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Review

Synergistic Approaches for Sustainable Remediation of Organic Contaminated Soils: Integrating Biochar and Phytoremediation

by
Hao Fang
1,2,3,4,
Cailing Zhou
1,3,*,
Dong-Xing Guan
5,
Muhammad Azeem
1,3,6 and
Gang Li
1,2,3
1
State Key Laboratory of Regional and Urban Ecology, Ningbo Observation and Research Station, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
Zhejiang Key Laboratory of Pollution Control for Port-Petrochemical Industry, CAS Haixi Industrial Technology Innovation Center in Beilun, Ningbo 315830, China
4
College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
5
State Key Laboratory of Soil Pollution Control and Safety, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China
6
Institute of Soil and Environmental Sciences, Pir Mehr Ali Shah Arid Agriculture University Rawalpindi, Rawalpindi 46300, Punjab, Pakistan
*
Author to whom correspondence should be addressed.
Agriculture 2025, 15(8), 905; https://doi.org/10.3390/agriculture15080905
Submission received: 28 February 2025 / Revised: 11 April 2025 / Accepted: 17 April 2025 / Published: 21 April 2025
(This article belongs to the Special Issue Risk Assessment and Remediation of Agricultural Soil Pollution)
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Abstract

Various industrial and agricultural activities have led to significant organic pollution in soil, posing an ongoing threat to both soil ecosystems and human health. Among the available remediation methods, phytoremediation and biochar remediation are recognized as sustainable and low-impact approaches. However, individual remediation methods often have limitations, such as plant susceptibility to adverse soil conditions and the desorption of pollutants from biochar. Therefore, integrating biochar with phytoremediation for the remediation of organic-contaminated soils provides a complementary approach that addresses the drawbacks of applying each method alone. The key mechanism of this combined technology lies in the ability of biochar to enhance plant resilience, plant absorption of pollutants, and the degradation capacity of rhizosphere microorganisms. Simultaneously, plants can completely degrade pollutants adsorbed by biochar or present in the soil, either directly or indirectly, through root exudates. This review systematically explores the mechanisms underlying the interactions between biochar and phytoremediation, reviews the progress of their application in the remediation of organic-contaminated soils, and discusses the associated challenges and prospects.

Graphical Abstract

1. Introduction

The improper disposal of toxic waste resulting from the rapid development of global industrialization, coupled with the excessive use of antibiotics, pesticides, and herbicides in agriculture, generates a range of organic pollutants. These pollutants migrate and undergo transformations within ecosystems through industrial and medical wastewater discharges, as well as agricultural activities, ultimately accumulating in soils. Common organic pollutants include polycyclic aromatic hydrocarbons [1], poly- and perfluorinated alkyl substances [2], microplastic [3], and antibiotics [4,5,6]. Such pollutants and their derivatives can result in severe soil contamination, which in turn reduces soil fertility, disrupts microbial diversity, and limits agricultural productivity [7,8]. Furthermore, organic pollutants can harm human health through food chain intake, absorption, or direct contact. These pollutants have been linked to endocrine disruption, which can impair normal physiological processes, potentially leading to conditions such as infertility and obesity [9,10]. In addition, they may cause damage to the nervous system, resulting in cognitive decline, memory loss, and other neurological impairments [11]. More severely, organic pollutants are carcinogenic, capable of inducing DNA mutations and promoting tumor formation [12,13].
Given the pressing issue of organic pollution, various remediation technologies, including physical and chemical techniques, have been developed to address contaminated soils. Physical remediation primarily includes technologies such as thermal desorption, electrokinetic remediation, and vapor extraction. Chemical remediation, on the other hand, can be achieved through techniques like chemical oxidation, plasma degradation, soil washing, and photocatalytic degradation [14]. Physicochemical remediation technologies offer significant advantages, particularly their high efficiency when addressing urgent and sudden pollution incidents. However, they also present notable drawbacks, including high costs, substantial energy consumption, and potential secondary pollution, among other associated risks [15,16]. Consequently, there is an increasing need for low-cost, environmentally friendly, and easy-to-operate remediation solutions. In recent years, phytoremediation has gained widespread attention due to its sustainability, cost-effectiveness, and efficiency [17]. For example, maize, rice, and ryegrass have the potential to degrade organic pollutants such as PAHs, polychlorinated biphenyls (PCBs), and PFAS in soil, either through direct uptake or via interactions between their root systems [18,19]. However, when phytoremediation is the only technique employed, the growth and development of plants, as well as their efficiency in removing pollutants, can be significantly hindered by several environmental stressors. These include soil drought, salinity, nutrient deficiency, and the toxic effects of the pollutants themselves [20,21]. Therefore, implementing additional measures can help to alleviate the limitations of phytoremediation.
Biochar is a carbon-rich material primarily produced through the pyrolysis of various biomass feedstocks, such as agricultural waste, animal manure, and sewage sludge, under high-temperature and anoxic conditions. Biochar possesses numerous microporous structures, high specific surface area, and abundant functional groups, including carboxyl, carbonyl, and hydroxyl groups. Pollutants can be sequestered directly by biochar through its physicochemical properties [22,23]. When incorporated into the soil, biochar can enhance water retention, increase the formation of soil macroaggregates, regulate soil pH, and improve the soil’s cation exchange capacity, thereby creating optimal conditions for plant growth and development [24,25]. Soil fertility can be directly enhanced by biochar through the supplementation of nutrients and the improvement of nutrient availability, thus promoting root growth. In addition, rhizosphere microorganisms could be protected by biochar, which serves as a shelter and a provider of nutrients [26]. This symbiotic relationship facilitates the uptake and degradation of organic pollutants by both the plant root system and rhizosphere microorganisms [27,28]. Therefore, the combination of biochar with phytoremediation exhibits a promising approach for more efficient and sustainable soil remediation [29,30].
When searching for “soil” and “organic pollutants” as a topic from the “Web of Science Core Collection” database, a total of 5395 papers published over the past decade (2014–2023) are available. The results reveal an overall upward trend in research on organic pollutants in soil, with a slight decline observed in 2023. Notably, the number of citations for the relevant literature has been steadily increasing (Figure 1a). These trends reflect a growing interest in soil remediation of organic pollutants over the past ten years and the accumulation of substantial research findings. Scientometric visualization of the first 76 keywords based on 5395 publications revealed the following key trends: (1) Regarding the types of organic pollutants, PAHs and PCBs have been the primary research focus in recent years. Additionally, the co-contamination of organic pollutants and heavy metals has emerged as a significant concern (the largest red sphere in Figure 1b). (2) Among the various remediation methods, phytoremediation within the context of bioremediation has become a critical technological approach (the largest blue sphere in Figure 1b). (3) As a remediation material, biochar has been extensively studied for its ability to remove pollutants through adsorption and other mechanisms (the largest green sphere in Figure 1b).
The potential of single biochar-based materials or plants for remediating organic contaminants in soils has been extensively investigated in the existing literature. However, given the limitations of individual remediation technologies, greater emphasis should be placed on exploring the potential of combining biochar with phytoremediation to enhance the effectiveness of soil contamination remediation. This review aims to provide a comprehensive analysis of the roles played by biochar and phytoremediation in organic contaminated soils, with a focus on the principles underlying the complex interactions between these two technologies. Specifically, this review covers the following aspects: (1) The current status and limitations of phytoremediation techniques in contaminated soils, including plant uptake, the secretion of degrading enzymes, and the promotion of beneficial root-associated microorganisms. (2) The current status and limitations of biochar-based materials for soil remediation, including mechanisms such as pore filling, electrostatic interactions, hydrogen bonding, and van der Waals forces. (3) The principles and practical applications of biochar–phytoremediation interactions, focusing on how biochar enhances plant nutrient accessibility, alleviates abiotic stress, promotes microbial activity, and facilitates pollutant degradation through interactions with both plant roots and rhizosphere microorganisms. Finally, we discuss the challenges and prospects of combining biochar with phytoremediation technologies, offering insights for the advancement of this field. This review is expected to be a valuable reference for future implementation in soil remediation for organic pollutants.

