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Article

Remediation of Cd, Cu, and Zn Metals in Soil Amended with Biochar and Animal Manure Using a Hyperaccumulator

by
George F. Antonious
*,
Anjan Nepal
and
Basanta Neupane
School of Agriculture and Natural Resources, College of Agriculture, Health and Natural Resources, Kentucky State University, Frankfort, KY 40601, USA
*
Author to whom correspondence should be addressed.
Pollutants 2025, 5(3), 22; https://doi.org/10.3390/pollutants5030022
Submission received: 2 April 2025 / Revised: 9 June 2025 / Accepted: 18 June 2025 / Published: 14 July 2025
(This article belongs to the Section Food Pollution)
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Abstract

The application of animal manure and organic soil amendments as an alternative to expensive inorganic fertilizers is becoming more prevalent in the USA and worldwide. A field experiment was conducted on Bluegrass–Maury silty loam soil at the Kentucky State University Research Farm using the Kennebec variety of white potato (Solanum tuberosum) under Kentucky climatic conditions. The study involved 12 soil treatments in a randomized complete block design. The treatments included four types of animal manures (cow manure, chicken manure, vermicompost, and sewage sludge), biochar at three application rates (5%, 10%, and 20%), and native soil as control plots. Additionally, animal manures were supplemented with 10% biochar to assess the influence of combining biochar with animal manure on the accumulation of heavy metals in potato tubers. The study aimed to (1) determine the concentration of seven heavy metals (Cd, Cr, Ni, Pb, Mn, Zn, Cu) and two essential nutrients (K and Mg) in soils treated with biochar and animal manure, and (2) assess metal mobility from soil to potato tubers at harvest by determining the bioaccumulation factor (BAF). The results revealed that Cd, Pb, Ni, Cr, and Mn concentrations in potato tubers exceeded the FAO/WHO allowable limits. Whereas the BAF values varied among the soil treatments, with Cd, Cu, and Zn having high BAF values (>1), and Pb, Ni, Cr, and Mn having low BAF values (<1). This observation demonstrates that potato tubers can remediate Cd, Cu, and Zn when grown under the soil amended with biochar and animal manure.

Graphical Abstract

1. Introduction

Potatoes (Solanum tuberosum) are a staple food crop globally, ranking fourth in consumption and contributing significantly to food security due to their adaptability, high yield, and potential for year-round cultivation [1]. In 2022, global potato production reached 375 million tons, with the USA contributing 17.8 million tons [2]. However, increasing soil contamination with heavy metals poses a threat to sustainable potato production and food safety.
Heavy metals have a profound influence on plant physiology and soil microbial activity. Essential micronutrients, such as Zn, Cu, Ni, Mn, K, and Mg, are required in trace amounts for plant growth and metabolic processes. Zn aids in photosynthesis and reproduction [3], Ni supports enzymatic activity and nitrogen metabolism [4,5], K mitigates stress [6], Mg contributes to chlorophyll production and metal stress tolerance [7], and Cu is absorbed in small amounts (5–20 µg g−1 dry matter) [8]. However, excessive accumulation can be toxic; for example, Zn levels above 300 µg g−1 in plants are harmful, and the tolerable intake limit for humans is 45 mg/day [9,10]. In contrast, non-essential metals like Pb and Cd have no biological function and persist in the environment. Pb interferes with nutrient uptake and is linked to severe health issues, including liver and brain damage [11,12,13]. At the same time, Cd is highly mobile in soil, harming plant growth and microbial communities [14,15,16,17,18].
Heavy metals, such as Cd, Cu, and Zn, can accumulate in agricultural soils through industrial discharge, irrigation with polluted water, and the excessive use of organic amendments, including animal manure [19,20]. While animal manure provides essential nutrients (N, P, K) and improves soil fertility [21,22,23], it often contains hazardous heavy metals, which may leach into groundwater or accumulate in crop tissues, including potato tubers [24,25,26]. The consumption of such contaminated crops poses severe risks to human health, as recognized by WHO and FAO guidelines [27,28]. Despite the agronomic benefits of animal manure, the unregulated use remains a global environmental concern due to its role in elevating toxic metal levels in soils. Therefore, safe and sustainable strategies are urgently needed to manage heavy metal accumulation in food crops, particularly in root vegetables such as potatoes, which are prone to absorbing metals from contaminated soil.
Among various remediation approaches [29,30], phytoremediation stands out as an environmentally friendly approach. The use of plants to extract or stabilize pollutants, combined with the application of biochar, has shown promise. Biochar, a carbon-rich product derived from pyrolysis, can immobilize heavy metals, enhance soil quality, and reduce metal uptake by plants [31,32,33]. However, the dual role of edible crops, such as potatoes, in phytoremediation and human consumption necessitates a careful evaluation of their safety and effectiveness.
While previous studies have explored the benefits of biochar and manure amendments individually, limited research has evaluated their combined effects on the accumulation of heavy metals in potatoes. Furthermore, the extent to which potatoes can safely function as both a food crop and a phytoremediator under these conditions remains underexplored. This study aims to fill this gap by assessing the accumulation of essential and non-essential metals in potato tubers grown in soils amended with animal manure and biochar. The objectives of this study were to (1) assess the impact of animal manure amended with biochar as an organic fertilizer on the accumulation of heavy metals in potato tubers; (2) investigate the potential of using three rates of biochar and biochar mixed with animal manure on the accumulation of essential and toxic metals in potato tubers at harvest, in relation to the FAO and WHO allowable limits; and (3) calculate the bioaccumulation factor (BAF) for the potential use of potatoes in phytoremediation technology.

