm remove PAHs from soil by bioaccumulation and stimulating microbial degradation.

    ● Biochar can adsorb PAHs and promote microbial degradation in soil.

    ● Earthworm improve the adsorption process of biochar by bioturbation.

    ● Biochar reduce the vermiaccumulation and improve the decomposition of PAHs by earthworm.

    Polycyclic aromatic hydrocarbons (PAHs) in soil pose a threat to the health of humans and other organisms due to their persistence. The remediation method of combined application of biochar and earthworms has received growing attention owing to its effectiveness in PAHs removal. However, the earthworm–biochar interaction and its influence on PAHs in soil has not been systematically reviewed. This review focuses on the effectiveness of combined application of earthworms and biochar in the remediation of PAHs-contaminated soils and the underlying mechanisms, including adsorption, bioaccumulation, and biodegradation. Earthworm–biochar interaction activates the functional microorganisms in soil and the PAHs-degrading microorganisms in earthworm guts, promoting PAHs biodegradation. This review provides a theoretical support for the combined application of biochar and earthworms in the remediation of PAHs-contaminated soils, points out the limitations of this remediation method, and finally shows the prospects for future research.

    Anandkumar Jayapal, Tanushree Chaterjee, Biju Prava Sahariah
    Soil Ecology Letters, 2023, 5(2): 220149.

    ● Mine tailings (MTs) are complex waste materials produced by mining activities and containing toxic organics and inorganics, including heavy metals present in the mining area, with high potential for environmental degradation.

    ● Bioremediation is an efficient and cost-effective technique for management of MTs, considering the complexity and wide coverage area by the later.

    ● Fortified with functional accessories provided by various cellular and molecular aspects of the cells of microorganisms and plants, pollutants in MTs are treated by mechanisms of biosorption, biodegradation, bioaccumulation, bioleaching and biosorption.

    Mine tailings (MTs) are the materials dumped on a mining site after mineral extraction, containing scattered traces of residual minerals, dug-up soils, and a disturbed ecosystem. Abandoned and untreated MT can pose threats to the surrounding ecosystem due to the presence of various primary and secondary toxic components, such as organic substances [PAH (polycyclic aromatic hydrocarbons), phenolics] and inorganic materials (sulfur, cyanide), metals and metalloids. All these pollutants originate from nature, and there is a possibility to remedy the problems generated from them. Conventional physical-chemical and biological techniques are often considered for treating the polluted environment and are recognized as having great efficiency. Physicochemical processes, such as incineration, and soil washing with solvents, encounter limitations of cost-effectiveness associated with further environmental concerns. The advantages accompanying bioremediation, the alternative to physicochemical treatment, are its cost-effectiveness, its environmentally benign nature, and complete mineralization of pollutants, instead of the generation of secondary toxic intermediates as in the case of the physicochemical process, make it more attractive for dealing with MT. This manuscript emphasizes use of basic treatment techniques and bioremediation mechanisms for dealing with pollutants from MT that target the revival of nature by utilizing natural agents, plants (phytoremediation), bacteria, fungi, and algae.

    Qi Zhang, Jing Ma, Alejandro Gonzalez-Ollauri, Yongjun Yang, Fu Chen
    Soil Ecology Letters, 2023, 5(1): 79-93.

    ● Vegetation restoration of monoculture is not satisfactory in mining land.

    ● Native plants accelerated vegetation restoration and soil nutrient accumulation.

    ● Microbial enzymes boosted the initially slow nutritional metabolism of plantations.

    ● Soil microbial enzymes promoted positive succession of ecosystems.

    The diversity of vegetation configuration is the key to ecological restoration in open-pit coal mine dump. However, the recovery outcomes of different areas with the same vegetation assemblage pattern are completely different after long-term evolution. Therefore, understanding the causes of differential vegetation recovery and the mechanism of plant succession is of great significance to the ecological restoration of mines. Three Pinus tabulaeformis plantations with similar initial site conditions and restoration measures but with different secondary succession processes were selected from the open-pit coal mine dump that has been restored for 30 years. Soil physicochemical properties, enzyme activities, vegetation and microbial features were investigated, while the structural equation models were established to explore the interactions between plants, soil and microbes. The results showed that original vegetation configuration and soil nutrient conditions were altered due to secondary succession. With the advancement of the secondary succession process, the coverage of plants increased from 34.8% to 95.5% (P < 0.05), soil organic matter increased from 9.30 g kg −1 to 21.13 g kg−1 (P < 0.05), and total nitrogen increased from 0.38 g kg −1 to 1.01 g kg−1 (P < 0.05). The activities of soil urease and β-glucosidase were increased by 1.7-fold and 53.26%, respectively. Besides, the secondary succession also changed the soil microbial community structure and function. The relative abundance of Nitrospira genus which dominates the nitrification increased 5.2-fold. The results showed that urease and β-glucosidase promoted the increase of vegetation diversity and biomass by promoting the accumulation of soil organic matter and nitrate nitrogen, which promoted the ecological restoration of mine dumps.

