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Article

The Biosorption of Cadmium, Lead, and Arsenic Using Garlic Byproducts and Their Potential for Metal Immobilization in Soil

by
Jin Hee Park
Department of Environmental and Biological Chemistry, Chungbuk National University, Cheongju 28644, Chungbuk, Republic of Korea
Sustainability 2025, 17(19), 8857; https://doi.org/10.3390/su17198857
Submission received: 4 August 2025 / Revised: 26 September 2025 / Accepted: 30 September 2025 / Published: 3 October 2025
(This article belongs to the Special Issue Sustainable Utilization of Agro-Wastes ＆ Pollution Reduction and Control)
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Abstract

Metal contamination poses serious environmental and human health risks, which results in the need for low-cost remediation approaches. The utilization of agricultural byproducts for the removal of metal contaminants is considered cost-effective and environmentally sustainable. Garlic byproducts are rich in sulfur-containing compounds, and various functional groups contribute to metal binding. This study aimed to evaluate the potential of garlic stem and peel for the removal of cadmium (Cd), lead (Pb), and arsenic (As) from aqueous solutions and for their immobilization in contaminated soils. Batch sorption experiments conducted at pH 7 for 24 h showed that garlic stem removed 71.5% of Cd and 70.8% of Pb, while garlic peel achieved 65.4% and 79.4% removal, respectively. The higher Pb removal by garlic peel might be attributed to its higher sulfur content. However, both byproducts were less effective in removing As(III) and showed negligible removal of As(V), as these species predominantly occur in neutral or negatively charged species at neutral pH, resulting in weak interactions with negatively charged surface functional groups. Soil incubation experiments were conducted using 1% and 5% amendments of garlic stem and peel in Pb- and As-contaminated soils. Extractable Pb concentrations significantly increased in soils treated with 1% garlic peel because of the formation of labile complexes of Pb with dissolved organic carbon. However, a column experiment to evaluate the impact on Pb mobility under saturated and unsaturated conditions showed that Pb concentration in soil pore water decreased with garlic stem. Pb concentration was lower under saturated conditions, possibly due to the precipitation of Pb as PbS. Although the short-term application of raw agricultural byproducts increased extractable metal concentrations, long-term incubation reduced Pb levels in pore water. These findings suggest that unmodified garlic stem is a promising, cost-effective amendment for Pb immobilization in soil. Nevertheless, caution is needed in its application to prevent unintended metal mobilization in soil.

