The Concentration of Trace Metals in Locally Sold Garlic (Allium sativum) and Potential Health Risk Assessment

Abstract

The present study evaluated the trace element’ concentrations in native and foreign garlic specimens obtained from Shyambazar and Karwanbazar retail markets of Dhaka, Bangladesh. The garlic samples were collected randomly, subjected to processing, and subsequently assessed to detect heavy metals via atomic absorption spectrophotometry (AAS). Lead (Pb), zinc (Zn), copper (Cu), and chromium (Cr) concentrations were measured, and they had mean concentrations in the range of 12.00–19.00, 28.62–42.22, 2.67–3.42, and 0.00–3.85 mg kg⁻¹, respectively, in the native garlic samples and 11.00–22.00, 29.34–44.43, 2.99–4.50, and 0.00–3.85 mg kg⁻¹ of dry weight in the analyzed foreign garlic samples, respectively. The average daily intake of Pb, Cu, Zn, and Cr in the native garlic ranged from 0.02–0.03, 0.00–0.01, 0.05–0.07, and 0.00–0.01 mg person⁻¹ day⁻¹ to 0.02–0.03, 0.00–0.01, 0.04–0.06, and 0.00–0.01 mg person⁻¹ day⁻¹ in the foreign garlic samples. The results revealed that the hazard quotient (HQ) values of Pb in all garlic samples were greater than 1 (dimensionless ratio) unlike the other concerned heavy metals. The hazard index (HI), i.e., the summation of HQ values, of both native garlic samples and Chinese garlic samples, exceeded 1, implying an increased potential for adverse health effects, especially through chronic exposure to heavy metals present in the studied garlic samples.

Keywords

Vegetables - Metal concentration - Average daily intake - Health risk - Shyambazar market - Karwanbazar market

Significance

This research addresses critical aspects of human health, food safety, and environmental protection. The subject matter of this study aligns directly with the UN Sustainable Development Goals: SDG 3: Good Health and Well Being, SDG 6: Clean Water and Sanitation (Indirectly), and SDG 12: Responsible Consumption and Production. Moreover, this work supports the UN’s mission for inclusive, safe, resilient, and sustainable food systems.

Introduction

As a major class of contaminants in the food chain, heavy metals are considered a major environmental concern[1]. Certain factors associated with heavy metals can reduce plant yield and potentially compromise the safety of food and feed products derived from plants.[2] In emerging nations, this problem is getting worse on a global scale.

Due to the vegetables absorbing metals from the soil, they contain both beneficial and detrimental elements in high amounts. The metals contaminate the soil, mix with the soil solution, and infiltrate the plant structure. Accordingly, even in cases when the soil has modest concentrations, the metals can accumulate in significant amounts within the edible parts of plants, as toxic metals penetrate and gather in meristematic tissues quicker than the rate at which they are discharged.[3] The substances that humans require in small amounts via their diet to maintain normal physiological activities are referred to as essential trace elements. Based on an examination of the possible hazards associated with trace elements, two types of toxicity have been identified: those associated with high intake that can have harmful effects,[4] and those associated with low intake that can result in malnourishment.[5]

Heavy metals are typically characterized by their non-biodegradability, presence for an extended duration in organisms, and the ability to accumulate in various organs of a human body, leading to adverse effects.[6] The heavy metals’ presence in agricultural water can occur from several sources, including the use of contaminated irrigation water, the utilization of metal-containing cultivators and insecticides, commercial discharges, conveyance, harvesting, and storing and distribution methods.[7] [8]

As the body cannot excrete them effectively, heavy metals can be extremely dangerous even in low amounts.[9] These metals can cause cancer, liver difficulties, heart problems, and can act as a host for other illnesses, making them highly risky to human health.

Prolonged or elevated exposure to heavy metals can lead to severe health effects, including cognitive impairments, liver and brain damage, kidney dysfunction, and central nervous system disorders.[10] Some metals, such as Pb, are particularly associated with neurological damage, while others, like cadmium and chromium, may cause kidney and liver toxicity.[11]

Elevated levels of various metallic elements in food products are positively correlated with the onset of many illnesses, especially those that impact the heart and circulation system, kidneys, bones, and nervous system.[12] [13] In Dhaka, Bangladesh, lead (Pb) contamination poses serious health risks particularly for children.[14] Studies have shown that 87.4% of primary school children have blood lead levels (BLLs) exceeding 10 μg/dL, with some as high as 63.1 μg/dL.[15] Approximately 80% of children exceed the CDC reference level of 5 μg/dL, primarily due to industrial emissions, recycling of lead-acid batteries, and adulteration of spices with lead chromate.[15] This underscores the critical need to address heavy metal contamination in widely consumed contaminated vegetables and spices like garlic.

However, the toxicity of heavy metals is often species-specific and dependent on their chemical form. For instance, chromium exists in both trivalent (Cr3⁺) and hexavalent (Cr6⁺) states, with the latter being highly toxic and carcinogenic, while Cr³⁺ is an essential nutrient in trace amounts.[16] Similarly, while copper (Cu) and zinc (Zn) are vital micronutrients, their elevated concentrations can cause adverse health effects.[17]

Estimating their bioavailability presents significant challenges as the chemical speciation of trace metals affects their solubility and absorption in the human body. Sometimes, the presence of competing ions can further alter the level of bioavailability of these metals.[18] Moreover, some dietary interactions can regulate absorption either positively or negatively, making it slightly difficult to accurately quantify specific cancer-inducing metal concentrations.[19] For this reason, analyzing the overall heavy metal contamination in edible plants are important in order to estimate the risk posed by them since they are carcinogenic in nature.

