Heavy metals in dates (Phoenix dactylifera L.) collected from Medina and Dhaka City markets, and assessment of human health risk

Abstract

Background

Constantly eaten foods (such as fruits, vegetables, cereal, etc.) that contain excessive concentrations of heavy metals pose a major risk to human health and deplete the food supply. The amounts of heavy metals in different date varietiies were measured after they were collected from three wholesale markets in the major cities of Dhaka, Bangladesh, and Medina. In order to look at the health risks associated with heavy metal consumption after intake of dates, the Average Daily Intake (ADI), Hazard Quotient (HQ), and Hazard Index (HI) were also calculated.

Results

Copper (Cu), Cadmium (Cd), Chromium (Cr), Iron (Fe), Lead (Pb), Manganese (Mn), Nickel (Ni), and Zinc (Zn) levels were evaluated. Several analyses of date fruit exhibited levels of Pb and Cd in different date varieties that beyond the Maximum Permissible Limit (MPL). In the majority of the samples, ADI was below the upper authorized tolerated daily consumption. The likelihood of a health risk from the regular eating of the investigated date fruits is revealed by the hazardous indexes of samples taken from New Market and Badamtali that surpassed unit value as a result of excessive air pollution brought on by greater industrial and vehicle traffic. According to the study, the majority of the analyzed heavy metals were identified in date samples and those from later samples at levels that were less harmful than the maximum acceptable threshold (MAL).

Conclusions

Some samples included higher levels of Pb and Cd. As a result, eating dates that contain more metal has a higher chance of harming your health. Additionally, it has been recommended that regular testing for heavy metals in date fruits may be useful in preventing health risks associated with eating fruits that are contaminated with heavy metals.

Background

Dates, which are grown by the date palm (Phoenix dactylifera L.), have become a sweet, healthful, and well-liked fruit in Bangladesh. Despite it is deemed a sacred fruit by Muslims, people of different beliefs appreciate and eat it due to its health benefits. Dates range in amount of carbohydrates from 47 to 85%; the majority of them have more than 70%. In accordance with Fayad and Showiman (1990), dates are a rich source of 21 distinct amino acids, several vital minerals, including Al, Ca, Cu, and Zn, as well as vitamins A, B1, B2, and C. Al-Farsi et al. (2005) discovered that dates also have antioxidant effects. Date varieties are common, although only 400 have been recorded (Hussain and El-Zeid 1975), contrasted with the 250 named by Nixon in 1954. Ajwa, Ambar and Medjool date varieties were selected in this study.

The unwanted heavy metal in dates may appear from the outside factors. It was found that contaminated soil may produce contaminated dates (Nawal 2014). Irrigation waters also contaminate dates whether the water was treated or groundwater (Al-Busaidi et al. 2015). Contamination may also occur by air dust that has heavy metal in it (Aldjain et al. 2011). Also the anthropogenic activities due to the population boom in the urban areas cause such contamination. Traffic emissions from fossil fuels, agriculture, waste incineration and sewage sludge are main sources of air pollution (Celik et al. 2005). Beside these sources of heavy metal, contamination is also caused by dust storm (NRDC 2005) in Saudi Arabia. Pollutants deposited from air falls on ground and exposed plant parts (Khairiah et al. 2004; Chojnacka et al. 2005; Hashmi et al. 2006). Pollutants deposited by air especially lead (Pb) and cadmium (Cd) are toxic and hazardous in food stuff but depends on concentration (Sensei et al. 1999; Jarup 2003). Consumers of dates containing such pollutants (Pb & Cd) may lead to serious health issues. So the assessments of contaminations in food like date fruit is important for the safety of human health (Gilbert 1984; Zakrzewski 1991; Kennish 1992).

Dates are not native fruit in Bangladesh; it is imported mostly from the Middle East and some African countries (Pintaud et al. 2013). Many countries have reported, like a test was conducted in a cultivar in Oman and found contaminations of heavy metals (Williams and Pillay 2011). Another date producing country is United Arab Emirates, where Pb, Cr, and Cd were found more than permissible limit (Zienab et al. 2022). Pb was found more than acceptable range in Palestine (Khalilia 2020). Contamination was found in the dust fallen on dates in Saudi Arabia and consumers were suggested to wash them before consuming (Hassan et al. 2017). High Pb was found in a Sudanese date cultivars and the consumers were suggested to wash before eating (Malik et al. 2021) also. A similar study was conducted in Egypt where it was shown that dates have higher than the range of Daily Intake Estimate of Pb, Cd, Cu, and Zn (Salama and Radwan 2006). Only one review that has found certain toxic elements like Ni, Pb, As in dates sold in Bangladesh and those are present within safe limit to consume according to their daily oral dose (Zamir et al. 2020).