2. Materials and Methods

2.1. Field Experimental Design

A field experiment consisting of 36 plots (three replicates of 12 treatments) was carried out during the summer of 2023 at the Harold and Benson Research and Demonstration Farm, Kentucky State University, in a randomized complete block design. Each plot measured 3.7 m in width and 22 m in length. The study included six soil management practices: cow manure obtained from Lowe’s (Frankfort, KY, USA); chicken manure sourced from Espoma Company (Millville, NJ, USA); vermicompost supplied by Wiggle Worm Soil Builder (UNCO Industries, INC, Union Grove, WI, USA); sewage sludge acquired from the Metropolitan Sewer District (Louisville, KY, USA); biochar applied at three rates (5%, 10%, and 20%) and acquired from Wakefield Agricultural Carbon, LLC (Valdosta, GA, USA); and a no-amendment control plots. Additionally, cow manure, vermicompost, chicken manure, and sewage sludge were each combined with 10% biochar, resulting in 12 treatments. Each treatment was replicated three times. The control treatment consisted of the native soil, classified as Bluegrass–Maury Silty Loam, with a composition of 56% silt, 38% clay, and 6% sand. The application rates for the soil amendments (excluding the unamended control) and their respective properties are detailed in Table 1A,B.

2.2. Cultivation Practices

Soil amendments were incorporated into the native soil at 5% N to minimize variations in potato tubers’ heavy metals content caused by differences in N composition among soil amendments (Table 1A,B). Each amendment was mixed into the top 15 cm of soil. White potato (Solanum tuberosum, var. Kennebec) was obtained from the Frankfort Service in Frankfort, KY, USA. The tubers were cut into appropriately sized pieces and planted in the prepared field at a depth of 4 inches, with a spacing of 30 cm between rows and plants. A drip irrigation system provided a consistent water supply and weed control measures were implemented as necessary. To prevent weed emergence, the pre-emergence herbicide trifluralin 4EC (Drexel Company, Memphis, TN, USA) was applied at a rate of 0.27 L hectare−1 [34].

2.3. Heavy Metals and Micronutrients Analyses

During the harvest, 10 tubers of similar size were randomly selected from each plot. A total of 30 tubers per treatment across three replicates were taken. The tubers were thoroughly washed with tap water, then deionized water, and then oven-dried at 65 °C for 48 h [35]. The dried samples were manually ground using a ceramic mortar and pestle to pass through a 1 mm non-metal sieve. It was followed by re-drying in an oven until a constant weight was achieved. For sample digestion, 1 g of each dried sample was mixed with 10 mL of concentrated nitric acid. The mixture was left to stand overnight and then heated for 4 h at 125 °C on a hot plate. The resulting mixture was diluted to 50 mL with double-distilled water and filtered using No. 1 filter paper. The concentrations of Cd, Pb, Cu, Cr, Ni, Zn, Mn, K, and Mg were measured using an inductively coupled plasma optical emission spectrometer (ICP-OES) (Model 720-ES, Perkin Elmer, Waltham, MA, USA) in standard mode, following USA EPA Method 6020a [36]. The detected metal levels in potato tubers were compared against the permissible limits established by the Codex Alimentarius Commission of the Joint FAO/WHO Food Standards [37] and the acceptable limits by the USA FDA [11].

2.4. Statistical Analysis

All data collected from this investigation were subjected to statistical analysis using SAS software (SAS Institute Inc., Cary, NC, USA, Version 9.1.3) [38]. A one-way analysis of variance (ANOVA) was performed to determine the effect of different soil amendment treatments on heavy metal accumulation in potato tubers. The assumptions of ANOVA (normality and homogeneity of variance) were checked using Shapiro–Wilk and Levene’s tests, respectively.
Where significant treatment effects (p ≤ 0.05) were detected, Duncan’s multiple range test (DMRT) was used for post-hoc mean separation to identify statistically distinct groups. The results are presented as mean ± standard error (SE) for each treatment. All figures displaying bioaccumulation factors and metal concentrations include error bars and significance groupings based on DMRT to facilitate visual interpretation.

