Biomonitoring-Supported Land Restoration to Reduce Land Degradation in Intensively Mined Areas of India

Abstract

Land degradation due to mining is a major concern leading to massive losses of biodiversity and ecosystem services. The biomonitoring of metals in mine voids can help to keep track of ecosystem health. The present study was carried out in a large mine void that is presently used for fly ash disposal in the Angul district of Odisha, India. For the biomonitoring of the fly ash, composite soil and plant samples (non-edible as well as edible, naturally growing in and around the mine void) were collected seasonally four times between April 2018 and February 2019 from the sampling locations. We monitored the metal uptake (Al, Cd, Cr, Fe, Mn, Ni, Pb, Zn) and bioaccumulation to assess the bioaccumulation factor (BAF) in the collected plant samples. The Fe concentration was reported to be high in Tragia involucrate (24.82 mg/kg) and Digitaria ciliaris (24.818 mg/kg), while the soil at the study site is also rich in Fe and Al. Higher concentrations of metals in fruit trees such as Psidium guajava and other plants such as Ficus religiosa, Ipomoea batatas, Delonix regia, Digitaria ciliaris, and Cynodon dactylon were reported from nearby areas. Understanding the presence of metals should be a guiding factor for reducing land degradation. Our study stresses the need for corporate commitment to ensure regular biomonitoring and biomonitoring-supported land restoration for degraded mining areas. Sustainable land restoration supported by biomonitoring has the potential to help achieve the global goals of the UN Decade on Restoration: Land Degradation Neutrality (UNCCD) and Sustainable Development Goals (SDGs) 12, 13, and 15.

1. Introduction

Since the 20th century, the growth of the global population, widespread urbanization, and rampant industrialization via the unreasonable exploitation of land resources have resulted in land degradation and the deterioration of the ecological environment [1,2,3]. Approximately 1–6 billion hectares of degraded land is spread across different parts of the world [4]. Mining-induced land depletion is a significant global concern because of the growing global demand for metallic mineral resources [5]. Mining activities have significantly impacted the environment by enhancing land degradation, deforestation, and losses of biodiversity and ecosystem services, followed by the displacement of millions of local households and multiple health hazards [6,7]. Opencast mines produce 8–10 times more waste than underground mines [8]. Overburden results in losses of nutrient-rich topsoil and may also result in the leaching of toxic metals into soil, groundwater aquifers, and freshwater bodies [5]. Metals tend to collect in the water, soil, residue, and living organic entities [6].

Metals may enter the food chain through agricultural activities and drinking water sources, and the concentration of some of these metals (e.g., Hg, Cd) increase at each tropic level, known as biological magnification [9]. Similarly, fly ash (FA), a coal combustion residue of thermal power plants, is another problematic solid and hazardous waste [7]. The conservative method of disposing of FA degrades and contaminates the fertile land [10]. The discarding and management of fly ash deposits is another problem, as it contaminates the soil, air, and water of the region and degrades the agricultural land [10].

In India, the energy demands and utilization rates are humongous, and have been increasing in the last two decades [6]. Odisha state in India has the second-largest coal reserves with more than 24 per cent of the total coal reserves [11]. The biggest solitary coalfield in India, Talcher coalfield, has coal reserves of ~39.64 BT [6]. Although the study of metal-accumulating plants for the remediation of larger metal impacts has received significant attention in the last few decades [10], there is still a vital need to use the findings to improve the mined areas. Biomonitoring can play an important role in characterizing degraded land for restoration using appropriate bioaccumulators. Wu et al. [12] reported that Boehmeria nivea, Chrysanthemum indicum, Miscanthus floridulus, Conyza canadensis, Rubus setchuenensis, Senecio scandens, and Arthraxon hispidus had phytostabilization abilities for Cr, Cd, Ni, and Cu, which can be used for potential phytoremediation [12], whereas Li et al. reported that ecological restoration in mining areas could benefit the structure of the plant community and the recovery of soil properties, which would eventually improve the ecological stability of mining areas [13]. An understanding of the potential for the aggregation of metals in different edible plants and regular biomonitoring are needed to avoid food chain contamination risks and to keep the locals and authorities informed about any probable environmental or health risks. The present study provides an overview of biomonitoring to assess the presence and concentration of metal in the fly ash, soil, and plants (non-edible and edible crops) close to the mine void. The study assesses the importance of the bioaccumulation of metals under the following broader objects:

