As a fossil fuel, coal is a predominant element in nature. It is mainly composed of carbon with variable amounts of other elements, including hydrogen, oxygen, nitrogen, and sulfur. China is the largest producer of coal. Open-cast mining generates toxic overburden dumps (OB) and coal dust that contain enormous amounts of toxic HMs and are responsible for metal contamination in adjacent agricultural land (Li et al., 2007). In descending order, metals Fe > Mn > Zn > Cu are present in coal mines: the most bioavailable and mobile element is Mn, followed by Zn and Cu, and the least mobile metal is Fe. The reason behind Fe’s lesser mobility is the residual fraction of Fe, which indicates its strong affinity toward minerals, the solid matrix, and strongly bounded clay minerals (Kartal et al., 2006). A pseudo-total concentration of HMs, including Zn (314 mg kg⁻¹), Mn (132 mg kg⁻¹), Pb (82 mg kg⁻¹), Cu (45 mg kg⁻¹), and Co (34 mg kg⁻¹), has been found in reclaimed mine soil (RMS). The bioavailable forms (DTPA-extractable) of Zn, Mn, and Cu are significantly higher in RMS than in control soil. Pb can selectively accumulate in leaves, stem bark, and root bark, whereas Zn and Mn accumulate in leaves, and Cu accumulates in stem wood and root wood. These indicate that the accumulation of metals might be tissue specific (Maiti et al., 2016). The most effective remediation pathway for OB dumps is trees, which can accumulate toxic HMs from OB. Trees that are used for the reclamation of OB dumps should be drought resistant, woody, fast-growing, and able to grow in arid areas and nutrient-deficient areas (Pratas et al., 2005). Various woody plant species, such as A. auriculiformis, M. azedarach, Leucaena leucocephala (Lam.) de Wit, Tectona grandis L. f., Gmelina arborea Roxb., Acacia mangium Wild., Bambusa arundanacea L., Cassia siamea Lam, and Azadirachta indica A. Juss, etc., are used for reclamation of coal OB dumps (Maiti et al., 2016). The Pb concentration in A. auriculiformis, hybrid eucalyptus trees, is significantly higher in root bark than leaf tissue as bark tissue can accumulate lead for longer time while leaves are shed periodically (Sawidis et al., 2011). Through bark exudates, Pb can be removed from plants, which is an important defense mechanism against HM toxicity (Alloway, 2012). In the case of Cu (BCF >1; TFleaf, TFstembark, and TFstem wood <1), two tree species, A. auriculiformis and M. azedarach, might be used for Cu phytostabilization (Sawidis et al., 2011).

Cu mines are a prime source of potentially toxic HMs (Cu, Zn, As, Cd, and Pb) (Cai et al., 2015). South Africa, Chile, and Peru are the largest producers of copper. Due to the chemical weathering process, waste rocks from the Predra Verde mine (Brazil) show potential risks to the environment (Perlatti et al., 2021). In Jiuhuashan, Jiangsu Province, and in eastern China, agricultural soil near abandoned mines contained high levels of copper (816.8 mg kg⁻¹ and 147 mg kg⁻¹, respectively) contamination (Qin et al., 2012; Wu et al., 2011). Acidic drainage compounds (Cu, Zn, and Fe) have been produced from the La Concordia Mine (Argentina) (Nieva et al., 2018). According to China et al. (2014), of environmentally available metal, that is, total metal excluding the silicate matrix-bound metals, Cu (154 mg kg⁻¹) is one of the most abundant heavy metals found in the Mosabani copper mine (India), followed by Ni (136 mg kg⁻¹) and Pb (9.9 mg kg⁻¹). The underground tissues of this plant have an average concentration of 1959 mg kg⁻¹ Cu, which is much higher than shoot (124 mg kg⁻¹ Cu). Therefore, it indicates that HM mobility is limited inside the plant as the translocation factor for Cu (0.06), Ni (0.36), Co (0.68), and Zn (0.24) is less than 1, while Mn is present in higher concentration in the above-ground tissue (TF > 1; Mn 1.37) (Das and Maiti, 2007). The toxicity level of Cu and Ni in plants is 20–100 mg kg^-−1 and 10–100 mg kg⁻¹, respectively (Kabata-Pendias, 2011). The bioavailability of copper also depends on soil pH, soil cation exchange capacity (CEC), and total copper content in soil (Bravin et al., 2009; Brun et al., 2001). Copper also plays an essential role in plant growth and development processes such as protein synthesis, CO₂ assimilation, ATP synthesis, maintaining homeostasis within chloroplast, photosynthesis, etc. (Hänsch and Mendel, 2009; Yruela, 2013). A high concentration of copper has a toxic effect on seed germination, decreases plant height, causes chlorosis of plant leaves, and reduces plant biomass and grain yield (Adrees et al., 2015).