3. Results and Discussions

Table 2 illustrates the elemental composition of soil amended with animal manure and a combination of manure and biochar used for white potato cultivation. The concentration of Pb was significantly higher (p ≤ 0.05) in soil treated with SS mixed with 10% Biochar (21.2 µg g−1) compared to soil amended with Vermi (17.5 µg g−1), while Pb levels varied among the other treatments. In contrast, Cd concentrations did not differ significantly across the treatments. However, Cd concentrations in potatoes cultivated with the soil amendments significantly surpassed the FDA/WHO permissible limit of 0.3 µg g−1 (Table 3).
Ni levels were higher in soil amended with 10% Biochar than those treated with Cow mixed with 10% Biochar, Vermi combined with 10% Biochar, and 5% Biochar. Cr levels varied, with the highest concentration found in 10% Biochar combined with CM (16.4 µg g−1), which was significantly higher (p ≤ 0.05) than that in the non-amended vermicompost (13.08 µg g−1) (Table 2). Notably, the Cr levels in potato tubers surpassed the maximum allowable limit of 0.1 µg g−1 (Table 3). Mn concentration in the soil was found to be too high. The Mn concentration range was the greatest in 10% Biochar amended with SS (1459.4 µg g−1). There was no significant difference in Mn concentration among the treatments. Antonious et al. [39] observed that higher heavy metal concentrations in soil do not necessarily indicate their availability to plants.
Table 3. The permissible limit of metals in potato, Solanum tuberosum tubers.
Table 3. The permissible limit of metals in potato, Solanum tuberosum tubers.
Heavy MetalsPermissible Limit in Potatoes,
Mg kg−1		Permissible Limit in Soil,
Mg kg−1
Cu10 [40] in plants100
Zn0.6 [40] in plants300
Ni0.1 [11]50 [41]
Cr0.1 [11]0.2 [42]
Mn2 [11]500 [43]
Cd0.3 [11]3 [42]
Pb1 [11]100 [42]
K--
Mg--
Cu concentration was higher in soil amended with CM (11.41 µg g−1), which was significantly greater than 5% Biochar and Vermi. Zn concentration was higher in soil amended with CM (23.34 µg g−1). However, there was no significant difference in Zn concentration among the treatments. The K concentration was found to be high in the soil. K concentration was significantly greater (p < 0.05) in soil amended with 10% Biochar, 20% Biochar, CM, and Cow (317.3, 302.9, 324.8, and 307.1 µg g−1, respectively) than in 5% Biochar, 10% Biochar amended with Cow, and 10% Biochar amended with Vermi (205.1, 220.6, and 200.7 µg g−1, respectively). The study also found that Mg concentration was high in the soil. Mg concentration was significantly greater (p ≤ 0.05) in 20% Biochar (864.5 µg g−1) than in 5% Biochar, 10% Biochar amended with Cow, 10% biochar amended with CM, soil amended with 10% Biochar, Vermi and SS (725.4, 708.9, 732.5, 730.9, and 706.8 µg g−1, respectively).
Table 2 highlights variations in Mg, Cu, and K concentrations among soil treatments, while Zn levels remained statistically similar across all treatments.
The maximum allowable limits of Mg and K in potato tubers are not explicitly defined by the FAO or health organizations. The maximum concentration of copper in potato tubers can vary, but a study found that Cu concentrations in potato samples ranged from 0.505 to 2.729 mg/kg. This range indicates typical levels rather than a regulatory maximum.