The air quality of Dhaka is now becoming a great point of concern as the rapid urbanization is taking place. Brickfields around Dhaka, exhausts of automobiles etc. are the major reasons behind such pollution. Such contaminated air directly injects heavy metal particles into surroundings (Rahman et al. 2013). In this circumstances, the selling and consumption of date increases during the holy month of Ramadan, which is a sacred month, when all Muslims fast from dawn to dusk and break their fast with dates. As the selling points are exposed to open air, such openly sold fruits are prone to air deposited heavy metal contamination. As a result, there is high possibility that the sold fruits including dates may carry toxic heavy metals. Yet the good thing is washing the surface of the fruit is useful to reduce contamination (Hassan et al. 2017).

As dates are not native in Bangladesh, very few works are done related to date’s food security. There were many reviews and studies about fruits and vegetables in Bangladesh, but very few included dates. In the current study, the goal is to calculate the amount of heavy metal available in dates and Health Risk Assessment of heavy metal contamination via dates. All samples were collected from wholesale and retail markets of Dhaka city and Medina. Dates contain appreciable amounts of Ca, Mg, P, K, Fe, Cu and Zn (Al-Hooti et al. 1995. The transition metals or metalloids (arsenic, cadmium, chromium VI, beryllium, and nickel) are considered as human carcinogens at extensive exposure (EPA 2002).

According to the EPA (2002), cadmium is a hazardous metal that has a serious negative influence on kidney function and bone metabolism to the point of cancer. Sewage sludge, which is utilized to enhance soil qualities, is the primary source of copper for plants in phosphate fertilizers (Ward 2000). 50 ng.g-1 is the maximum amount of Cd that is permitted in fruits (FAO/WHO 2001). A range of 15.5–24.74 ppb was found in earlier research on Egyptian dates (Awadallah et al. 1999), whereas the concentration in dates from Saudi Arabia was 5.65 mg·kg-1 (Amotida 2002) and 27 ng·g-1 in dates from Pakistan (Waheed et al. 2004).

Lead (Pb) and cadmium (Cd) are hazardous air pollutants and toxic to humans when their concentrations is high in food stuff (Järup 2003). Thus the presence of (Pb and Cd) in date fruits above the permissible limit induces severe health hazards to the consumers. Therefore the estimation of the extent of these contaminants in dates vital important to the safety and human health (Kennish 1992).

The objectives of this study was to ascertain the trace metal concentration of common date varieties, such as Ajwa, Medjool, and Ambar dates by using atomic absorption spectroscopy. In order to evaluate the likelihood of health risks and carcinogenicity in the human body, it is also necessary to calculate the Hazard Quotient (HQ) and (HI).

Materials and methods

Sample collection

As Bangladesh is not a date producer, here year long and especially during Ramadan, date fruits are imported from predominantly middle-east countries. Sample collection zone have been selected on the basis of date fruit selling hotspots as those places were densely populated (Table 1a). Open market and kitchen markets were everywhere distributed. Retailers selling date fruits without commercial packaging and labeling. Date of expiry was not provided.

Table 1 a The sample collection details from Dhaka city markets with GPS location. b The sample collection details from Medina city markets with GPS location

In this investigation, the most popular date variety named-Ajwa, Amber, and Medjool shown in Fig. 1a-c, were purchased from different local outlets of Dhaka city (Badamtali, New Market and Mirpur) before Ramadan (February–March, 2023), as during this tenure most dates entered markets and also from the wholesale markets in Medina, during Hazz period (July, 2022) (Table 1b). Densely populated local outlets have been selected as sample collection zones. The origin of the imported dates sold in the Dhaka city markets and outlets of Dhaka city from where date samples were collected in presented in the Table 1a.

Fig. 1

a–c Date samples

Zipper bags were used for dates sample collection from the collection points to avoid additional contamination. Collected samples were directly sent to the laboratory of the Department of Soil, Water and Environment, University of Dhaka for heavy metal analysis after labeling the bags with the name of place of date and collection point code. Three replicated samples (3 shops) were collected from each market place. The sample collection details with GPS locations are shown in Table 1a, b and Figs. 1 and 2.

