Introduction

Food safety is one of the most chief issues of public health in the world today. Considering the growing threat of food contamination from pesticides, heavy metals, and toxins, there has been a recent focus on research on food safety concerns. The presence of trace elements in plants, especially vegetables and fruits, is influenced by various factors such as weather conditions, environmental pollution, soil health, and plant growth stage at the time of harvest (Yüksel et al., 2023). The potential contamination of plants with elements poses a significant risk to both agricultural systems and human well-being (Alengebawy et al., 2021). In addition, the use of fertilizers can contribute to the accumulation of elements in plants and aggravate the contamination of metals in vegetables (Shaheen et al., 2016). Fertilizers can contain heavy metals originating from various sources such as atmospheric deposition, organic and chemical fertilizers, pesticides, agricultural production activities, manure, biosolids, waste disposal, and irrigation water (Liu et al., 2023). When compared to chemical fertilizers, organic fertilizers generally have elevated concentrations of heavy metals. Additionally, industrial activities in specific areas can substantially contribute to the pollution of fertilizers with a variety of trace elements (S N et al., 2023).

There is a lot of scientific evidence on the body's need for vitamins and minerals to promote health and prevent diseases, so consuming food such as fresh fruits, vegetables and fiber is needed by the body due to its essential substances. The consumption of these foods may also contain harmful metals at different levels, which requires monitoring and inspection (Mawari et al., 2022). Long-term exposure to toxic elements can cause various complications in humans (Godwill Azeh et al., 2019). Chronic poisoning with heavy metals can lead to degenerative processes that affect muscles, physical health, and neurological functions and cause diseases like muscular dystrophy, multiple sclerosis, Alzheimer's disease and Parkinson's disease (Jaishankar et al., 2014; Shavaly-Gilani et al., 2023). Additionally, long-term exposure to specific heavy metals may elevate the risk of cancer development. For example, continual arsenic exposure can induce immutable modifications in vital organs and contribute to the onset of lung cancer, skin cancer, liver cancer (angiosarcoma), bladder cancer, and potentially colon and kidney cancers (Coradduzza et al., 2024). Moreover, lead toxicity resulting from extended exposure can lead to psychosis, muscular weakness, birth defects, weight loss, autism, allergies, hyperactivity, paralysis, dyslexia, mental retardation, brain damage, kidney damage, coma, and even fatality (Jaishankar et al., 2014; Maral et al., 2021).

According to information from various sources, many foods such as fruits are more exposed to heavy metal contamination (Kilic, 2024; Kılıç et al., 2015). Pineapple, mango and cherry showed the highest levels of arsenic (As), lead (Pb), and cadmium (Cd) while berries had the lowest concentration of these substances (Yuksel et al., 2015, 2017). Also, The most common trace elements found in citrus fruits comprise iron (Fe), chromium (Cr), arsenic (As), nickel (Ni), copper (Cu), cadmium (Cd), zinc (Zn), lead (Pb) and manganese (Mn), (Kargarghomsheh et al., 2023b; Karimi, et al., 2023; Rathebe & Mosoeu, 2023; Tooryan et al., 2024).

Today, various methods have been introduced to prepare samples, comprising extraction preparation by ultrasound device, acid digestion of microwave-assisted, and analysis directly of solid samples (Ki et al., 2017; Shariatifar et al., 2017; Shariatifar et al., 2020; Tajdar-Oranj et al., 2018). Next, for identifying of elements in different food matrices, various technology are applied like GFAAS (graphite furnace atomic absorption spectrometry), FAAS (flame atomic absorption spectrometry), and ICP with detector of OES or MS (mass). Amongst mentioned equipment, equipment of ICP-OES technology was the most time saving, specificity and sensitive (Fathabad et al., 2018; Karami et al., 2021b; Karimi et al., 2021; Kiani et al., 2021).