2. Phytoremediation of Organic Contaminated Soils

Phytoremediation is a technology that uses plants to transform or decompose environmental pollutants into harmless or less toxic substances directly or indirectly [31]. The effectiveness and mechanisms of phytoremediation vary depending on the plant species and the nature of the pollutants involved [32]. Compared to physical and chemical remediation methods, phytoremediation is widely adopted due to its cost-effectiveness, environmental friendliness, and broad applicability to various environmental contaminants [33].

2.1. Phytoremediation Mechanisms

The mechanisms of phytoremediation involve processes such as uptake, translocation, immobilization, and degradation of pollutants (Figure 2). Plants generally absorb pollutants through their roots and subsequently transfer them to other tissues for eventual release into the environment via transpiration [34]. Additionally, endophytes within the plant directly metabolize and degrade these pollutants [35]. On the root surface, the interaction between root exudates and soil immobilizes contaminants, alters their bioavailability, and reduces their translocation within the soil [36]. Roots also degrade pollutants into less toxic small molecules through the secretion of oxidoreductases [37]. In addition to the direct removal of pollutants via the mechanisms described above, plants also indirectly participate in pollutant transformation [38]. The root system provides energy sources, such as sugars, amino acids, and organic acids, which enhance microbial activity. These changes further promote the mineralization of pollutants by soil microorganisms [39].

2.2. The Current Status of Phytoremediation Applications

The physicochemical properties and bioavailability of pollutants, soil characteristics, and plant species collectively determine the mechanisms and efficiency of phytoremediation. Plant species are regarded as the primary determinant influencing the remediation of organic pollutants. Plant species employ distinct mechanisms for the removal of pollutants. For instance, weeds remove PFAS from the soil primarily through direct uptake [40], whereas alfalfa achieves the remediation of total petroleum hydrocarbon-contaminated soil through the action of rhizosphere microorganisms [41]. Table 1 summarizes the remediation efficiency of phytoremediation for soil contaminants and the primary mechanisms of action.

2.2.1. Applications of Direct Phytoremediation

Plants can directly remove pollutants through root uptake, translocation via stems and leaves, and microbial or enzymatic metabolism within plant tissues. For example, weeds primarily absorb short-chain PFAS through their roots, preferentially accumulating them in the shoots, with removal rates reaching up to 41.4% [40]. The ability of plants to absorb PFAS is influenced by the molecular size and hydrophilicity of the PFAS, as well as the morphological characteristics of the plants (Figure 3a). In a study by Li et al., it was found that when Fire Phoenix plants absorb PAHs, biotrophic interactions between the plants and endophytic bacteria enhance the degradation of PAHs. This is achieved through the upregulation of citric acid, succinic acid, and malic acid, promoting the growth of Bacillus, Mycobacterium, and Nocardia species within the plants, leading to a degradation rate of up to 78.95% [50] (Figure 3b).

2.2.2. Applications of Indirect Phytoremediation

Enhancing microbial activity and abundance to promote the indirect removal of contaminants from soil is another pathway of phytoremediation. For instance, under copper stress, Elsholtzia sp. altered soil properties, including the levels of inorganic nutrients such as nitrogen, phosphorus, and potassium, as well as pH, thereby indirectly shaping the rhizosphere microbial community and promoting the removal of phenanthrene and PCBs [47] (Figure 3c). Yang et al. found that high levels of humic substances in the root exudates of dicotyledonous and monocotyledonous plants were associated with a higher degree of defluorination of 6:2 FTOH. This was facilitated by the dominant strain Rhodococcus jostii, which promoted the transformation of 6:2 FTOH and produced a more diverse range of metabolites [52]. However, recent studies suggest that the release of maize root exudates induces changes in water-soluble phenolics and dissolved organic carbon (DOC), indirectly affecting reactive oxygen species (ROS) production. The generated ROS facilitate the removal of PAHs, with the overall degradation efficiency of 31.4–43.3%, alleviating pollutant-induced stress on plants ultimately [51]. The ROS-mediated abiotic transformation of PAHs in the rhizosphere offers a new perspective for the phytoremediation of organic pollutants in soils (Figure 3d).