Ferrochromium is the only natural and economical resource of chromium produced in chromite mines by carbothermic smelting (Beukes et al., 2010). It is a crystalline alloy generally composed of chromium and iron compounds. Globally, South Africa has the most chromite ores, followed by Kazakhstan, India, Albania, and Turkey (ICDA, 2022). The active and abandoned mine wastes are reservoirs of heavy metals that have lethal effects on water, soil, and living beings (Fernández-Caliani et al., 2009). These mine wastes are generally composed of different types of toxic HMs, mainly chromium (Cr) and Nickel (Ni), along with other metals such as Cu, Cd, Pb, Ni, and Mn present in lesser quantities (Bueno et al., 2009). Chromium (Cr) is generally utilized in industrial activities such as the processing and finishing of leather, the production of refractory steel by the stainless steel industry, electroplating cleaning agents, drilling muds, the production of chromic acid and other chemicals, and food preservation (Shanker et al., 2005). Chromium exhibits different levels of toxicity depending on its chemical form, pH, reaction with other elements, and solubility index (Thatoi et al., 2014). Cr (VI) exhibits high toxicity and bioavailability due to its better solubility than Cr (III) (Abyaneh and Fazaelipoor, 2016). A lack of Cr (III) in human and animal diets can cause metabolic deterioration, cardiac problems, and diabetes, but an excess presence in the body has harmful health effects (WHO, 2000). Hexavalent chromium tends to act as a strong oxidizing agent; therefore, Cr (VI) is 10–100 times more toxic than Cr (III) (Zayed et al., 1998). The toxicity level of hexavalent chromium for plants in solution is as low as 0.5 mg kg⁻¹ and 5 mg kg⁻¹ for soil (Turner and Rust, 1971). Highly carcinogenic chromium and asbestos exposure may lead to cancer, mesothelioma, pneumoconiosis, skin irritations, and other respiratory problems such as irritation of the larynx and pharynx, edema, coughing, asthma, etc. (Bloise et al., 2008; Pugnaloni et al., 2013). Cr is mostly accumulated in plant roots rather than in the shoot due to its reduced mobility in root vacuoles. However, Ni accumulation is higher in the shoot than in the root due to greater mobility of Ni through xylem tissue (Pulford et al., 2001; Shanker et al., 2005). The Cr and Ni concentration in the Roro chromite mine waste soil is 3,120 mg kg⁻¹ and 1,620 mg kg^−1, respectively, which exceeds the safety level (Cr:75–100 mg kg⁻¹; Ni: 100 mg kg⁻¹) of metals present in soil (IS, 1993). In similar studies in the Almadén mine site in Spain and southern Togo mine sites, Cr and Ni concentrations are 86–35 Cr mg kg⁻¹ and 21.2–126 Ni mg kg⁻¹ and 182–1,029 Cr mg kg⁻¹ and 15–432 Ni mg kg⁻¹, respectively, due to deposition of mine tailings in agricultural soil (Gnandi and Tobschall, 2002; Bueno et al., 2009). In the Daduk mine area of Korea, due to the dispersion of metals from tailings and watercourses, various toxic metals are reported in nearby paddy fields (Lee et al., 2001). In another study in the Co Dinh mine of Vietnam, high levels of potentially toxic elements are also detected in rice fields (5,750 Cr mg kg⁻¹, 375 Co mg kg⁻¹, and 5,590 Ni mg kg⁻¹) (Kien et al., 2010). Based on the dynamic translocation factor (TF dyn>1), Cr and Ni accumulation is higher in plant parts of Oryza sativa growing in contaminated agricultural fields that might have a potential risk of transfer of toxic HMs to livestock or humans (Kien et al., 2010; Kumar and Maiti, 2014).