Garlic is an essential ingredient in our meal. Garlic is generally utilized as a condiment in our daily lives. It is not just useful for cooking; it can also be used for cosmetics, perfume manufacture, religious rituas, medical applications, and in some cases, as a vegetable. Garlic is one such ingredient that has both therapeutic and anti-inflammatory properties. However, depending on the variant consumed, the taste, nutritional value, and trace metal concentrations may vary. For this reason, a native variant versus a foreign species of garlic needs to be studied alongside. The level of heavy metals in this stem vegetable, if ingested every day, will be quite concerning throughout a person’s lifetime due to the concentrations of different heavy metals. Therefore, given that these metals have a cancerous effect in our bodies, detailed study is required determining the quantity of such metals in garlic.

Many of Bangladesh’s economic sectors lack adequate environmental management. When it comes to agricultural water supplies, especially for the production of vegetables and other such consumables, unclean industrial effluents[20] and contaminated water[21] are commonly used in rural areas. The scarcity of natural water resources intensifies during the dry spell, and the quality of irrigation water drops. In agricultural fields, herbicides, chemical fertilizers, and irrigation water all carry heavy metals.[22] Instead of being concerned about the contaminants present, priority is given to the ingestion of garlic for its nutritional values. For this reason, extensive research is required to determine the daily ingestion of contaminants associated with garlic use in day-to-day life.

The research’s primary goals were to ascertain the quantity of certain carcinogenic elements (Cu, Cr, Pb, and Zn) present in garlic samples that were gathered from Dhaka’s retail markets in Shyambazar and Karwanbazar. Garlic samples found in both these markets in Dhaka city were sourced from local production farms, while some species were imported. The heavy metal content of both the native and imported garlic samples was analyzed. To examine the potential health risks related to consuming these contaminants, the average daily intake (ADI), hazard quotient (HQ), and hazard index (HI) values were utilized. The study is important because garlic is a widely consumed spice vegetable used as seasonings or for raw consumption, and understanding its heavy metal concentrations is critical for assessing potential public health risks and guiding regulatory and agricultural interventions.

Results and Discussion

Vegetables are vital to the human diet and provide well-known nutrients to maintain normal physiological functions. However, heavy metal contamination of vegetables by natural and anthropogenic activities is now an increasing concern in Bangladesh due to its potential to cause health hazards. In Bangladesh, several factors, including prolonged fertilizer usage, contaminated irrigation water, the use of pesticides and preservatives, and industrialization, are major contributors to the heavy metal poisoning of vegetables.[20] Exposure to heavy metals by consuming contaminated vegetables and their associated toxicity is a serious concern. [Tables 1] and [2] summarize the metal concentrations in all native and foreign garlic samples.

Table 1 Heavy metal concentrations in native Garlic samples

Types of Garlic	Metal concentration (mg kg−1 dw)
	Cr	Cu	Pb	Zn
Shyambazar Native Garlic 1	0.00 a	2.67 a	19.00 d	32.82 b
Shyambazar Native Garlic 2	0.00 a	3.04 d	14.00 b	36.34 c
Shyambazar Native Garlic 3	0.72 b	3.07 d	15.00 b	38.61 d
Karwanbazar Native Garlic 1	0.00 a	2.81 b	12.00 a	28.62 a
Karwanbazar Native Garlic 2	4.28 c	2.97 c	17.00 c	42.22 f
Karwanbazar Native Garlic 3	0.00 a	3.42 e	15.00 b	40.31 e
MPL (mg kg−1)	2.301	10.002	0.30 2	50.002

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Table 2 Heavy metal concentrations in foreign Garlic samples

Types of Garlic	Metal concentration (mg kg−1 dw)
	Cr	Cu	Pb	Zn
Shyambazar Chinese Garlic 1	3.85 c	2.99 a	15.00 b	29.34 a
Shyambazar Chinese Garlic 2	0.00 a	3.56 b	22.00 d	39.78 e
Shyambazar Chinese Garlic 3	0.00 a	3.96 d	18.00 c	44.43 f
Karwanbazar Chinese Garlic 1	0.00 a	3.98 d	19.00 c	33.70 b
Karwanbazar Chinese Garlic 2	0.86 b	4.50 e	16.00	36.23 d
Karwanbazar Chinese Garlic 3	0.00 a	3.72 c	11.00 a	34.56 c
MPL (mg kg−1)	2.301	10.002	0.30 2	50.002

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The outcomes of this investigation indicated that the concentration of chromium in native garlic samples that were collected fell between 0.00 and 4.28 mg kg⁻¹ of dry weight (DW), as shown in [Table 1]. The maximum permissible limit (MPL) (2.30 mg kg⁻¹) was surpassed by Karwanbazar Native Garlic 2. In comparison to the MPL, the mean Cr concentration in Karwanbazar Native Garlic 2 was 46.26% greater. The Shyambazar Native Garlic 1, Shyambazar Native Garlic 2, Karwanbazar Native Garlic 1, and Karwanbazar Native Garlic 3 did not exhibit any significant variations from one another. However, they did differ considerably from Shyambazar Native Garlic 3 and Karwanbazar Native Garlic 2. Arrangement of the garlic samples according to their Cr concentration in the decreasing order is shown in [Table 1] – Karwanbazar Native Garlic 2 > Shyambazar Native Garlic 3 > Shyambazar Native Garlic 1, Shyambazar Native Garlic 2, Karwanbazar Native Garlic 2, and Karwanbazar Native Garlic 3.

