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Abstract

This Study quantified heavy metal contamination in commonly consumed vegetables Eggplant, String Beans, Cucumber, Sweet Potato, Bitter Gourd, Lady Finger, Pumpkin, Indian Spinach, Wax Gourd and in the soils where they are grown, obtained from the 9 integrated farm in Noakhali, Bangladesh. It also assessed the potential human health risks linked to dietary exposure to these contaminated vegetables. Vegetable and soil samples were randomly collected, prepared using standard procedures, and analyzed for metal concentrations using atomic absorption spectrophotometry. Among the analyzed vegetables, Bitter Gourd, Lady Finger and Pumpkin exhibited the greatest accumulation of heavy metals (As, Pb, Cd, Cr, Fe, and Cu) and the estimated average daily intake of lead and cadmium through vegetable consumption was found to be 2.4128, 0.3644 mg/person/day, surpassed the permissible limits established by the FAO/WHO. The cancer risk value of lead content in Bitter Gourd, Lady Finger & Pumpkin was 1.37 × 10⁻³, 1.43 × 10⁻³, 1.79 × 10⁻³, chromium content in Bitter Gourd was 2.32 × 10⁻³ and cadmium content in Bitter Gourd and Lady Finger was 4.80 × 10⁻⁴, 5.47 × 10⁻⁴ which exceeded the threshold value of 10−⁴, indicating a potential carcinogenic risk and suggesting that consumption of these particular vegetables could be unsafe for human health. The overall health risk index indicated that consuming certain vegetables from the integrated farm in the study area may pose potential health hazards. Consequently, continuous monitoring of heavy metal levels is highly recommended.

Keywords

heavy metal integrated farm total target hazard quotient (TTHQ)carcinogenic risk estimated daily intake

Introduction

With growing concerns about the impact of contaminated food on human health, increasingly threatened by contaminants such as heavy metals, pesticides, chemical fertilizers, and various toxins, it has become a major area of focus for environmental scientists.¹ Vegetables are vital to a healthy diet because they provide dietary fiber, essential vitamins, and minerals necessary for growth and the prevention of nutritional deficiencies.² Therefore, ensuring that vegetables are free from pollutants is of utmost importance for public health.³ Vegetables inherently contain a range of essential and non-essential metals, but the intrusion of toxic metals into agricultural systems can result from multiple sources. These include environmental pollution, climatic influences, the use of wastewater for irrigation, industrial effluents, contaminated soils, and the over application of chemical fertilizers and pesticides.⁴ Although certain metals found in vegetables are beneficial to human health, the inclusion of toxic heavy metals can lead to significant health concerns. The U.S. Environmental Protection Agency (USEPA) classifies arsenic (As), lead (Pb), cadmium (Cd), chromium (Cr) and copper (Cu) as metals of particular toxicological importance.⁵ When these metals accumulate in vegetables and are consumed, they may lead to mutagenic or carcinogenic effects in the human body. Lead (Pb) and cadmium (Cd) are especially dangerous, as their intake is linked to respiratory problems, heart disease, kidney damage, neurological disorders, and bone-related illnesses.⁶ Chromium (Cr), commonly found in rocks and soil, interferes with biological processes in plants and vegetables. Consuming vegetables contaminated with Cr can result in DNA damage, as well as mutagenic and cancer-causing effects in humans.⁷ Trace amounts of zinc, copper, and nickel are essential for normal human growth and physiological functions. In contrast, elements such as mercury, lead, arsenic, and cadmium are highly toxic even at minimal concentrations, posing greater risks to vulnerable populations, particularly pregnant women and young children.^8,9 The increase in human exposure to these harmful heavy metals is largely due to population growth, which puts additional pressure on infrastructure and the environment. Improper management of chemical waste and industrial discharges contaminates agricultural soils. Moreover, anthropogenic activities including mining, fertilizer-intensive agriculture (and aquaculture), as well as the use of chemicals in fishing significantly contribute to the accumulation and dissemination of heavy metals within soil and aquatic environments.¹⁰ There is increasing international concern regarding the extensive contamination of culinary herbs and spices including curry powder, oregano, black pepper, and turmeric by heavy metals such as lead.¹¹ Despite stringent regulations, markets in countries with strong regulatory systems, such as the United States and Europe, continue to report contamination cases involving herbs and spices. For instance, several turmeric brands sold in the U.S. were recently found to contain high levels of lead, raising serious concerns about the health risks associated with consuming such products.¹² Following investigations by the U.S. FDA, the affected turmeric products were withdrawn from the market. In contrast, regulatory agencies in developing countries like Bangladesh rarely conduct routine testing of spices to assess heavy metal contamination possibly due to a lack of recognition of these metals as significant hazards. Moreover, limited research has been conducted in Bangladesh to evaluate the potential health risks from heavy metal contamination in spices. A study by Rahman, M.A. and colleagues reported lead concentrations in turmeric sold without branding in Dhaka city that were double the permissible limit, using atomic absorption spectroscopy.¹³ Similarly, Akter, S. and co-researchers found comparable results in Pakistan using Ion Beam Analysis. Another investigation in Chattogram analyzed only 3 spice samples for heavy metal content. Beyond these isolated studies, there has been no comprehensive research focusing on heavy metal levels in the diverse range of spices commonly used in Bangladesh. Additionally, there is a significant gap in assessing the associated carcinogenic and non-carcinogenic risks posed by spice intake among Bangladeshi consumers. Even at the global level, most risk assessments related to heavy metals in spices are based on random market samples rather than on actual consumer consumption patterns.¹⁴