Fig. 2

Sample collection points (a New Market, b Badamtali and c Mirpur)

Sample preparation and preservation

After collecting the date samples, edible parts of the dates were sliced into little pieces, and then they were mixed well together and weighed. After drying at 65–70 °C for 7 days in an induction oven, the dry weight was observed again and the moisture contain was determined (Fig. 3).

Fig. 3

Sample preparation steps

The digestion and analysis of the sample

A common acid–base digestion technique was used for sample digestion (Alain et al. 2021; Blum et al. 1996; Samuel and Babatunde 2021). The digestion method was carried out using concentrated HNO₃ and concentrated HClO₄ in a ratio of 3:2 in a closed system (Blum et al. 1996).

The concentration of heavy metals such cadmium (Cd), lead (Pb), nickel (Ni), copper (Cu), zinc (Zn), iron (Fe), and manganese (Mn) in the extracts was determined by using an Atomic Absorption Spectrophotometer (Varian 240, origin-Australia). The metal contents were determined based on the dry weight of the samples.

Average daily intake (ADI)

Human health risks generated by contaminants entering the body are routinely evaluated using a variety of indices, including average daily intake (ADI), hazard quotient (HQ), and hazard index (HI) (Cui et al. 2004; Gall et al. 2015; Zhuang et al. 2009). A pilot survey was conducted among some people of all classes and different Dhaka city areas regarding the contamination of date fruits in which majority was male around 63.45 and 36.5% was female. Structured questionnaires were asked to find out daily intake of date per person per day and other information like food habit, knowledge regarding date fruits contamination, long time chronic diseases. An interview of 40 persons of the 25–60 years age group and in the range of 63–75 kg body weight was conducted at different Dhaka city areas and the interview was aimed to obtain data regarding daily date fruits consumption. An average consumption rate of date fruits per person per day was calculated from these data. From the survey the average daily consumption of dates is 29 g per person per day was calculated which was similar to Dhar et al. (2019). Then the following equation was used to calculate ADI (Kacholi and Sahu 2018):

$$ADI \, = \, Av_{consumption} \times \, \% \, DW_{date} \times \, C_{heavy \, metal}$$

In this context, ADI refers to the average daily intake of heavy metals per person per day (mg/person day), while Av_consumption represents the average daily consumption of dates per person per day (g/person day), %DW_date is the percentage of the dry weight of dates (%DW = [(100 − % moisture)/100]), and C_{heavy metal} is the average heavy metal concentration of dry weight date (mg/g). According to Dhar et al. (2019), the average daily consumption of dates is 29 g per person. The value 29 g/person day was therefore used in calculating the ADI values, and the average weight of a person was considered to be 60 kg (FAO/WHO 1993; Sultana et al. 2020). A variety of health risks may arise when the ADI value exceeds the maximum permissible value.

Hazard quotient (HQ)

The ratio of a contaminant's exposure to the point at which there won't be any anticipated health risks is known as the hazard quotient (HQ). If the Hazard Quotient (HQ) exceeds 1, it indicates the possibility of potential health risks associated with the exposure to a particular contaminant. (Bermudez et al. 2011; Chary et al. 2008). The hazard quotient was calculated using the following equation (Granero and Domingo 2002):

${\text{HQ}}\, = \,{\text{ADI }}/{\text{ R}}_{{\text{f}}} {\text{D}}.$

Here, R_fD shows the oral reference dose of the metal (mg/kg-day), while ADI shows the average daily intake of dates (mg/kg-day). R_fD is the amount of a specific contaminant that a person can be exposed to every day without experiencing any significant health risks over the course of their lifetime. The WHO/FAO (2013) has established the R_fD values in mg/kg/day units for Pb (0.004), Zn (0.30), Cu (0.04), Cd (0.0005), Ni (0.02), Fe (0.70), and Mn (0.14).

Hazard index (HI)

Hazard index (HI) is used to analyze the potential health hazards when a person is exposed to numerous contaminants at once, as opposed to hazard quotient (HQ), which is used to measure the health risks caused by any one contaminant. The key reason for this is the additive impact of several contaminants. Consequently, determining HI is an effective technique to comprehend the potential health concerns linked to simultaneous human exposure to various contaminants. In the same way that the hazard quotient does, an HI value greater than 1 denotes potential health risks.