1. Introduction

Agricultural activity to produce fruits and vegetables generates substantial amounts of waste including stems, peels, leaves, and shells that are often discarded. Recently, there has been growing interest in converting agricultural residues into value-added materials for application in energy and environmental sectors. Biomass feedstock such as corn stover, wheat straw, and manure are used for bioethanol and biogas production through biochemical processes and anaerobic digestion, respectively [1]. Agricultural residues can also be used as a soil amendment to improve soil quality and mitigate environmental impacts such as global warming and pollution [1]. Utilization of agricultural byproducts to remove metal contaminants from wastewater is economically beneficial and effective because of various functional groups present in the organic residue [2]. Generally, agricultural byproducts contain cellulose, hemicellulose, and lignin with functional groups such as alcohol, aldehydes, and aromatic rings that adsorb metals [3]. Simón et al. (2022) [4] showed that pine sawdust, sunflower seed hull, and corn residue removed more than 50% of Ni, Zn, and Cd in a solution. In addition, they suggested a disposal method by stabilizing the spent biosorbents as clay ceramics for construction material. The advantages include low cost, high efficiency, reusability, minimal sludge generation, and strong affinity and selectivity for metals [5].
Agricultural residues are sometimes physicochemically modified to enhance sorption capacity through acid and base treatment, polymerization, and pyrolysis. Generally, modified biosorbents show enhanced sorption capacity because of improved surface area, porosity, and functional groups [6]. However, modification does not always lead to an increase in metal removal [7]. In addition, the modification process requires additional energy, chemicals, and equipment, thereby increasing production costs and reducing environmental sustainability. Therefore, utilizing unmodified agricultural byproducts is sustainably and economically feasible for field scale application. Various agricultural byproducts including orange peel, banana peel, sugarcane bagasse, oil palm bagasse, coconut husk, walnut shell, corn cob, peanut hull, rice husk, and rice bran were used for metal adsorption [5,8,9,10,11].
Garlic byproducts are effective in metal adsorption because of their high organic matter content such as pectic acid, sulfuric acid, polyphenols, and alliin, which are rich in hydroxyl, carboxylic, and amino groups [12,13]. The presence of functional groups, particularly associated with sulfur-containing compounds unique to garlic, facilitates strong binding interactions with heavy metals such as cadmium (Cd) and lead (Pb), thereby enhancing removal efficiency [14,15]. Although there are some studies on the use of garlic peels, few studies have been conducted on metal adsorption by garlic stem. In addition, there have been no comprehensive studies investigating the application of garlic byproducts for both the removal of metals and their stabilization in contaminated soils.
The economic advantage of utilizing garlic byproducts lies in their low cost, wide availability, and elimination of additional waste management requirements. Agricultural byproducts serve as an alternative to synthetic and commercially activated adsorbents that are often expensive and energy-intensive. Given that garlic stems are produced in large quantities than garlic peels in agricultural practices, the on-site application of the garlic stem reduces disposal and treatment costs. Unlike conventional adsorbents, which require costly synthesis and may pose secondary pollution risks, garlic byproducts offer a low-cost, biodegradable, and environmentally friendly alternative. However, several challenges remain including optimizing reaction processes, improving adsorption kinetics, and developing modification to enhance performance without increasing extra cost. The reuse and disposal of spent biosorbents also need to be considered because improper processing or disposal of spent biosorbents could pose ecological risks. Nevertheless, employing garlic byproducts as biosorbents represents a more sustainable and environmentally responsible strategy that aligns with waste-to-resource approaches for sustainable agriculture and environmental remediation.
Heavy metals and metalloids such as Cd, Pb, and arsenic (As) are of significant environmental and health concern because of their high toxicity, persistence in the environment, and potential for bioaccumulation [16]. Chronic exposure to Cd adversely affects kidney health, leading to functional impairment and renal damage [17]. Pb is especially toxic to children, causing behavioral problems, learning deficits, and a reduced intelligence quotient (IQ). Long-term exposure to Pb can lead to anemia and damage to the brain and kidneys [18]. Arsenic, a carcinogen that causes skin lesions, often originates from natural sources, making watershed remediation necessary [19]. To prevent the contamination of food crops by these metals and metalloids, the remediation of contaminated water and soil is crucial for sustainable agriculture. Because of the high sulfur content of garlic byproducts, they have a high potential for metal stabilization not only by adsorbing metals through functional groups, but also by forming metal sulfides. While previous research has focused on garlic peels because of their availability in the market, garlic stem remains underexplored despite being produced in greater quantities in the field. Based on the functional groups and sulfur containing compounds, I hypothesized that both garlic stem and peel would effectively remove metal(loid)s from aqueous solutions without modification and immobilize metal(loid)s in soil. Therefore, this study aimed to evaluate the potential of garlic stem and peel for the removal of Cd, Pb, and As from aqueous environments and their immobilization in contaminated soils.

2. Materials and Methods

2.1. Preparation of Soil and Garlic Byproducts

Soil used for the incubation experiment was collected from an area near an abandoned mine, while the soil for the column experiment was obtained from a shooting range. Soil samples were air-dried and sieved to less than 2 mm. Soil samples (1.5 g) were digested with 14 mL aqua regia (1:3 mixture of HNO3 and HCl) at 130 °C for 2 h on a graphite block digestion system (ODLAB, Gwangmyeong, South Korea) to analyze total metal concentrations. The digested solution was diluted with deionized water to 50 mL, and metal concentrations were analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES, Horiba, Kyoto, Japan). Total metal concentrations in the soils used for the experiment are presented in Table 1. Garlic stem and peel were collected from a garlic field after harvesting and were used in the experiments. Garlic stem and peel were washed with deionized water and dried in an oven at 60 °C. The dried samples were ground using a blender, and the ground samples were sieved to less than 1 mm. A total of 0.2 g of ground garlic stem and peel were weighed into a 100 mL Erlenmeyer flask, and 5 mL HNO3 and 3 mL H2O2 solution were added. The sample solution was left to stand for 16 h and decomposed on a 140 °C hot plate for 1.5 h. The digested samples were diluted to 20 mL with distilled water and filtered using a 0.45 μm syringe filter. The digested solution was analyzed for element content using ICP-OES.