Although heavy metal contamination of vegetables has been widely studied in different regions of Bangladesh, there is limited location-specific evidence from the Noakhali region, particularly considering its unique coastal and agro-ecological characteristics. Existing studies often focus on soil or water contamination alone, without comprehensively linking metal concentrations in edible vegetables to human health risk assessments such as Estimated Daily Intake (EDI), Target Hazard Quotient (THQ) and carcinogenic risk.¹⁰ Moreover, seasonal variability, crop-specific accumulation patterns and exposure differences between adults and children remain underexplored. Therefore, a systematic assessment integrating metal concentration analysis with quantitative health risk evaluation in commonly consumed vegetables from Noakhali is needed to generate region-specific data to inform food safety monitoring and public health policy. In Bangladesh, vegetables are a key component of the daily diet, regularly consumed by the population. The average daily vegetable intake among Bangladeshis ranges between 70 and 191 g, depending on the type of vegetable.¹⁵ In light of such consumption levels, assessing heavy metal content in vegetables is necessary to determine the potential health impacts.¹⁶ Although various types of vegetables are cultivated year-round across the country, existing studies on heavy metal contamination have mostly been region-specific, with limited data available for broader comparison. Furthermore, no study has yet systematically compared heavy metal levels across different vegetable types.¹⁷ Noakhali, a coastal district in Bangladesh, hosts several industrial operations. Coastal regions like Noakhali are particularly vulnerable to heavy metal contamination, largely due to industrial discharge from sectors such as food processing, pharmaceuticals, and paper manufacturing.¹⁸ These pollutants can enter coastal waters and lead to bio-magnification within the food chain, posing significant environmental risks.^19,20 Despite this concern, there is a notable absence of data regarding heavy metal contamination in vegetables cultivated in the Noakhali region. Due to the limited information on heavy metal concentrations in commonly consumed vegetables in Noakhali, Bangladesh, as well as the variation in metal levels among different vegetable types, this study aims to quantify the concentrations of arsenic (As), lead (Pb), cadmium (Cd), chromium (Cr), iron (Fe) and copper (Cu) in selected vegetable samples and to evaluate the potential health risks associated with their consumption. In addition, the study investigates the sources and variability of heavy metal contamination across the analyzed vegetables. The study findings have significant implications for public health and food safety, as they demonstrate potential health risks associated with the consumption of certain widely consumed vegetables. The outcomes provide valuable evidence for policymakers and agricultural authorities to strengthen surveillance programs, implement improved soil and crop management strategies, and promote public awareness initiatives aimed at minimizing heavy metal exposure and safeguarding human health.

Methods and Materials

Sampling Procedure

The study was conducted in the Noakhali district of Bangladesh (N22°49’28.7”, E91°6’6.24”) during 2024 to 25. Nine soil and commonly consumed vegetable samples were collected directly based on local dietary patterns and market availability from 9 integrated farms across 4 Upazilas in Noakhali (Figure 1). For each vegetable species, 3 replicate samples were obtained from each farm. In total, 54 samples were collected. This sample size was considered adequate to capture spatial and crop-specific variation while ensuring statistical reliability for heavy metal concentration analysis and subsequent health risk assessment. All samples were thoroughly washed, placed in clean polyethylene bags, and transported to the laboratory for subsequent analysis.

Figure 1.

Sampling site of the study area Noakhali, Bangladesh.

Sample Collection

In the year 2024, the sample was collected and divided into 2 groups. Group-I: Nine types of vegetables and Group-II: Nine types of soils from cultivated farm where the vegetables were grown (Table 1). Soil and vegetable sampling was carried out from local 9 integrated farm of Noakhali Sadar region. The sampling sites were chosen based on their widespread consumed in Noakhali.

Table 1.

Classification of the Collected & Analyzed Vegetables and Soils Sample.