(i)

The bioaccumulation potential of metals in non-edible plants;

(ii)

The bioaccumulation of metals in edible plants (agriculture and horticulture);

(iii)

A biomonitoring-supported restoration model for improve sustainable land restoration (SLR)

The bioaccumulation factor (BAF) and plant-based bioremediation were used to understand the variations and capabilities of different plants to be used as effective agents for restoration. Biomonitoring was used as an important tool to assess and reduce land degradation risks by using the broader understanding of the hyperaccumulators to be used in contaminated soil to efficiently restore these landscapes. Biomonitoring-supported sustainable land restoration can be an efficient approach to SLR in heavily mined areas. This also includes climate-sensitive restoration planning for highly degraded mine voids [14]. Biomonitoring-supported restoration planning has the potential to enhance the SLR within a fairly small span of time in countries where mining is quite common across different agroclimatic zones. With an emphasis on the UN Decade on Restoration 2021–2030 goal of restoring degraded lands and national commitments to enhance carbon sinks outside forest areas (tree outside forests), understanding the mine voids, their characters, their contaminants, and the degraded land restoration challenges can help to formulate an effective strategy and restoration plan to help countries’ achieve their global biodiversity, land degradation neutrality (LDN), forest landscape restoration (FLR), and climate targets (especially achieving in nationally determined contributions, also known as NDCs) [3].

2. Study Area and Climate

The study area was in Odisha, a state on the east coast of India, which has a tropical humid coastal climate region [15]. The study was carried out in an abandoned coal mine void that is presently considered for fly ash disposal generated by the thermal power plant at Talcher (Angul district) in Odisha state. The mine void is in a micro-watershed at latitudes 20°52′00″ N to 20°59′00″ N and longitudes 85°07′30″ E and 85°15′30″ E (Figure 1).

The soil is mainly composed of black soil and laterite soil with low levels of organic carbon and nitrogen [16]. The flora in the study area is dominated by plants of the Fabaceae, Anacardiaceae, Mimosaceae, Moraceae, Apocynaceae, Caesalpiniaceae, Combretaceae, and Verbenaceae families [17]. Various sampling points marked in and around the mine void area for this study are presented via Google Earth satellite imagery (Figure 2).

3. Materials and Methods

To understand the potential for biomonitoring-supported SLR development, we performed a field-based study to understand the characteristics of the contaminants, especially the metals, in the degraded mine void that is to be used for dumping fly ash, another potential hazardous byproduct from thermal power plants. We used the following procedure for continuous biomonitoring in the mine void and adjoining areas to understand the extent of toxicity and the bioaccumulation potential of the plants (non-edible, agriculture, and horticulture). Statistical analyses were conducted to find out the mean and standard deviation using MS-Excel 2013 (Microsoft Inc. Redmond, Washington, DC, USA), as well as bioaccumulation factor of the metals in plants.

3.1. Sample Collection and Analysis

Plant, fly ash, and soil samples were collected seasonally four times between April 2018 and February 2019 from the sampling locations. To understand the metal concentrations in the different plants, we sampled non-edible plants near the mine void as well as edible plants growing in nearby human habitations. This gave us a comparative understanding of the metal uptake rates by various plants. The topsoil (0–15 cm depth) from agricultural lands of the villages close to the mine void was collected using a steel shovel to understand the metal concentration. Plant (herbs, shrubs, and trees) and soil samples were collected within the buffer distance of 5 to 10 m from the mine void area and also from the villages close to the mine void, with a focus on edible plants from horticulture and agriculture, as many edible crops tend to bioaccumulate metals in the fruits. Twenty different plant species were considered for the study and 3 replicate samples for each species from each location were collected from the study area. Out of these, 5 species were collected from the mine void and 15 from the nearby locations. For the herb and shrub samples whole plants were taken, while for tree sample only the leaves were taken for the bioaccumulation study. The soil, fly ash, and plant samples were stored in airtight plastic zip-lock bags, and codes were assigned to these samples. GPS locations of the various samples collection points were recorded with the help of a hand-held GPS device (Garmin make, model-Montana 650).