The chromium concentrations in the foreign garlic samples are shown in [Table 2] and significant variations were found in the mean concentrations except for Shyambazar Chinese Garlic 1 and Karwanbazar Chinese Garlic 2. It was discovered that Shyambazar Chinese Garlic 1 has a higher chromium concentration above the MPL. The average Cr content was between 0.00 and 3.85 mg kg⁻¹ in the studied foreign garlic samples. The research additionally disclosed that the average Cr concentration in Shyambazar Chinese Garlic 1 was 40.26% greater than that of the MPL. According to [Table 2], the mean Cr levels in the foreign garlic samples dropped in the subsequent series of: Shyambazar Chinese Garlic 1 > Karwanbazar Chinese Garlic 2 > Shyambazar Chinese Garlic 2, Shyambazar Chinese Garlic 3, Karwanbazar Chinese Garlic 1, and Karwanbazar Chinese Garlic 3.

So, for chromium, when the native and foreign varieties of garlic are compared, a clear observation can be made that the chromium concentrations in the native garlic samples were a bit higher than the concentrations in the foreign ones in some samples. However, this aspect can be ignored as most of the samples showed little to no Cr contamination.

Concentrations of Cu in the collected six native garlic samples and the Cu concentration observed in this study are represented in [Table 1]. The concentration of copper in all the studied native garlic samples showed levels below the MPL, and they varied from 2.67 to 3.42 mg kg⁻¹ of dry weight. Arranging the samples in the descending order of concentration of copper: Karwanbazar Native Garlic 3 > Shyambazar Native Garlic 3 > Shyambazar Native Garlic 2 > Karwanbazar Native Garlic 2 > Karwanbazar Native Garlic 1 > Shyambazar Native Garlic 1 ([Table 1]).

According to [Table 2], the mean Cu concentration of the examined foreign garlic samples varied significantly. Similar to the native ones, the concentration of copper in every sample was discovered to be within the MPL, the range being 2.99–4.50 mg kg⁻¹. Arranging the six foreign garlic samples according to the descending order of Cu concentration in them, it would look like: Karwanbazar Chinese Garlic 2 > Karwanbazar Chinese Garlic 1 > Shyambazar Chinese Garlic 3 > Karwanbazar Chinese Garlic 3 > Shyambazar Chinese Garlic 2 > Shyambazar Chinese Garlic 1, as shown in [Table 2].

Contrary to the Cr concentration, the foreign garlic samples showed slightly higher copper concentration than the native ones. However, even though there were some amounts of Cu found in almost all the native and foreign samples, none of the studied samples showed values more than the MPL.

According to [Table 1], the Pb concentrations of all the native garlic samples were higher than the MPL, which is declared by the WHO/FAO, with values ranging from 12.00 to 19.00 mg kg⁻¹.[24] In [Table 1], they are shown in the descending order of their Pb content: Shyambazar Native Garlic 1 > Karwanbazar Native Garlic 2 > Shyambazar Native Garlic 3 and Karwanbazar Native Garlic 3 > Shyambazar Native Garlic 2 > Karwanbazar Native Garlic 1. [Table 2] shows that the mean Pb concentration of the six foreign garlic samples varied significantly. In every foreign garlic sample, the amount of lead calculated was more than the MPL as declared FAO/WHO.[24] The average Pb concentration in different garlic samples varied from 11.00 to 22.00 mg kg⁻¹. From [Table 2], the average Pb concentrations in the foreign garlic samples in descending order are shown as: Shyambazar Chinese Garlic 2 > Karwanbazar Chinese Garlic 1 > Shyambazar Chinese Garlic 3 > Karwanbazar Chinese Garlic 2 > Shyambazar Chinese Garlic 1 > Karwanbazar Chinese Garlic 3.

All the garlic samples were very high in Pb concentration resulting in each of the samples having lead levels highly exceeding the MPL. Comparing the native garlic samples against the foreign ones, although marginal but the foreign garlic samples had more Pb concentration.