Sample name	Group-I vegetables	Sample ID
Eggplant		V1 (farm-1)
String Beans		V2 (farm-2)
Cucumber		V3 (farm-3)
Sweet Potato		V4 (farm-4)
Bitter Gourd		V5 (farm-5)
Lady Finger		V6 (farm-6)
Pumpkin		V7 (farm-7)
Indian Spinach		V8 (farm-8)
Wax Gourd		V9 (farm-9)
	Group- II soil
Under Eggplant cultivation		S1 (farm-1)
Under String Beans cultivation		S2 (farm-2)
Under Cucumber cultivation		S3 (farm-3)
Under Sweet Potato cultivation		S4 (farm-4)
Under Bitter Gourd cultivation		S5 (farm-5)
Under Lady Finger cultivation		S6 (farm-6)
Under Pumpkin cultivation		S7 (farm-7)
Under Indian Spinach cultivation		S8 (farm-8)
Under Wax Gourd cultivation		S9 (farm-9)

Potential Sources of Heavy Metals in Soils and Vegetables

Potential determinants of heavy metal accumulation in soils and vegetables were identified through field surveys, stakeholder interviews and review of relevant literature. Anthropogenic inputs considered included the use of synthetic fertilizers and pesticides, application of animal manure, irrigation with potentially contaminated water, vehicular emissions from adjacent roads, improper waste disposal and nearby small-scale industrial activities. Natural contributors such as soil parent material, inherent mineral composition, coastal sediment deposition, tidal effects and seasonal flooding were also evaluated.

Sample Preparation

Group-I: The vegetables sample was cleaned with distilled water. The samples were boiled in an oven at 60 °C to 80 °C for 15 minutes then cooling. A distilled water-rinsed spoon was used to break separately. Skin and leaf were heated oven dried for necessary time to remove all moisture. For the wet digestion procedure, take 0.5 g of each dried sample.

Group-II: The soil sample were heated oven dried for necessary time to remove all moisture. A distilled water-rinsed spoon was used to break separately. For the wet digestion procedure, take 0.5 g of each dried sample.

Wet Digestion of Samples

Dried samples were digested using a wet digestion method. A 1:4 mixture of concentrated HNO₃ and H₂SO₄ (5 ml) was added to each weighed sample. The tubes were heated at 130°C, then gradually increased to 170°C to 200°C for approximately 1 hour before cooling. Subsequently, 2 ml of H₂O₂ was added, followed by repeated cycles of heating and cooling with additional H₂O₂ until a clear solution and white fumes were obtained. The final digest was filtered through Whatman filter paper into a 50 ml volumetric flask and diluted to volume with double-distilled deionized water.²¹

Standard Solution Preparation

To prepare the standard solution for the flame technique 25, 50, 100, and 200 μl AAS standard solutions (1000 ppm) were taken to make 0.25, 0.5, 1, and 2 ppm Cu and iron solutions, which were transferred separately into a 50 ml volumetric flask using a micropipette. To achieve the desired working concentrations, the solutions were each diluted with 2% (v/v) of nitric acid.

To prepare the standard solution for the furnace technique, the necessary amount of AAS standard solutions (1000 ppm) was taken to make 50 ppm solutions for different concentrations of As, Pb, Cd, Cr, Fe and Cu. To make a 100 ml solution of standards, the standard solutions were individually diluted with 2% (v/v) nitric acid to achieve the desired working concentrations.

Quality Control

Comprehensive quality assurance and quality control (QA/QC) procedures were implemented during sample collection, preparation, and laboratory analysis to ensure data reliability. All glassware and digestion equipment were pre-cleaned with 10% nitric acid and rinsed thoroughly with deionized water to minimize contamination, while samples were collected using non-metallic tools and stored in sterile polyethylene bags. Analytical accuracy and precision were verified through the inclusion of reagent and procedural blanks, duplicate samples representing 10% of the total, and certified reference materials (CRMs) for plant matrices, with acceptable recovery rates ranging from 90% to 110%. Calibration was performed using standard solutions with correlation coefficients (R²) of at least .99, and instrument performance was routinely monitored. Limits of detection (LOD) and quantification (LOQ) were determined according to established analytical guidelines, ensuring the validity and reproducibility of the heavy metal measurements.

Heavy Metal Determination with Atomic Absorption Spectroscopy (AAS)

Heavy metal concentrations were analyzed using a Perkin-Elmer novAA 400p Atomic Absorption Spectrometer with single-beam operation and deuterium background correction.²² Instrument calibration was performed with metal-specific standard solutions and a blank using linear calibration through zero. Hollow cathode lamps for As, Cd, Cr, Pb, Fe, and Cu were operated at their respective wavelengths. Each digested sample was analyzed in triplicate. Calibration curves showed good linearity (R² = 0.9687-0.998). The detection limit was 0.01 ppm/ml, with a measurement time of 3 seconds.