    Baile Xu, Gaowen Yang, Anika Lehmann, Sebastian Riedel, Matthias C. Rillig
    Soil Ecology Letters, 2023, 5(1): 108-117.

    ● PFAS significantly increased litter decomposition and soil pH.

    ● Soil respiration was significantly inhibited by PFAS.

    ● Perfluorooctanesulfonic acid suppressed soil water-stable aggregates.

    ● Three PFAS exerted varying degrees of impact on soil health.

    Soils are impacted globally by several anthropogenic factors, including chemical pollutants. Among those, perfluoroalkyl and polyfluoroalkyl substances (PFAS) are of concern due to their high environmental persistence, and as they might affect soil structure and function. However, data on impacts of PFAS on soil structure and microbially-driven processes are currently lacking. This study explored the effects of perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutanesulfonic acid (PFBS) at environmental-relevant concentrations on soil health, using a 6-week microcosm experiment. PFAS (even at 0.5 ng g–1 for PFBS) significantly increased litter decomposition, associated with positive effects on β-glucosidase activities. This effect increased with PFAS concentrations. Soil pH was significantly increased, likely as a direct consequence of increased litter decomposition affected by PFAS. Soil respiration was significantly inhibited by PFAS in week 3, while this effect was more variable in week 6. Water-stable aggregates were negatively affected by PFOS, possibly related to microbial shifts. PFAS affected soil bacterial and fungal abundance, but not microbial and certain enzyme activities. Our work highlights the potential effects of PFAS on soil health, and we argue that this substance class could be a factor of environmental change of potentially broad relevance in terrestrial ecosystem functioning.

    Yumei Mao, Xiaoping Li, Warren A. Dick, Linkui Cao
    Soil Ecology Letters, 2023, 5(1): 128-136.

    ● Gypsum can effectively decrease dissolved P loss via runoff and leachate from the areas with high soil P levels by increasing P uptake by ryegrass.

    ● Both surface application and mixing of gypsum into the topsoil reduced dissolved P losses.

    ● The effect of gypsum application method on dissolved P losses varied by soil texture.

    ● Flue gas desulfurization gypsum did not affect ryegrass biomass and also didn’t increase the accumulation of trace elements in soil and ryegrass.

    Controlling dissolved phosphorus (DP) loss from high P soil to avoid water eutrophication is a worldwide high priority. A greenhouse study was conducted in which flue gas desulfurization gypsum (FGDG) was applied by using different application methods and rates to two agricultural soils. Phosphorus fertilizer was incorporated into the soils at 2.95 g kg–1 to simulate soil with high P levels. The FGDG was then applied at amounts of 0, 1.5, and 15 g kg–1 soil on either the soil surface or mixed throughout the soil samples to simulate no-tillage and tillage, respectively. Ryegrass was planted after treatment application. The study showed that FGDG reduced runoff DP loss by 33% and leachate DP loss 38% in silt loam soil, and runoff DP loss 46% and leachate DP loss 14% in clay loam soil, at the treatment of 15 g kg–1 FGDG. Mixing applied method (tillage) provided strong interaction with higher FGDG. To overall effect, the mixing-applied method performed better in controlling DP loss from silt loam soil, while surface-applied (no tillage) showed its advantage in controlling DP loss from clay loam soil. In practice it is necessary to optimize FGDG concentrations, application methods, and DP sources (runoff or leachate) to get maximized benefits of FGDG application. The FGDG application had no negative effects on the soil and ryegrass.

    Xin Sun, Mingjie Sun, Ying Chao, Xiaoyang Shang, Hui Wang, Hong Pan, Quangang Yang, Yanhong Lou, Yuping Zhuge
    Soil Ecology Letters, 2023, 5(1): 118-127.

    ● Pb pollution significantly affected the diversity of microbial community structure.

    ● Pb pollution reduced the soil microbial biomass-carbon and nitrogen.

    ● Pb pollution increased invertase but reduced catalase activity.

    Lead (Pb) pollution is one of the most widespread and harmful environmental problems worldwide. Determination of changes in soil properties and microbial functional diversity due to land use is needed to establish a basis for remediation of soil pollution. This study aimed to investigate soils contaminated by Pb from different sources and to analyze the functional diversity and metabolism of soil microbial communities using Biolog technology. Pb pollution (> 300 mg kg−1) significantly influenced the diversity and metabolic functions of soil microbial communities. Specifically, Pb contamination significantly reduced soil microbial biomass carbon (C) and nitrogen (N) levels and catalase activity while increasing invertase activity. Furthermore, Biolog EcoPlate assays revealed that Pb pollution reduced the general activities of soil microorganisms, suppressing their ability to utilize C sources. In Pb-contaminated areas lacking vegetation cover, Shannon, Simpson, and McIntosh diversity indices of soil microorganisms were significantly reduced. The microbial diversity and biomass C and N levels were affected by land use and soil properties, respectively, whereas soil enzyme activity was primarily affected by the interaction between land use and soil properties. Our results provide a reference and a theoretical basis for developing soil quality evaluation and remediation strategies.