2.2. Batch Adsorption of Cd, Pb, and As by Garlic Stem and Peel

To evaluate the removal of Cd, Pb, As(III), and As(V) by garlic stem and peel, 0.02 g of powdered garlic stem and peel were mixed with 20 mL of Cd, Pb, As(III), and As(V) solutions, respectively, in 50 mL conical tubes. Cadmium (20 mg/L), Pb (10 mg/L), As(III) (0.2 mg/L), and As(V) (0.2 mg/L) solutions were prepared using cadmium chloride, lead chloride, sodium arsenate, and sodium arsenite of analytical grade (≥99% purity), respectively. The pH of the solutions was adjusted to 7 using 0.1 M NaOH and 0.1 M HCl. The solution was shaken in an orbital shaker at 180 rpm for 24 h and filtered through a 0.45 µm membrane filter. After filtration, the solution was acidified, and the remaining Cd, Pb, and As concentrations in the solution were analyzed using ICP-OES.
Functional groups of garlic stem and peel were investigated using attenuated total reflectance–Fourier-transform infrared (ATR-FTIR) spectroscopy (Cary 670, Agilent, Santa Clara, CA, USA) in the 500–4000 cm−1 range with 32 scans before and after Pb adsorption. Surface morphology and element composition were analyzed using scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDX, Germini 560, Zeiss, Oberkochen, Germany) before and after Pb adsorption.

2.3. Incubation of Metal Contaminated Soil with Garlic Stem and Peel

To evaluate the immobilization of As, Cd, and Pb by powdered garlic stem and peel in soil, 5 g of metal contaminated soil was treated with 1% and 5% (w/w) of garlic stem and peel and incubated for 1 week at 25 °C in an incubator. To analyze extractable Cd, Pb, and As concentrations, 5 g of soil was mixed with 40 mL of 1 M ammonium acetate solution in a 50 mL conical tube for 4 h on an orbital shaker. After extraction, the samples were centrifuged at 4000 rpm for 10 min, and the supernatant was filtered through a 0.45 µm syringe filter. Metal concentrations in the extracted solution were analyzed using ICP-OES. The pH and electrical conductivity (EC) of the soil after incubation were measured using a 1:5 (w/v) = soil/water extractant by a calibrated pH and EC meter (Thermo Fisher Scientific, Waltham, MA, USA). Dissolved organic carbon (DOC) was extracted from soil by mixing with deionized water at a 1:10 (w/v) soil-to-water ratio for 1 h at 180 rpm. The suspension was centrifuged at 4000 rpm for 10 min and filtered through a 0.45 μm syringe filter. Total carbon (TC) and total inorganic carbon (TIC) in the solution were analyzed using a total organic carbon (TOC) analyzer (Shimadzu, Kyoto, Japan), and DOC was calculated by subtracting TIC from TC in the solution and converting the concentration to a soil basis.

2.4. Column Incubation of Pb-Contaminated Soil with Garlic Stem

Column (8.5 cm diameter and 30 cm height) was packed with 1.5 kg of Pb-contaminated soil by intermittent tapping. Soil treated with 1% garlic stem was packed using the same method and compared with a control column without garlic stem. The soil in the column was moistened by adding 600 mL of water, and a water tank was connected to the bottom of the columns. The water level in the tank was kept at about 10 cm from the bottom of the columns to keep the lower part of the columns saturated and the upper part unsaturated. Pore water was collected using a Rhizon sampler (Rhizosphere, Wageningen, The Netherlands) horizontally placed in the saturated and unsaturated parts of the column. During the column experiment, pore water sampling was conducted once a week. The collected pore water was filtered with a 0.45 μm syringe filter, and Pb concentrations were measured using ICP-OES. Dissolved organic carbon in pore water was analyzed using a TOC analyzer.

2.5. Statistical Analysis

Experiments were conducted in triplicate, and data are presented as the mean ± standard deviation of three replicates. Statistical analysis was carried out using SPSS 27 software (IBM). One-way Analysis of Variance (ANOVA) was used to compare the means, followed by Duncan’s multiple range test. Data were tested for normality and homogeneity prior to ANOVA. A significance level of p < 0.05 was considered significant for all analyses.