Heavy metal concentrations obtained from calibration curves (mg/L) were converted to mg/kg dry weight using²³:

\begin{array}{l} mg / kg = (Concentration \times Final digestion volume) \\ / Sample weight \end{array}

(1)

Health risk assessment was based on estimated daily intake (EDI) of detected metals, compared with WHO reference doses (RfD). EDI was computed in mg/kg-weight as²⁴:

EDI = (C_{mental} \times IR) / BW

(2)

where Cₘₑₜₐₗ is the metal concentration in sample vegetables (mg/kg), IR (gram per day per person) was the ingestion rate of sample vegetables taken from household income and expenditure survey (HIES),¹⁰ and BW was the 60 kg body weight of a person.²⁵

Non-carcinogenic risk was evaluated using Target Hazard Quotient (THQ): The Total Hazard Quotient (THQ) was applied to evaluate the potential non-carcinogenic health risks arising from prolonged exposure to heavy metals through consuming vegetables. THQ represents the ratio between the estimated exposure to a contaminant over a defined period and its corresponding reference dose (RfD). THQ values below 1 suggest that the likelihood of adverse health effects is minimal. In contrast, consumption of contaminated vegetables may pose significant health risks when the calculated THQ is equal to or exceeds 1.²⁶

THQ = EDI / RfD

(3)

The reference dose (RfD) values for As, Pb, Cd, Cr, Fe, and Cu are 0.0050, 0.0035, 0.0005, 0.0003, 0.007, and 0.040 mg kg−¹ day−¹, respectively.²⁷

Total non-carcinogenic risk from multiple metals was assessed using TTHQ: The Total Target Hazard Quotient (TTHQ) was employed to quantify the cumulative non-carcinogenic health risks associated with exposure to multiple heavy metals.²⁸ A TTHQ value greater than 1 indicates a potential for adverse health effects within the exposed population.²⁹

\begin{array}{l} TTHQ = THQ (As) + THQ (Pb) + THQ (Cd) \\ + THQ (Cr) + THQ (Fe) + THQ (Cu) \end{array}

(4)

Cancer risk denotes the elevated probability of an individual developing cancer following exposure to carcinogenic heavy metals, including Pb, Cd, and Cr.³⁰

Cancer risk = EDI \times CSF

(5)

where CSF = Cancer Slope Factor (mg/kg/day).

The U.S. Environmental Protection Agency considers a cancer risk ranging from 1 × 10−⁶ to 1 × 10−⁴ to fall within an acceptable threshold for risk management.³¹

Statistical Analysis

Descriptive statistics (mean, standard deviation), EDI, THQ, and TTHQ were calculated using MS Excel and SPSS. The data was cleaned and all outliers were discarded after verification. Data editing, coding, re-coding, missing values and other problems about data was identified and rechecked if necessary. Data were analyzed using SPSS 23.0. Results are presented as mean ± standard deviation and evaluated using one-way ANOVA to determine significant differences in heavy metal concentrations among vegetables (P < .05).

Results and Discussion

Concentration of Heavy Elements in the Studied Samples

The concentrations of heavy metals, specifically (As, Pb, Cd, Cr, Fe, and Cu), detected in edible vegetable and soil samples (mg/kg fresh weight) are reported in Table 2. Metal accumulation differed considerably among vegetable types. The levels of these metals followed the ascending order: As < Pb < Cd < Cr < Fe < Cu. Among the vegetables, the average metal concentrations were highest in Bitter Gourd, Lady Finger and Pumpkin, followed by Eggplant, Indian Spinach and the lowest in Eggplant. Lead, Cadmium and Chromium was found in the highest concentration across Bitter Gourd, Lady Finger and Pumpkin vegetables and also in the soil where the Bitter Gourd cultivation took place in the integrated farm. The average concentrations of metals (Lead, Cadmium and Chromium) in Bitter Gourd, Lady Finger and Pumpkin exceeded the guideline values proposed by the World Health Organization (WHO, 1996). Lead and Chromium was found in the highest concentration across Bitter Gourd vegetables, which in Bangladesh is largely attributed to the use of industrial and untreated water for irrigation, along with the application of chemical fertilizers and pesticides. Compared to soil of the cultivated land, soils from cultivated farm contained higher levels of Pb and Cd. Although some of previous study has shown that vegetables tend to accumulate more heavy metals due to their broad surface area and high absorption capacity from soil, the actual metal content in vegetables is influenced by both the properties of the soil and the plants’ ability to accumulate these elements.