To decrease the risk of consuming toxic elements and other toxins in fruits, it is necessary to wash with water, peel, soak the fruits with salt solution and disinfectants. Therefore, these measures and strategies can reduce the risk of contact to trace elements and pollution. Since the consumption of fruits in Iran is high due to the cheap price and high availability, and since there has not been a comprehensive research on the amount of trace elements (toxic and essential) in fruits (pulp and skin) so far, it seems required to do so. Consequently, the objective of this investigation is to assess the levels of trace elements in peel and pulp of some fruits (including oranges, apples, kiwis, beets, tangerines, grapefruits and lemons) in Tehran using OCP-OES. Also, the risk assessment was evaluated according to the per capita consumption of these fruits in children and adults.

Materials and methods

Study area and collection of sample

Fruit samples were purchased from the market of Tehran. The samples included north oranges, tangerines, kiwis, south oranges, grapefruits, quince, apples, and sweet lemons. The peel and pulp of these fruits underwent examination to detect heavy metals. This process was conducted in duplicated for each sample, resulting in a total of 56 samples.

Chemicals, standards and reagents

The standards, reagents and chemicals used in the study (analytical grade) acquired from Merck Company of (Darmstadt, Germany) such as hydrogen peroxide and nitric acid and mix standard (Mix standard CRM: 92,091 Supelco LOT BCCB9855, TraceCERT®, thirty-three elements, ten milligrams per liters in HNO3). De-ionized water was employed in all experiments, and spectroscopic-grade nitric acid (65%) was supplied by Merck Compony (Darmstadt, Germany).

Sample preparation

In this step, the concentrations of 19 trace elements (Ag, Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn) were investigated in fruit samples. For this purpose, closed vessel and acid decomposition in the microwave oven system (Multiwave 5000, Anton Paar, Austria) was applied. To carry out examinations, each fruit sample (2 g) (in duplicate) was poured into microwave containers or vessels. Hydrogen peroxide/nitric acid solution (1:9, v/v, 20 mL) was added to each sample and shaken (thoroughly), then homogenized and kept at room temperature for ten minutes. Afterwards, the prepared samples were heated for fifteen minutes at eighty percent of their total power (1800 watts), following a 1 phase of digestion. To the mass of semi-dried, the subsequent solutions were evaporated, and then to remove the extra acid, diluted with water (deionized) to 50.0 mL in flasks (volumetric). The stock solution of sample was then reserved in flasks (volumetric) for usage as a solution of stock sample (Farhadiyan et al., 2024; Fathabad et al., 2018; Karami et al., 2021b; Karimi et al., 2021; Kiani et al., 2021).

The conditions of ICP-OES technology

The ICP-OES utilized was the Spectro Arcos (SPECTRO, Germany) equipped with a Flared end EOP Torch 2.5 mm. The optimal operating parameters included an RF generator power of 1400 W, Ar (Argon) serving as the plasma, auxiliary, and gas of nebulizer, and specific flow rates for gas of auxiliary (0.9 L/min), gas of plasma (14.5 L/min), and gas of nebulizer (0.85 L/min). Subsequently, the sample uptake time was 240 s, time of rinse was 45 s, and initial stabilization time was also 45 s with zero delay time and time among replicate analyses. The measurement was replicated 3 times at a frequency of 27.12 MHz for the RF generator's resonance frequency. The detector type used was solid state and the spray chamber type included CCD Cyclonic, and Modified Lichte, respectively. The type of sample delivery pump employed was a four-channel, software-controlled peristaltic pump enabling precise sample flows. The speed of prewash pump was set at 60 rpm for 15 s and then reduced to 30rpm for 30s with a prewash time of 45s; finally, the speed of sample injection pump was maintained at 30rpm (Arabameri et al., 2023; Fathabad et al., 2018; Karami et al., 2021b; Karimi et al., 2021; Kiani et al., 2021).

Validation of the analytical technique

The parameters assessed were repeatability, limits of detection (LOD), and quantification (LOQ), precision and recovery (Table 1). Matrix effects were done by using process of standard addition, by adding solutions of standard mixed (200μL) to the original samples. The recoveries were within 97.6% and 103.7% for all studied elements. The wavelengths used for measurement of the concentration of metals, according to signals of baseline and their interference was observed experimentally during the measurement period in selected lines (Table 1S).