    Qirui An, Yunyang Li, Na Zheng, Jincai Ma, Shengnan Hou, Siyu Sun, Sujing Wang, Pengyang Li, Xiaoqian Li, Chunmei Zhao
    Soil Ecology Letters, 2023, 5(1): 94-107.

    • The relative abundance of rhizosphere soil bacteria has significantly positive correlation with BCF of Cd and Cu.

    • Obvious variations of predominant species of bacterial communities in rhizosphere soil would emerge in the additions with different concentrations of Cd-Cu mixtures.

    • In the additions with Cd and Cu, the mean of rhizosphere soil bacterial community diversity index was ranked as: Cu alone>Cd-Cu mixtures>Cd pollution.

    • The PCA and PERMANOVA analysis showed that Cu may be the main factor changing the composition of rhizosphere soil bacteria.

    To study the effects of combined Cd and Cu pollution on rhizosphere bacterial community. High-throughput sequencing was used to examine the response of rhizosphere bacterial communities to heavy-metal stress under single and mixed pollution of cadmium (Cd) and copper (Cu). With additions of Cd and Cu, the mean diversity index of rhizosphere bacterial community was in the order Cu alone>Cd-Cu mixtures>Cd alone. In all Cd and Cu treatments, the dominant phyla were Proteobacteria, Actinobacteria, Chloroflexi and Acidobacteria. In the additions with different concentrations of Cd-Cu mixtures, LEfSe indicated that there were differences in the predominant species of rhizosphere bacterial communities. Some genera such as Streptomyces and Microbacterium belonging to Actinobacteria as biomarkers were significantly enriched in both control and treatments, while some genera such as Pseudoxanthomonas and Rhodopseudomonas belonging to Proteobacteria as biomarkers were observed to be enriched in the additions with single and mixture of Cd and Cu. According to the Nonmetric multidimensional scaling (NMDS) analysis, the structure of rhizosphere bacterial community was different between treatments and the CK. Principal Component Analysis (PCA) and permutational multivariate analysis of variance (PERMANOVA) showed that there were significant differences among treatments (p<0.01), and that the addition of Cu might be the primary factor affecting the composition of rhizosphere bacterial communities.

    Simin Li, Zhu Li, Xin Ke, Longhua Wu, Peter Christie
    Soil Ecology Letters, 2022, 4(4): 435-443.

    • AgNPs transferred and accumulated though soil animal food chain.

    • Ÿ AgNPs trophic transfer disturbed nutrient element N transfer.

    • Ag accumulated in body tissue, but no biomagnification effects.

    • Ag2S was harmful to F. candida on survival and reproduction.

    The development of nanotechnology has accelerated the use of silver nanoparticles (AgNPs) in household chemicals and the accumulation of Ag in sewage treatment systems. The application of sewage sludge products to soils raises concerns over the safety of Ag in the function and biogeochemical cycles of the soil belowground ecosystem. Here, we assess the potential risk of the accumulation and transfer of Ag under AgNPs exposure and its effects on the trophic transfer of nitrogen (N) through a soil animal food chain (Folsomia candidaHypoaspis aculeifer). The formation of stable silver sulfide (Ag2S) was also studied via a single species test using F. candida. Concentrations of Ag in F. candida increased with increasing AgNPs concentration, as did those in the predator H. aculeifer, but the Ag bioaccumulation factors of both animals were<1. Folsomia candida body tissue 15N abundance declined markedly compared with that of H. aculeifer. Silver sulfide did have adverse effects on the survival and reproduction of F. candida. The Ag concentrations of F. candida increased with increasing Ag2S concentration in sludge-treated soils. Silver sulfide showed ecotoxicity to the collembolan, therefore ecotoxicity resulting from the transformation and fate of AgNPs in soils needs to be considered before biosolid products are applied to agricultural soils.

    Eva F. Leifheit, Hanna L. Kissener, Erik Faltin, Masahiro Ryo, Matthias C. Rillig
    Soil Ecology Letters, 2022, 4(4): 409-415.

    • Tire abrasion particles reduced aboveground and belowground biomass.

    • Soil respiration and soil pH increased with increasing amount of added tire particles.

    • Litter decomposition is affected by addition of tire particles.

    • Effects are apparent already at the lowest added concentration.

    Tire particles (TPs) are a major source of microplastic on land, and considering their chemical composition, they represent a potential hazard for the terrestrial environment. We studied the effects of TPs at environmentally relevant concentrations along a wide concentration gradient (0–160 mg g−1) and tested the effects on plant growth, soil pH and the key ecosystem process of litter decomposition and soil respiration. The addition of TPs negatively affected shoot and root growth already at low concentrations. Tea litter decomposition slightly increased with lower additions of TPs but decreased later on. Soil pH increased until a TP concentration of 80 mg g−1 and leveled off afterwards. Soil respiration clearly increased with increasing concentration of added TPs. Plant growth was likely reduced with starting contamination and stopped when contamination reached a certain level in the soil. The presence of TPs altered a number of biogeochemical soil parameters that can have further effects on plant performance. Considering the quantities of yearly produced TPs, their persistence, and toxic potential, we assume that these particles will eventually have a significant impact on terrestrial ecosystems.