3. Results and Discussion

3.1. Removal of Cd, Pb and As Using Garlic Stem and Peel

Cd and Pb concentrations significantly decreased in aqueous solution treated with garlic stem and peel (Figure 1a). The removal efficiency of Cd and Pb by garlic stem was 71.5 and 70.8%, respectively, and 65.4 and 79.4% by garlic peel, respectively. The removal amount calculated based on the amount of garlic stem and peel was 12.64 and 11.56 mg/g for Cd, 7.91 and 8.87 mg/g for Pb, 0.03 and 0.03 mg/g for As(III), and 0.01 and 0.005 mg/g for As(V), respectively. The results indicate that both garlic stem and peel have a strong capacity to remove heavy metals from aqueous environments, suggesting their potential as low-cost and eco-friendly biosorbents. The ATR-FTIR spectra of garlic stem and peel showed broad bands at 3330 cm−1 corresponding to O-H group stretching vibrations (Figure 2) [20]. The peaks at 2919 and 2851 cm−1 are attributed to C-H stretching vibrations, and the peak at 1734 cm−1 is attributed to the C=O group present in hemicelluloses. The peak at 1605 cm−1 corresponds to the C=C bond of the aromatic group in lignin. The peaks at 1417 and 1320 cm−1 are assigned to the bending vibration of -CH2 [21]. The peaks at 1234 and 1015–1025 cm−1 are attributed to -SO32− and S=O, respectively [20,22]. After Pb adsorption the peak at 1025 and 1015 cm−1 in garlic stem and peel, respectively, shifted slightly to 1013 cm−1, indicating Pb adsorption to sulfur-containing functional groups (Figure 2). Liu et al. (2014) [23] reported that Pb was adsorbed on the garlic peel through chelation with oxygen or nitrogen. According to Liu et al. (2014) [23], the principal functional groups of C=O, C-O, and S-O in garlic peel were present, which might contribute to metal removal. These groups are known to form stable complexes with heavy metals, thereby facilitating the adsorption process. The SEM image revealed a porous and rough surface, as well as visible fibers of the garlic byproducts (Figure 3). Sun et al. (2018) [13] also demonstrated that the porous structure and carboxyl group contributed to Cd adsorption by garlic peel. The high porosity increased the availability of active adsorption sites. Although the removal was high for Cd and Pb, competing ions such as Ca2+, Mg2+, SO42−, and HCO3− may reduce adsorption efficiency under field conditions. Therefore, the effect of competing ions on metal(loid) removal by garlic byproducts should be considered to better assess the practical applicability of the garlic byproducts as biosorbents.
Removal efficiency by garlic peel was higher for Pb than Cd. Garlic peels contain higher sulfur content, which might contribute to higher removal efficiency of Pb (Table 2). The EDX results confirmed the presence of sulfur in both the garlic stem and peel, along with the evidence of Pb adsorption (Figure 3). Sulfur-containing ligands such as thiol and sulfide groups bind metals, leading to the removal of metals from water and wastewater [15]. These functional groups contribute to chemisorption mechanisms, where the metals are not just physically adsorbed but chemically bound to the biosorbent surface. Hoa et al. (2007) [24] reported that sulfide-rich effluent removed 85–95% of Pb as lead sulfide precipitate by sulfate-reducing bacteria (SRB). Sulfur-containing functional groups such as SO32− identified by FT-IR analysis in garlic stem and peel may also contribute to Pb immobilization through precipitation or strong complexation [20]. Yang et al. (2019) [25] showed that ferric-activated sludge-based adsorbent precipitated Pb as lanarkite (Pb(SO4)·PbO).
Soleymani-Bonoti et al. (2024) [26] showed that maximum absorption was achieved for Pb, followed by Cd, Ni, and Zn, by garlic peel. Compared to Pb and Cd adsorption by garlic byproduct, As removal efficiency was much lower. This trend was attributed to the sulfur-rich composition in garlic peel, which has a higher binding affinity for Pb and Cd compared to other metal ions. The interaction between sulfur ligands and Pb plays a key role in the selective adsorption behavior, suggesting the effectiveness of garlic byproducts for certain heavy metals. Similarly, Liang et al. (2013) [27] reported higher Pb removal compared to Cu and Ni from aqueous solution by garlic peel, suggesting an adsorption mechanism involving ion exchange between divalent heavy metal and calcium ions present in garlic peel. While garlic peel demonstrated higher Pb removal efficiency compared to garlic stem, the removal of Cd and As by both materials was relatively low and statistically insignificant. This could be due to the different physicochemical characteristics of these metals including ionic radius, electronegativity, hydration energy, and preferred coordination environments.
Garlic byproducts were less effective in the removal of As(III) and As(V), with negligible removal for As(V). Garlic stem and peel removed 18.9 and 18.5% of As(III) and 5.0 and 4.0% of As(V), respectively (Figure 1b). Arsenic(V) mainly exists as negatively charged species including H2AsO4− and HAsO42− at neutral pH, leading to electrostatic repulsion with negatively charged surface functional groups [28]. Arsenic(III) mainly exists as nonionic H3AsO3 at pH below 9, which could be bound by biomass resulting in relatively higher As(III) adsorption compared to As(V) [29]. Prajapati and Mondal (2019) [30] tested activated carbon produced from garlic stem to remove As(III) in aqueous solution and proposed a mechanism of As(III) removal. Protonation and formation of positively charged OH2+, -COOH2+, and =COH+ on available surface functional groups occurred in an acidic medium along with the partial transformation of As(III) to As(V) and the subsequent formation of H2AsO4−, which is attracted to the protonated surface functional groups. At alkaline pH, the electronegativity increased, and the repulsion force between surface functional group and As(III) and As(V) decreased adsorption [30].
While garlic peel proves to be an effective biosorbent for Pb and Cd, its limited capacity for As suggests that garlic byproducts are more suitable for targeted removal of specific contaminants rather than broad-spectrum metal remediation. Although further experiments under varying pH conditions and reaction temperatures would be necessary to determine the optimal conditions for metal(loid) removal, the primary objective of this study was to assess the feasibility of applying garlic byproducts for in situ stabilization of metal(loid)s in contaminated soils, and maximum adsorption capacities were not evaluated. Nevertheless, to improve the adsorption performance especially for As, further modification of the biosorbents such as chemical activation with acids and bases and pyrolysis could potentially enhance the adsorption capacity. However, the economic feasibility of such treatments should be considered for practical application of agricultural byproducts.