The following equation (from Kacholi and Sahu 2018) illustrates how the hazard index (HI) is the total of the hazard quotients for each pollutant:

$\text{HI}\hspace{0.17em}=\sum_{i=1}^{n}HQ$

Statistical analysis

For every sample, there were three replicates. The statistical software SPSS-20 (SPSS Inc., Chicago, IL, USA) was used to evaluate the data statistically. Using IBM SPSS statistics version 20, the data were statistically examined using ANOVA (Analysis of Variance), and the mean was statistically compared using Duncan's Multiple Range Test at p, 0.05% level, in accordance with Gomez and Gomez's (1984) guidelines. The goal underlying ANOVA is to compare many sources of variance and make inferences about their relative sizes. In this study, a one-way ANOVA was used to assess the mean metal concentrations in date palm samples from three shops in Madina and other areas in Dhaka city, including Babadamtali, New Market, and Mirpur. Microsoft Excel was also used for data analysis. During the analysis, the significance of mean value differences was evaluated using the letter, and a probability level of 0.05 was selected for the statistical evaluation.

Results and discussion

Heavy metal concentration in Ajwa date fruits

Cadmium concentrations

Cadmium concentrations in collected date fruit samples from various Dhaka city markets ranged from 0.10 to 1.08, 0.1–0.76 and 0.11–1.07 mg/kg, for Ajwa, Medjool and Ambar date varieties, respectively which showed significant differences (Table 2). Ajwa and Ambar dates collected from New Market shop-1 had the highest Cd concentration (1.08 and 1.07 mg/kg) while those collected from Mirpur shop-2 had the lowest Cd concentration (0.10 and 0.11 mg/kg). Most of the Cd values found exceeded maximum permissible limit of 0.2 mg/kg, for the collected three date fruit varieties, endorsed by FAO/WHO (2001). The values of Cd concentration of Ajwa, Medjool and Ambar dates collected from all the shops of Badamtali, shop-1 and shop-2 of New Market were significantly different from those collected from Medina (0.13 mg/kg). In a study conducted in Saudi Arabia, the highest value of Cd in dates was 0.041 mg/kg (Walid 2020), which is approximately 26 times less than the highest value (1.08 and 1.07 mg/kg) found in this experiment (Table 2).

Table 2 Heavy metals concentration (mg/kg) in different varieties of date fruits collected from different markets in Dhaka city

The date palm growing in Naseriah Road and Bat-ha-manfooha Road, Riyadh, exhibited the highest concentration of Cd (0.64 and 0.62 μg g⁻¹ dry wt., respectively) in washing residues as compared to plants growing in other sites of Riyadh, reported earlier by Ibrahim and Mollah (2011).

Air pollutants especially lead (Pb) and cadmium (Cd) are hazardous and toxic to human beings depending on their concentrations in the food stuff (Järup 2003). Presence of these pollutants (Pb and Cd) in date fruits above the permissible limit may lead to severe health hazards to the people consuming it.

Due to bioconcentration and biomagnification, the amounts of Cd in air, water and sediment have been rising, which has had a major negative impact on fish, humans, and invertebrates' health (Sahadat et al. 2019). The total average Dhaka city air concentrations of As, Cd, Cu, Fe, Pb, and Zn in PM_2.5 were 6.3, 13, 94, 433, 204, and 381 ng m^–3, respectively (Salam et al. 2008). The Pb concentration in Dhaka shows a decreasing tendency, presumably due to the ban on the use of leaded fuel (Salam et al. 2008).

The present study revealed that level of heavy metals concentration in samples collected from three shops in Medina were within the safe limit (Tables 2and 3). But it was also revealed that level of Cd was very low as compared to that of the Pb. The variation in Cd level occurring among the samples collected from different sites might be due to the uptake capacity of plant that depend on the genetic make-up of plant and on the heavy metals content in the soil. Lower level of heavy metals in the fruit of date palm growing at different locations of Riyadh was also reported by Ibrahim and Mollah (2011).