Table 2.

Concentration of Heavy Metals (mg/kg fw) in Study Sample Vegetables and Soil in Noakhali.

Sample ID	As	Pb	Cd	Cr	Fe	Cu
Vegetables Mean ± SD (mg/kg fresh weight)
V1 (farm-1) Eggplant	0.47E-03 ± 6.00E-04	0.78E-03 ± 1.00E-03	0.23 ± 0.01	1.20 ± 0.07	0.07 ± 0.35	0.84 ± 0.04
V2 (farm-2) String Beans	0.01E-06 ± 2.00E-06	0.03E-05 ± 1.00E-05	0.07 ± 0.001	0.11 ± 0.03	0.86 ± 0.11	0.39 ± 0.10
V3 (farm-3) Cucumber	0.18E-03 ± 1.00E-03	0.77E-03 ± 8.00E-04	0.01 ± 0.006	0.25 ± 0.08	0.79 ± 0.27	0.78 ± 0.16
V4 (farm-4) Sweet Potato	0.76E-05 ± 4.00E-06	0.55E-04 ± 1.00E-04	0.003 ± 0.001	0.07 ± 0.01	0.37 ± 0.07	0.57 ± 0.05
V5 (farm-5) Bitter Gourd	0.48E-03 ± 7.00E-04	4.78E-03 ± 1.00E-03	0.17 ± 0.02	3.10 ± 0.07	1.07 ± 0.35	0.74 ± 0.04
V6 (farm-6) Lady Finger	2.01E-06 ± 2.00E-06	3.03E-05 ± 1.00E-05	0.27 ± 0.001	0.11 ± 0.03	0.86 ± 0.11	0.39 ± 0.10
V7 (farm-7) Pumpkin	1.18E-03 ± 1.00E-03	3.77E-03 ± 8.00E-04	0.21 ± 0.006	0.25 ± 0.08	0.79 ± 0.27	0.78 ± 0.16
V8 (farm-8) Indian Spinach	0.76E-05 ± 4.00E-06	0.55E-04 ± 1.00E-04	0.003 ± 0.001	2.07 ± 0.01	0.37 ± 0.07	0.57 ± 0.05
V9 (farm-9) Wax Gourd	0.48E-03 ± 7.00E-04	0.78E-03 ± 1.00E-03	0.17 ± 0.02	0.10 ± 0.07	1.07 ± 0.35	0.74 ± 0.04
Soil Mean ± SD (mg/kg)
S1 (farm-1) Under Eggplant cultivation	2.43E-02 ± 1.0	4.10E-02 ± 3	0.14 ± 0.01	0.10 ± 0.07	1.07 ± 0.35	0.74 ± 0.04
S2 (farm-2) Under String Beans cultivation	2.09E-02 ± 8	2.34E-03 ± 4.00E-04	2.26 ± 0.13	3.98 ± 1.52	9.67 ± 3.12	0.47 ± 0.19
S3 (farm-3) Under Cucumber cultivation	2.55E-03 ± 1.00	1.64E-03 ± 1.00E-04	0.12 ± 0.02	3.98 ± 0.98	9.66 ± 1.94	0.34 ± 0.09
S4 (farm-4) Under Sweet Potato cultivation	4.12E-02 ± 2.00E	2.05E-03 ± 1.00E-03	0.23 ± 0.09	0.21 ± 0.03	9.65 ± 1.07	0.39 ± 0.10
S5 (farm-5) Under Bitter Gourd cultivation	1.74 ± 0.04	4.77 ± 0.83	6.16 ± 0.02	4.29 ± 0.03	1.07 ± 0.32	0.74 ± 0.04
S6 (farm-6) Under Lady Finger cultivation	0.39 ± 0.10	3.66 ± 1.36	0.15 ± 0.07	0.31 ± 0.002	0.97 ± 0.25	0.39 ± 0.10
S7 (farm-7) Under Pumpkin cultivation	0.78 ± 0.16	7.58 ± 2.11	0.14 ± 0.09	0.30 ± 0.07	1.06 ± 0.59	0.78 ± 0.16
S8 (farm-8) Under Indian Spinach cultivation	0.57 ± 0.05	1.44 ± 0.94	0.25 ± 0.07	0.07 ± 0.01	0.37 ± 0.07	0.57 ± 0.05
S9 (farm-9) Under Wax Gourd cultivation	0.29 ± 0.03	1.07 ± 0.32	3.98 ± 1.52	0.10 ± 0.07	1.07 ± 0.35	0.74 ± 0.04