3.2. Sample Digestion

All samples were digested following the Unites States Environmental Protection Agency (USEPA) methodology No. 3050B and the metal analyses were carried out via inductively coupled plasma–optical emission spectrometry (ICP-OES) (Thermo Fisher Model- iCAP6300 DUO). Here, 1 gm composite dried samples were digested with 10 mL of nitric acid and 5 mL of hydrogen peroxide and boiled in a digestion block at 180–220 °C until the solution turned transparent. The processed examples were then made up to 50 mL with deionized distilled water. The final solution was filtered with the help of cellulose filter paper (USEPA, 2013). Calibration curve plots of the prepared standards were plotted with an accuracy of 99.9% using ICP-OES. Various plant, fly ash, and soil samples were analyzed for metal using ICP-OES.

3.3. Bioaccumulation Factor for Metal in Plant Samples

A plant’s ability to accumulate a particular metal with respect to its concentration in the soil is known as the bioaccumulation factor (BAF) [18]. The BAF provides an insight into the effectiveness of a plant in terms of metal accumulation and translocation [19]. The bioaccumulation factor for each sample plant was evaluated following the given equation [20]:

$$\mathrm{BAF}=\mathrm{Concentration} \mathrm{of} \mathrm{metal} \mathrm{in} \mathrm{plant} \mathrm{tissue} ÷ \mathrm{Concentration} \mathrm{of} \mathrm{metal} \mathrm{in} \mathrm{soil}$$

(1)

4. Results and Discussion

An analysis of the samples provided a broader understanding of the different toxic, semi-toxic, and non-toxic metals present in the different plant, fly ash, and soil samples from the study area. The analysis of the metal content in the fly ash revealed that the fly ash was enriched with Al (4.14 mg/kg) as the most abundant metal, followed by Mn > Fe > Ni > Cr > Pb > Cd. In the soil samples, the concentration of Fe (64.35 mg/kg) was observed to be relatively high, followed by Al, Zn, Mn, Cr, Pb, Cd, and Ni (

Table 1. Concentrations of metals in samples of fly ash; soil; non-edible plants; and crops, vegetables, and fruits (mg/kg).

Sl. No.	Metals	Fly Ash		Soil		Non Edible Plants		Edible Plants (Crops/Vegetables/Fruits)
		Concentration (mg/kg) Min–Max	X ± SD	Concentration (mg/kg) Min–Max	X ± SD	Concentration (mg/kg) Min–Max	X ± SD	Concentration (mg/kg) Min–Max	X ± SD
1	Al	0.187–4.140	1.909 ± 1.494	123.120–238.420	172.430 ± 59.429	0.660–11.129	3.930 ± 2.702	1.690–11.836	6.205 ± 3.240
2	Cd	0–0.001	0 ± 0	0.010–0.020	0.016 ± 0.005	0–0.007	0.001 ± 0.002	0.000–0.048	0.005 ± 0.012
3	Cr	0.001–0.040	0.016 ± 0.017	0.150–0.410	0.323 ± 0.150	0–0.402	0.090 ± 0.113	0.000–0.297	0.089 ± 0.082
4	Fe	0.021–9.200	2.118 ± 3.566	99.870–224.460	171.486 ± 64.353	0–53.784	8.003 ±12.280	0.070–39.668	10.266 ± 11.558
5	Mn	0.084–1.050	0.533 ± 0.406	1.800–25.440	11.596 ± 12.328	0.025–3.405	0.561 ± 0.841	0.085–3.710	0.766 ± 0.844
6	Ni	0.003–0.052	0.029 ± 0.017	0.140–0.360	0.266 ± 0.113	0.001–0.240	0.036 ± 0.054	0.000–0.540	0.085 ± 0.133
7	Pb	0–0.003	0.001 ± 0	0.030–0.170	0.113 ± 0.073	0–0.042	0.012 ± 0.013	0.001–0.200	0.047 ± 0.050

).