Table 3 Heavy metals concentration (mg/kg) in Ajwa date fruits collected from Medina

Higher Cd concentrations in some date fruit samples may be the result of pesticide residue or they may be adulterated by the seller as a preservative or color in Bangladesh. The total average Cd concentrations in Dhaka city air ranged from 0.2 to 34.9 ng m^–3 higher than that of reported by Salam et al. (2008) and was higher than the WHO (1999) guideline value of 0.2 ng m^–3 for urban areas. Cadmium (Cd) finds its most prominent application in Ni/Cd batteries and is also utilized as a corrosion-resistant coating for vessels and vehicles. Additionally, cadmium is often present as an impurity in various products, including phosphate fertilizers, detergents, and refined petroleum products. Since date fruits are sold outside, in open air, the greater Cd concentration in the fruits at majority of the sampling sites in the current investigation may be the result of air deposition of Cd from Dhaka city air.

The highest risks for exposure occur in occupations involving heating cadmium-containing products, such as ore smelting operations, drying of cadmium pigments, soldering or welding of cadmium-containing ores, petroleum refining, and manufacturing of batteries (Ni–Cd) or plastics (ATSDR 2015). At lower levels of exposure, non-specific symptoms such as headache, chills, muscle aches, nausea, vomiting, and diarrhea can occur and kidney damage is the critical health effect associated with long-term cadmium exposure (ATSDR 2015).

Copper concentration

In case of Cu, the highest concentration was 3.90, 3.65, and 3.98 mg/kg for Ajwa, Medjool and Ambar date samples collected from Badamtali shop-2, and Madina shop 2, while the lowest value of 1.62 mg/kg was found in the sample collected from New Market for Ajwa date samples. All of the Cu values were below the maximum permissible limit of 40 mg/kg, issued by FAO/WHO (1989). The Cu concentration of samples of Badamtali shop-3 and New Market shop-1 are significantly different from Badamtali shop-2 and New Market shop-3 (Table 2).

Cu, Pb, Cd, and Zn are among the heavy metals found in dates, according to analysis of their composition. Although these metal levels are normally under safe consumption limits for all collected samples, they can change depending on the surrounding conditions. According to studies, the quantities of copper in Medjool dates can range from 1.5 to 36 ppm, occasionally surpassing advised levels (Ghazala et al. 2021).

Copper concentration in fruit samples collected from Super shops in Dhaka city by Shahnaz (2018) were observed to be higher compared to other published results. Copper is commonly found in drinking water due to the presence of copper pipes, as well as additives used to regulate algal growth. Copper is also added to the diets as growth promoters in the poultry industry. The manures produced from animals on such diets contain high concentration of Cu which may also have the potential to cause contamination of soil (Sumner 2000). The application of micronutrient fertilizers and copper-based fungicides can occasionally lead to an increase in copper levels to alarming levels (Radwan and Salama 2006).

Iron concentration

The highest Fe concentration (79.24, 79.91, and 79.91 mg/kg, respectively for Ajwa, Medjool, and Ambar) was found in the samples collected from New Market and the lowest concentration (8.51, 12.83, and 7.85 mg/kg, respectively for Ajwa, Medjool, and Ambar) was found in samples collected from Mirpur. Only the values from New Market shop-2 and Mirpur shop-3 showed significant differences from each other for Ajwa Dates. All these values are within the maximum permissible limit of 450 mg/kg, for the three collected dates, addressed by FAO/WHO (1989). Most of the Fe concentration values ranged from 8 mg/kg to 30 mg/kg. Similar Fe concentrations were found in a study conducted in Al Ain city in the United Arab Emirates (Zienab et al. 2022).

The results of this study are nearly in line with the findings of the study by Aldjain et al. (2011), which revealed that the ranges for Fe were 32.1–103.7 mg/kg of the date samples taken beside highway roads that may be the source trace elements.

Manganese concentration

In this study, the Mn concentrations ranged from 1.60–9.16, 1.54–6.16, and 1.27–7.49 mg/kg, respectively for Ajwa, Medjool and Ambar date samples collected from Dhaka city markets (Tables 2and3). was found in New Market Shop-3 which is up to 9.16 mg/kg, and the lowest concentration was found in samples from New Market Shop-1 which was 1.60 mg/kg. However, higher Mn concentrations were found for the Ajwa dates collected from Medina, ranging from 17.48 -22.24 mg/kg (Table 3). However, all these values are within the maximum permissible limit of 500 mg/kg, addressed by FAO/WHO (1989). Similar manganese (Mn) concentrations have been documented in studies conducted by Habib and Ibrahim (2011) and Brima (2019), indicating a range of 1.1 mg/kg to 3.5 mg/kg, with an average concentration of 2.9 mg/kg. In contrast, Kuras et al. (2020) reported a wide range of manganese (Mn) content in date fruit, spanning from 3.7 to 12 mg/kg.