2.3. Limitations of Phytoremediation

Although some plants can effectively remove organic pollutants from soil through their own mechanisms and the assistance of rhizosphere microorganisms, there are certain limitations associated with phytoremediation. First, the root system is often directly damaged in severely contaminated soils, impairing the plants’ ability to absorb and degrade pollutants. For instance, nanoscale microplastics can directly penetrate plant root tissues and subsequently be translocated to various organs through transpirational pull, ultimately inducing both cytotoxic effects and phytotoxicity in plants [53,54]. Second, adverse soil conditions, such as drought, high salinity, or excessive alkalinity, further indirectly hinder remediation by inducing osmotic stress, ionic toxicity, and metabolic disturbances in plant cells, thereby suppressing growth and reducing efficiency [55,56]. Under saline-alkali stress, the ionic homeostasis in plant tissues is disrupted. The elevated pH level impairs root ion absorption efficiency. Furthermore, alkaline stress induces the precipitation of magnesium, an essential element for chlorophyll synthesis, thereby significantly compromising photosynthetic capacity [57,58]. Under drought stress conditions, water deficit directly creates an imbalance where root water consumption exceeds absorption capacity, leading to plant water deficit that inhibits normal growth and metabolic processes. Additionally, mechanical damage occurs to protoplasts and cell walls, accompanied by impairment of the biomembrane system and alterations in membrane permeability. The concomitant reduction or complete closure of stomatal apertures ultimately results in a marked decline in photosynthetic rate [59]. To overcome these combined limitations, integrating phytoremediation with complementary approaches is essential to enhance both plant resilience and pollutant removal capacity. Consequently, it is essential to integrate phytoremediation with other remediation approaches to address these limitations.

3. Remediation of Organic Pollutants by Biochar

Biochar, derived from anoxic pyrolysis of biomass, holds substantial promise for soil pollutant remediation and amelioration of infertile soils [60,61]. In recent years, biochar produced from various biomass sources and at different pyrolysis temperatures has been widely applied for the remediation of soils contaminated with PAHs, antibiotics, pesticides, and other pollutants [62,63,64].

3.1. Remediation Mechanism of Biochar

3.1.1. Direct Adsorption

Biochar adsorbs organic pollutants via a range of mechanisms, primarily including pore filling, electrostatic interactions, hydrogen bonding, and π–π stacking interactions [65] (Figure 4). The effectiveness of these mechanisms and the adsorption efficiency are primarily influenced by the fundamental properties of biochar, the molecular size and hydrophobicity of the contaminants, as well as the properties of the soil [66,67]. The properties of biochar are the most significant determinants of organic pollutant adsorption, and these properties are influenced by the biomass source and pyrolysis temperature [68]. Biochar’s rich microporous structure makes pore filling a particularly significant mechanism for pollutant adsorption [69]. The larger specific surface area of biochar derived from rice straw and wheat straw, compared to that obtained from pig manure, enhances the capacity to adsorb pollutants [70]. Secondly, electrostatic interactions are critical in the adsorption of ionic organic pollutants. Negatively charged biochar can attract cationic organic pollutants through electrostatic forces [71]. Biochar produced via low-temperature pyrolysis contains more oxygen-containing functional groups, which can enhance pollutant adsorption by facilitating electron donation and acceptance [72]. Additionally, aromatic organic pollutants can be removed through π–π bonding interactions, since the surface of biochar is rich in aromatic compounds, and the π-electron cloud of these compounds interacts with the aromatic ring structures of pollutant molecules, forming π–π hydrophobic interactions [73]. Hydrogen bonding is another important mechanism of biochar adsorption. It primarily relies on the interaction between the surface polar functional groups of biochar (e.g., hydroxyl, carboxyl) and the polar groups in pollutant molecules, which is particularly effective for the adsorption of polar organic pollutants [74]. Different soil types can also affect the efficiency of biochar in removing pollutants. It was observed that in soils with a pH greater than 8, the biochar application significantly increased soil pesticide residues by 98.6%. Conversely, under neutral (pH 6–8) and acidic conditions (pH < 6), the effect was not significant, although the effect size tended to increase with rising pH. This suggests that applying biochar in alkaline soil conditions potentially increases pesticide persistence. Additionally, a significant increase in soil pesticide residue concentration was noted in soils with low soil organic carbon (<2%), where residues increased by 66% [75].

3.1.2. Enhancing Microbial Metabolic Activity

The application of biochar improves soil properties and enhances microbial activity. Soil microorganisms possess the ability of pollutants degradation, while they usually suffer from deteriorated soil conditions and pollutant toxicity [76,77,78,79]. When biochar is added to soil, the rough surface and porous structure of biochar supply a secure niche for microorganisms, reducing their exposure to toxic conditions, extending their lifespan, and strengthening the microbial community structure, and finally promoting the degradation of organic pollutants [80]. Biochar increases both porosity and bulk density, thereby providing more space for microbial movement [81]. In acidic soils, biochar can mitigate soil acidification, maintaining a pH level that is conducive to microbial activity. And microorganisms can obtain an unstable carbon source from biochar, along with essential nutrients, including nitrogen, phosphorus, potassium, and trace elements [82,83]. As a result, biochar significantly enhances the microbial degradation of organic pollutants in the soil of an extreme environment.