    Xiongkun Zhang, Shan Wu, Xiaojie Sun, Monika Mortimer, Yichao Wu, Ming Zhang, Qiaoyun Huang, Peng Cai
    Soil Ecology Letters, 2022, 4(3): 213-223.

    1. Basic principles of microfluidics are introduced

    2. Microfluidics to study bacterial spatial distribution and functions

    3. Challenges of microfluidics for soil microbiome in future

    Microfluidics confers unique advantages in microbiological studies as these devices can accurately replicate the micro- and even nano-scale structures of soil to simulate the habitats of bacteria. It not only helps us understand the spatial distribution of bacterial communities (such as biofilms), but also provides mechanistic insights into microbial behaviors including chemotaxis and horizontal gene transfer (HGT). Microfluidics provides a feasible means for real-time, in situ studies and enables in-depth exploration of the mechanisms of interactions in the soil microbiome. This review aims to introduce the basic principles of microfluidic technology and summarize the recent progress in microfluidic devices to study bacterial spatial distribution and functions, as well as biological processes, such bacterial chemotaxis, biofilm streamers (BS), quorum sensing (QS), and HGT. The challenges in and future development of microfluidics for soil microbiological studies are also discussed.

    Xiong Dai, Xingjian Yang, Bihai Xie, Jiajia Jiao, Xiuping Jiang, Chengyu Chen, Zhen Zhang, Zhili He, Hang Lin, Weisong Chen, Yongtao Li
    Soil Ecology Letters, 2022, 4(1): 1-17.

    • This study reviewed the sorption of sex hormones onto soils and sediment.

    • Hydrophobic and other specific interactions are the main sorption mechanisms.

    • The sorption of sex hormones is affected by pH, temperature, and ionic strength.

    • Future research should focus on the coupled leaching-sorption processes.

    Sex hormones are a group of potent endocrine disruptors that can be released into agricultural soils and sediment via wastewater discharge and manure fertilization. Sorption represents a critical determinant for the transport potential and risks of sex hormones in the environment. Therefore, this study reviewed the sorption and desorption mechanisms of sex hormones in soil- and sediment-water systems, and summarized the effects of various factors on sorption and desorption processes. A total of 359 set of sorption data were collected from the literature. Sex hormones were mostly described by the linear model. The sorption magnitudes (logKoc) of estrogens, androgens, and progestins were in the range of 2.77–3.90, 2.55–4.18, and 2.61–4.39, respectively. The average logKoc values of the sex hormones were significantly correlated with their logKow values (R2= 0.13, p<0.05), while the R2 values were much lower than those when fewer sex hormones were included for analysis. In addition, the Kd values of most sex hormones were significantly correlated with the OC% of soils and sediment (R2= 0.16−0.99, p<0.05), but were insignificantly correlated with the particle size distribution and surface area. These results indicated that hydrophobic partitioning interaction and other specific interactions are responsible for sex hormone uptake in soil- and sediment-water systems. The sorption of sex hormones in soil- and sediment-water systems can also be affected by other environmental variables, including pH, temperature, and ionic strength. Future studies should focus on the coupled leaching-sorption processes in manure-water-soil systems under field-scale conditions.

    Fang Wang, Yu Wang, Leilei Xiang, Marc Redmile-Gordon, Chenggang Gu, Xinglun Yang, Xin Jiang, Damià Barceló
    Soil Ecology Letters, 2022, 4(2): 97-108.

    • Microplastics and phthalate acid esters concentrations are positively correlated in soils.

    • Phthalate acid esters levels are greatest in Chinese soils.

    • Microplastics and phthalate acid esters share common sources and sinks.

    • Microplastics and phthalate acid esters are taken up by plants.

    • Microplastics and phthalate acid esters exert confounded influences on soil ecosystems.

    Microplastics (MPs) and Phthalate acid esters (PAEs) co-occur as emerging contaminants of global importance. Their abundance in soil is of increasing concern as plastic-intensive practices continue. Mulching with plastic films, inclusion in fertilizers, composts, sludge application, and wastewater irrigation are all major and common sources of MPs and PAEs in soil. Here, we review studies on the concentration and effects of MPs and PAEs in soil. While there is limited research on the interactions between MPs and PAEs in agroecosystems, there is evidence to suggest they could mutually affect soil ecology and plant growth. Therefore, we propose new research into 1) establishing an efficient, accurate, and simple method to quantify different types of microplastics in soils and plants; 2) exploring the behavior and understanding the mechanisms of co-transfer, transformation, and interactions with soil biota (especially in vegetable production systems); 3) assessing the risk and consequences of combined and discreet impacts of MPs and PAEs on plants and soil biota, and 4) preventing or reducing the transfer of MPs and PAEs into-and within- the food chain.

    Anika Lehmann, Eva F. Leifheit, Linshan Feng, Joana Bergmann, Anja Wulf, Matthias C. Rillig
    Soil Ecology Letters, 2022, 4(1): 32-44.