Globally, the production of crude steel has expanded drastically since 2000 to meet increasing demand. Iron ores are the backbone of the world economy (World Steel Association, 2021). Australia, Brazil, and China are the top three countries for the production of iron (around 69%) (Holmes et al., 2022). To maintain the growing demand, iron ore industries have continuously increased mining activity. As a result, huge concentrations of Cd, Mn, As, Ni, Pb, Zn, and Cr have been found in the agricultural soil near iron mines (Hosseini et al., 2018). Toxic tailing wastes from iron mining are dumped into a tailings pond located at the Noamundi–Jodda belt, India. As a result, during monsoon season, the toxic fine particles washed off by heavy wind and rain are deposited into nearby water bodies and soil, thereby causing air, water, and soil pollution. Although Fe is essential for the synthesis of chlorophyll, chloroplast structure and its functions, excessive concentrations of iron might enter into the food chain and show toxic effects on plant, animal, and human health (Maiti et al., 2005). According to Dhatrak et al. (2017), the health status of mine workers and a nearby population around an open-cast iron mine showed noise-induced hearing loss (NIHL) and anemia as major health effects. Iron mining plays an important role in economic development and simultaneously causes air pollution by blasting, drilling, unloading, and loading minerals and overburdens by wind at mineral handling plants, workshops, etc. These air pollutants affect the flora and fauna of the local environment (Tripathi et al., 2014; Chaturvedi and Patra, 2016). Some native plant species, such as Cassia sophera Eupatorium odoratum, Techtona grandis, Alstonia scholaris, Cassia tora, etc., can be found in Fe tailings. Techtona grandis can accumulate a higher concentration of HMs than Alstonia scholaris, but these HMs have not shown any detrimental effect on native plants. Rather, higher Fe content promotes lavish growth, as stated by Maiti et al. (2005).

Worldwide, Kazakhstan is the largest producer of uranium, followed by Australia, Namibia, Uzbekistan, and Canada. Jaduguda, India’s first, oldest, and most productive underground uranium (U) mine, consists of uraninite and other associated accessory minerals such as copper, nickel, arsenic, cobalt molybdenum, and magnetite, etc. (Sethy et al., 2014). Uranium occurs naturally in the earth’s crust with a mean concentration of approximately 3 mg kg⁻¹ (Gupta and Singh, 2003). Hexavalent U is the most soluble form and is present as the uranyl cation (UO₂)⁺² in 80%–90% of the soil. It prevails in solutions predominantly as a stable ion (UO₂)⁺² and as soluble carbonate complexes, that is, UO₂CO₃, UO₂(CO₃)₂ ⁻², UO₂(CO₃)₃ ^–4, (UO₂)₂CO₃(OH)⁻³ and (UO₂)₃(CO₃)₆ ^–6. In the absence of dissolved inorganic ligands (fluoride, carbonate, sulfate, and phosphate) and a pH range within 4–7.5, the hydrolysis ion UO₂OH⁺ in water and soil forms complexes with these inorganic ligands. As a result, these complexes increase the total solubility of U (Shahandeh and Hossner, 2002). Uranium is a radioactive element that undergoes a continuous decaying process, emits alpha (α), beta (β), and gamma (γ) rays, and produces various isotopes. This transformation stops when the stable product lead (²⁰⁶Pb) is formed (Sarangi, 2003). The radiation that is emitted from these naturally occurring isotopes is very low and does not penetrate due to its high density, which acts as a shield against its own radiation (Wang et al., 2009). According to WHO (2012), a mean concentration of U in ambient air has been reported to be approximately 0.02 ng m⁻³ in Tokyo, Japan, and 0.076 ng m⁻³ in New York City, United States of America. Uranium enters the kidney through water or food, and the uranyl ion forms bicarbonate and citrate complexes in blood plasma and affects the proximal tubules of the kidney, causing tubular degeneration, liver damage, genetic malfunction, cancer, and necrosis (Miller et al., 2004; Sethy et al., 2011). The Environmental Protection Agency (EPA) of the United States has categorized U as a carcinogenic element, and in drinking water, the