3.2. Current Status of Biochar Applications

Biochar has been extensively used to remediate various organic pollutants in soil due to its eco-friendliness, low cost, and high efficiency. Table 2 summarizes the effectiveness of biochar-based materials derived from various biomass sources and pyrolysis conditions in removing organic pollutants from soil, along with the associated mechanisms. For example, among the biochars derived from peanut shells, chestnut shells, bamboo, rice husks, and corn stover, rice husk-derived biochar exhibited the highest adsorption capacity for oxyfluoroethers, primarily relying on pore filling, hydrophobic interactions, and π–π bonding [84]. Another study indicated that wheat straw biochar produced at 500 °C under pyrolysis conditions (300 °C, 500 °C, and 700 °C) achieved the highest removal efficiency of 96% for tetracycline after ball milling [85]. This was attributed to the increased surface area and mesopore volume of the biochar after ball milling. In addition, at the pyrolysis temperature of 500 °C, more hydrophilic and oxygen-containing functional groups, such as carbonyl groups, were induced on the biochar surface. These changes collectively facilitated tetracycline removal through hydrogen bonding and surface complexation. Gao et al. found that, in addition to atrazine adsorption via pore filling, π–π electron interactions, surface complexation, and hydrogen bonding, ion exchange also contributed as a mode of action. These mechanisms collectively resulted in a 78.4% removal efficiency for atrazine in soil [86]. Results from a long-term field experiment demonstrated that biochar effectively adsorbed bisphenol A in soil due to its porous structure. In addition, the biochar application increased the soil’s total carbon from 14.54% to 27.04% and available potassium from 4.67% to 27.46%, and significantly enhanced the abundance of nitrogen fixation genes nifH and Hao in soil [87].
Moreover, the microbial degradation of pollutants is indirectly promoted by biochar. In soils contaminated with chlorpyrifos and atrazine, biochar promoted the growth of pollutant-degrading bacteria and enhanced the expression of functional genes associated with relevant metabolic pathways. This effect was attributed to biochar’s ability to reduce the bioavailability of chlorpyrifos and atrazine, thereby limiting their accessibility to microorganisms. At the same time, biochar supports microbial growth and upregulates the expression of metabolic genes. Interestingly, Zhang et al. found that biochar played different roles in soils contaminated with varied concentrations of PAH. In soils with low PAH contamination, biochar removed the pollutant primarily through adsorption and immobilization, reducing PAH bioavailability and inhibiting microbial mineralization. However, in soils with high PAH contamination, biochar promoted the mineralization of PAH by enriching specific PAH-degrading bacteria and enhancing the expression of relevant PAH degradation genes [88]. A six-year long-term field study on the remediation of PAH-contaminated soils using biochar demonstrated that the biochar application enhanced microbial degradation, resulting in total PAH concentrations in the amended plots (15.80–39.40 ng·g−1) that were two orders of magnitude lower than the preventive threshold limits set by the Brazilian legislation (8100 ng·g−1) and certain European soil regulations (3000 ng·g−1) [89].
Table 2. Application of biochar in the remediation of organic-contaminated soil and removal mechanisms.
Table 2. Application of biochar in the remediation of organic-contaminated soil and removal mechanisms.
FeedstockPyrolysis ConditionOrganic PollutantsRemoval EfficiencyMain Removal MechanismsReference
Wheat straw500 °CTetracycline96%π–π interactions, hydrophobic interaction, and hydrogen bonding[85]
Wheat straw700 °CPAHs40%Adsorption, redox, aggregation[64]
Corn straw600 °CSulfamethoxazole67.5%•OH- and O2−-mediated oxidation[63]
Reed straw800 °CHerbicide46%Pore filling, hydrogen bonding, π–π conjunction, electrostatic attractions, and other chemical interactions[90]
Wood450 °CPesticide thiamethoxam22.8%Pore filling and complexation, and oxygen-containing[62]
Beech wood900 °CPAH100%π–π electron donor–acceptor interactions[91]
Rice hull500 °COxyfluorfen Pore-filling mechanism, hydrophobic and π–π interactions[84]
Algal800 °CAtrazine78.4%Hydrogen bonding formation and π–π interactions[86]
Waste timber800–900 °CPFAS23–100%Hydrophobic interactions[92]
Bamboo820 °CPCBs78.9%Enhanced microbial degradation in the soil and biochar-induced redox or adsorption[93]
Corn straw300 °CPAHs31%Promoting the growth of Sphingobacteria and Agaricomycetes to degrade pollutants[94]
Wheat straws 300 °C, 500 °CPhenanthrene44.7%The selective stimulation of specific degrading genera and PAH-degradative nidA gene[88]
Rice straw550 °CDi-(2-ethylhexyl) phthalate68.6%π–π electron donor–acceptor interactions, chemisorption, and coordination[95]
Salix viminalis800 °CPAHs70%Pore adsorption[96]
Peanut shell450 °CAtrazine71.4%Hydrophobic partition, π–π electron donor–acceptor interactions, H-bonding, and pore-filling mechanism[97]
Burcucumber 700 °CSulfamethazine69%Cation exchange process of dominant cationic forms as well as the sorption of zwitterionic forms.[98]
Maize straw500 °CAtrazine47.8%Stimulating atrazine-degrading microbial communities in soil[99]
Pine750 °CPFOS88.7%Electrostatic interactions and hydrophobic interactions[100]
Mentha arvensis Chlorpyrifos atrazine76% 77%Promoting bacterial degradation of pollutants and upregulation of related functional genes[101]

3.3. Limitations of Biochar Remediation

Although biochar has been widely applied in the remediation of organic contaminated soils, it also has certain drawbacks with potential environmental risks. The adsorption and immobilization are important processes in pollutant remediation by biochar. However, biochar possesses limited remediation capacity, beyond which its effectiveness cannot be maintained for sustained remediation [102]. Biochar undergoes a gradual aging process as it remains in the soil over time. As a result, the surface morphology of biochar becomes rougher and more fragmented, leading to pore clogging and a reduction in specific surface area [103]. The redox processes in the soil can increase the hydrophilicity of the biochar surface, which reduces its hydrophobic adsorption of contaminants [104]. Additionally, cytosolic enzymes released during microbial oxidative respiration can alter the aromatic structure of biochar, which will affect π–bond interactions [105]. The physical, chemical, and biological mechanisms involved in the aging process of biochar collectively contribute to the release of adsorbed pollutants back into the soil, hindering the complete removal of contaminants [103,104,105]. In addition, the large-scale application of biochar in soil may excessively alter soil pH, thereby inhibiting the activity of certain microbial communities. Due to its strong adsorption capacity, biochar may also reduce the effectiveness of pesticides or fertilizers [104]. Consequently, the biochar application alone may not achieve complete pollutant remediation. To mitigate the potential risks associated with biochar, recent studies have highlighted the integration of biochar with phytoremediation as a key focus of current research for the treatment of organic pollutant-contaminated soils.