[Table 1] shows the zinc levels in six native garlic samples. Variations in Zn concentrations were substantial. Zinc content in native garlic samples was less than the MPL (50.00 mg kg⁻¹ dw). Native garlic samples had Zn concentrations from 28.62 to 42.22 mg kg⁻¹ of DW, suggesting that all native garlic samples had mean Zn concentrations below the MPL. According to [Table 1], the mean Zn concentration in the native garlic samples decreased in the order of Karwanbazar Native Garlic 2 > Karwanbazar Native Garlic 3 > Shyambazar Native Garlic 3 > Shyambazar Native Garlic 2 > Shyambazar Native Garlic 1 > Karwanbazar Native Garlic 1. Similar to the native garlic samples, the concentrations of Zn in six foreign garlic samples represented in [Table 2] showed significant differences. The MPL of 50 mg kg⁻¹ for zinc set by FAO/WHO[24] was not exceeded by any of the foreign garlic samples. In Shyambazar Chinese Garlic 3, the Zn concentration was the highest at 44.43 mg kg⁻¹, whereas in Shyambazar Chinese Garlic 1, it was the lowest at 29.34 mg kg⁻¹. The Zn content found in the foreign garlic samples in decreasing amounts is as follows: Shyambazar Chinese Garlic 3 > Shyambazar Chinese Garlic 2 > Karwanbazar Chinese Garlic 2 > Karwanbazar Chinese Garlic 3 > Karwanbazar Chinese Garlic 1 > Shyambazar Chinese Garlic 1 according to [Table 2].

One possible explanation for the existence of heavy metals in the garlic samples under study is soil contamination. Contaminated soil is primarily caused by sludge applications, vehicle exhaust, agrochemicals, and the dumping of solid waste. Thus, the increased heavy metal uptake by garlic as a result of anthropogenic soil contamination impacts the safety and quality of food.[25]

The observed variations in heavy metal concentrations in garlic samples can be attributed to several factors. Few of the main reasons for the level of contamination variance at different cultivation sites include the use of contaminated irrigation water, fertilizers, or due to nearby industrial effluents.[20] Moreover, proximity to frequently used roads and industrial areas can be a prime reason behind the increased exposure to airborne pollutants, such as Pb from vehicle emissions and dry deposits.[22] All these factors can individually or combinedly impact the variability in the metal concentrations in the studied garlic samples. In other words, the field’s location being close to a busy road, use of agrochemicals, or due to industrial waste and effluents being dumped into nearby areas, or any combination of these factors, could be the cause of the higher metal contents found in the garlic samples.[22] Agricultural goods that were applied to the soil as fertilizes may be the source of strong metals such as Zn and Cu found in the field. Pb, on the other hand, is a known source of contamination due to activities related to traffic, including burning of gasoline and lubricant oil usage, wearing of the tires and brakes, abrasion on the road, and runoff on the road.[26] All of these factors may affect vegetables cultivated alongside roads in one way or another. Similar results have been seen in the garlic samples cultivated from individual gardens in the Copșa Mică polluted area in Romania.[27] Therefore, lead bioaccumulation in garlic is more frequent throughout the world.[27]

Assessment of Public Health Risks

Average Daily Intake

Determining the health risks to an organism requires an estimation of the heavy metal exposure levels.[28] Depending on the daily consumption, the level of the threat can be quantified.[29] A person’s daily diet consists of 4 grams of garlic among their vegetable components.[30] For this study, ADI calculations were based on four metals taking into consideration the average body mass of a human as 60 kg, equivalent dry weight of the garlic samples, and average metal concentrations in their edible parts.

Six native garlic samples are shown in [Fig. 1], together with the mean daily intake and permitted highest possible tolerated intake each day (PMTDI) of Cr. Differing amounts of chromium (Cr) were consumed on average each day (ADI). As per the Recommended Dietary Allowances (RDA),[31] the native garlic samples did not exceed the permitted maximum tolerable daily intake (PMTDI) of 0.20 mg person⁻¹ day⁻¹. This was demonstrated by the ADI of native Cr, which spanned from 0.00 to 0.007 mg person⁻¹ day⁻¹. The contribution hierarchy for the Cr intake was as follows: Karwanbazar Native Garlic 2 > Shyambazar Native Garlic 3 > Shyambazar Native Garlic 1, Shyambazar Native Garlic 2, Karwanbazar Native Garlic 1 and Karwanbazar Native Garlic 3 according to [Fig. 1]. In [Fig. 2], the average daily consumption of Cr in the imported garlic samples is presented. Based on the data, it was evident that the ADI values did not differ much. From [Fig. 2], the ADI values of all foreign Cr were found to be less than the RDA[31] suggested PMTDI of 0.20 mg person⁻¹ day⁻¹. Garlic’s ADI values for Cr in the samples ranged from 0.00 to 0.01 mg person⁻¹ day⁻¹. The contribution hierarchy for the Cr intake for foreign garlic is as follows: Shyambazar Chinese Garlic 1 > Karwanbazar Chinese Garlic 2, Shyambazar Chinese Garlic 2, Shyambazar Chinese Garlic 3, Karwanbazar Chinese Garlic 1 and Karwanbazar Chinese Garlic 3, according to [Fig. 2]. Chromium is a crucial part of diets because it affects lipid metabolism and insulin action, according to Ahmed et al.[32] On the other hand, prolonged exposure to Cr can harm the kidneys, liver, and lungs.[33]

Fig. 1 Average daily intake of native garlic samples.

Fig. 2 Average daily intake of foreign garlic samples.