maximum contaminant level (MCL) of U is 30 µg L⁻¹ (EPA, 1999). The proposed interim maximum acceptable level (IMAC) of U in Canada is 20 µg L^−1, whereas WHO strictly recommended the permissible level to be 2 µg L⁻¹ (Shin et al., 2002). In humans, the ingestion and intake dose is very low (2 µSv.Y⁻¹), which is far below the WHO permissible level (100 uSv.Y⁻¹). The mean metal pollution index (MPI) value indicates the overall pollution level in ground and surface water to be below the maximum threshold value of 100 (Mohan et al., 1996). Several experiments have been conducted for the accumulation of U in native plant species to determine the mechanism of U uptake absorption by plants and for biological exploration of U from soil (Petrova, 2006). Uranium accumulation varies depending upon plant species as well as genotypes, lines within species, and cultivars; moreover, U is accumulated higher in the root portion than in the shoot. Therefore, only a small portion is translocated to the shoot. Less than 1 mg kg⁻¹ of U is found to be toxic in the soil (Sheppard et al., 1992; Stojanović et al., 2010). According to (Pentyala and Eapen, 2020), Vetiveria zizanioides L. Nash showed good ability for phytoextraction (84%–95% of recovery) of U from hydroponic solution at a concentration below 200 ppm under controlled experimental conditions. U is generally restricted in the root portion of vetiver, but at concentrations above 1,000 ppm, it is translocated from the root to the shoot.

The term “phytoremediation” is derived from Greek (“phyton”) and Latin (“remedium”), which means “plant” and “to correct,” respectively (Cunningham et al., 1996). Phytoremediation is a bioremediation process in which plants (alone or in association with microbes) are used as purifying agents to remove, stabilize, or destroy the toxic metals from air, water, and soil in an eco-friendly manner (Wani et al., 2012). Supplementary Table S1 shows different mechanisms of phytoremediation, and Supplementary Figure S2 shows images of such mechanisms. Generally, plants can extract essential nutrients (Fe, Zn, Ni, Mn, and Cu) as well as non-essential metals (Cr, Cd, As, Pb, and Hg) that are not required in their physiological process and can store an enormous amount of the toxic metals (hyper-accumulator) in their parts from contaminated soil and water (Tangahu et al., 2011). Several studies have been done regarding different mechanisms of phytoremediation strategies, as shown in Supplementary Table S2. The advantages of phytoremediation are as follows: 1) inexpensive technology (60%–80% lesser than traditional process); 2) minimize soil deterioration; 3) solar-driven remediation process; 4) no generation of secondary hazardous compounds; 5) suitable and broad-spectrum treatment; 6) sustainable and environment-friendly technique. One limitation is that plants require time for their growth and development (Morikawa and Erkin, 2003). Techniques like phytoextraction and phytostabilization are commonly used for remediating HM-polluted sites. Several plant species have demonstrated the ability to absorb, bioaccumulate, immobilize, and degrade heavy metals (HMs) from contaminated sites. Some examples include C. citrates, H. petiolaris, V. zizanioides L, Pennisetum purpureum cv. Mott, Conocarpus lancifolius, and Cordyline fruticose, etc. (Andra et al., 2009; China et al., 2014; Herlina et al., 2020; Rasheed et al., 2020; Kowitwiwat and Sampanpanish, 2020; Saran et al., 2020). These species are key in cleaning contaminated soils either by extracting HMs into their tissues or stabilizing them in the soil. Vegetation helps limit pollutant transport, reduce wind dispersion, and prevent water erosion (Perronnet et al., 2000). Unlike conventional methods that disturb soil physical properties, phyto-strategies maintain and enhance soil quality. Successful phytoremediation implementation requires considerations of biomass production, heavy metal concentration in plant material, and the time needed for soil remediation (Robinson et al., 1998). Phytodegradation involves the uptake of toxic compounds by plants, where plant enzymes break down these substances into less harmful