4. Biochar Combined with Phytoremediation

Compared to the use of individual plants or biochar alone for remediation, the combination of biochar with phytoremediation enhances the overall effectiveness of organic pollutant removal. Biochar improves plant resilience, promotes the contaminants uptake by plants, and improves the degradation capacity of rhizosphere microorganisms [106,107]. Furthermore, root exudates and microbial activity facilitate the complete degradation of pollutants adsorbed by biochar [108,109]. This integrated approach enables more efficient and thorough remediation of organic contamination in soils (Figure 5).

4.1. Improving Plant Resilience

Normal physiological functions of plants guarantee the soil phytoremediation of organic contaminates. However, plant growth and development are often inhibited in heavily contaminated soils. And these soils impose various abiotic stresses on plants, including nutrient deficiencies, drought, salinity stress, and other environmental factors. These stresses further limit the effectiveness of phytoremediation [110,111]. The challenges posed by nutrient-poor environments can be mitigated by biochar through the direct supply of essential nutrients [112,113,114]. Nutrients in biochar exist in different forms, and each form is utilized through distinct mechanisms. Soluble nutrients are quickly absorbed by plants to satisfy their short-term nutritional requirements. In contrast, stabilized mineral nutrients persist in the soil as nutrient pools, which can be gradually decomposed and utilized, thereby providing a long-term source of fertilizer for plant growth [115]. Under drought conditions, biochar promotes root growth and alters root morphology by creating a favorable physico-spatial environment that enhances the root system’s water uptake capacity [116]. The addition of biochar effectively improved the water and osmotic potentials of tomato plant roots under drought stress [117]. Additionally, biochar enhances plant cell structure, enzyme activity, and the expression of key stress-responsive genes, enabling plants to better cope with salt stress [118]. Recent studies have shown that the addition of 5% biochar under salt stress alleviates the adverse effects of salinity by upregulating the expression of genes involved in antioxidant defense, osmoregulation, and ion transport, thereby enhancing wheat germination and seedling vigor [119]. Biochar helps to mitigate the impact of various stresses on the normal physiological processes of plants, thus boosting the efficiency of phytoremediation of organic pollutants in soil.

4.2. Enhancing Plant Absorption of Pollutants

Biochar directly enhances the plant uptake of organic pollutants by affecting the pollutants’ utilization in the root system and their availability in the soil [100,120]. For example, a study by Zhang et al. found that adding biochar improved the physiological functions of Lupinus grass and promoted the uptake of PFAS in the soil, with a removal rate of 9.11 ± 0.85% [106]. In their recent research, they observed that biochar also promoted the uptake of specific PFAS compounds, such as PFOA, PFHpA, PFHxA, and PFOS, in a grass–legume mixture. This can be attributed to the high water solubility and mobility of these compounds, as well as the hydrophobic properties of biochar [121].

4.3. Enhancement of Rhizosphere Microbial Degradation Capacity

In addition, biochar selectively promotes the growth of beneficial plant-associated microorganisms, thereby strengthening the symbiotic relationship between plants and microorganisms. Furthermore, the activity of enzymes involved in organic matter decomposition can be influenced as well as the microbial metabolism in the rhizosphere [122,123]. These direct and indirect mechanisms enable biochar to enhance the microbial degradation of organic pollutants in the soil. For instance, studies have demonstrated that the synergistic effect of biochar and the inter-root secretion of oxalic acid significantly increased microbial populations, enzyme activities, and the abundance of genera and genes involved in the degradation of PAHs. This presents an effective strategy for remediating soils contaminated with high concentrations of PAHs [107]. Moreover, another study has shown that adding biochar to soils contaminated with petroleum hydrocarbons contributed to the more stable bacterial communities in the ryegrass rhizosphere. This treatment also increased the activities of catalase and dehydrogenase, which have been used as indicators of hydrocarbon degradation in the course of bioremediation [124].

4.4. Promoting Complete Degradation of Contaminants

Direct adsorption is generally the primary method for biochar to remove pollutants from soil, although it cannot completely degrade contaminants. Root exudates can enhance the bioavailability of organic pollutants adsorbed onto biochar, facilitating their further degradation. Additionally, biosurfactants, with both hydrophilic and hydrophobic fractions, can be produced by rhizospheric microorganisms. These biosurfactants help disperse hydrophobic organic pollutants into smaller droplets, thereby promoting the microbial degradation [125]. Meanwhile, the desorption and degradation of organic pollutants from biochar can generate new adsorption sites, which in return promote the further adsorption of more pollutants by biochar. It has been demonstrated that in soil contaminated with HCB, oxalic acid secretion in the ryegrass root system promotes the desorption of HCB from biochar and biochar-amended soil. This process enhances the bioavailability of HCB and enriches the soil with potential HCB-degrading bacteria, such as Pseudomonas spp., which further completely degrade HCB in the soil [108]. Another study has shown that the active components of organic acids in root secretions facilitate the desorption of atrazine from biochar through specific interactions, thus enhancing its bioavailability and subsequent degradation [109].