Table 1 Concentration of trace elements (ppm) in all samples of fruits
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Exposure and risk assessment

Using the non-carcinogenic health risk assessment by the MCS, the contamination level of the selected heavy metals in the fruit samples was estimated by the THQ (target hazard quotient)) as follows (Yaminifar et al., 2021):

$$\mathrm{THQ }= \frac{\mathrm{CDI}}{\mathrm{RfD}}$$
(1)
$$\mathrm{CDI}=\frac{\mathrm{C}\times \mathrm{EDi}\times \mathrm{EFi}\times \mathrm{IR}}{\mathrm{BW}\times \mathrm{AT}}$$
(2)
$$\mathrm{HI}=\sum \mathrm{THQ}$$
(3)
$$\mathrm{ILCr}=\mathrm{CSF }\times \mathrm{ CDI}$$
(4)

where CDI is chronic daily intake, HI is total target hazard quotient, C is the level of the selected PTEs; The oral reference doses for pb, Cd, Ni, As, Co and cr were based on 0.0035, 0.001, 0.02, 0.0003, 0.005 and 0.003 mg/kg.d, respectively (EPA, 2022), C is the selected PTEs concentration in milk (per μg/kg dry. weight); EF (days/year) is the exposure frequency (350 days/year)(Moazzen et al., 2022); Edi (year) is the exposure duration (children = 6 years and elders = 30); IRi is the ingestion rate (children = 30 g/day and elders = 12 g/day) (Fathabad et al., 2018); BWi is e average consumers’ body weight (children = 20 and elders = 70 kg) (Seilani et al., 2021), AT is The average time (days) (Mehraie et al., 2022). ILCR is the possibility of developing cancer of Pb, and As, CSF relates to the carcinogenic slope factor of 0.5 (mg/kg/day) − 1 for Cr, 1.5 (mg/kg/day) − 1 for As, 0.38 (mg/kg/day) − 1 for Cd recommended by USPEA.When THQ < 1 and TTHQ ≤ 10, It means the risk of health to populations of human is acceptable (Seilani et al., 2021).

Statistical analysis

Statistical analyses for the calculation of the mean and SD (standard deviation) of measured levels were done with the software of SPSS V.18.0 (SPSS Inc., USA). Normality and homogeneity of variances were carried out by tests of Kolmogorov–Smirnov and Levene median. Owing to the non-normality of the data, the test of Mann–Whitney was used to estimate the statistical significance for the studied pollutants. All investigates of current research were carried out in triplicate. Probabilistic risk assessments were performed by software of Crystal Ball © based on MCS.

Results and discussions

The amount of trace elements in all fruit samples

Table 1 shows the amount of elements in all fruit samples. According to the outcomes obtained from Table 1, the highest and lowest average detected elements in all fruits samples were related to aluminum (1842.18 ± 645.00) and vanadium (0.28 ± 0.11) ppm, respectively. Hg and Sb were not found (not detected or ND) in any samples.

In the research of Kalagbor et al., that analyzed of trace elements was conducted on pineapple, orange, avocado pear, and pawpaw, and they reported these elements were Fe (19.0–29.6 mg/kg), Cu (0.23–5.29 mg/kg), Mn (1.03–12.6 mg/kg), Cd (0.08–0.22 mg/kg), Ni (1.16–5.87 mg/kg), Co (1.43–3.56 mg/kg) and Pb (1.69–5.80 mg/kg) (Kalagbor & Eresiya, 2014).

Papa et al. measured Pb, V, Cd, Cu, Cr and Ni, in various skin and pulp of vegetables and fruit [plum (Prunus domestica L.), lettuce (Lactuca sativa L.), peach (Prunus persica L.), courgette or marrow (Cucurbita pepo L.) and tomato (Solanum lycopersicum L.)] and reported the amount of these elements were ranged from 0.31 to 3.31, from ND to 10.4, from 0.09 to 3.58, from 5.49 to 37.8, from 0.11 to 11.3 and from 1.10 to 8.39 mg/kg dry weight, respectively (Papa et al., 2009).