3.1. BAF Values for Non-Essential Heavy Metals

Figure 1A revealed that the concentration of Cd in potato tubers of plants grown in Vermi and SS amended with 10% Biochar was greater compared to CW and Vermi amended with 10% Biochar. The bioaccumulation factor (BAF) of potato tubers, obtained by dividing the concentration of Cd in tubers by Cd concentration in soil, was found to exceed 1 (BAF > 1) in all the treatments tested reaching a maximum of 3.9 and 3.8 µg g−1 tissue, in Vermi and NA, respectively (Figure 1B). The BAF value in tubers of plants grown in Vermi was significantly higher compared to those grown in Vermi amended with 10% Biochar. In addition, all the treatments investigated successfully accumulated Cd in the tubers, with the most significant accumulation in plants grown in Vermi-amended soil. This observation proved that potato tubers can remediate soil contaminated with Cd. Accordingly, potatoes grown in such amendments are not edible and should be considered hazardous waste due to their higher concentrations of Cd. However, these findings have significant implications for the reclamation of soil contaminated with Cd.
Figure 2A also revealed that the concentrations of Pb in potatoes grown under the studied soil amendments dramatically exceeded the FDA/WHO allowable limit of 1 µg g−1 for Pb (Table 3) in potato tubers at harvest. Significant concentrations of Pb were detected in the potato tubers grown in 10% Biochar, Cow, NA, and SS (5.7, 5.6, 5.5, and 5.6 µg g−1 tissue, respectively). On the contrary, mixtures of 20%, 5%, and 10% Biochar mixed with SS had the lowest concentrations of Pb. These results indicate that even NA is contaminated with Pb. Pb is the most common heavy metal and is resistant to corrosion. Food can be contaminated by naturally occurring Pb in the soil and by atmospheric fallout. However, the BAF of Pb in all tested tubers collected from the twelve soil treatments was below 1 (BAF < 1), reaching a maximum of 0.31 and 0.32 µg g−1 tissue in Vermi and SS, respectively (Figure 2B). The low BAF values of Pb in tubers grown in NA and soils amended with animal manure and Biochar treatments at three application rates indicate that Pb is not mobile from soil to potato tubers, a significant advantage for human safety.
The Cr levels in potato tubers surpassed the maximum allowable limit of 0.1 µg g−1 (Table 3). As depicted in Figure 3A, potato tubers from plants cultivated in various treatments including 10% Biochar, a mix of 10% Biochar with Cow, CM, Cow alone, NA, SS, and Vermi showed significantly elevated (p ≤ 0.05) Cr concentrations (4.97, 4.8, 4.95, 4.96, 4.95, 4.96, and 4.95 µg g−1, respectively) compared to those grown with 5% Biochar (4.87 µg g−1) and 10% Biochar mixed with SS (4.90 µg g−1). Furthermore, the Cr bioaccumulation factor (BAF) in Vermi was significantly greater (p ≤ 0.05) than in the 10% Biochar combined with CM (Figure 3B). All BAF values for Cr were below 1, indicating that potato tubers do not accumulate chromium. Cr does not play a biological role in plant physiological processes [44], and elevated soil concentrations of Cr can hinder the uptake of essential nutrients like Fe, Mg, Ca, and P by forming insoluble complexes [45].

3.2. BAF Values for Essential Heavy Metals

Figure 4A shows that the Ni content in potato tubers surpassed the maximum permissible limit of 0.1 µg g−1. Tubers from plants grown with 10% biochar had a Ni concentration of 3.9 µg g−1, significantly higher (p ≤ 0.05) than those from plants grown with 20% Biochar, 5% Biochar, or 10% Biochar combined with Cow, CM, SS, or Vermi, which recorded concentrations of 3.42, 3.15, 3.07, 3.09, 3.38, and 3.11 µg g−1, respectively. No significant differences in Ni concentrations were noted among tubers from the other treatments (Figure 4A). Additionally, the Ni bioaccumulation factor (BAF) showed no significant variation across treatments (Figure 4B), with all values remaining below 1, suggesting that potato tubers do not act as accumulators of Ni.
The results showed that Zn concentration in potato tubers in 10% Biochar was greater (22.8 µg g−1) compared to 20% Biochar, 5% Biochar, and 10% Biochar amended with SS (15.0, 14.0, and 13.9 µg g−1, respectively (Figure 5A). BAF values of Zn in tubers of plants grown in 10% Biochar, 10% Biochar mixed with Cow, NA, SS, and Vermi were above 1 (BAF > 1). These results indicate that potato tubers can be used to remediate soil contaminated with Zn. Whereas potato tubers grown in 20% Biochar and 10% Biochar mixed with SS had low BAF values (BAF < 1) (Figure 5B).
The permissible limit of Zn in edible plants is 0.6 mg g−1 as recommended by WHO [40]. Zn reduces heavy metal toxicity by restricting its availability as it plays a significant role in heavy metal homeostasis [46].
Figure 6A shows that potato plants grown in 10% Biochar (22.5 µg g−1) and NA (21.91 µg g−1) had significantly greater (p< 0.05) concentrations of Cu in their tubers compared to tubers of plants grown in 20% Biochar, 5% Biochar, 10% Biochar mixed with Cow, 10% Biochar mixed with SS, 10% Biochar mixed CM and 10% biochar mixed with Vermi (7.97, 7.75, 8.1, 7.5, 8.35, and 7.6 µg g−1 tissue, respectively). The BAF values of Cu in tubers grown in the NM control and 10% Biochar treatments show a BAF > 1 that is significantly greater than (p < 0.05) compared to tubers of plants grown in 20% Biochar, 5% Biochar, 10% Biochar mixed with Cow, 10% Biochar mixed with SS, 10% Biochar mixed CM, 10% Biochar mixed with Vermi and CM (Figure 6B). These high (>1) BAF values indicate that potato tubers of plants grown in the twelve treatments are Cu accumulators.
Figure 7A also shows that soil amended with SS (13.8 µg g−1) had a significantly higher (p ≤ 0.05) Mn concentration in potato tubers than 20% Biochar, 5% Biochar, 10% Biochar mixed with Cow, 10% Biochar mixed with Vermi, CM, Cow, and NA (11.62, 11.07, 9.95, 11.09, 10.96, 10.68, and 11.03 µg g−1 tissue, respectively). In addition, the BAF value of Mn in all the soil treatments investigated was below 1 (BAF < 1) (Figure 7B). Soil amended with SS had significantly greater (p ≤ 0.05) BAF than the other treatments. These Mn BAF values indicate that potato tubers are not Mn accumulators. Mn is both a heavy metal and an essential micronutrient. It is a part of photosynthetic enzymes and proteins in plants [47].