In all plant samples, Al and Fe showed relatively high concentrations, except for in Sorghastrum nutans, where Fe was absent (

Table 2. Concentrations of metals in non-edible plant samples (mg/kg).

Sl.No	Plant Species	Botanical Name	Al *	Cd **	Cr **	Fe **	Mn* *	Ni **	Pb **	Zn **
	Permissible Limit		15	0.02	1.30	20	200	10	2	0.60
1	Billygoat weed	Ageratum conyzoides	2.040	BDL	BDL	0.130	0.025	0.006	BDL	0.125
2	Indian Lilac	Azadirachta indica	5.083	0.001	0.077	12.188	2.383	0.084	0.024	0.331
3	Crown Flower	Calotropis gigantea	8.176	0.002	0.118	20.6	0.662	0.034	0.015	0.494
4	Common hackberry	Celtis occidentalis	1.790	BDL	0.007	0.190	0.040	0.002	BDL	0.030
5	Dhoob	Cynodon dactylon	4.853	0.001	0.052	7.678	3.405	0.240	0.018	0.236
6	Nut grass	Cyperus rotundus	5.858	0.002	0.026	3.657	0.294	0.069	0.024	0.513
7	North Indian Rosewood	Dalbergia sissoo	2.711	0.001	0.296	2.284	0.087	0.084	0.027	0.227
8	Non edible Crabgrass	Digitaria ciliaris	8.535	0.003	0.170	24.818	0.830	0.018	0.007	0.565
9	Royal Poinciana	Delonix regia	1.949	0.002	0.402	2.513	0.669	0.061	0.028	0.531
10	Peepal	Ficus religiosa	2.645	0.007	0.050	1.960	0.910	0.030	0.001	0.210
11	Weeping fig	Ficus benjamina	4.310	BDL	0.070	15.910	0.070	0.020	BDL	0.130
12	Spanish Flag	Lantana camara	6.783	0.002	0.179	11.450	0.276	0.023	0.042	0.294
13	Bitter vine	Mikania micrantha	0.660	BDL	0.001	0.240	0.120	0.002	BDL	0.040
14	Rangoon Creeper	Combretum indicum	0.660	BDL	0.001	0.240	0.130	0.002	BDL	0.040
15	Black Locust	Robinia pseudoacacia	3.710	BDL	0.020	0.640	0.041	0.003	0.007	0.060
16	Non edible Sugarcane	Saccharum spontaneum	3.660	0.002	0.093	10.163	1.214	0.028	0.034	0.355
17	Indian Grass	Sorghastrum nutans	1.320	BDL	0.005	BDL	0.040	0.001	0.003	0.050
18	Narrowleaf Cattail	Typha angustifolia L.	3.073	BDL	0.015	1.333	0.187	0.009	0.005	0.113
19	Broadleaf cattail	Typha latifolia	3.427	BDL	0.007	11.280	0.040	0.010	0.008	0.070
20	Indian stinging nettle	Tragia involucrata	11.129	0.001	0.303	53.784	1.165	0.094	0.006	0.558

BDL, below detection limit. * permissible limit reported by Jaishankar et al., 2014 [21]. ** permissible limit according to World Health Organization, 1998 [22]; Shah et al., 2013 [23].