    • Polyester fibers increased aboveground biomass.

    • Under drought conditions the AM-fungal-only treatment had the highest biomass.

    • Colonization with AM fungi increased under microfiber addition.

    • The mean weight diameter of soil aggregates decreased under microplastic contamination and drought stress, respectively.

    • Under drought conditions AM fungi increased litter decomposition

    Microplastics are increasingly recognized as a factor of global change. By altering soil inherent properties and processes, ripple-on effects on plants and their symbionts can be expected. Additionally, interactions with other factors of global change, such as drought, can influence the effect of microplastics. We designed a greenhouse study to examine effects of polyester microfibers, arbuscular mycorrhizal (AM) fungi and drought on plant, microbial and soil responses. We found that polyester microfibers increased the aboveground biomass of Allium cepa under well-watered and drought conditions, but under drought conditions the AM fungal-only treatment reached the highest biomass. Colonization with AM fungi increased under microfiber contamination, however, plant biomass did not increase when both AM fungi and fibers were present. The mean weight diameter of soil aggregates increased with AM fungal inoculation overall but decreased when the system was contaminated with microfibers or drought stressed. Our study adds additional support to the mounting evidence that microplastic fibers in soil can affect the plant–soil system by promoting plant growth, and favoring key root symbionts, AM fungi. Although soil aggregation is usually positively influenced by plant roots and AM fungi, and microplastic promotes both, our results show that plastic still had a negative effect on soil aggregates. Even though there are concerns that microplastic might interact with other factors of global change, our study revealed no such effect for drought.

    Shengnan Yuan, Zhongxin Tan*
    Soil Ecology Letters, 2022, 4(3): 237-253.

    • The adsorption capacity of Cu(II) by C-O-Fe structure biochar is 98.039 mg g1.

    • The biochar skeleton can produce Fe-O–Cu complex with Cu(II).

    • About 49.5% of Cu(II) is immobilized through ion exchange.

    To improve the adsorption effect of biochar on heavy metal Cu(II), we prepared new biochar and explored its modification process influence on original biochar’s physical structure and chemical composition as well as its adsorption mechanism for Cu(II) in an aqueous solution. Through research work, we have reached some significant conclusions: (1) The modified biochar (M2-800) can adsorb Cu(II) at the rate of 98.039 mg g1, 38.8 times higher than that of the original biochar C800 (2.525 mg g1); (2) The biochar modification process boosts its etching and pore expansion, helping Cu(II) enter the inner surface of the adsorbent, but chemical adsorption is still the most essential fixation method for Cu(II); (3) The alkaline modification process promotes the formation of oxygen-containing functional groups, in which-OH/–COOH and iron ions would form C-O-Fe structures such as hydroxyl bridges (Fe-O–) and carboxy bridges (Fe-OOC–); (4) Carboxyl is the primary site of Cu(II) fixation in M2-800, and M2-800 has higher electronegativity (−47.8 mV) and larger pH (11.61), so that Cu(II) can be removed by electrostatic attraction and precipitation.

    Shaowen Xie, Fei Wu, Zengping Ning, Manjia Chen, Chengshuai Liu, Qiang Huang, Fangyuan Meng, Yuhui Liu, Jimei Zhou, Yafei Xia
    Soil Ecology Letters, 2021, 3(3): 266-278.

    • Remediated soil treated by thermal curing exhibited strong inherent resistance to acidic attack with the formation of ZnCr2O4 spinel.

    • A two-step calculation method to calculate the sum of the leaching and acid-soluble fraction contents of heavy metals in remediated soils for risk evaluation have been proposed.

    • Compared with the traditional one-step calculation method, this two-step calculation method can effectively avoid underestimating the risk of remediated soils.

    The centralized utilization of heavy-metal-contaminated soil has become the main strategy to remediate brownfield-site pollution. However, few studies have evaluated the ecological and human health risks of reusing these remediated soils. Considering Zn as the target metal, systematic pH-dependent leaching and the Community Bureau of Reference (BCR) extraction were conducted at six pH values (pH= 2, 4, 6, 8, 10, 12) for the remediated soil treated through thermal curing. The pH-dependent leaching results showed that with the formation of ZnCr2O4 spinel phases, the remediated soil exhibited strong inherent resistance to acidic attack over longer leaching periods. Furthermore, the BCR extraction results showed that the leaching agent pH value mainly affected the acid-soluble fraction content. Moreover, a strong complementary relationship was noted between the leaching and acid-soluble fraction contents, indicating that the sum of these two parameters is representative of the remediated soil risk value. Therefore, we proposed a two-step calculation method to determine the sum of the two heavy metal parameters as the risk value of remediated soil. In contrast to the traditional one-step calculation method, which only uses the leaching content as the risk value, this two-step calculation method can effectively avoid underestimating the risk of remediated soil.

    Haijian Bing, Shaojun Qiu, Xin Tian, Jun Li, He Zhu, Yanhong Wu, Gan Zhang
    Soil Ecology Letters, 2021, 3(3): 189-206.