3.3. BAF Values for Essential Nutrients

Figure 8A shows that K concentration in potato tubers was significantly greater (p< 0.05) in soil amended with CM (18,738 µg g−1) than 20% Biochar, 5% Biochar, 10% Biochar mixed with Cow, and 10% Biochar mixed with Vermi (14,517, 12,512, 15,989, and 12,840 µg g−1, respectively). Whereas, the BAF values of K were exceedingly higher than 1, there was no significant difference in BAF values among the treatments (Figure 8B). This suggests that plants absorb and accumulate K in higher concentrations, which may be due to its importance as a macronutrient.
Figure 9A shows that Mg concentration in potato tubers was significantly greater (p< 0.05) in CM and Cow (1020.21 and 999.18 µg g−1) than in the other treatments. Meanwhile, 10% Biochar mixed with SS and 5% Biochar had the lowest Mg content in potato tubers compared to all other treatments. BAF values of Mg were significantly greater (p ≤ 0.05) in 10% Biochar mixed with CM, SS, and CM (BAF > 1) compared to soil amended with 10% Biochar, 20% Biochar, 5% Biochar, 10% Biochar mixed with SS and NA (Figure 9B). This indicates that potato tubers may accumulate Mg at different levels depending on the type of soil amendment.
Heavy metals BAF values below 1 imply that the potato tubers do not accumulate heavy metals at a higher concentration than in the soil, and vice versa for BAF values greater than 1 [48]. Our study found that BAF values for Cd, Cu, and Zn were greater than 1, indicating that potato tubers are good accumulators of these heavy metals. Conversely, BAF values for Pb, Ni, Cr, and Mn were less than 1. However, if edible crops are used for phytoremediation, one should check the permissible limit of specific heavy metals before consumption. If the accumulated concentration of heavy metals in the potato tuber is below the allowable limit, then the tubers can be deemed edible. In this study, Ni, Cr, Mn, Cd, and Pb concentrations were above the permissible limit. This shows that the potato tubers used in this research cannot be used for consumption purposes but can be used for phytoremediation.
There has been little research on the bioaccumulation of heavy metals using potato tubers grown under animal manure. Orellana-Mendoza et al. [49] conducted research on bioaccumulation of heavy metals by potato tubers using CM as a soil amendment and found that CM increases soil concentrations of Cu and Zn above the permissible limit and leads to higher accumulation of Zn, Cu, and Pb in potato tubers compared to other fertilizers. They further found BAF less than 1 for Cd, Cu, Pb, Cr, and Zn in potato tubers and deemed them safe for human consumption.
Heavy metal uptake by crops depends on how the roots of crops interact with different heavy metals in the soil [50]. The concentration of heavy metals is primarily shaped by root activities within the rhizosphere. These activities can significantly influence the solubility and availability of nutrients and heavy metals through root exudates and their interactions in the soil. Various processes, including adsorption, desorption, precipitation, dissolution, oxidation, and reduction, regulate the bioavailability and toxicity of metal ions in the soil solution. Root exudates can modify the leachability of elements [50], affecting their mobilization and immobilization. Furthermore, the solubility and bioaccumulation of heavy metals in soil are significantly influenced by the levels of organic matter present in the animal manures [41,51,52]. In our study, the interaction between potato tubers and the specific heavy metals and the variation in the organic matter present in the animal manures and biochar might have made differences in the accumulated heavy metal concentration in the potato tubers.
Again, monitoring heavy metal uptake in crops grown in recycled waste is essential for identifying appropriate animal manures for organic fertilizers and understanding how metals are absorbed and moved within plants. Animal manures that increase metal accumulation in edible plants should be avoided to reduce the risk of human exposure to heavy metals through the food chain. Higher BAF values are expected for essential plant nutrients such as Mg, K, Cu, and Zn. The ways in which different plant species and animal manures influence bioaccumulation can vary significantly. There is a clear relationship between the types of crops and the soil amendments employed in metal remediation. Additionally, careful consideration should be given to the final disposal of plants and other residues after achieving phytoremediation activities.