Czech et al. analyzed the concentrations of lead and cadmium in different part (pulp, peel, and whole fruits) of fruits including pomelo, orange, lemon, mandarin, key lime, green grapefruit, white grapefruit and red grapefruit, and reported the highest level of Pb (2.47 μg/100 g) was detected in red grapefruit pulp, and the highest concentration of Cd (0.116 μg/100 g) was detected in white grapefruit pulp. The lowest concentration of Pb was detected in mandarin pulp (0.354 μg/100 g), while content of Cd was lowest in lime pulp (0.004 μg/100 g) (Czech et al., 2021).

Other research by Naghipour et al. that evaluated the existence of trace elements in Kiwi samples and reported the mean of As, Cd, Cu, Fe, Ni, Pb and Zn was 0.413, 0.13, 3.3483, 305.56, 24.691, 0.8241 and 8.545 mg/kg, respectively. Also, the outcomes indicated that specific metals presented a non-cancer risk when consumed by both adults and children. The risk assessment indicated the consumption of Kiwi fruit by children posed a potential non-carcinogenic health risk for Cd, Cu, Fe, Ni, and Pb (THQ > 1) (Naghipour et al., 2024).

In another study by Stojanović et al., which was conducted elements analyses of peel and pulp of seeds and fruits of quince (Cydonia oblonga Mill.). They reported the highest amount of trace elements was related to Fe that most found in the seeds (13.56 mg/kg to 88.69 mg/kg) while in peel it ranged from 5.812 to 17.23 mg/kg and in pulp from 1.825 to 5.398 mg/kg. Also, Al varied from 1.395 mg/kg to 8.770 mg/kg, Ni varied from 0.022 to 1.894 mg/kg, the Cd was not identified in any portion of the fruit, while As was not identified in the seeds. The amount of Pb was higher (generally) in seed samples than to peel and pulp (Stojanović et al., 2017).

Prabhakar et al. analyzed heavy metals in grape fruit samples. They reported that the amount of elements in fruit samples varied from 0.05 to 0.2 for Ni, from 0.2 to 1.9 for Zn, from 0.3 to 1.3 for Cu. Also, Pb and As lower than 0.05 mg/kg (Prabagar et al., 2021).

Tooryan et al. measured trace elements in some vegetables and reported the maximum and minimum mean of essential elements were Ca (5334 ± 178 mg/kg in Brassica oleracea) and Se (0.0021 ± 0.0001 mg/kg in Romaine lettuce), respectively. The maximum and minimum mean of toxic elements were Pb (6.26 ± 0.12 µg/kg in Brassica oleracea) and Hg (lower than LOD in Brassica oleracea), respectively (Tooryan et al., 2024).

Generally, in different studies, the results of trace elements in fruits vary widely depending on the type of fruit, environmental pollutants (water, soil and air), fruit size and age, the location where it was grown, and the methods used to analyze the samples (Arabameri et al., 2023; Farhadiyan et al., 2024; Karami et al., 2021b; Kargarghomsheh et al., 2023a; 2023b; Karimi et al., 2023; Kiani et al., 2021; Tooryan et al., 2024).

The amount of trace elements in different fruits and in different parts of the fruit (peel and pulp)

Table 2 shows the level of trace elements in different fruit samples. Our outcomes indicated, the maximum mean of elements in quince, lemon, grapefruit, kiwi, orange south, orange north and tangerine samples was related to Fe (2048.32 ppm), Zn (753.45 ppm), Fe (1056.33 ppm), Al (9794.41 ppm), Zn (717.78 ppm), Fe (1334.87 ppm) and Fe (974.93 ppm), respectively.