4.5. Application of Biochar Combined with Phytoremediation Technology for Organic Contaminants

Soil contamination by PAHs represents a significant environmental concern which has been widely studied due to their teratogenic, carcinogenic, and mutagenic properties. In addition, emerging contaminants such as antibiotics and chlorinated organic compounds pose serious threats to both environmental and human health, and have attracted increasing attention in recent research (Table 3).
Table 3. Application of biochar combined with phytotechnology organic-contaminated soil and removal mechanisms.
Table 3. Application of biochar combined with phytotechnology organic-contaminated soil and removal mechanisms.
BC TypePlant SpeciesOrganic PollutantsRemoval EfficiencyMechanism of SynergismReference
Maize straw biocharRyegrassPAHsAbout 55%Biochar and root exudates enhanced microbial biomass and activity to promote PAHs dissipation.[121]
Wheat straw biocharLolium multiflorum L.PAHs62.5%Direct adsorption of biochar and its synergistic stimulation of microbial activity involved in the degradation of PAHs.[126]
Woody biomass biocharBuchloe dactyloidesPAHs27.1%The combination of plants and biochar increased soil enzyme activity, altered the structure and function of soil microorganisms, and promoted the expression of functional genes.[127]
Maize straw biocharRyegrassPAHs15.9%The enhanced symbiosis among bacterial members is beneficial for the resistance of the soil microbiome to PAH stress.[128]
Rice husk biochar AlfalfaPAHs65.3%Rice husk biochar and alfalfa enhanced the growth of Steroidobacter, Bacillus, and Sphingomonas in rhizosphere soils to remove PAH.[129]
Oak leaves biocharTrifolium arvenseTotal petroleum hydrocarbons56.4%The positive interactions in the rhizosphere between the microorganisms and root were responsible for the decomposition and/or removal of the TPH.[130]
Woodchip biocharWhite cloverTotal petroleum hydrocarbons68%Direct uptake of biochar and its effect on promoting the degradation of TPHs by inter-root and endophytic bacteria.[131]
Wheat stalks BiocharRyegrassAntibiotics The enzymes secreted by the roots of ryegrass and the decomposition of surrounding microorganisms and the strong direct adsorption capacity of biochar to antibiotics.[132]
Forest wood waste biocharTimothy-grassPFAS9.1%Biochar promotes the direct uptake of PFAs by forage grasses.[117]
Wood biocharGrassPFAS10%The biochar stabilizes the soil, and the shoots directly take up nutrients.[118]

4.5.1. Polycyclic Aromatic Hydrocarbons (PAHs)

The serious contamination of soil by PAHs was released in the course of industrial activities [133,134]. Biochar combined with ryegrass have been widely applied in the remediation of PAH-contaminated soils. Guo et al. [126] demonstrated that the inter-root exudates of ryegrass, in conjunction with biochar, facilitated PAH remediation by enhancing the biomass and activity of inter-root microorganisms, such as Sphingomonas, Bacteriap25, Haliangium, and Dongia. This combination also increased urease and dehydrogenase activities, as well as the abundance of the PAH-RHDα gene, thereby promoting rhizoremediation of PAH-contaminated soils. As a result, the combination of remediation techniques led to an 18.7% and 26.6% increase in the removal rate of PAHs in the soil, compared to treatments using either ryegrass or biochar alone (Figure 6a). Further analysis of soil enzymes, microbiome, and metabolome revealed that the combination of biochar and ryegrass significantly increased soil dehydrogenase and urease activities, which are commonly used to characterize metabolic activities. It also indicates the recovery of bacterial communities as well as improves bacterial xenobiotic degradation and metabolic functions. These changes contributed to the mitigation of PAH stress [128].
In contrast to enhancing the abundance and diversity of all rhizosphere microorganisms, biochar can selectively promote the activity of specific microbial populations for the removal of PAHs. Shang et al. [129] examined the role of rice husk biochar in alfalfa inter-root soils co-contaminated with heavy metals (Zn, Cr) and PAHs. The combination of biochar and alfalfa selectively promoted the growth of Sterrobacter spp., Bacillus spp., and Sphingomonas spp., while reducing the abundance and diversity of other bacterial populations in the soil. Although the application of combined remediation techniques negatively affected the majority of soil microorganisms, the treatment resulted in the highest PAH removal rate of 65.26%, compared to the other approaches, indicating that these three bacteria played a dominant role in the remediation process (Figure 6b). Zhang et al. in their study on the remediation of phenanthrene-copper contaminated soils, also found that biochar selectively facilitated the colonization of specific microorganisms such as PAH-degrading bacteria Bacillus on its surface and within its pores. This self-selection process was shown to promote the degradation of phenanthrene, further supporting the role of biochar in enhancing the breakdown of organic pollutants [135].

4.5.2. Antibiotics

The widespread application of antibiotics in clinical practices and animal husbandry in recent years has contributed to the environmental accumulation of these substances [136,137]. Liang et al. [132] demonstrated that the removal of tetracycline from soil treated with a combination of biochar and ryegrass in animal manure treatment was highly effective. In contrast, the residues of sulfamethazine showed no significant reduction. Although biochar can provide a favorable environment to both ryegrass and soil microorganisms, tetracycline antibiotics are relatively unstable in terms of their chemical and molecular structure, making them more susceptible to decomposition by enzymes secreted by the ryegrass rhizosphere and surrounding microorganisms (Figure 6c). In contrast to conventional plant-biochar remediation technology, Sun et al. examined how low-molecular-weight organic acids, commonly found in root exudates, affect the adsorption of sulfamethoxazole by biochar in a plant-free system. The findings indicate that small-molecule organic acids enhance biochar porosity by removing soluble organic residues via a washing effect, leading to a greater than five-fold enhancement in sulfamethoxazole adsorption efficiency [138].