4. Conclusions

This study provides critical insights into the phytoremediation potential of potato tubers for Cd, Cu, and Zn in soils mixed with animal manures and biochar. High BAF values (BAF > 1) for Cd, Cu, and Zn across treatments confirm the capacity of potato tubers to uptake and accumulate these metals from the contaminated soils. However, accumulating Cd and Pb beyond the permissible limits in all treatments makes the tubers unfit for human consumption. This reinforces the need to distinguish between crops used for food and crops employed for phytoremediation.
Further, the low mobility (BAF < 1) of Pb, Ni, Cr, and Mn in most treatments suggests a limited risk of transfer of these metals to potato tubers. This highlights biochar-manure combinations as promising tools for reducing metal translocation in the food chain. These findings underscore the dual role of certain animal manures and amendments in both enhancing soil fertility and remediating metal uptake. However, there is a pressing need to identify and standardize the optimal manure-biochar mixing formulations that maximize the phytoremediation efficiency while minimizing food safety risks. Further studies should focus on the identification of such formulations. More research should also explore the molecular and physiological mechanisms driving uptake and transport in potatoes, especially regarding the application of animal manure. Studies should also refine using non-food crops or inedible crop varieties for phytoremediation to avoid safety conflicts.

Author Contributions

Writing, original ideas, field design, methodology, review, and editing: G.F.A.; field, laboratory work, and data collection report: A.N. and B.N. All authors have read and agreed to the published version of the manuscript.

Funding

This research project was funded by the United States Department of Agriculture, National Institute of Food and Agriculture (USDA/NIFA), under a grant to Kentucky State University, Agreement #KYX-10-23-80P, Accession 7005611.

Data Availability Statement

The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author at george.antonious@kysu.edu.