In the study by Aldjain et al. (2011) reported the ranges for Mn were 51.4–58.6 mg/kg of the date samples collected beside high way road that may be the source trace elements, are almost in agreement with the result obtained in this study.

Nickel concentration

Nickel is an element naturally present in the environment at minimal concentrations and essential in small quantities. There were no significant differences in the Ni concentration values for the Ajwa date fruit samples, but Medjool and Ambar showed significant differences (Table 2). Most of these values were within the maximum permissible limit of 1 mg/kg, issued by FAO/WHO (1989). However, Badamtali shop-3 and New Market shop-2 exceeded the MPL limit FAO/WHO (1989) issued for all dates. Selling of date fruits in the open air, traffic congestion and automobile exhaustion, rapid urbanization, use of Ni–Cd batteries, fueling brick production and brickfields in the outskirts of Dhaka city emitting toxic metals with gases in alarming quantity and reckless housing of welding workspaces have directly injected metal particles into surroundings (Rahman et al. 2013). Feven et al. (2024) reported the higher Ni concentrations in date palm fruit samples ranged from 25.1–42.2 mg/kg.

The primary application of nickel (Ni) is as an ingredient in the production of steel and various other metal products. The major sources of nickel contamination in the soil are metal plating industries, combustion of fossil fuels, and nickel mining and electroplating (Khodadoust et al. 2004). Nickel (Ni) is released into the atmosphere through emissions from power plants and trash incinerators, eventually settling on the ground following precipitation reactions. Removal of nickel from the air typically occurs over an extended period. When present in wastewater streams, nickel can also find its way into surface water. The majority of released nickel compounds tend to adsorb onto sediment or soil particles, rendering them immobile. However, in acidic soils, nickel can become more mobile and may leach into adjacent groundwater (Wuana and Okieimen 2011).

Nickel plays a crucial role as an essential trace element in various animal species, plants, and prokaryotic organisms. It undergoes redox metabolism, leading to the formation of the trivalent form and generating reactive oxygen species (ROS) (Wang et al. 1993). Also, in experimental animals, nickel has been shown to induce cancer with nickel subsulphide and β-nickel mono sulphide considered the most potent carcinogens (Jarup 2003).

Lead concentration

The samples of Ajwa, Medjool, and Ambar dates from New Market had the highest and lowest lead (Pb) concentrations in Mirpur (Table 2).

The lowest concentration, 0.0 mg/kg, was found in dates from Mirpur shop-3. Only the values from New Market shop-1 and shop-2; and Mirpur shop-3 are significantly different from each other. The sample from Madina shows a moderate concentration of Pb, about 1.47 mg/kg. But all these values were within the maximum permissible limit of 5 mg/kg, addressed by FAO/WHO (1989). Traffic congestion and automobile exhaustion in Dhaka city is polluting the air, and have directly injected metal particles into open air selling products (Rahman et al. 2013). The date fruit obtained from Saudi Arabia contained high Pb and Cd in areas with heavy traffic density was also reported (Aldjain et al. 2011). In their study, Aldjain et al. (2011) reported high Pb and Cd contents in dates grown in proximity highway of roads in Riyadh.

Zinc concentration

The Zn concentration in the samples ranged from 17.73 mg/kg (Mirpur, shop-2) at its lowest to 30.91 mg/kg (New Market, shop-3) at its highest for Ajwa dates (Table 2). Similar values were also observed for Medjool and Ambar date samples (Table 2). The results were not significantly indifferent from one another. Samples collected from Mirpur consistently show a lower amount of Zn concentration (17.73 mg/kg to 21.99 mg/kg), Whereas, Zn concentration of samples collected from New Market were higher (24.77 mg/kg to 30.91 mg/kg) than other collection sites. None of these values exceed the MPL (Maximum Permissible Limit) value of 60 mg/kg, issued by FAO/WHO (2013). Similar Zn concentrations were found in a study conducted on date fruits in Palestine and another study in Saudi Arabia (Walid 2020; Hassan et al. 2017).

Radwan and Salama (2006) and Onianwe (2001) have documented zinc (Zn) levels in various fruits as follows: 5.35 mg/kg and 2.38 mg/kg for watermelon, 7.40 mg/kg and 2.20 mg/kg for orange, and 5.59 mg/kg and 1.50 mg/kg for banana, respectively.