    • Trace metal contamination in soils of 29 China’s mountains was investigated.

    • Cd was the priority control metal with moderate to heavy contamination.

    • Cd and Pb contamination were higher in northwest, south and southwest China.

    • Atmospheric deposition was the main sources of Cd and Pb in soils.

    • Climate, vegetation and soil properties regulated spatial distribution of trace metals.

    Trace metal contamination in soils is a threat with an uncertain limit to maintain planet safety, and the issue of trace metal contamination in mountain soils is still of low concerned. In this study, we assessed the contamination of six trace metals (Cd, Cr, Cu, Ni, Pb, and Zn) in mountain soils across China and deciphered the potential drivers of their spatial distribution. The results showed that concentrations of Cd and Pb decreased significantly with soil depth, and their concentrations were markedly higher in north-west, south, and south-west China than elsewhere. Among the metals, Cd was the priority for control with moderate to heavy contamination, followed by Pb, whereas the other metals did not show evident contamination. The altitudinal pattern and isotopic tracing revealed that the significant enrichment and marked contamination of Cd and Pb in surface soils were primarily attributed to deposition through long-range transboundary atmospheric transport and condensation. Ore mining, nonferrous smelting, and coal and fuel combustion were identified as primary anthropogenic sources of the Cd and Pb. Soil organic matter content, pH, and soil forming processes directly determined the accumulation of trace metals in the soils, and orographic effects, including local climate, vegetation composition, and canopy filtering, regulated the spatial distribution of the metals. This study highlights the significance of soil Cd contamination in mountains, which are considered of low concern, and suggests that long-term monitoring of trace metal contamination is necessary to improve biogeochemical models that evaluate the responses of the mountain critical zone to future human- and climate-induced environmental changes.

    Fuhao Liu, Xunrong Huang, Hanghang Zhao, Xiongfei Hu, Lu Wang, Xin Zhao, Pengcheng Gao, Puhui Ji
    Soil Ecology Letters, 2021, 3(3): 242-252.

    • After modification, the adsorption capacity of fly ash to heavy metals is enhanced.

    • Modified fly ash has significant effect on stabilization of Cadmium and lead.

    • The activity of heavy metals stabilized after 6 months of operation of the column.

    • DOC, pH, and organic matter play an important role in heavy metal remediation.

    This study investigated the stabilization of heavy metals by adding modified fly ash (FA) to contaminated soils, and two similar materials, NaOH-zeolite (ZE) and natural zeolite (ZO) were introduced into the soils for comparison. Column leaching tests were conducted to analyze the difference of stabilization effects between the three materials. Leaching columns were run for 6 months, and a considerable stabilization of heavy metals in the soils was observed. The concentration of cadmium (Cd) and lead (Pb) in the amended soil substantially decreased (p<0.05). The results indicated that after 11 weeks of column leaching, Cd and Pb concentrations in the soil leachate decreased to below the detection limit due to amendment stabilization. Among the three amendments, the ZE amendment showed the optimum capacity for heavy metal immobilisation in the soils. In addition, after 6 months of leaching, Pb and Cd concentrations in the soils with the three different amendments decreased to various degrees. The amendments of modified FA and ZE were better than those of natural ZO. Coal FA, after modification, is a useful amendment for the remediation of heavy metals in the contaminated soil.

    Yan He, Peng Cai
    Soil Ecology Letters, 2021, 3(3): 167-168.
    Chong Liu, Mo-ming Lan, Er-kai He, Ai-jun Yao, Guo-bao Wang, Ye-tao Tang, Rong-liang Qiu
    Soil Ecology Letters, 2021, 3(3): 220-229.

    • We compared the phenomic and exudate metabolomic responses of roots of two rice cultivars to Cd.

    • JY841 suffered serious root membrane damage and up-regulated phenylethanoid glycosides.

    • TY816 up-regulated lipids and fatty acids to actively cope with oxidative stress.

    • Reprogramming of root architecture and exudates contributed to contrasting Cd uptake.

    To cope with heavy metal stress, plant root systems undergo root structure modification and release of multifarious metabolites. Elucidation of the resistance strategies to heavy metals mediated by the root system is crucial to comprehend the resistance mechanisms of plants. Here two rice varieties with contrasting grain cadmium (Cd) accumulation traits were selected and the responses of their root systems to Cd stress were evaluated by morphological and metabolomics analysis. The phenomic and metabolomic responses of the root system varied between the two cultivars under Cd stress. The low-Cd accumulation rice cultivar (TY816) had a more highly developed root system that coped with Cd stress (10 μM) by maintaining high root activity, while the root cells of the high-Cd accumulation cultivar (JY841) lost viability due to excessive Cd accumulation. TY816 upregulated lipids and fatty acids to reduce Cd uptake, whereas JY841 upregulated phenylethanoid glycosides to cope with Cd-induced oxidative stress. The combination of metabolomics and phenomics revealed that rice roots employ multiple strategies to increase their tolerance of Cd-induced oxidative stress. Differing capacities to shape the root system architecture and reprogram root exudate metabolites may contribute to the contrasting Cd accumulation abilities between JY841 and TY816.