Except for lead, cadmium and Chromium, the metal concentrations were near the permissible limits established by FAO/WHO.³² Among all the vegetables, the highest lead concentrations were recorded in Bitter Gourd, with a mean value of 4.78E-03 mg kg−¹. The mean Pb, Cd and Cr levels exceeded those reported in earlier studies from Bangladesh and Pakistan,³³ while the iron levels were greater than those found by Ahmed et al³⁴ and consistent with results from Sultana et al.³⁵ The observed enrichment of heavy metals in the investigated vegetables is likely influenced by site-specific environmental and anthropogenic factors. These include cultivation near high-traffic roads, irrigation using polluted water sources, intensive agricultural chemical application, and the release of industrial effluents into surrounding farmLands.³⁶ Elevated Cu and Zn concentrations are commonly associated with fertilizer and pesticide inputs, whereas Pb contamination is primarily attributed to traffic-derived emissions such as exhaust fumes, wear of tires and brake linings, road surface degradation, and stormwater runoff, all of which contribute to metal uptake by roadside vegetables.³⁷

Correlation Analysis

Pearson’s correlation analysis revealed strong positive associations between Copper (Cu) and lead (Pb; r = .846) and Copper (Cu) and Chromium (Cr; r = .648), indicating that these metals likely share common sources of contamination. In contrast, Arsenic (As) showed negative correlations with cadmium metals (r = −.251), suggesting distinct accumulation pathways.

Dietary Intake of Heavy Metals

Assessing dietary intake from food sources is an essential approach for estimating nutrient and contaminant exposure, enabling the identification of potential deficiencies as well as associated health risks. Using the average concentrations of heavy metals detected in the analyzed vegetables, the estimated daily intake (EDI) for adults was computed and is summarized in Table 3. The calculated daily intakes for arsenic (As), lead (Pb), cadmium (Cd), chromium (Cr), iron (Fe), and copper (Cu) through vegetable consumption were 0.0736, 2.4128, 0.3644, 0.01098, 12.4201, and 0.5712 mg/day, respectively.

Table 3.

Pearson’s Correlation Coefficient Matrix for Heavy Metal Contents in Studied Vegetables.

Metal	As	Pb	Cd	Cr	Fe	Cu
As	1
Pb	.827	1
Cd	−.251	.250	1
Cr	.742	.761	−0.183	1
Fe	.181	.426	.621	.162	1
Cu	.296	.846	.264	.648	.265	1

Comparison of these values with the maximum tolerable dietary intake (MTDI) limits established by FAO/WHO indicates that, with the exception of lead and cadmium, the estimated intakes of all metals fall below the recommended thresholds.³⁶ This suggests that consumption of the vegetables analyzed poses minimal non-carcinogenic health risks for most metals. However, the elevated dietary exposure to lead, chromium and cadmium warrants careful consideration, as these metals are associated with significant toxicological effects even at relatively low concentrations. Continued monitoring and control measures are therefore vital to ensure consumer safety in the studied region (Table 4).

Table 4.

The Estimated Daily Intake (EDI) of Heavy Metals Through Consumption of the Studied Vegetables.

Sample ID	Estimated daily intake (EDI; mg/ kg body weight/ day)
Sample ID	As	Pb	Cd	Cr	Fe	Cu
V1 (farm-1) Eggplant	0.0063	0.0023	0.0061	0.0002	2.5361	0.0012
V2 (farm-2) String Beans	0.0014	0.0235	0.0126	0.00012	1.234	0.0056
V3 (farm-3) Cucumber	0.0023	0.0065	0.0022	0.00086	2.321	0.0047
V4 (farm-4) Sweet Potato	0.0021	0.0035	0.00561	0.0028	0.269	0.0235
V5 (farm-5) Bitter Gourd	0.0156	0.9845	0.07862	0.00567	0.235	0.0089
V6 (farm-6) Lady Finger	0.0186	0.7568	0.08963	0.00027	1.231	0.4567
V7 (farm-7) Pumpkin	0.0124	0.5632	0.08561	0.00046	2.236	0.0259
V8 (farm-8) Indian Spinach	0.0089	0.0156	0.0048	0.00042	1.235	0.0078
V9 (farm-9) Wax Gourd	0.0060	0.0569	0.0793	0.00018	1.123	0.0369
MTDL (mg/kg/day)	0.5 ^a	0.21 ^b	0.046 ^b	0.2 ^c	17 ^b	50 ^d

Abbreviations: MTDL, maximum tolerable daily limit.