[Fig. 1] shows the native garlic samples daily average copper intake values. The results showed no significant variations in the ADI of Cu. The range of the ADI for copper in native garlic samples of this study was 0.00 to 0.006 mg person⁻¹ day⁻¹. The contribution to the intake of Cu was made in the following order: Karwanbazar Native Garlic 3 > Shyambazar Native Garlic 2, Shyambazar Native Garlic 3, Karwanbazar Native Garlic 1, and Karwanbazar Native Garlic 2 > Shyambazar Native Garlic 1 ([Fig. 1]). The average ADI of Cu for all native garlic samples, as indicated in [Fig. 1] of the study, weighed less than the FAO/WHO[23] advised PMTDI of 2.00 mg person⁻¹ day⁻¹.

The average values of the ADI of copper shown in [Fig. 2] did not differ significantly from one another. Foreign garlic samples had ADI values between 0.00 and 0.01 mg person⁻¹ day⁻¹. Cu was consumed below the Permitted Maximum Tolerable Daily Intake of 2.00 mg person⁻¹ day⁻¹ endorsed by FAO/WHO.[23] The decreasing order of the mean ADI of Cu was: Shyambazar Chinese Garlic 2, Shyambazar Chinese Garlic 3, Karwanbazar Chinese Garlic 1, Karwanbazar Chinese Garlic 2, and Karwanbazar Chinese Garlic 3 > Shyambazar Chinese Garlic 1 ([Fig. 2]).

Copper is a vital micronutrient that acts as a bio-catalyst. It is necessary for body pigmentation and, together with iron, helps maintain a healthy neurological system and prevent anemia; it also interacts with the activities of zinc and iron in the body.[34] Copper is still required in modest amounts even if consuming too much of it might damage the kidneys, liver, and intestines.

The ADI of lead is demonstrated by [Fig. 1]. JECFA[35] reports that in native garlic samples, the Pb ADI showed a range of 0.022–0.031 mg person⁻¹ day⁻¹, constantly maintaining levels below the PMTDI of 0.21 mg person⁻¹ day⁻¹ for lead (Pb). For native garlic samples, the average daily Pb intake was as follows: Shyambazar Native Garlic 1 > Karwanbazar Native Garlic 2 > Shyambazar Native Garlic 3 > Karwanbazar Native Garlic 3, Shyambazar Native Garlic 2 > Karwanbazar Native Garlic 1, ([Fig. 1]). Insignificant variations in the average daily lead consumption calculated from the dietary intake of six foreign garlic samples are shown in [Fig. 2]. ADI values of lead ranged from 0.02 to 0.03 mg person⁻¹ day⁻¹ for foreign garlic on average. It was observed that the values of ADI for the consumption of half of the studied foreign garlic samples were above the PMTDI (0.21 mg person⁻¹ day⁻¹).[35] The sequence of Pb ADI values from highest to lowest in the studied garlic samples is Shyambazar Chinese Garlic 2, Shyambazar Chinese Garlic 3, and Karwanbazar Chinese Garlic 1 > Shyambazar Chinese Garlic 1, Karwanbazar Chinese Garlic 2, and Karwanbazar Chinese Garlic 3 ([Fig. 2]).

Lead consumption that exceeds the PMTDI accumulates in the brain and other organs. Renal, central nervous system, and gastrointestinal tract complications are further concerns associated with lead. Exposure to lead can have detrimental consequences on development, IQ, and hyperactivity; kids under the age of six are particularly vulnerable in terms of attention span and mental health. A recent study states that individuals exposed to lead usually experience anorexia, memory loss, nausea, and joint weakness as well as slower reaction times.[36]

The wide ranges in the native garlic samples under the study’s mean average daily zinc consumption are seen in [Fig. 1]. Zinc’s ADI in native garlic samples ranged from 0.05 to 0.07 mg/person⁻¹ day⁻¹, with highest value decreasing in the order of Karwanbazar Native Garlic 2, Karwanbazar Native Garlic 3 > Shyambazar Native Garlic 2, Shyambazar Native Garlic 3 > Shyambazar Native Garlic 1, and Karwanbazar Native Garlic 1 ([Fig. 1]). According to FAO/WHO,[1] the recommended PMTDI value is 20.00 mg person⁻¹ day⁻¹, but the mean ADI values of zinc consumed from all the studied native garlic samples were lower. The average zinc intake per day from consuming foreign garlic samples is shown in [Fig. 2], which also demonstrates a significant range in mean ADI values. Zinc levels in six samples of imported garlic ranged from 0.04 to 0.06 mg person⁻¹ day⁻¹ on average. The decreasing order of ADI values in foreign garlic for zinc intake is Shyambazar Chinese Garlic 2, Shyambazar Chinese Garlic 3 > Shyambazar Chinese Garlic 1, Karwanbazar Chinese Garlic 1, and Karwanbazar Chinese Garlic 3 > Karwanbazar Chinese Garlic 2 ([Fig. 2]). According to [Fig. 2], all samples of imported garlic had ADI of zinc below the PMTDI of 20.00 mg person⁻¹ day⁻¹ set by FAO/WHO.[23]

For a human being to grow and develop properly, zinc is one of the most essential nutrients. Zinc toxicity in the gastrointestinal tract, anxiety, depression, and fatigue are just a few of the negative effects of increasing zinc consumption through the diet. A zinc deficiency may raise the risk of cancer development, even though zinc is not mutagenic to people.[37]

Using the concentrations of each metal in the samples, the ADI for heavy metals was determined for garlic, both imported and domestic. When native and imported garlic is taken through diet, [Figs. 1] and [2] display the mean ADI values and the PMTDI of the metals under consideration. The ADI values of all the heavy metals were below the PMTDI by the consumption of native and foreign garlic samples. Compared to other garlic samples, the levels of heavy metals in Karwanbazar Native Garlic 2 were higher, but it was still below the PMTDI levels.