Acknowledgments

We appreciate E. Turley and the farm crew at Kentucky State University Research Farm for their support during the fieldwork.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Concentration of Cd in potato tubers grown under twelve soil management practices (A) and Cd bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
Figure 1. Concentration of Cd in potato tubers grown under twelve soil management practices (A) and Cd bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
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Figure 2. The concentration of Pb in potato tubers grown under twelve soil management practices (A) and Pb bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
Figure 2. The concentration of Pb in potato tubers grown under twelve soil management practices (A) and Pb bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
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Figure 3. Concentrations of Cr in potato tubers of plants grown under twelve soil management practices (A) and Cr bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
Figure 3. Concentrations of Cr in potato tubers of plants grown under twelve soil management practices (A) and Cr bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
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Figure 4. Concentration of Ni in potato tubers grown under twelve soil management practices (A) and Ni bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
Figure 4. Concentration of Ni in potato tubers grown under twelve soil management practices (A) and Ni bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
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Figure 5. Concentration of Zn in potato tubers grown under twelve soil management practices (A) and Zn bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different(p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
Figure 5. Concentration of Zn in potato tubers grown under twelve soil management practices (A) and Zn bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different(p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
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Figure 6. Concentrations of Cu in potato tubers of plants grown under twelve soil management practices (A) and Cu bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple test for mean comparisons.
Figure 6. Concentrations of Cu in potato tubers of plants grown under twelve soil management practices (A) and Cu bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple test for mean comparisons.
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Figure 7. Concentrations of Mn in potato tubers grown under twelve soil management practices (A) and Mn bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
Figure 7. Concentrations of Mn in potato tubers grown under twelve soil management practices (A) and Mn bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
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Figure 8. Concentrations of K in potato tubers grown under twelve soil management practices (A) and K bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
Figure 8. Concentrations of K in potato tubers grown under twelve soil management practices (A) and K bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
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Figure 9. Concentration of Mg in potato tubers grown under twelve soil management practices (A) and Mg bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
Figure 9. Concentration of Mg in potato tubers grown under twelve soil management practices (A) and Mg bioaccumulation factors (B). Statistical analysis was carried out among the soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) are significantly different (p ≤ 0.05) using Duncan’s multiple tests for mean comparisons.
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Table 1. (A) Application rate of soil amendments used for growing white potato at the Kentucky State University research farm. (B) Characteristics of the soil amendments and native soil (control) used in the experiment.
Table 1. (A) Application rate of soil amendments used for growing white potato at the Kentucky State University research farm. (B) Characteristics of the soil amendments and native soil (control) used in the experiment.
(A)
Soil AmendmentsLbs. Plot−1Lbs. Acre−1Kg Hectare−1
Sewage Sludge (SS)40.212000.002241.70
Chicken Manure (CM)182.829090.9010,189.55
Cow Manure (Cow)402.2120,000.0022,417.02
10% Biochar279.3613,888.8815,567.36
5% Biochar139.686944.447783.68
Vermicompost (Vermi)201.1110,000.0011,208.51
10% Biochar SS40.21 + 279.362000.00 + 13,888.882241.70 + 15,567.36
10% Biochar CM182.82 + 279.369090.90 + 13,888.8810,189.55 + 15,567.36
10% Biochar Cow402.21 + 279.3620,000.00 + 13,888.8822,417.02 + 15,567.36
20% Biochar279.36 + 279.3613,888.88 + 13,888.8815,567.36 + 15,567.36
10% Biochar Vermi201.11 + 279.3610,000.00 + 13,888.8811,208.51 + 15,567.36
(B)
Soil ParametersSewage SludgeVermicompostCow ManureChicken ManureBiocharNative Soil (Control)
P (%)0.30 b1.23 a0.72 ab0.79 ab0.30 b0.14 c