The ranges given for the Zn content of Iraqi dates were 7.4–18.2) mg/kg are almost in agreement with the result obtained in the study by Yousif and Kado (1982).

Most Zn is added during industrial activities, such as mining, coal and waste combustion and steel processing. High concentrations of available Zn in soils may arise from various sources of pollution, including: atmospheric deposition from a nearby industrial source, excessive applications of zinc rich materials and high zinc sewage sludge’s or industrial waste waters. Plants often have a Zn uptake that their systems cannot handle, due to the accumulation of Zn in soils (Greany 2005). Though, in this study, Zinc concentrations were found below the MAC value endorsed by FAO/WHO (2001), but they were higher than the findings of previous study regarding this topic.

Assessment of public health risk

Average daily intake (ADI) of heavy metals

Estimating heavy metal exposure level is indispensable in determining organism health risk (Singh et al. 2010). From the pilot survey, the average daily consumption of dates is 29 g per person per day, which was similar to Dhar et al. (2019). In the present study, the Average Daily Intake of seven metals was calculated based on 29 g of edible fruits part in a person’s daily diet (Ali and Hau 2001; Dhar et al. 2019) by considering the mean concentration of each metal in fruits, corresponding to dry weight of fruits and average body weight of 60 kg of a person.

Heavy metals are toxic and their harmful effects are only observed when these are consumed for the long term. (Bahemuka and Mubofu 1999). It has also been reported that essential body nutrients are significantly reduced by the consumption of heavy metal-contaminated food, which results in immunological deficiency, growth retardation, disability, and a high rate of upper gastrointestinal cancer (Iyengar and Nair 2000; Turkdogan et al. 2003).

The calculation of ADI of heavy metals were done according to the concentration of each metal in different date samples collected from different places in Dhaka and Medina. The ADI of the studied dates were represented in Table 4 and Figs. 3 and 4.

Table 4 Average daily intake of heavy metals (mg/person/day) in Ajwa date fruits collected from Dhaka city markets and Medina

Fig. 4

Heavy metals concentration (mg/kg) in Ajwa date fruits collected from Medina

Permitted Maximum Tolerable Daily Intake (PMTDI) of Pb, Cd, Cu, Fe, Mn, Ni, and Zn are 0.046, 2.00, 2.00, 17.00, 0.3, and 20.00 mg/person/day respectively. With the exception of a few Pb sampling locations, the average daily intake values of Cd, Zn, Ni, Pb, and Cu were found to be primarily below the Permitted Maximum Tolerable Daily Intake (PMTDI) value (Table 4, Figs. 5 and 6).

Fig. 5

Average daily intake of heavy metals (mg/person/day) in Medjool date fruits collected from Dhaka city markets and Medina. The order of contribution for Cd, Zn, Ni, Pb, Cr, Cu intake via dietary consumption of studied fruits are given below: Cd: Green Apple > Pomegranate (Edible portion) > Pear > Fuji Apple > Red Grape > Malta (edible portion) > Green Grape. Zn: Pomegranate (Edible portion) > Fuji Apple > Green Grape > Pear > Malta (Edible portion) > Red Grape > Green Apple. Ni: Green Grape > Pomegranate (Edible portion) > Red Grape > Pear > Fuji Apple > Green Apple > Malta (Edible portion). Pb: Fuji Apple > Green Grape > Green Grape, Pomegranate (Edible portion), Red Grape, Pear, Fuji Apple, Malta (Edible portion), Green Apple. Cr: Pear > Green Grape > Fuji Apple > Red Grape > Pomegranate (Edible portion) > Green Apple > Malta (Edible portion). Cu: Pomegranate (Edible portion) > Red Grape > Pear > Green Apple > Fuji Apple > Malta (Edible portion) > Green Grape.

Fig. 6

Average daily intake of heavy metals (mg/person/day) in Ambar date fruits collected from Dhaka city markets and Medina

Hazard quotient (HQ) and hazard index (HI)

Health risk correlated to heavy metals intake through the consumption of date fruits is often estimated using hazard quotient (HQ) and hazard index (HI). Hazard quotient (HQ) is a useful parameter which has been appreciated for assessment of risk associated with consumption of metal contaminated foods (Zhuang et al. 2009; Bermudez et al., 2011), and hazard index (HI) is evaluated as the sum of hazard quotients when more than one heavy metal is taking part in (Si et al. 2015). There is a possible health risk to those consuming date fruits which health index value are greater than 1. From the results, the HQ value of all heavy metals in all dates was below one. It means that there is no health risk due to any heavy metals (Figs. 7, 8 and 9).