3.2. Immobilization of Pb and As Using Garlic Stem and Peel

While garlic stem and peel effectively removed Cd and Pb in aqueous solution, the extractable Pb concentration did not decrease in garlic-byproduct-treated soil after incubation. Cd was not detected in any of the treatments, and therefore the results are not presented. Particularly, 1% garlic peel significantly increased extractable Pb concentration (Figure 4a). Unlike in aqueous systems, the behavior of heavy metals in soil is governed by more complex interactions involving the soil matrix, organic matter, and microbial activity. The application of garlic byproducts led to increased soil pH, EC, and DOC (Table 3). Among these, DOC plays a critical role in the mobilization, complexation, and transformation of heavy metals in the soil environment [31]. The dissolved organic matter (DOM) can act as a chelating agent, forming soluble organo-metallic complexes with Pb that enhance its mobility.
The DOM also serves as a carbon source for microorganisms, resulting in the release of Pb from organic–metal complexes and Pb fixed in soil colloids. The microbial activity can lead to the release of Pb from organo-mineral complexes or humic substances, increasing the fraction of extractable Pb. Unmodified organic matter such as fresh plant residues, typically produces higher amounts of low-molecular-weight DOC, which is more reactive and microbially degradable, compared to stabilized or composted organic amendments. Therefore, fresh manure increases extractable Pb compared to composted manure because of the presence of various organic ligands contained in DOM, which are capable of chelating with Pb in soil. The DOC transformed residual Pb into an easily mobile form, thereby increasing the mobility of Pb in soil [31]. Variation in the molecular size of DOC affects metal–DOC complexes in solution and mobility in soil. Small molecules are prone to microbial degradation, leading to the desorption of Pb. The metal released by DOC can be resorbed by forming non-labile soluble organic complexes at high DOC [32]. Therefore, further increase in DOC with 5% garlic peel did not increase extractable Pb in soil. The larger molecular weight fractions of carbon are less mobile and contribute to an increase in Pb immobilization in soil.
Extractable As concentration significantly increased with 5% garlic stem and 1% garlic peel (Figure 4b), which is attributed to the increase in DOC and phosphate. Kalbitz and Wennrich (1998) [33] showed that element concentrations, soil pH, clay and oxide contents, CEC, and DOC concentrations affected As mobilization. In particular, DOC can form soluble complexes with As, increasing its mobility and bioavailability in the soil solution. Degradation of labile molecules, which is higher in DOM, coupled with reductive dissolution of iron oxides governed As mobilization [34]. The DOC enhances microbial respiration, leading to localized anaerobic conditions that favor the reductive dissolution of Fe and Mn oxides, which are major sorbents for As(III) and As(V), thereby releasing previously immobilized As into the soil. Kim et al. (2018) [35] reported that DOC from biochar and biochar-induced reductive dissolution of Fe oxides in soil increased As mobility in the soil.
Phosphorus contained in garlic byproducts might also contribute to the release of As. This is because phosphate and arsenate share structural similarity and compete for the same sorption sites on soil minerals. Competitive desorption by DOC and phosphate from biochar derived from granular sludge, rice straw, and spent coffee grounds increased As mobility because phosphate is a chemical analogue for arsenate [35]. Phosphorus concentration was higher in garlic stem than garlic peel, which is attributed to the higher extractable As concentration in 5% garlic-stem-treated soil (Table 2). Therefore, agricultural byproducts with a high amount of small molecular DOC are not appropriate for soil As remediation.