forms (Sun et al., 2012; Hamdi et al., 2012). Plant species like Arabidopsis thaliana and Azolla filiculoides are used for phytodegradation of pollutants such as 2,4-DNT and bisphenol A in the United States and Iran (Yoon et al., 2008; Zazouli et al., 2014). Phytovolatilization occurs when plants transform the contaminant into volatile compounds and emit them into the atmosphere through transpiration or radial diffusion from their leaves, stems, and roots (Limmer and Burken, 2016; Peter et al., 2017). Rhizodegradation is the breakdown of contaminants facilitated by rhizospheric microorganisms, where root-released enzymes and exudates help decompose pollutants into non-toxic forms (Jia et al., 2016; Gkorezis et al., 2016). Plants like Pteris vittata (Sakakibara et al., 2010) and Salicornia bigelovii (Shrestha et al., 2006) are involved in phytovolatilization of arsenic and selenium in Japan and the United States, respectively. The efficacy of phytoremediation depends on selecting appropriate plant species and various environmental factors. Overall, phytoremediation is a complex process involving multiple plant mechanisms. Understanding these processes can enhance plant adaptation to metal stress and improve efficiency, providing sustainable solutions for heavy metal contamination and ecosystem restoration.

Naturally, plants interact constantly with many microorganisms in their rhizospheric region. Beneficial microorganisms, especially arbuscular mycorrhizal fungi (AMF), have a symbiotic association with plant roots where AMF increase plant nutrient uptake ability, improve biomass accumulation, amplify photosynthesis capacity, and provide protection against heavy metal toxicity. Successively, the plant provides exudates of amino acids, carbon, and photosynthetic products to the AMF for growth and development (Mitra et al., 2020).

Around 80% of terrestrial plants and 90% of agricultural plants have mycorrhizal associations in their roots, where fungal hyphae enter the cortical cells of plant roots, forming vesicles, hyphae, and arbuscles (Smith and Read, 2010). Supplementary Figure S1 denotes the schematic diagram of the heavy metal detoxification mechanism through AMF. AMF help immobilize heavy metals by binding them at the cortical region, preventing translocation to the upper ground part (shoot, stem, leaves), and preventing damage to leaves. Plants are categorized based on TF value into hyper-accumulators (TF > 1) and non-hyperaccumulators (TF < 1). The translocation factor (TF) is higher in non-mycorrhizal-associated plants than in mycorrhizal-associated plants (Arshad et al., 2008). Endomycorrhizal fungi AMF belong to the phylum Glomeromycota. They are considered an eco-friendly, sustainable strategy to enhance plant growth, increase shoot biomass, improve soil health and water uptake capacity, provide protection to the plant against biotic and abiotic stress, and detoxify heavy metal-induced stress (Mishra et al., 2019). Glomeromycota are obligate symbiotic organisms, so they require around 20% of carbon from host plant cells for their survival. Simultaneously, they provide water and nutrients (P, N) through their arbuscles and intracellular and extracellular hyphae to the host plant (Parniske, 2008). AMF combat heavy metal stress by immobilization, precipitation, chelation, and sequestration in the rhizosphere and vacuoles and activate the plant anti-oxidant defense system (Mitra et al., 2020). Another AMF defense mechanism is to secrete a hydrophobic unique glycoprotein called glomalin, which is composed of carbon (39%–59%), phosphorus (0.03%–0.1%), nitrogen (3%–5%), hydrogen (4%–6%), oxygen (33%–49%), and a trace amount of iron (Schindler et al., 2007; Zhang et al., 2017). This protein is basically an N-linked glycoprotein produced from the spores and hyphae of AMF, which helps in soil aggregation, cellular function, toxic heavy metal stress, carbon storage, etc. (Emran et al., 2012; Wu et al., 2015). Easily extractable glomalin-related soil protein (EE-GRSP) and total glomalin-related soil protein (T-GRSP) are both readily quantified from the soil with the help of a citrate buffer (Wright and Upadhyaya, 1996).