N (%)0.47 b1.40 b1.75 b4.12 a0.56 c0.14 c
K (%)0.24 b0.54 ab1.22 a0.50 ab0.33 b0.26
OM (%)3.20 b7.60 a5.63 a6.19 a7.60 a2.45 b
C (%)3.6 c12.1 b26.1 a17.7 b3.7 c1.5 c
C/N ratio7.6 c8.64 bc14.91 a4.29 c17.61 a10.71 b
pH8.4 a5.71 a7.95 a6.15 a6.8 a6.8 a
P, ppm10.54 a0.23 c0.30 c2.56 b1.16 bc18.59 a
Cd, ppm6.63 a6.65 a6.73 a6.82 a6.75 a0.66 b
Ni, ppm9.22 a0.34 c4.06 b6.27 b5.12 b6.83 b
Mn, ppm497.86 b213.46 c308.62 b201.2 c327.98 b1262.5 a
Cr, ppm19.43 a2.49 b3.31 b5.06 b3.2 b14.15 a
Mg, ppm2045.25 b1564.7 c2400.28 b6705.89 a2198.37 b847.71 d
Cu, ppm182.29 a1.05 d18.647 c37.793 b9.08 c8.58 c
K, ppm928.75 d506.2 d8279.41 b17741.03 a2251.29 c292.55 d
Zn, ppm441.85 a122.1 ab58.73 b225.09 ab28.33 bc19.72 c
Soil organic matter (SOM) was determined as dry weight minus ash content. The pH was calculated using a glass electrode in soil/distilled water slurry (1:5 w/v). Elemental analysis was conducted using an inductively coupled plasma-optical emission spectrometer ICP/OES. Each value is the average of three replicates ± standard error. Statistical comparisons among soil treatments in each row were carried out using analysis of variance (ANOVA). Values accompanied by different letter (s) in each row are significantly different (p ≤ 0.05).
Table 2. Elemental composition (µg g−1 dry soil) of native soil and soil amended with animal manure and three biochar application rates used for growing white potato, Solanum tuberosum, var. Kennebec.
Table 2. Elemental composition (µg g−1 dry soil) of native soil and soil amended with animal manure and three biochar application rates used for growing white potato, Solanum tuberosum, var. Kennebec.
Soil TreatmentPbCdNiMnCr
10% Biochar19.448 ± 0.81 ab0.688 ± 0.01 a7.128 ± 0.229 a1334.8 ± 59.57 a15 ± 0.572 ab
20% Biochar20.391 ± 0.96 ab0.70233 ± 0.03 a6.68 ± 0.19 abc1424 ± 88.09 a15.247 ± 1.587 ab
5% Biochar19.347 ± 1.76 ab0.7 ± 0.03 a5.994 ± 0.38 c1241.2 ± 156.09 a15.194 ± 1.655 ab
10% Biochar Cow19.704 ± 0.51 ab0.703 ± 0.01 a5.918 ± 0.17 c1307.2 ± 37.79 a14.845 ± 0.537 ab
10% Biochar CM20.771 ± 0.93ab0.71367 ± 0.01 a6.095 ± 0.38 bc1363.4 ± 88.11 a16.427 ± 0.788 a
10% Biochar SS 21.176 ± 0.54 a0.713 ± 0.00 a6.501 ± 0.23 abc1459.4 ± 57.65 a15.667 ± 0.452 ab
10% Biochar Vermi19.489 ± 2.06 ab0.67667 ± 0.03 a5.963 ± 0.22 c1319.5 ± 201.97 a14.84 ± 1.812 ab
CM19.341 ± 0.37 ab0.67467 ± 0.01 a6.707 ± 0.14 abc1293.8 ± 70.23 a15.192 ± 0.782 ab
Cow20.21 ± 0.93 ab0.703 ± 0.01 a7.133 ± 0.14 a1326.6 ± 42 a15.715 ± 0.221 ab
NA (control)18.593 ± 0.59 ab0.66733 ± 0.01 a6.836 ± 0.14 ab1262.5 ± 38.44 a14.155 ± 0.563 ab
SS17.82 ± 1.19 ab0.65433 ± 0.01 a6.232 ± 0.18 bc1169.6 ± 104.44 a13.598 ± 0.68 ab
Vermi17.48 ± 0.10 b0.65 ± 0.02 a6.8423 ± 0.25 ab1190.2 ± 46.08 a13.088 ± 0.21 b
Soil TreatmentMgCuKZn
10% Biochar856.85± abc9.111 ± 0.52 ab317.38 ± 9.81 a19.14 ± 0.76 a
20% Biochar864.5 ± 39.17 a8.906 ± 0.15 ab302.9 ± 42.80 a20.701 ± 2.38 a
5% Biochar725.47 ± 56.19 de7.738 ± 0.57 b205.13 ± 37.39 cd17.36 ± 1.12 a
10% Biochar Cow708.93 ± 20.48 e9.09 ± 0.66 ab220.63 ± 1.66 bcd20.392 ± 0.87 a
10% Biochar CM732.53 ± 37.49 bcde8.311 ± 0.57 ab276.11 ± 21.15 abc19.745 ± 2.02 a
10% Biochar SS 788.83 ± 37.78 abcde9.824 ± 1.01 ab260 ± 14.18 abcd21.176 ± 2.22 a
10% Biochar Vermi730.98 ± 48.89 cde10.1 ± 1.52 ab200.74 ± 25.42 d21.544 ± 3.12 a
CM791.37 ± 26.56 abcde11.419 ± 2.96 a324.88 ± 19.18 a23.348 ± 6.42 a
Cow859.99 ± 40.12 ab8.233 ± 0.36 ab307.17 ± 12.94 a19.194 ± 1.65 a
NA (control)847.71 ± 40.36 abcd8.579 ± 0.257 ab292.55 ± 15.48 ab19.723 ± 0.893 a
SS706.87 ± 34.05 e8.698 ± 0.955 ab275.86 ± 25.01 abc18.431 ± 2.054 a
Vermi787.28 ± 24.68 abcde7.811 ± 0.369 b250.72 ± 13.08 abcd17.52 ± 1.533 a
Cow, CM, SS, and Vermi denote cow manure, chicken manure, municipal sewage sludge, and vermicompost treatments, respectively. Each value in the table represents the average of three replicates ± standard error. Statistical analysis was carried out among soil treatments using analysis of variance (ANOVA). Values accompanied by a different letter(s) in each column are significantly different (p ≤ 0.05), as determined by using Duncan’s multiple range test for mean comparisons.
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Antonious, G.F.; Nepal, A.; Neupane, B. Remediation of Cd, Cu, and Zn Metals in Soil Amended with Biochar and Animal Manure Using a Hyperaccumulator. Pollutants 2025, 5, 22. https://doi.org/10.3390/pollutants5030022

AMA Style

Antonious GF, Nepal A, Neupane B. Remediation of Cd, Cu, and Zn Metals in Soil Amended with Biochar and Animal Manure Using a Hyperaccumulator. Pollutants. 2025; 5(3):22. https://doi.org/10.3390/pollutants5030022

Chicago/Turabian Style

Antonious, George F., Anjan Nepal, and Basanta Neupane. 2025. "Remediation of Cd, Cu, and Zn Metals in Soil Amended with Biochar and Animal Manure Using a Hyperaccumulator" Pollutants 5, no. 3: 22. https://doi.org/10.3390/pollutants5030022

APA Style

Antonious, G. F., Nepal, A., & Neupane, B. (2025). Remediation of Cd, Cu, and Zn Metals in Soil Amended with Biochar and Animal Manure Using a Hyperaccumulator. Pollutants, 5(3), 22. https://doi.org/10.3390/pollutants5030022

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