). The Al, Fe, and Mn concentrations were observed to be relatively high due to their geogenic nature and being present in high concentrations in the laterite soil belt [16]. The soil in Odisha state is rich in minerals, while Fe and Mn mining is predominant across the state, which has resulted in high uptake rates of Fe and bioaccumulation by non-edible plants. Certain plants such as Tragia involucrata were observed to have relatively high concentrations of Al (11.120 mg/kg), Cr (0.030 mg/kg), and Fe (53.780 mg/kg) amongst the metals. Cynodon dactylon, Digitaria ciliaris, Ficus religiosa, and Lantana camara showed relatively high concentrations of Mn (3.400 mg/kg) and Ni (0.240 mg/kg), Zn (0.560 mg/kg), Cd (0.007 mg/kg), and Pb (0.040 mg/kg) respectively. Cd was either absent in most of the sampled and analyzed non-edible plants or it was relatively low in concentration amongst the other metals (Table 2).

The concentrations of metals in edible plants indicated that Psidium guajava and Oryza sativa contained relatively high of Al (11.830 mg/kg) and Fe (39.660 mg/kg), whereas Cd was observed to have relatively low concentrations amongst the metals. The Cr (0.290 mg/kg), Mn (1 mg/kg), Ni (0.540 mg/kg), Pb (0.200 mg/kg), and Zn (2.970 mg/kg) concentrations were observed to be relatively high in Momordica charantia, Solanum lycopersicum, Ipomoea batatas, Psidium guajava, and Oryza sativa, respectively (

Table 3. Concentrations of metals in edible crop, vegetable, and fruit plant samples (mg/kg).

Sl. No.	Plant Species	Botanical Name	Al	Cd	Cr	Fe	Mn	Ni	Pb	Zn
	Permissible Limit		15	0.02	1.30	20	200	10	2	0.60
1	Okra	Abelmoschus esculentus	5.566	0.003	0.099	25.205	0.800	0.010	0.060	0.267
2	Spleen amaranth	Amaranthus dubius	3.953	0.048	0.024	3.248	0.884	0.115	0.025	0.200
3	Capsicum	Capsicum annuum	4.660	0.001	0.010	1.460	0.085	0.000	0.004	0.175
4	Papaya	Carica papaya	5.316	0.001	0.090	15.663	0.655	0.061	0.045	0.564
5	Turmeric	Curcuma longa	5.230	0.001	0.060	2.930	0.180	0.210	0.023	0.370
6	Mango	Mangifera indica	11.125	0.002	0.070	15.090	0.400	0.080	0.043	0.385
7	Bitter Gourd	Momordica charantia	4.403	BDL	0.297	1.215	0.104	0.003	0.011	0.137
8	Drumstick	Moringa oleifera	10.983	0.003	0.242	2.024	0.730	0.026	0.043	0.969
9	Banana	Musa balbisiana	5.186	0.002	0.090	23.881	0.540	0.073	0.050	0.389
10	Rice	Oryza sativa	8.470	0.001	0.149	39.668	0.696	0.031	0.053	2.973
11	Tomato	Solanum lycopersicum	1.765	BDL	0.010	1.355	1.000	0.016	0.005	0.090
12	Brinjal	Solanum melongena	6.430	0.003	0.047	6.208	0.978	0.070	0.032	0.235
13	Guava	Psidium guajava	11.836	0.004	0.081	8.911	0.861	0.089	0.200	0.797
14	Pomegranate	Punica granatum	1.690	BDL	0.049	0.270	0.170	0.003	0.001	0.060
15	Sweet Potato	Ipomoea batatas	3.210	0.002	BDL	0.070	3.710	0.540	0.120	0.450
16	Indian Jujube	Ziziphus mauritiana	9.451	0.001	0.102	17.064	0.465	0.032	0.035	1.368

).

4.1. Bioaccumulation Factor for Metals in Non-Edible Plant Samples

Our study attempted to analyzed the native plant diversity in the area, which has the potential to bioaccumulate metals leached in the soil due to mining activities. The bioaccumulation factor (BAF) values for naturally growing non-edible plant samples, crops, vegetables, and fruit plant samples varied from 0.34 to 6.11 for Al, followed by a below detection limit (BDL) of 24.0 for Cd, a BDL of 44.66 for Cr, a BDL of 9.39 for Fe, a BDL of 34.70 for Mn, a BDL of 25.71 for Ni, a BDL of 76.92 for Pb, and a range 0.03 to 3.16 for Zn. Details are provided in Appendix A. The bioaccumulation factors for all the metals were highest in grass, except for Cr and Cd, whereas the bioaccumulation factors for Cd and Cr were found to be highest in trees (Figure 3).