Table 2 Concentration of trace elements (ppm) in different fruit samples
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Table 3 shows the concentration of trace elements (ppm) in in various peel and pulp samples of fruits. Our outcomes revealed, the highest mean of elements in kiwi peel, kiwi pulp, orange North peel, orange North pulp, orange South peel, orange South pulp, quince peel, quince pulp, grapefruit peel, grapefruit pulp, lemon peel, lemon pulp, tangerine peel and tangerine pulp was related to Al (17967.79 ppm), Al (1621.03 ppm), Fe (1350.01 ppm), Al (1457.66 ppm), Zn (934.71 ppm), Fe (728.06 ppm), Fe (2768.11 ppm), Fe (1328.54 ppm), Zn (1008.54 ppm), Fe (1198.00 ppm), Zn (683.35 ppm), Zn (823.55 ppm), Fe (1182.59 ppm), and Fe (767.27 ppm), respectively.

Table 3 Concentration of trace elements (ppm) in in various peel and pulp samples of fruits (ppm)
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According to the guidelines set by WHO/FAO (David et al., 2021), the Fe levels in quince pulp and peel, grapefruit pulp, kiwi pulp and peel, southern orange peel, northern orange pulp and peel, and tangerine peel exceeded the permitted limit of 1mg/kg. Additionally, the Cu content in the peel and pulp of kiwi fruit and southern orange pulp exceeded the allowable limit of 0.02 mg/kg. Moreover, the concentration of Cr, Ni, and Zn in the peel of southern orange exceeded the permissible limits for these metals (0.05 mg/kg for Cr, 0.2 mg/kg for Ni, and 1.5 mg/kg for Zn).

The amount of elements in different fruits can be higher or lower due to reasons such as the type of fruit, geographical region, type of soil, level of environmental pollution (water, air and soil) and the desired fruit type, which can affect the pulp or peel of the fruit (Arabameri et al., 2023; Farhadiyan et al., 2024; Karami et al., 2021b; Kargarghomsheh et al., 2023a; 2023b; Karimi et al., 2023; Kiani et al., 2021; Tooryan et al., 2024).

Human health risk assessment

Chronic daily intake (CDI)

This research applied MCS to assess uncertainty in input values, analyze probability distributions simulate exposure, and evaluate the risk of the non-carcinogenic and carcinogenic. The probability frequency distributions of CDI value for all fruit samples (peel and pulp) samples are presented in Table 4. The results revealed that the rank order of THQ (percentile 95%) for trace elements in fruit samples (peel and pulp) for both adults and children was Al > Fe > Zn > Sn > Cu > Ni > Ba > Mn > Pb > Cr > Co > As > Mo > Ag > Se > Cd > Sb > V. The levels were below the acceptable risk limit, indicating no safety issues for consumers. However, it should be noted that fruit samples only slightly contribute to daily food intake. Vanadium had the lowest daily intake (adults, 1.82E-07 mg/kg body weight/day; and children, 2.47E-07 mg/kg body weight/day), while Aluminum had the highest daily intake (adults, 1.16E-03 mg/kg body weight/day; and children, 1.65E-03 mg/kg body weight/day) in samples. In the various studies, the assessed heavy metals dietary exposure from foodstuff consumption had a different trend. For example, Czech et al. (2021) stated the dietary intake of heavy metals in citrus fruits (mandarin; orange; pomelo; key lime; lemon; and green red, and yellow grapefruit) was well less the acceptable daily intake (Czech et al., 2021).