    Mingzhe Xu, Yongxing Cui, Jingzi Beiyuan, Xia Wang, Chengjiao Duan, Linchuan Fang
    Soil Ecology Letters, 2021, 3(3): 230-241.

    • The microbial metabolism was limited by soil carbon (C) and phosphorus (P) under heavy metal stress.

    • The increase of heavy metal concentration significantly increased the microbial C limitation.

    • Heavy metal pollution can increase the loss of soil C by affecting microbial metabolism.

    • Microbial metabolism limitation can be used as a potential index to evaluate the toxicity of heavy metals.

    Heavy metals can exist in soil for a long time and seriously affect soil quality. The coexistence of various heavy metal pollutants leads to biotoxicity and alters the activity of microorganisms. Soil microbial metabolism plays an important role in nutrient cycling and biochemical processes of soil ecosystem. However, the effects of heavy metal contamination on microbial metabolism in soil are still unclear. This study aims to reveal the responses of microbial metabolic limitation to heavy metals using extracellular enzyme stoichiometry, and further to evaluate the potential impacts of heavy metal pollution on soil nutrient cycle. The results showed that soil microbial metabolism reflected by the ecoenzymatic activities had a significant response to soil heavy metals pollution. The metabolism was limited by soil carbon (C) and phosphorus (P) under varied heavy metal levels, and the increase of heavy metal concentration significantly increased the microbial C limitation, while had no effect on microbial P limitation. Microorganisms may increase the energy investment in metabolism to resist heavy metal stress and thus induce C release. The results suggest that energy metabolism selected by microorganisms in response to long-term heavy metal stress could increase soil C release, which is not conducive to the soil C sequestration. Our study emphasizes that ecoenzymatic stoichiometry could be a promising methodology for evaluating the toxicity of heavy metal pollution and its ecological effects on nutrient cycling.

    Yongxing Cui, Xia Wang, Xiangxiang Wang, Xingchang Zhang, Linchuan Fang
    Soil Ecology Letters, 2021, 3(3): 169-177.

    •Ÿ Five methods of soil HM pollution evaluation based on enzyme activity were reviewed

    Ÿ•Ÿ This review examined the performance and ecological implications of these methods

    •ŸŸ Enzymatic stoichiometry methods reflect changes in soil functions under HM stress

    •ŸŸ Microbial metabolic limitation is a promising indicator to assess soil HM pollution

    Soil enzyme activities have been suggested as suitable indicators for the evaluation of metal contamination because they are susceptible to microbial changes caused by heavy metal stress and are strictly related to soil nutrient cycles. However, there is a growing lack of recognition and summary of the historic advancements that use soil enzymology as the proposal of evaluation methods. Here, we review the most common methods of heavy metal pollution evaluation based on enzyme activities, which include single enzyme index, combined enzyme index, enzyme-based functional diversity index, microbiological stress index, and ecoenzymatic stoichiometry models. This review critically examines the advantages and disadvantages of these methods based on their execution complexity, performance, and ecological implications and gets a glimpse of avenues to come to improved future evaluation systems. Indices based on a single enzyme are variable and have no consistent response to soil heavy metals, and the following three composite indices are characterized by the loss of many critical microbial processes, which thus not conducive to reflect the effects of heavy metals on soil ecosystems. Considering the dexterity of ecoenzymatic stoichiometry methods in reflecting changes in soil functions under heavy metal stress, we propose that microbial metabolic limitations quantified by ecoenzymatic stoichiometry models could be promising indicators for enhancing the reality and acceptance of results and further improving the potential for actual utility in environmental decision-making.

    Qing Zhang, Weiping Mei, Longfei Jiang, Qian Zheng, Chunling Luo, Gan Zhang
    Soil Ecology Letters, 2021, 3(3): 178-188.

    • Mechanisms of soil sorption and plant uptake of OPFRs were measured.

    • Humid acids contribute to electrostatic interaction, hydrogen bonding, etc.

    • Hydrolysis is an important transformation behavior of OPFRs in the soil-plant system.

    • RCF showed no significant correlation with hydrophobicity of OPFRs in soil experiments.

    Organophosphate flame retardants (OPFRs), as a replacement for polybrominated diphenyl ethers (PBDEs), are of increasing concern due to their high production over the years. Soil is the major environmental reservoir and interchange for OPFRs. OPFRs in soil could be transferred to the food chain, and pose potential ecological and human health risks. This review focused on the environmental fate and effects of typical OPFRs in the soil-plant system. We concluded that the sorption and transformation behaviors of OPFRs due to their crucial impact on bioavailability. The root uptake and translocation of OPFRs by plants were summarized with analyses of their potential affecting factors. The in planta transformation and potential ecological effects of OPFRs were also briefly discussed. Finally, we highlighted several research gaps and provided suggestions for future research, including the development of simulative/computative methods to evaluate the bioavailability of OPFRs, the effects of root exudates and rhizosphere microorganisms on the bioavailability and plant uptake of OPFRs, and the development of green and sustainable technologies for in situ remediation of OPFRs-contaminated soil.