Hazard Quotient (HQ) and Hazard Index (HI)

Assessing the potential health danger due to heavy metal contamination from various garlic samples acquired from Shyambazar and Karwanbazar in Dhaka city, the HI and HQ were computed. HQ values were calculated based on the oral reference doses ($R_{f}D$). An index of risk called Hazard Index (HI) for the people residing in Dhaka city, who ingested these metals by consuming this stem vegetable, was estimated by summation of the HQ of all heavy metals for each native and foreign garlic sample. Bermudez et al.[38] state that there might be negative health effects if the HQ is higher than 1.

[Fig. 3] presents the HQ measurements of heavy metals for native garlic samples. While all of the native garlic samples had Pb HQ values significantly greater than 1, the results indicated that only Karwanbazar Native Garlic 2 exhibited Cr HQ values greater than 1. So, it is hard to say that individuals who consume the locally grown garlic samples that are being studied are safe, at least not due to the significantly high lead levels. The HQ values in [Fig. 3] correspond to Zn, Cr, Cu, and Pb, which were 0.17–0.22, 0.00–2.22, 0.11–0.14, and 5.50–7.79, respectively. The following order describes how the metals’ HQ values declined when native garlic samples were compared: For Cr, Karwanbazar Native Garlic 2 > Shyambazar Native Garlic 3 > Shyambazar Native Garlic 1, Shyambazar Native Garlic 2 , Karwanbazar Native Garlic 1, & Karwanbazar Native Garlic 3; for Cu, Karwanbazar Native Garlic 3 > Shyambazar Native Garlic 2, Shyambazar Native Garlic 3 & Karwanbazar Native Garlic 1 > Karwanbazar Native Garlic 2 > Shyambazar Native Garlic 1; for Pb, Shyambazar Native Garlic 1 > Karwanbazar Native Garlic 2 > Shyambazar Native Garlic 3 > Karwanbazar Native Garlic 3 > Shyambazar Native Garlic 2 > Karwanbazar Native Garlic 1; for Zn, Karwanbazar Native Garlic 2 & Karwanbazar Native Garlic 3 > Shyambazar Native Garlic 2, Shyambazar Native Garlic 3 > Shyambazar Native Garlic 1 > Karwanbazar Native Garlic 1 ([Fig. 3]).

Fig. 3 Hazard quotient and hazard index of native garlic samples.

The HI values expressed health risks upon consumption of all the native garlic samples. HI of native garlics was above unity and had the potential to cause health hazards due to consumption. The highest HI value reported about Karwanbazar Native garlic 2 (9.17), while the lowest value recorded was 5.80 for Karwanbazar Native garlic 1. So, the decreasing order for HI values according to [Fig. 3] was: Karwanbazar Native Garlic 2 > Shyambazar Native Garlic 1 > Shyambazar Native Garlic 3 > Karwanbazar Native Garlic 3 > Shyambazar Native Garlic 2 > Karwanbazar Native Garlic 1 ([Fig. 3]).

The HQ levels of major metals in samples of imported garlic are displayed in [Fig. 4]. The results indicated that Pb had a dramatically higher than 1 HQ value in all foreign garlic samples and that of Cr had a higher than 1 HQ value in Shyambazar Chinese Garlic 1 (2.06). Therefore, people who consume the analyzed foreign garlic samples are still in danger. For Cr, Cu, Pb, and Zn, the range of the HQ values was, respectively, 0.00–2.06, 0.12–0.16, 4.09–8.20, and 0.15–0.21 according to [Fig. 4].

Fig. 4 Hazard quotient and hazard index of foreign garlic samples.

It was discovered that the metals’ HQ values decreased in the following order: for Cr, Shyambazar Chinese Garlic 1 > Karwanbazar Chinese Garlic 2 > Shyambazar Chinese Garlic 2, Shyambazar Chinese Garlic 3, Karwanbazar Chinese Garlic 1, and Karwanbazar Chinese Garlic 3; for Cu, Karwanbazar Chinese Garlic 1 > Karwanbazar Chinese Garlic 2, Karwanbazar Chinese Garlic 3, & Shyambazar Chinese Garlic 3 > Shyambazar Chinese Garlic 2 > Shyambazar Chinese Garlic 1; for Pb, Shyambazar Chinese Garlic 2 > Karwanbazar Chinese Garlic 1 > Shyambazar Chinese Garlic 3 > Shyambazar Chinese Garlic 1 > Karwanbazar Chinese Garlic 2 > Karwanbazar Chinese Garlic 3; for Zn, Shyambazar Chinese Garlic 3 > Shyambazar Chinese Garlic 2 > Karwanbazar Chinese Garlic 1 > Karwanbazar Chinese Garlic 3 > Shyambazar Chinese Garlic 1 > Karwanbazar Chinese Garlic 2 ([Fig. 4]).