Fig. 7

Hazard quotient of different sites for Ajwa Dates

Fig. 8

Hazard quotient of different sites for Ambar Dates

Fig. 9

Hazard quotient of different sites for Medjool Dates

It was observed that the HI value of four out of ten sample sites for ajwa date fruits was greater than 1, however for other date varieties HI values were less than 1 Fig. 10).

Fig. 10

Hazard Index for three varieties of Dates collected from Dhaka city markets

The highest HI value was found in the Ajwa date fruit samples collected from New Market Shop 2 which was 1.385. Others are 1.326, 1.326 and 1.234 which were the value of the Ajwa date sample of New Market Shop 1, Badamtali Shop 2 and Badamtali Shop 3 respectively. The lowest HI value was 0.289 which was collected from Mirpur Shop 3 and the value was 0.289. The hazard indicates among all the Ajwa date samples studied decreased in the order of New Market Shop 2 > New Market Shop 1 > Badamtali Shop 2 > Badamtali Shop 3 > Mirpur shop 1 > Badamtali Shop 1 > New Market Shop 3 > Medina > Mirpur Shop 2 > Mirpur Shop 3.

The study showed that the date samples from New Market and Badamtali had more health risks than the samples from Mirpur and Medina (Fig. 11). The changeableness in HI between date samples from different locations and shops could be due to differences in soil, irrigation water, date variety, fertilizers, and plant varieties (Al Juhaimi et al. 2020; Kuras et al. 2020; Perveen and Bokahri 2020. Also transportation was a big factor for the high health index (HI).

Fig. 11

Hazard Index for three varieties of Dates collected from Medina

In a prior study conducted in Riyadh by Aldjain et al. (2011), date palm fruits collected from various locations exhibited notable levels of lead (Pb) and cadmium (Cd). The concentration of Pb in the dust and fruit tissue increased with increasing anthropogenic sources. The variation in cadmium levels observed among samples collected from the three investigated sites could be attributed to the plant's capacity for absorption, which depends on the heavy mineral content in the soil and the genetic characteristics of the plant. Cadmium exposure can contribute to kidney and lung diseases, as well as skeletal issues, and it is associated with an increased risk of developing cancer. In contrast, lead poses a non-cancer risk factor (Salama et al. 2019). The present study revealed a lower concentration of cadmium (Cd) compared to lead (Pb), indicating the plant's ability to accumulate these heavy metals (Walid 2020). Cadmium deposition in edible tissues can occur due to agricultural practices such as the use of polluted sewage water, specific soil types, and the application of phosphate fertilizers (Walid 2020).

Mean concentrations were found below the PMTDI value for all date fruit samples collected from Dhaka city markets. The reason may be the low fruit consumption rate (g/person) in the daily diet in Bangladesh (HIES 2010). The Hazard Quotient (HQ) and Hazard Index (HI) values for all metals were below 1 which signify that these fruits were not carcenogenic.

Hence, it is recommended to conduct regular monitoring of heavy metal exposure through date fruits available in Dhaka city markets, as well as at the production sites. This is crucial to prevent the excessive accumulation of these heavy metals in the human food chain.

Conclusion

Ajwa and Medjool dates have been found to contain various heavy metals like copper (Cu), lead (Pb), cadmium (Cd), and zinc (Zn). Limited information exists regarding the concentration of heavy metals in Ambar dates. But given the growing conditions and farming methods, they may have trace levels of heavy metals like other date kinds. Precise measurements will only be possible with more investigation.

The current investigation revealed that the Ajwa dates do not pose any risk to human health. However, it is a concern that the amount of Pb and Cd are high and pretty much close to the margin of average daily intake. Comparing concentration with MPL and ADI with R_fD, we can say there is no big health risk regarding dates bought from Dhaka or Medina. Among the samples of Dhaka, the samples of Mirpur were consistently good for human health as they had the least concentration and ADI; as a result, its HI values were also less than others.

To better understand the amount of cadmium and lead pollution in the environment, human tissue, and food chain, additional experimental study is required. It is crucial to look at the underlying causes of cadmium and lead pollution. Furthermore, to lessen the detrimental effects of cadmium and lead pollution on health in Bangladesh, legislative measures and robust national policies are required.