Table 4 The Simulation results of CDI (mg/kg bw/day) of heavy metal in fruit samples
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The estimated THQ value for trace elements all through the consumption of fruit samples (peel and pulp) adults are presented in Table 5. The results indicated the rank order of THQ (percentile 95%) for heavy metal in fruit samples (peel and pulp) for adults was As(1.20E-2) > Cr(6.53E-3) > Ni(3.54E-3) > Pb(3.35E-3) > Cd(6.64E-4) > Sb(5.83E-4) > Mo(2.47E-4) > Mn(2.35E-4) > Ba(1.54E-5); and for children was As(1.64E-2) > Cr(9.22E-3) > Ni(5.03E-3) > Pb(4.71E-3) > Cd(9.23E-4) > Sb(1.08E-3) > Mo(3.34E-4) > Mn(3.39E-4) > Ba(2.34E-3). HI in the adults and children due to fruit juice ingestion was 2.94E-2 and 4.36E-2, respectively. The health risks of different exposure samples didn’t exceed the acceptable non-carcinogenic risk limit of the Environmental Protection Agency (EPA) (Roudbari et al., 2021). However, all THQ/HRI indexes were below 1, indicating no potential health hazards for the population from consumption. Likewise, Karami et al. (2021a) evaluated the health risk assessment of the level of heavy metal of fruit juices (commercial and traditional) in Iran. Based on the human health risk assessment, no significant non-carcinogenic risk (THQ < 1) for all people in Tehran. Continuous exposure patterns to trace elements can provide valuable data for exposure assessment and analysis of associations between biomarkers and health outcomes. This data collection can help clarify the true relationship between long-term trace element exposure and disease risk {Yüksel et al., 2023 #276}.

Table 5 The Simulation results of THQ of heavy metal in fruit samples
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The distribution frequency of ILCR for children and adults is shown in Fig. 1. An ILCR greater than ILCR > 1 × 10−4 is considered harmful with a significant cancer risk due to pollution, whereas an ILCR less than ILCR < 1 × 10−6 is regarded as insignificant with a negligible cancer risk. The order of ILCR (95th percentile) for trace elements through the fruit for adults was Cr (7.58E-6) > As(4.09E-6) > Cd(1.92E-7), and for children was Cr(1.13E-5) > As(6.07E-6) > Cd(2.85E-7). The ILCR indexes were lower than 1 × 10−4, indicating no potential cancer risk for the population from consumption (Fathabad et al., 2018). In the same way, the intake of heavy metals through fruit and vegetable consumption varies greatly across countries, with some elements like Cr, As, and Cd displaying higher levels in developing nations than in developed ones (Yan et al., 2022). This difference in heavy metal contamination in fruits between regions can be linked to consumption habits and the route of exposure to harmful substances. Iran's swift industrial growth in recent years has raised significant environmental worries, particularly regarding soil and water pollution from heavy metals. One way to decrease heavy metal contamination is by educating farmers and consumers on methods to minimize heavy metal intake, such as improving water conservation, decreasing waste, and optimizing the use of fertilizers and pesticides(Yan et al., 2022). Despite substantial efforts to control and address heavy metal pollution, it continues to present carcinogenic and non-carcinogenic health hazards to consumers.

Fig. 1
figure 1

The Simulation results for probability ILCR in fruit

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Conclusions

The concentration of trace elements in fruits (in their peel and pulp) from Tehran’s market by ICP-OES technique was evaluated in the study. The findings indicated that Quince pulp contained the highest levels of Ag, while quince peel had the highest concentration of Co. Kiwi peel exhibited the highest amounts of vanadium and Al. Notably, orange peel from South Iran demonstrated the highest quantities of Cr, As, Fe, Cu, Ag, Ba, Mn, Ni, Mo, Sb, Sn, Zn and Se. Additionally, South orange pulp was found to contain the highest levels of Cd and Pb. Fe in 64%, Cu in 21%, Cr, Ni, and Zn in 7.1% of fruit peel and pulp samples were higher than the limit set by WHO/FAO. The uncertain analysis of the health risks of investigated heavy metals in fruit peel and pulp samples showed that there is no significant non-carcinogenic risk (THQ < 1) and carcinogenic risk (ILCR < 1E-4) for adults and children. It is recommended to incorporate health risk assessment findings and details contributing to trace elements in dietary patterns into carefully planned food monitoring data. It is suggested to evaluate this contamination (trace elements) in similar products. And it is also suggested to evaluate the fruits during their growth in the future and to investigate the effect of water, soil, etc. pollution on the amount of fruit contamination. This study highlights the importance of educating farmers and consumers on ways to limit heavy metal intake and the implementation of best practices in food production to minimize heavy metal contamination.