3.3. Lead Release in Saturated and Unsaturated Soil Column

Since the application of garlic byproducts increased the extractable Pb concentration in soil, a column experiment was conducted to evaluate its effect on Pb concentration in soil pore water under saturated and unsaturated conditions. Lead concentration was higher in unsaturated conditions possibly because of the dilution effect in saturated condition (Figure 5a). In saturated columns, the water-filled pore spaces allow for greater diffusion and dilution of soluble Pb, resulting in lower measured concentrations in pore water compared to unsaturated columns where water movement is more restricted.
Despite the dilution effect, continuously decreasing Pb concentration in saturated conditions compared to unsaturated conditions can be attributed to the precipitation of Pb as PbS in saturated conditions. However, this mechanism was not directly confirmed due to lack of solid-phase analysis and mass balance data while the observed decrease in pore-water Pb concentrations under reducing conditions suggests possible PbS precipitation. Saturated conditions often create reducing environments, especially in the presence of biodegradable organic matter, which promote the activity of SRB. The oxidation–reduction potential (ORP) was monitored in the saturated part of the column and indicated that the garlic-stem-amended soil showed more reducing conditions compared to the control. Specifically, the ORP in the control treatment ranged from +167 to −280 mV, while the garlic stem treatments showed a broader and more negative range from +179 to −450 mV. The garlic stem amendments promoted more anaerobic conditions, potentially influencing metal speciation and mobility in the soil. The pH slightly increased from 7.1 to 7.9 in the control and from 7.2 to 7.8 in the garlic stem treatment, corresponding with the development of more reducing conditions with increasing incubation time (Figure 5b).
The SRB generate sulfide, which reacts with Pb to form insoluble lead sulfide, thereby decreasing soluble Pb concentrations over time. Brink et al. (2019) [36] reported that Pb was removed by precipitation both in aerobic and anaerobic aqueous solutions. In anaerobic conditions, sulfide from sulfur-containing amino acids precipitated Pb as PbS, as well as PbO and elemental Pb by bacterial reduction, which were also found in aerobic conditions. Allium species such as garlic and onion contains alliins, which are sulfur-containing secondary metabolites [37]. Because the sulfur concentration of garlic is relatively high compared to other plant materials, application of garlic byproduct as a soil amendment could potentially enhance the stabilization of metals that readily form complexes with sulfur such as Cd and Pb. Therefore, under specific redox conditions, garlic byproducts may serve not only as adsorbents but also as chemical precursors that support the long-term immobilization of heavy metals through sulfur-mediated mechanisms.
The behavior of Pb in column showed different results from batch incubation experiment. Although Pb concentration was initially higher in garlic-stem-treated soil, after 15 days, Pb concentrations in pore water were lower than in the control, indicating that garlic stem decreased Pb mobility in soil column. Schwab (2005) [38] also showed different effects of citrate between a short-term batch experiment and column leaching experiment. In the batch experiment, adsorption of Pb significantly decreased with citrate, while in the soil column Pb was not released from the soil because of the rapid biodegradation of citrate resulting in the loss of chelation with Pb. The initial higher Pb concentration compared to the control can be attributed to DOC released from garlic stem. As the DOC decreased, Pb concentration in pore water also decreased (Figure 5a,c). The DOC concentration decreased after 8 days in unsaturated soil, leading to a reduction in Pb concentration in the pore water. The degradation of DOM decreased Pb binding by humic-like components [39]. Therefore, garlic stem can serve as a promising soil amendment for the long-term immobilization of Pb in soil.