U.S. Environmental Protection Agency³⁸

FAO/WHO. Joint FAO/WHO Food Standards Program³⁹

Organization WH. Permissible Limits of Heavy Metals in Soil and Plants. Switzerland; 1996.⁴⁰

World Health Organization⁴¹

Principal Component Analysis (PCA)

Figure 2 represents Principal component analysis (PCA) was employed to elucidate the distribution patterns and potential sources of heavy metals in vegetable samples. The rotated component plot revealed that the first 2 principal components accounted for the major proportion of total variance, indicating that these components effectively summarize the contamination structure. Two principal components (PCs), including PC 1 and PC 2, explained 60.53 and 39.42% of the total variance due to having 18 values greater than 1. Pb, Cd, and As exhibited strong positive loadings on the first principal component (PC1), suggesting a common origin and possible anthropogenic inputs such as agrochemicals (fertilizers and pesticides) and natural soil background levels. Cu also loaded positively on PC1 but showed separation along the second principal component (PC2), implying partial differences in its source contribution or geochemical behavior. In contrast, Cr demonstrated a strong positive association with PC2, indicating a distinct contamination pathway, potentially related to specific irrigation water and localized contamination. Fe displayed negative loadings on both components and was clearly separated from the other metals, suggesting a predominantly natural origin derived from soil parent materials. Overall, the PCA results highlight mixed anthropogenic and geogenic contributions to heavy metal accumulation in vegetables and provide valuable insight into potential pollution sources and associated environmental health risks.

Figure 2.

Principal component analysis (PCA) score plot for 2 components.

Non-Carcinogenic and Carcinogenic Health Risk

Table 5 summarizes the assessment of non-carcinogenic and carcinogenic health risks associated with the consumption of the analyzed vegetables, based on the Target Hazard Quotient (THQ) and Total Target Hazard Quotient (TTHQ). The THQ values indicate the likelihood of adverse health effects from long-term exposure to individual metals. For lead (Pb), chromium (Cr) and cadmium (Cd), THQ values exceeded the threshold of 1 for Bitter Gourd, Lady Finger and Pumpkin vegetable, suggesting that regular consumption may pose significant non-carcinogenic health risks. These elevated values highlight the potential for chronic toxicity, particularly given the cumulative nature of these metals in human tissues.

Table 5.

The Target Hazard Quotients (THQ; Noncarcinogenic) of Heavy Metals Through Consumption of Studied Vegetables.

Sample ID	Target hazard quotients (THQ)						TTHQ
Sample ID	As	Pb	Cd	Cr	Fe	Cu	TTHQ
V1 (farm-1) Eggplant	0.00156	0.00201	0.90030	1.01102*	0.00014	0.00114	1.9161*
V2 (farm-2) String Beans	0.00456	0.00321	0.00021	0.00012	0.81023	0.00275	0.82108
V3 (farm-3) Cucumber	0.12450	0.00012	0.00206	0.00046	0.74003	0.00369	0.87086
V4 (farm-4) Sweet Potato	0.05681	0.00789	0.00369	0.00128	0.00012	0.00023	0.07002
V5 (farm-5) Bitter Gourd	0.00256	4.2356*	3.2141*	1.0235*	0.00148	0.00782	8.4850*
V6 (farm-6) Lady Finger	0.01475	2.3568*	2.1044*	0.00266	0.70038	0.01402	5.1931*
V7 (farm-7) Pumpkin	0.00369	3.4589*	1.0234*	0.00145	0.00206	0.00799	4.4974*
V8 (farm-8) Indian Spinach	0.23041	0.00456	0.00078	0.00035	0.01278	0.00461	0.25349
V9 (farm-9) Wax Gourd	0.00012	0.00702	0.00924	0.00706	0.03569	0.00932	0.06845

THQ and **TTHQ values for these samples are greater than the standard limit (>1).

Lead (Pb), cadmium (Cd) and chromium (Cr), the THQ values for those metals also surpassed 1 in most of the examined vegetables, indicating an additional level of concern. When multiple metals are ingested simultaneously, their combined effects may further elevate the overall risk, as reflected by the TTHQ values. Elevated TTHQ scores point to the possibility of additive or synergistic toxic effects, underscoring the need for continuous monitoring and stricter control of heavy metal contamination in vegetables consumed in the region.

Similar findings were reported in an Indian study,³¹ where cadmium and nickel posed health risks due to HQ values surpassing safe limits. Among the vegetables, the order of total THQ was highest in bitter ground, followed by Sweet Potato, Bitter Gourd, and lowest in Pumpkin, ladies’ finger.

When Lead (Pb), cadmium (Cd) and chromium (Cr) metals were assessed together, the total THQ or hazard index (HI) for vegetables was 18.60, far exceeding the safety threshold of 1. This indicates a clear potential health risk, suggesting these vegetables should not be consumed regularly. Combined exposure to multiple heavy metals may also produce additive or interactive toxic effects, further elevating overall risk.