4.5.3. Chlorinated Organics

Common chlorinated organic pollutants include PCBs, organochlorine pesticides, chlorobenzenes, and others [139]. Research has demonstrated that biochar, when used in conjunction with plants like alfalfa, beans, and ryegrass, can effectively remediate organic chlorine-contaminated soils. For instance, the addition of biochar increased the biomass of alfalfa, and the root exudates from alfalfa promoted the growth of Bacteroidetes, which produced a variety of glycosyl transferases and degrading enzymes to break down iprodione [140] (Figure 6d). Another study on the combination of biochar and beans for chlorpyrifos remediation indicates that biochar mitigates chlorpyrifos toxicity by adsorbing it, whereas healthy bean plants with extensive root systems can absorb and degrade the pesticide [141]. Furthermore, a study using green garden waste biochar in combination with ryegrass to remediate PCB-contaminated soil showed that biochar not only promoted ryegrass growth under pollutant stress, but also increased the abundance of degrading bacteria in the rhizosphere, resulting in a PCB removal rate of up to 85% [142].
Agriculture 15 00905 g006
Figure 6. (a) Straw biochar combined with ryegrass enhances the microbial community for PAH degradation [126]. (b) The combination of rice husk biochar and alfalfa selects specific bacteria for PAH removal. Different letters represent significant differences at the p < 0.05 level among different treatments. The same below (CK: co-contaminated soil without rice husk, biochar or alfalfa; H: soil added with 2% rice husk) [129]. (c) Straw biochar combined with ryegrass decomposes antibiotics either directly or indirectly (ARGs represents antibiotics and resistance genes, and EMF represents ecosystem multifunctionality) [132]. (d) Biochar and alfalfa synergistically promote the degradation of iprodione by Bacteroidetes (CK, the control; AP, alfalfa planting) [140].
Figure 6. (a) Straw biochar combined with ryegrass enhances the microbial community for PAH degradation [126]. (b) The combination of rice husk biochar and alfalfa selects specific bacteria for PAH removal. Different letters represent significant differences at the p < 0.05 level among different treatments. The same below (CK: co-contaminated soil without rice husk, biochar or alfalfa; H: soil added with 2% rice husk) [129]. (c) Straw biochar combined with ryegrass decomposes antibiotics either directly or indirectly (ARGs represents antibiotics and resistance genes, and EMF represents ecosystem multifunctionality) [132]. (d) Biochar and alfalfa synergistically promote the degradation of iprodione by Bacteroidetes (CK, the control; AP, alfalfa planting) [140].
Agriculture 15 00905 g006

5. Future Perspectives

Integrating biochar and phytoremediation offers a promising new approach for remediating organic contaminated soils. Biochar combined with phytoremediation address the limitations of each method when used independently, providing the potential for long-term, sustainable, and environmentally friendly remediation. However, several challenges remain in current research, and the following aspects should be considered to ensure the sustainable development of biochar-based phytoremediation (Figure 7).
(1) Firstly, emerging pollutants, such as microplastics, pesticides, and endocrine-disrupting compounds, have become significant contaminants in soils. Co-contamination with heavy metals is also frequently observed in soils contaminated by organic pollutants. Comprehensive studies on emerging pollutants and co-contamination in combined remediation technologies are limited. It is crucial to assess the applicability of biochar combined with plants for the remediation of these diverse pollution issues. Further research should focus on understanding the removal mechanisms of specific pollutants and evaluating the effectiveness of co-remediation technologies in addressing these complex contamination problems.
(2) Secondly, most existing studies have primarily focused on laboratory-scale experiments conducted over relatively short periods to assess the remediation effects. Additionally, some feedstocks used in biochar production, particularly sewage sludge, may contain toxic elements such as heavy metals [143]. During pyrolysis, biochar can also generate hazardous substances, including PAHs [144], polycyclic diphenyl dioxins (PDDs) [145], and persistent free radicals [146]. These toxic compounds have the potential to be released into the soil over time. Therefore, before this remediation technology has been widely applied, extended field studies are necessary to evaluate its effectiveness, analyze the biogeochemical processes, and assess the long-term stability and ecological benefits of biochar.
(3) Subsequently, polluted soils often present unfavorable conditions for microbial survival, which can negatively impact the biomass and activity of rhizosphere microorganisms, thereby reducing the phytoremediation capacity. Given the complexity and variability of soil environments, loading specific microorganisms onto biochar can enhance the microbial degradation capacity of combined remediation technologies. Additionally, analyzing the differences in the practical application of various combined remediation strategies is essential.
(4) Finally, different pyrolysis temperatures and biomass sources of biochar are key factors influencing the physicochemical properties of biochar, such as surface functional groups, porosity, and specific surface area. These biochar properties influence both the effectiveness and mechanisms of pollutant remediation. In terms of economic analysis, the cost of biochar production varies depending on the pyrolysis temperature and the type of biomass used. For instance, higher pyrolysis temperatures may increase energy consumption, thus raising production costs. Meanwhile, the choice of biomass source also affects the overall cost; agricultural residues may be more cost-effective compared to some industrial byproducts [147,148]. Additionally, the cost of biochar application in phytoremediation should consider factors such as transportation, storage, and the specific methods of biochar incorporation into the soil. It is also worth noting that while the initial investment for biochar technology might be relatively high, the long-term environmental benefits and potential for improved soil quality and crop yield can lead to significant economic returns [149,150]. Therefore, it is necessary to analyze multiple sample datasets and comprehensively consider factors such as cost, efficiency, and environmental benefits to determine the optimal solution.

6. Conclusions

This review summarizes the current status and limitations of phytoremediation and biochar-based remediation, as well as the mechanisms of interaction between biochar and phytotechnology in the remediation of organic contaminated soils. Phytoremediation involves the plant uptake, the secretion of degrading enzymes, and the promotion of beneficial root-associated microorganisms by plants, with the efficacy of this process often limited by suboptimal soil conditions. Biochar remediates pollutants primarily through adsorption such as pore filling, electrostatic interactions, hydrogen bonding, and van der Waals forces and improving microbial degradation, but its effectiveness is hindered by the desorption of pollutants over time. The combination of biochar with plants enhances remediation while mitigating individual technique limitations, with a focus on how biochar enhances plant nutrient availability, reduces abiotic stress, and promotes the degradation of contaminants by rhizosphere microorganisms. In turn, plants facilitate the desorption and complete degradation of pollutants adsorbed by biochar through root exudates and associated microbial activity. Finally, the practical applications of combining biochar with phytoremediation in soils contaminated with PAHs, antibiotics, and chlorinated organics are discussed. This integrated approach offers promising potential for the sustainable and effective remediation of contaminated soils.

Author Contributions

Conceptualization, writing—original draft, writing—reviewing and editing, H.F., C.Z. and G.L.; supervision, validation, writing—original draft, writing—reviewing and editing, C.Z.; writing—reviewing and editing, D.-X.G. and M.A.; supervision, writing—reviewing and editing, funding acquisition, G.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Key Project of Science and Technology Innovation in Ningbo City (2022Z169, 2023Z114) and the Ningbo S&T project (2021-DST-004).