4. Conclusions

Garlic stem and peel effectively removed Cd and Pb, with peel showing higher Pb removal, likely due to its higher sulfur content. However, both garlic byproducts showed limited efficiency for As(III) and negligible removal of As(V). Because the optimum conditions for metal adsorption were not evaluated in this study, the maximum adsorption capacity could increase with the optimization of pH and temperature and modification of garlic byproducts. However, the use of unmodified agricultural byproducts offers significant economic advantages as they require no additional processing or activation steps. The use of native agricultural byproducts may initially promote metal mobilization due to the release of DOC, which forms soluble complexes with metals. To address this issue, modification techniques can be employed to minimize DOC release; however, modification of agricultural byproducts often require additional chemicals and energy, resulting in higher treatment costs. Although the application of raw agricultural byproducts increased extractable metal concentrations in soil in the short term, the long-term incubation reduced Pb concentrations in pore water. Considering the cost-effectiveness of unmodified agricultural byproducts for metal removal in aqueous systems, unmodified garlic stem is promising as a soil amendment. Nevertheless, the use of agricultural byproducts should be applied with care to prevent unintended metal release from contaminated soil. In particular, site-specific assessments are necessary to evaluate potential risks and benefits before large-scale application of garlic byproducts in contaminated soils. In addition, the heterogeneity in garlic byproduct quality and availability of the byproduct can be a challenge in scaling up the process. To overcome issues of availability and seasonal variability of garlic byproducts, garlic residues can be dried, ground, and stored after harvesting for a sustainable supply.

Funding

This study was supported by funding from the academic research program of Chungbuk National University in 2025.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author [J.H. Park], upon reasonable request.

Conflicts of Interest

The author declares no conflicts of interest. The funder had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Abbreviations

The following abbreviations are used in this manuscript:
ICP-OESInductively coupled plasma–optical emission spectroscopy
ECElectrical conductivity