Cancer Risk (CR) from Heavy Metals

The total cancer risk (CR) posed by heavy metals in vegetables commonly cultivated in local integrated farm of Noakhali was assessed in this study. Among the analyzed vegetables, lead (Pb) content in Bitter Gourd, Lady Finger & Pumpkin, chromium (Cr) content in Bitter Gourd and cadmium content in Bitter Gourd, Lady Finger exceeded the threshold of 10−⁴, indicating a potential carcinogenic risk and suggesting that consumption of these particular vegetables could be unsafe for human health. In contrast, all other vegetable samples exhibited cancer risk values within the range of 10−⁶ to 10−⁴, which is generally considered acceptable and indicates negligible risk under typical dietary exposure.⁴² These findings highlight the importance of monitoring heavy metal contamination in commonly consumed vegetables to ensure food safety (Figure 3).

Figure 3.

Cancer risk (CR) by consuming study sampled vegetable through heavy metals.

Strengths and Limitations

This study offers a comprehensive assessment of heavy metal contamination in both soil and commonly consumed vegetables in the Noakhali region of Bangladesh, providing valuable insights into the soil-to-plant transfer of metals and associated human health risks, including estimated daily intake and carcinogenic potential. By analyzing multiple metals (As, Pb, Cd, Cr, Fe, and Cu) and comparing their concentrations with FAO/WHO permissible limits, the research provides robust evidence for policymakers and agricultural authorities to develop monitoring strategies and promote food safety. The inclusion of samples from multiple integrated farms enhances the representativeness of the findings. However, the study has limitations, including its geographic focus on selected farms, which may restrict generalization to other regions, and the absence of seasonal variation assessment, which could influence metal accumulation. Additionally, soil physicochemical properties affecting metal bioavailability were not extensively examined, and the health risk assessment relied on estimated consumption rates and standard exposure assumptions, which may not fully reflect individual dietary patterns or long-term exposure.

Conclusion

This study assessed heavy metal contamination in commonly consumed vegetables from the Noakhali district of Bangladesh and evaluated related health risks using THQ and TCR metrics. Most vegetables contained Pb, Cd, and Cr at levels exceeding the MAC, though only Cr surpassed the FAO/WHO MTDI based on EDI calculations. The combined THQ values for Pb and Cd were greater than 1, indicating potential non-carcinogenic health risks associated with regular consumption. These findings highlight the urgent need for intervention to reduce exposure and improve food safety. Future studies should aim to identify contamination sources, evaluate alternative exposure pathways, and investigate environmental influences on heavy metal accumulation. Effective collaboration among policymakers, regulatory bodies, and stakeholders is essential to establish strict regulations, enhance monitoring, and implement remediation strategies. Additionally, public education campaigns are vital to inform both farmers and consumers about the dangers of heavy metals and to promote safer farming practices.

Footnotes

Acknowledgements

The authors would like to thank Bangladesh Ministry of Science & Technology (MOST), Department of Agriculture and Food Technology & Nutrition Science of Noakhali Science & Technology University for their help. The authors are also indebted to local integrated farm holder in 4 upazilla (sub-district), Noakhali, Bangladesh who assisted in collecting samples and cooperated enthusiastically to this study.

ORCID iDs

Kawsar Hossen

Nahian Rahman

Zannatul Ferdowsi

Tahmina Ferdous

Author Contributions

Dr. Kawsar Hossen and Nahian Rahman conceptualized the idea, conducted the study, study design, collected and analyzed updated evidence, developed the document and drafting after conducting a data analysis. Zannatul Ferdowsi and Tahmina Ferdous also helped in data analysis, preparation of manuscript and comparison with other studies.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors were supported by the “Special Research Grants (NST) 2023-24,” Ministry of Science & Technology, Bangladesh to conduct the study.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data Availability Statement

Data will be made available on request.

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Assessment of Heavy Metal Levels and Associated Health Risks Linked to Vegetables Grown in Noakhali Region of Bangladesh

Abstract

Keywords

Introduction

Methods and Materials

Sampling Procedure

Sample Collection

Potential Sources of Heavy Metals in Soils and Vegetables

Sample Preparation

Wet Digestion of Samples

Standard Solution Preparation

Quality Control

Heavy Metal Determination with Atomic Absorption Spectroscopy (AAS)

Statistical Analysis

Results and Discussion

Concentration of Heavy Elements in the Studied Samples

Correlation Analysis

Dietary Intake of Heavy Metals

Principal Component Analysis (PCA)

Non-Carcinogenic and Carcinogenic Health Risk

Cancer Risk (CR) from Heavy Metals

Strengths and Limitations

Conclusion

Footnotes

Acknowledgements

ORCID iDs

Author Contributions

Funding

Declaration of Conflicting Interests

Data Availability Statement

References