The HI values represented in [Fig. 4] expressed health risks for consumption of all the foreign garlic samples. HI values for foreign garlic samples were above the unity and had the potential to cause health hazards due to consumption. The greatest HI value was 8.53 in Shyambazar Chinese Garlic 2, and the lowest HI value was 4.40 for Karwanbazar Chinese Garlic 3. According to [Fig. 4], the following is the HI readings given in descending order: Shyambazar Chinese Garlic 2 > Shyambazar Chinese Garlic 1 > Karwanbazar Chinese Garlic 1 > Shyambazar Chinese Garlic 3 > Karwanbazar Chinese Garlic 2 > Karwanbazar Chinese Garlic 3.

Conclusion

The present study has generated data on heavy metals in garlic collected from Karwanbazar and Shyambazar market of Dhaka city of Bangladesh and the associated risk assessment for consumer’s exposure to heavy metals. The investigation quantified the concentration of chromium, copper, zinc, and lead in the edible parts of garlic found in common marketplaces. Among them, the concentration of lead was particularly higher. In other words, the concentration of lead in garlic was higher than the MPL, unlike the other studied metal concentrations. The ADI values for Pb were significantly higher than the PMTDI levels. The HQ values for all metals were below 1 except for Pb in all of the samples. Since the arithmetic sum of all the HQ values were added to determine the HI, the calculated HI values in all the garlic samples was higher than 1. The HQ value of Pb had a big role in the HI being more than 1. As a result, it can be concluded from the current study that garlic may be carcinogenic. Given its potential effects on the health of humans and animals, the environmental heavy metal pollution in soil, water, plants, and air is a serious concern. The harmful effects of the majority of the heavy metals studied here are not immediately identified. Typically they take effect after decades of exposure. Immediate remedies like soil remediation and safe irrigation practice can potentially help in reducing carcinogenic metal levels in cultivated garlic. Moreover, long-term monitoring of the irrigation water quality, soil pH levels, and application of soil amendments like biochar to immobilize the heavy metals can temporarily reduce the risks. Therefore, it is recommended that further comprehensive studies be conducted to monitor and evaluate the levels of heavy metals in garlic obtained from both marketplaces and production sites. These studies are necessary to assess the potential health risks to humans and to prevent the excessive accumulation of these heavy metals in the human food chain. Scarce documented data exist about the levels of heavy metals in garlic obtained from market locations in Bangladesh.

Experimental Section

Study Area and Sampling

Garlic (Allium sativum) is a common Bangladeshi stem vegetable that was collected from Karwanbazar and Shyambazar market, two of the most prominent wholesale vegetable markets in Dhaka city including varieties of tiny roadside markets nearby. Fruits and vegetables in these markets are sourced from various locations such as Savar, Kushtia, Narsingdi, Kishoregonj, Munshiganj, Rajshahi, Bogra, Jessore, Mymensingh, Chittagong, etc., ensuring a diverse supply chain. The two main hubs for distribution are Karwanbazar and Shyambazar, which deliver a variety of goods, like rice, fish, vegetables, and other things, to the city of Dhaka’s fresh marketplaces.

This study sets out to offer a representative assessment of the amount of heavy metal being present in garlic that may be extrapolated to represent the levels observed in other vegetable markets throughout the city of Dhaka. Laboratory analyses were conducted at the Advanced Research Laboratory at the Department of Soil, Water, and Environment, University of Dhaka. Samples of different sources of garlic, i.e., native and foreign were gathered from various stores and replicated three times and were brought to the laboratory for additional research work.

Sample Preparation and Preservation Methods

To ensure the accuracy and reliability of the findings, careful sample-preparation steps were implemented to reduce any unnecessary surface contamination, as only the edible part of the garlic was focused in this study. The garlic samples were visually inspected to remove any potential damage, or decayed bulbs. Each sample was washed carefully under running distilled water to remove any surface contaminants such as soil, dust, or any other residues. Following the washing step, the garlic bulbs were peeled to remove outer layers, which are typically discarded during household preparation and are more likely to retain surface contaminants, and also potentially removing any part that are not typically used in households.

The cleaned and peeled off samples were then left to air-dry at room temperature in order to remove any excess surface moisture. The fresh weight is measured from the air-dried samples and then subsequently they were oven-dried at 60—70 °C for 72–96 h until all the moisture from the samples gets vaporized away.

To ascertain the samples’ dry weight, they were weighed once more after drying. Moreover, for getting a uniform and fine texture, samples of dried garlic cloves were carefully ground using a sterilized mortar and pestle. After that, they were sieved using a 0.2 mm sieve. The powdered samples that were obtained were carefully stored at room temperature in clean, dry, and labeled polythene bags to maintain their integrity for digestion ([Fig. 5]).

Fig. 5 Flowchart for sample preparation and preservation.

Digestion Procedure of the Samples

To digest the plant material, a commonly used acid-based digestion procedure was employed.[39] [40] [41] Precisely, a mixture of 2mL of conc. HCl₄ and 10 mL of conc. HNO₃ (analysis grade, Merck-Germany) were added to 1g of the oven-dried sample that had been weighed into a 100 mL beaker. A heated plate between 150 and 200 °C was used to carry out the digestion. Once digested, the samples were taken out and allowed to cool down to room temperature. After the samples cooled, they were filtered into a volumetric flask of 100 mL. Distilled water was added to the filtrate to level up to 100 mL. This 100 mL sample stock solution was thereafter preserved carefully in a plastic bottle for the AAS analysis ([Fig. 6]).