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Figure 1. Cadmium (Cd) and lead (Pb) concentrations remaining in solution (a) and trivalent arsenic (As(III)) and pentavalent arsenic (As(V)) concentrations remaining in solution (b) after adsorption using garlic stem and peel. Different lowercase letters indicate significant differences among treatments for As(III), while uppercase letters indicate significant differences for As(V) as determined by one-way ANOVA followed by Duncan’s multiple range test (p < 0.05).
Figure 1. Cadmium (Cd) and lead (Pb) concentrations remaining in solution (a) and trivalent arsenic (As(III)) and pentavalent arsenic (As(V)) concentrations remaining in solution (b) after adsorption using garlic stem and peel. Different lowercase letters indicate significant differences among treatments for As(III), while uppercase letters indicate significant differences for As(V) as determined by one-way ANOVA followed by Duncan’s multiple range test (p < 0.05).
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Figure 2. Attenuated total reflectance–Fourier-transform infrared (ATR-FTIR) spectra of garlic stem and garlic peel before and after Pb adsorption.
Figure 2. Attenuated total reflectance–Fourier-transform infrared (ATR-FTIR) spectra of garlic stem and garlic peel before and after Pb adsorption.
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Figure 3. Scanning electron microscopy (SEM) image and energy dispersive X-ray (EDX) spectroscopy of garlic stem (a), garlic stem after Pb adsorption (b), garlic peel (c), and garlic peel after Pb adsorption (d).
Figure 3. Scanning electron microscopy (SEM) image and energy dispersive X-ray (EDX) spectroscopy of garlic stem (a), garlic stem after Pb adsorption (b), garlic peel (c), and garlic peel after Pb adsorption (d).
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Figure 4. Extractable lead (Pb) (a) and arsenic (As) (b) concentrations in soil after incubation with 1% and 5% of garlic stem and peel, respectively. Different letters on the bars indicate significant differences as determined by one-way ANOVA followed by Duncan’s multiple range test (p < 0.05).
Figure 4. Extractable lead (Pb) (a) and arsenic (As) (b) concentrations in soil after incubation with 1% and 5% of garlic stem and peel, respectively. Different letters on the bars indicate significant differences as determined by one-way ANOVA followed by Duncan’s multiple range test (p < 0.05).
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Figure 5. Concentrations of lead (Pb) (a), pH (b), and dissolved organic carbon (DOC) (c) in soil pore water of saturated and unsaturated soil columns treated with garlic stem.
Figure 5. Concentrations of lead (Pb) (a), pH (b), and dissolved organic carbon (DOC) (c) in soil pore water of saturated and unsaturated soil columns treated with garlic stem.
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Table 1. Total metal concentrations of soils used for incubation and column experiments.
Table 1. Total metal concentrations of soils used for incubation and column experiments.
Soil TextureCEC (cmolc/kg)As (mg/kg)Cd (mg/kg)Cu (mg/kg)Pb (mg/kg)Zn (mg/kg)
Soil for incubationSandy loam3.01254 ± 2122 ± 1ND *2032 ± 194222 ± 8
Soil for columnSandy loam2.8220 ± 37.7 ± 2.5116 ± 661613 ± 16688 ± 14
* ND: Not detected.
Table 2. Element concentrations in garlic stem and peel.
Table 2. Element concentrations in garlic stem and peel.
Ca (mg/kg)K (mg/kg)Mg (mg/kg)Fe (mg/kg)P (mg/kg)S (mg/kg)Cd (mg/kg)Pb (mg/kg)As (mg/kg)
Garlic stem873.9 ± 28.52445.1 ± 44.2137.9 ± 0.77.2 ± 0.1604.8 ± 17.71138 ± 34.4ND *ND0.044 ± 0.01
Garlic peel983.1 ± 33634.7 ± 3100.4 ± 2.16.3 ± 1.4549.7 ± 25.91323.1 ± 56.1NDND0.079 ± 0.034
* ND: Not detected.
Table 3. pH, electrical conductivity (EC), and dissolved organic carbon (DOC) of soil after incubation. Different letters in the same column indicate significant differences as determined by one-way ANOVA followed by Duncan’s multiple range test (p < 0.05).
Table 3. pH, electrical conductivity (EC), and dissolved organic carbon (DOC) of soil after incubation. Different letters in the same column indicate significant differences as determined by one-way ANOVA followed by Duncan’s multiple range test (p < 0.05).
pHEC (μS/cm)DOC (mg/kg)
Control5.10 ± 0.14 b82.7 ± 4.1 e68.4 ± 0.6 e
Garlic stem 1%5.76 ± 0.36 a322.1 ± 6.0 b860.1 ± 5.7 c
Garlic stem 5%5.93 ± 0.04 a143.0 ± 0.9 d4140.2 ± 16.7 a
Garlic peel 1%5.99 ± 0.51 a177.7 ± 5.0 c480.4 ± 1.2 d
Garlic peel 5%5.66 ± 0.05 a632.1 ± 29.2 a3751.0 ± 9.7 b
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Park, J.H. The Biosorption of Cadmium, Lead, and Arsenic Using Garlic Byproducts and Their Potential for Metal Immobilization in Soil. Sustainability 2025, 17, 8857. https://doi.org/10.3390/su17198857

AMA Style

Park JH. The Biosorption of Cadmium, Lead, and Arsenic Using Garlic Byproducts and Their Potential for Metal Immobilization in Soil. Sustainability. 2025; 17(19):8857. https://doi.org/10.3390/su17198857

Chicago/Turabian Style

Park, Jin Hee. 2025. "The Biosorption of Cadmium, Lead, and Arsenic Using Garlic Byproducts and Their Potential for Metal Immobilization in Soil" Sustainability 17, no. 19: 8857. https://doi.org/10.3390/su17198857

APA Style

Park, J. H. (2025). The Biosorption of Cadmium, Lead, and Arsenic Using Garlic Byproducts and Their Potential for Metal Immobilization in Soil. Sustainability, 17(19), 8857. https://doi.org/10.3390/su17198857

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