Digitaria sanguinalis was observed to have relatively high concentrations of three metals, i.e., Al (4.400 mg/kg), Fe (4.330 mg/kg), and Zn (0.600 mg/kg); similarly, Cynodon dactylon was observed to have relatively high concentrations of two metals, i.e., Mn (34.700 mg/kg) and Ni (11.440 mg/kg) (Appendix A). It has been proven in past too that Digitaria sanguinalis has relatively high bioaccumulation potential for Al, Fe, and Zn [24,25], while Cynodon dactylon has high bioaccumulation potential for Mn and Ni [26,27,28,29]. Since Digitaria ciliaris and Cynodon dactylon are capable of accumulating three (Al, Fe, Zn) or two metals (Mn, Ni) at relatively high concentrations, it is an efficient phytoremediation plant that can be introduced as a pioneer species for rapid soil amelioration and to create a substrate ready for SLR in mine voids and adjoining degraded landscapes. The high concentrations of Al and Fe in Digitaria ciliaris may also have been due to the fact that the study area’s soil is rich in Al and Fe, being an Fe ore and Mn mining belt. The other toxic element with a high concentration observed in the samples was Cd, which showed a relatively high concentration (3.500 mg/kg) in leaf samples of Ficus religiosa. There is clear evidence that Ficus religiosa is a very strong biosorbent and that its leaves absorb Cd from liquid as well as semi-liquid solutions [30,31,32]. Salman et al. (2020) [31] reported that Ficus religiosa has the potential to uptake Cr, while Tariq et al. (2019) [33] reported the bioaccumulation potential of Cu in Ficus religiosa.

4.2. Bioaccumulation Factor for Metals in Edible Plant Samples

In the case of edible plants (vegetables), Ipomoea batatas had relatively high concentrations of two metals i.e., Mn (25.710) and Ni (25.710) (Figure 4). The other two plants with relatively high concentrations of Fe (6.931) and Zn (3.166) were Oryza sativa and Psidium guajava, with relatively high concentrations of Al (6.112) and Pb (76.923) (Figure 4). Apart from Mn and Ni, it was also reported that Ipomoea batatas has high bioaccumulation affinity towards Cd, Pb, Zn, As, Fe, and Cu [34,35], but in our study Ipomoea batatas showed high affinity towards Mn and Ni. Zhou et al. (2020) [36] reported the bioaccumulation of Cu, Pb, Fe, and Zn in Oryza sativa [37,38].

The BAF for Cr (44.667) was also relatively high in Delonix regia species present in the study area. Saralathambavani and Prathipa (2012) [39] reported Delonix regia to have strong bioabsorbance for Cr from the soil in polluted industrial areas. Krishnani et al. (2021), Yap et al. (2021), and Maiti et al. (2015) [40,41,42] also confirmed the strong bioaccumulation of metals by fruiting plants such as Psidium guajava, Mangifera indica, and Eucalyptus globulus, similar to our findings for Psidium guajava and Mangifera indica. These findings need special consideration to avoid these plants in the restoration of mine voids, as they may facilitate the entry of metals and the contamination of the food chain.