Fig. 6 Methodological flowchart showing heavy metal analysis of garlic samples.

Analysis of the Sample using AAS

Heavy metal concentrations in the extracts, notably those of Cr, Cu, Pb, and Zn, were measured using the Varian AA 240 atomic absorption spectrophotometer (AAS). Four different wavelengths (357.9, 324.7, 283.3, and 213.9 nanometers) were used in the study to test Cr, Cu, Pb, and Zn using a hollow cathode lamp. 1.7963, 20.0, 100, and 5.1260 gL⁻¹ were found to be the corresponding detection limits for the previously stated elements. The standard solutions were intermittently utilized to verify and uphold the sensitivity.

Health Risk Assessment

Average Daily Intake (ADI)

The ADI of heavy metals was determined by multiplying the average daily vegetable consumption per person, the percentage of dry weight of vegetables, and the average concentration of heavy metals per unit dry weight of vegetables, as expressed in the following equation[27]:

$$\mathrm{ADI}={A_v}_{\text{consumption}}\times \%\mathrm{D}{\mathrm{W}}_{\text{vegetable}}\times C_{\text{heavy metal}}$$

where ${A_v}_{\text{consumption}}$ denotes the average daily consumption of vegetables per person per day (g day⁻¹), ADI represents the average daily consumption of heavy metals in each individual (mg person⁻¹ day⁻¹), and % DW_vegetable is the percentage of the dry weight of the vegetable, the weight of the vegetable that remains after subtracting the moisture content ($\%\mathrm{DW}=\frac{100-\%\text{moisture}}{100}$), and the average concentration of heavy metals in the vegetable’s dry weight (mg g⁻¹) is indicated by the term C_{heavy metal}. The ADI values are computed using the value 4 g person⁻¹ day⁻¹ specifically for garlic.[30] Furthermore, the computation takes into account each person’s average weight of 60 kg.[42] There may be several health concerns and hazards when the ADI exceeds the maximum permitted daily intake (MTDI) threshold.

Hazard Quotient (HQ)

The percentage of the likely exposure to a chemical or element to the amount at which no adverse effects are observed is called the Hazard Quotient or HQ in short. According to Bermudez et al.,[38] the ratio of less than one indicates that there are no expected health impacts from exposure, whereas a quotient of more than one indicates possible health hazards. The following formula illustrates how the HQ is computed as a percentage of the concluded dosage of the benchmark dose:

$$\mathrm{HQ}=\frac{\mathrm{ADI}}{R_{f}D}$$

where $R_{f}D$ is the metal’s oral reference dose (mg kg⁻¹ day⁻¹) and ADI is the average daily vegetables intake (mg kg⁻¹ day⁻¹). Valued at $R_{f}D$, this represents the anticipated daily tolerable exposure that an individual is expected to experience over their lifetime without a noteworthy risk of adverse effects. WHO/FAO[43] states that the $R_{f}D$ for Pb, Zn, Cu, and Cr are 0.004, 0.3, 0.04, and 0.003 mg kg⁻¹ day⁻¹ respectively.

Here the ADI that was calculated previously is used and that value is divided by the reference dose ($R_{f}D$), or approximate daily tolerable exposure without any significant health risk. Thus, HQ or Hazard Quotient is calculated as a dimensionless unit.

Hazard Index (HI)

There are compounding effects when many pollutants are exposed. The HI is therefore an essential metric that evaluates the total likely effects of exposure to many contaminants. When a food’s HI value is more than 1, it may have substantial negative impacts on one’s health. Each contaminant’s HQs are added up to determine the HI, as shown in the following equation[27]:

$$\mathit{HI}={\sum }_{i=1}^n\mathrm{HQ}$$

Statistical Analysis

The test was conducted in triplicates, i.e., 3 replications were done for each type of sample. The data represented in the tables were the arithmetic mean of the original values quantified through the AAS machine. For further accuracy, IBM SPSS statistics version 20 was used to statistically examine the experiment’s data and ANOVA (Analysis of Variance) and Duncan’s Multiple Range Test, using the technique outlined by Gomez and Gomez.[44] Differences among means were tested using one-way ANOVA followed by Duncan’s Multiple Range Test (DMRT) at the 0.05 significance level, i.e., P-value ≤ 0.05 was chosen as the significance level for statistical inference and are expressed using letters (a, b, c, d, and so on).

Contributors’ Statement

Afrose Sultana Chamon: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing - review & editing. Gulshan Akhter Shimi: Data curation, Formal analysis, Investigation, Methodology, Project administration, Software, Writing – original draft. Sharnali Akhter: Formal analysis, Methodology, Software, Validation, Visualization, Writing – review & editing. Md Marshad: Formal analysis, Software. Md Nadiruzzaman Mondol: Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Supervision, Validation, Visualization.

Conflict of Interest

The authors declare that they have no conflict of interest.

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Publication History

Received: 20 July 2025

Accepted after revision: 27 October 2025

Article published online:
15 December 2025