Data Availability Statement

Data will be made available on request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) Publications and citations using the topic “soil” and “organic pollutants” from 2014 to 2023, based on the Web of Science database. (b) Scientometric visualization of the first 76 keywords based on 5395 publications published from 2014 to 2023. Keyword co-occurrence analysis was performed using VOS viewer (https://app.vosviewer.com/, accessed on 16 April 2025), where each circle represents a keyword and the size of the circle represents the frequency of keyword occurrence.
Figure 1. (a) Publications and citations using the topic “soil” and “organic pollutants” from 2014 to 2023, based on the Web of Science database. (b) Scientometric visualization of the first 76 keywords based on 5395 publications published from 2014 to 2023. Keyword co-occurrence analysis was performed using VOS viewer (https://app.vosviewer.com/, accessed on 16 April 2025), where each circle represents a keyword and the size of the circle represents the frequency of keyword occurrence.
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Figure 2. Phytoremediation mechanisms of organic pollutants in soil, including direct and indirect effects (ops refers to organic pollutants).
Figure 2. Phytoremediation mechanisms of organic pollutants in soil, including direct and indirect effects (ops refers to organic pollutants).
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Figure 3. (a) Adsorption of PFAS by weeds [40]. (b) Degradation mechanisms of PAHs by Fire Phoenix plants and their associated endophytes [50]. (c) Under copper stress, Elsholtzia sp. promotes the removal of phenanthrene and PCB 28 (ck is the plant-free treatment group) [47]. (d) Mechanisms of maize-mediated inter-root ROS-driven abiotic transformation of PAH [51].
Figure 3. (a) Adsorption of PFAS by weeds [40]. (b) Degradation mechanisms of PAHs by Fire Phoenix plants and their associated endophytes [50]. (c) Under copper stress, Elsholtzia sp. promotes the removal of phenanthrene and PCB 28 (ck is the plant-free treatment group) [47]. (d) Mechanisms of maize-mediated inter-root ROS-driven abiotic transformation of PAH [51].
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Figure 4. Mechanisms of biochar remediation of organic matter pollutants in soil. (a) Direct uptake of pollutants. (b) Promotion of microbial degradation of pollutants.
Figure 4. Mechanisms of biochar remediation of organic matter pollutants in soil. (a) Direct uptake of pollutants. (b) Promotion of microbial degradation of pollutants.
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Figure 5. Mechanisms of biochar combined with phytoremediation interactions.
Figure 5. Mechanisms of biochar combined with phytoremediation interactions.
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Figure 7. Future perspectives of biochar integrated with phytotechnology for soil remediation.
Figure 7. Future perspectives of biochar integrated with phytotechnology for soil remediation.
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Table 1. Application of plants in the remediation of organic contaminated soil.
Table 1. Application of plants in the remediation of organic contaminated soil.
PlantsOrganic PollutantsRemoval EfficiencyMain Removal MechanismsReference
WeedsPFAS41.4%Weeds transported PFAS to roots and buds by direct absorption.[40]
Lolium perenne L.PAHs55.7%Plants promoted the degradation of high-cyclic PAHs by Pseudomonas and Bacillus species.[42]
Lolium perenne L.Pyrene59.4%Ryegrass increased the abundance of PAHs-degrading genera Gemmatimonas, Ohtaekwangia, Luteimonas, Lacibacterium, and Steroidobacter to remove pyrene.[43]
CloverPCBs60.0%Root exudates improved the bioavailability of pollutants and promoted the degradation of PCBs by Rhizobiales, Burkholderiales, and Xanthomonadales.[44]
AlfalfaTPHs74.1%Low molecular weight organic acids enhanced soil desorption of oil and improved the potential for microbial degradation by root-associated microbes.[41]
Ludwigia octovalvisGasoline79.8%Plants provided suitable conditions for rhizosphere bacteria to degrade hydrocarbons.[45]
Nicotiana tabacum L.Bisphenol A80%Nicotiana tabacum L. promoted the degradation of Bisphenol A by promoting the activities of Proteobacteria, Acidobacteria, and soil enzymes in the rhizosphere bacterial community.[46]
Elsholtzia splendensPhenanthrene biphenyl 2884.9%, 65.9%Elsholtzia splendens shifted the soil microbial community, harbored unique degraders’ community, and enriched degradation genes.[47]
Transgenic Arabidopsis thalianaPCBs85.9%Plants took up PCBs from the soil and their aerobic conversion to chlorobenzoic and chlorinated fatty acids.[48]
Bok choyDibutyl phthalate (DBP)91%Bok choy promoted the dissipation of DBP by regulating the DOM in rhizosphere soil and the enrichment of rhizosphere secretions.[49]
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Fang, H.; Zhou, C.; Guan, D.-X.; Azeem, M.; Li, G. Synergistic Approaches for Sustainable Remediation of Organic Contaminated Soils: Integrating Biochar and Phytoremediation. Agriculture 2025, 15, 905. https://doi.org/10.3390/agriculture15080905

AMA Style

Fang H, Zhou C, Guan D-X, Azeem M, Li G. Synergistic Approaches for Sustainable Remediation of Organic Contaminated Soils: Integrating Biochar and Phytoremediation. Agriculture. 2025; 15(8):905. https://doi.org/10.3390/agriculture15080905

Chicago/Turabian Style

Fang, Hao, Cailing Zhou, Dong-Xing Guan, Muhammad Azeem, and Gang Li. 2025. "Synergistic Approaches for Sustainable Remediation of Organic Contaminated Soils: Integrating Biochar and Phytoremediation" Agriculture 15, no. 8: 905. https://doi.org/10.3390/agriculture15080905

APA Style

Fang, H., Zhou, C., Guan, D.-X., Azeem, M., & Li, G. (2025). Synergistic Approaches for Sustainable Remediation of Organic Contaminated Soils: Integrating Biochar and Phytoremediation. Agriculture, 15(8), 905. https://doi.org/10.3390/agriculture15080905

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