5. Biomonitoring-Supported Sustainable Land Restoration

The extensive biomonitoring in the study area at Talcher helped the authors to design an appropriate site-specific SLR system. We suggest the use of a biomonitoring-supported restoration model to maximize the outputs for enhanced SLR success. To initiate the implementation of the framework, strong bioaccumulator plants for different metals should be identified (e.g., Digitaria sanguinalis, Cynodon dactylon, Calotropis gigantean, Delonix regia, Tragia involucrate) followed by their mass propagation, as many of them are less known and underutilized non-edible plants. Further scientific interventions will be needed to develop seed germination and vegetative propagation protocols for these plants, as many of them might be lesser known and underutilized wild edibles. We suggest this approach to be implemented in three strategically relevant stages (Figure 5). In the first stage, an appropriate combination of potential herbs and shrubs should be planted (with a focus on nitrogen-fixing, fast-growing, high-biomass-yielding species), which can serve as pioneers for the degraded landscape. For stage two, in the next plantation and restoration season (the monsoon season is the preferred season in India), the non-performers (non-acclimatized species, dead plants) should be replaced by performers (after undertaking regular monitoring of the survivability and mortality of all planted plants), along with the mass plantation of shrubs and small trees. Stage three should follow same process and should continue with a regular plantation and replacement of non-performers until complete SLR targets are achieved for the larger landscape. Manure, fertilizer, and mycorrhizal combinations should be applied regularly to enhance soil amelioration and facilitate plant growth. The regular biomonitoring of the plants and soil on a yearly basis is necessary to determine the existing metal concentrations in the plants and soil. Dead and decayed plants should be used for mulching and biochar preparations to enhance the soil carbon content, water-holding capacity, and uptake of metals. The suggested SLR approach has the potential to accelerate the process of land restoration and enhance the biodiversity values in a record time period of 4–5 years if appropriate care is taken.

In the present study, we observed two herbs showing relatively high bioaccumulation rates of metals, e.g., Tragia involucrate (Al, Cd, Cr, Fe, Ni, Zn) and Cynodon dactylon (Mn, Ni, Pb). Of the shrubs, Calotropis gigantea had a relatively higher affinity to bioaccumulate metals than other shrubs in the study area. The right mixture of herbs and shrubs should be planted in heavily degraded mine voids to initiate habitat succession, soil amelioration, and soil formation. The involvement of local communities can help them with livelihood and alternative livelihood opportunities, with support from indigenous and traditional knowledge in the selection of species, mass propagation, seed collection, germination, nursery raising, and planting. Azadirachta indica was observed to have the potential to bioaccumulate metals (Al, Cd, Mn, Ni, Pb, etc.). We explored research papers to identify which other plants in this combination can also be included to enhance the regeneration and restoration rates.

Table 4. Plants having bioaccumulation potential for metals.

Sl. No.	Species	Metals	References
	Herbs
1	Tragia involucrata	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [43]
2	Digitaria sanguinalis	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [19,20]
3	Cynodon dactylon	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [24,25,26,27]
4	Cyperus rotundus	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [44,45]
5	Saccharum spontaneum	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [46,47,48]
6	Typha latifolia	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [49,50]
7	Typha angustifolia	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [51]
8	Ageratum conyzoides	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [52,53]
9	Sorghastrum nutans	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [54]
10	Pteris vittata	Cu, Ni, Zn, As	Present Study, [55,56]
11	Helianthus annuus	Cd	[57,58]
12	Brassica napus	Cd	[59,60]
13	Amaranthus viridis	Cd, Cr, Co, Cu, Fe, Zn, Mn	[61,52]
14	Medicago polymorpha	Cd, Cr, Co, Cu, Fe, Zn, Mn	[52]
15	Parthenium hysterophorus	Cd, Cr, Co, Cu, Fe, Zn, Mn	[52]
	Shrubs
1	Calotropis gigantean	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [62]
2	Lantana camara	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [63,64]
3	Quisqualis indica	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [65]
4	Mikania micrantha	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [66]
5	Tetraena qatarensis	Cd, Cr, Cu, Ni	[67]
	Trees
1	Azadirachta indica	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [68,69]
2	Ficus benjamina	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [70]
3	Delonix regia	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [71]
4	Ficus religiosa	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [28,29]
5	Dalbergia sissoo	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [72]
6	Robinia pseudoacacia	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study. [73]
7	Celtis occidentalis	Al, Cd, Cr, Fe, Mn, Ni, Pb Zn	Present Study, [74]
8	Millettia pinnata	Cr, Cu, Pb, Zn, Mn, Fe. Ni, Cd	[75]
9	Tectona grandis	Cr, Cu, Pb, Zn, Mn, Fe. Ni, Cd	[75]
10	Senna siamea	Cr, Cu, Pb, Zn, Mn, Fe. Ni, Cd	[75]
11	Dendrocalamus strictus	Cr, Cu, Pb, Zn, Mn, Fe. Ni, Cd	[75]