For plant growth and nutrition, AMF increase the surface area with the help of extracellular and intracellular hyphae for better absorption of nutrients, water, and the ions that are generally present in an immobilized form in soil. AMF also improve the plant's ability to acquire nutrients from the depleted zone of the rhizosphere (Smith and Read, 2010; Smith and Smith, 2011). As stated by Nakmee et al. (2016), native species of AMF Glomus aggregatum, Acaulospora scrobiculata, and F. mosseae provide positive effect on plant nutrient uptake (total N, P, K) and enhance plant biomass, leaf number, and plant height of sorghum. It was observed that those wheat plants inoculated with AMF culture (F. mosseae and R. intraradices) contain a 1.13–2.76 times higher concentration of Zn than non-inoculated wheat plants (Coccina et al., 2019). Various abiotic stresses include salinity, heavy metals, drought, flooding, extreme temperature, etc. AMF communities independently withstand these unfavorable stress conditions for their host plants, provide sufficient water in drought stress, supply nutrients (phosphorus), and balance osmotic pressure in flooding stress conditions (Zhu et al., 2017; Caradonia et al., 2019). Under drought conditions, tomato plants containing AMF (R. intraradices) colonized on their roots provide sufficient water-based nutrients to the tomato plant for better growth during water-stress situations. Inoculation with G. etunicatum enhances total chlorophyll content, root-shoot height-weight, increased N, P, K, Ca, Zn, Cu concentration, flavonoid content, soluble sugar, proline, glycine betaine, polyamine, POD, and CAT activity in Pistaciavera L under stress conditions (Abbaspour et al., 2012). Studies revealed that G. etunicatum F. mosseae and R. irregularis increased the growth and grain yield of Triticum aestivum L., regulate nutrient uptake capacity, and decreased Na+ and Cl-concentration at times of salinity stress (Daei et al., 2009). According to Hashem et al. (2016), oxidative stress generates a high concentration of malonaldehyde and hydrogen peroxide in Solanum lycopersicum L. AMF strains (Glomus mosseae, Glomus intraradices, and Glomus etunicatum) help to decrease the concentration of these elements and boost the plant’s defense system against Cd stress. AMF also provide protection against biotic stress. Various pathogens, such as root-rot fungi, pathogenic bacteria, nematodes, and other harmful microorganisms, can cause various diseases. However, the presence of AMF significantly reduce pathogen-induced damage and infection by enhancing nutrient availability, stimulating root growth, and improving root morphology. AMF secrete beneficial enzymes in the rhizosphere, strengthening plant defenses and enabling plants to better withstand biotic stress (Vos et al., 2012; Spagnoletti et al., 2020). Fusarium wilt causes damage to Cicer arietinum L, but treatment with an AMF strain (Glomus hoi) provides protection against wilt disease and increases the nitrogen and phosphate content in treated plants as compared with non-treated plants (Singh et al., 2010). Similarly, Glomus sp. synthesizes antimicrobial compounds that help to arrest the mycelia growth of Fusarium oxysporum on L. esculentum plants and increase the chlorophyll, N, P, and K content of the plants. Furthermore, in Capsicum annum, Glomus sp. reduces the activity of the pathogen Pythium aphanidermatum and provides better yield of the plant (Kumari and Prabina, 2019; Kumari and Srimeena, 2019).