    Xiaoming Wan, Mei Lei, Tongbin Chen
    Soil Ecology Letters, 2021, 3(3): 279-287.

    •Ÿ Hawk moth showed foraging preference to P. vittata fronds with low As concentation.

    •Ÿ Hawk moth can not exclude As by excretion.

    •Ÿ The main As speciation of hawk moth is As(III)-SH.

    The development of an effective and green bioinsecticide is a research hotspot. This study demonstrated the possibility of using an arsenic (As) hyperaccumulator as a bioinsecticide. When the As concentration in the Pteris vittata fronds exceeded 138 mg kg−1, the larva of the hawk moth (Theretra clotho) displayed apparent preference to lower-As-concentration P. vittata fronds. The As concentration in the larva body was as high as 850 mg kg–1 Such high concentration of As in the larva body might have been the case that T. clotho lacks a process to exclude As. The larval frass showed an As concentration of only 1%–4% of that in the larva body. The predominant As species in the larva body and frass was As(III)-SH. The percentage of As(III)-SH was slightly higher in the frass than that in the larval body. Chelation with thiols may be a universal detoxification mechanism for As in both plants and insects. In general, the adoption of P. vittata as a bioinsecticide should be feasible. However, the exact processes to achieve this goal still need further study. The mechanism of different animals to detoxify As is another interesting research topic.

    Jipeng Luo, Jiabin Liang, Yuchao Song, Xinyu Guo, Youzheng Ning, Nanlin Liu, Heping Zhao, Tingqiang Li
    Soil Ecology Letters, 2021, 3(3): 253-265.

    • Cd extractability of eleven kinds of fruit residue extractions was compared.

    • The most effective volume ratio of LRE, GLDA and tea saponin in Cd phytoextraction was 15:4:1.

    • CPC improved plant growth, Cd phytoextraction performance and soil organic matter content.

    • CPC induced less changes in bacterial community composition and had no evident influence on MBC and bacterial α-diversity.

    A chelating agent is known as the enhancer for metal phytoextraction; however, there is still a lack of efficient and environmentally sustainable chelators. Here, lemon residue extraction (LRE), prepared from 11 kinds of fruit wastes, was combined with N, N-bis (carboxymethyl) glutamic acid (GLDA), and tea saponin (T.S.) for the compounded plant-derived chelator (CPC), and their influences on Cd phytoextraction by the hyperaccumulator Sedum alfredii was evaluated. Among these fruits, the lemon residue extracted the most significant amount of Cd from the soil. The most effective CPC was at the volume ratio of three agents being 15:4:1 (LRE: GLDA: T.S.). Compared with the deionized water, the solubility of three Cd minerals was increased by 36~311 times, and Cd speciation was substantially altered after CPC application. In the pot experiment, CPC addition caused evident increases in plant shoot biomass, Cd phytoextraction efficiency, and organic matter content compared with EDTA and nitrilotriacetic acid (NTA) application. CPC induced fewer changes in bacterial community composition compared with EDTA and had no pronounced influence on microbial biomass carbon and bacterial α-diversity, suggesting CPC had a subtle impact on the microbiological environments. Our study provides a theoretical base for the reutilization of fruit wastes and the development of environmental-friendly chelator that assists Cd phytoextraction.

    Jiayin Feng, Ashley E. Franks, Zhijiang Lu, Jianming Xu, Yan He
    Soil Ecology Letters, 2021, 3(3): 207-219.

    •Ÿ Rice microbiota responded to lindane pollutant was studied spatiotemporally.

    •ŸŸ Growth time, soil types and rhizo-compartments had significant influence.

    Ÿ Lindane stimulated the endosphere microbiota of rice which was highly dynamic.

    •ŸŸ Root–soil–microbe interactions induced an inhibited redox-coupled lindane removal.

    •ŸŸ This work was beneficial to better regulation of plant growth against adversity.

    Soil-derived microbiota associated with plant roots are conducive to plant growth and stress resistance. However, the spatio-temporal dynamics of microbiota in response to organochlorine pollution during the unstable vegetative growth phase of rice is not well understood. In this study, we focused on the rice (Oryza sativa L.) microbiota across the bulk soil, rhizosphere and endosphere compartments during the vegetative growth phase in two different soils with and without lindane pollutant. The results showed that the factors of growth time, soil types and rhizo-compartment had significant influence on the microbial communities of rice, while lindane mostly stimulated the construction of endosphere microbiota at the vegetative phase. Active rice root-soil-microbe interactions induced an inhibition effect on lindane removal at the later vegetative growth phase in rice-growth-dependent anaerobic condition, likely due to the root oxygen loss and microbial mediated co-occurring competitive electron-consuming redox processes in soils. Each rhizo-compartment owned distinct microbial communities, and therefore, presented specific ecologically functional categories, while the moderate functional differences were also affected by plants species and residual pollution stress. This work revealed the underground micro-ecological process of microbiota and especially their potential linkage to the natural attenuation of residual organochlorine such as lindane.