shows different species of herbs, shrubs, and trees that can be used for the bioaccumulation and reclamation of mine voids in site-specific situations. Biomonitoring-supported restoration is an effective approach to help meet the UN Decade on Restoration (2021–2030) goals and SDGs 12, 13, and 15, followed by the LDN targets of the UNFCCC.

6. Conclusions

The study area is an extensively mined and heavily industrialized zone containing high concentrations of various metals. However, during the continuous biomonitoring, some metals such as Fe were observed to be above the permissible limits in certain samples (Table 1). The bioaccumulation factors for all metals were found to be highest in grass, except for Cr and Cd, whereas the bioaccumulation factors for Cd and Cr were found to be the highest in trees. However, Fe is non-toxic, while the other metals are toxic in nature, even in low concentrations; hence, their concentrations need to be monitored very frequently to avoid any potential hazard due to the consumption of these plants by livestock or humans. It is important to understand that fruiting trees that are consumed by local people should be avoided in the early stages of restoration. Preference should be given to trees and plants with timber, fuelwood, and other non-edible purposes. These results also show that the mine void and adjoining areas falling under the study area, despite containing heavy metals, are not under a severe threat of metal toxicity, and active restoration or assisted natural regeneration every year followed by the regular biomonitoring of heavy metals in the mine void surroundings can help reduce the metal concentrations in the soil via effective phytoremediation measures (restoration using non-palatable native plants with effective biomass removal at regular intervals). Our observations in the nearby surrounding areas indicate higher concentrations of bioaccumulated metals in the fruit, leaves, or other plant parts of Psidium guajava, Ficus religiosa, Ipomoea batatas, Delonix regia, Digitaria ciliaris, and Cynodon dactylon, which is further supported by other studies. Most of these trees and fruiting plants are planted without a scientific consultation with the mining authorities; hence, this study discourages the planting of fruit trees, even in vicinity of the mine void location. Hence, the SLR approach should avoid the planting of fruiting trees in the contaminated site, supported by the use of grazing restrictions. The biomonitoring of edible plants (agriculture, horticulture, and vegetable crops) is required to avoid any chances of food chain contamination in the extensively mined and industrialized zones of the country. Our study provides substantial scientific evidence to support biomonitoring as an important tool for sustainable land restoration by using plant-based phytoremediation to absorb toxic metals from contaminated soil and to promote soil amelioration, in turn reducing risks for not only lower invertebrates but also larger mammals such as livestock reared by the local inhabitations. This approach can ensure human well-being by addressing the risks and using the sustainable land restoration approach in the long run to reduce toxicity. Native species that have fruit and leaves that are not consumed by livestock, humans, or wild animals can be used in an organized manner following the natural course of succession of native trees to ameliorate soils contaminated by fly ash and other mining wastes dumped in the mine void areas. Since Digitaria ciliaris and Cynodon dactylon are capable of accumulating three semi toxic (Al, Fe, Zn) and two toxic metals (Mn, Ni) at relatively high concentrations, they can be considered efficient phytoremediation plant that can be introduced at the pioneer stage for rapid soil amelioration and to create a substrate ready for SLR in mine voids and the adjoining degraded landscapes. These plants follow the natural course of succession (the combination of pioneer, seral, and climatic climax stages) when combined to grow together and have synergistic effects in absorbing and bioaccumulating multiple metals from the soil that can help to restore the soil health and ameliorating soil characteristics to improve the ecosystem health in the long run.