Investigation of major, toxic, and trace element contents and mineral safety index (MSI) of parts of Elaeagnus angustifolia L. and total element contents in the soil using the ICP OES technique

2.1. Materials

The samples were collected in November 2018 at the stage of ripening; leaves and fruit were collected from different trees, and soil samples were taken from 30, 60, and 90 cm depths from the coordinates (37.947359, 40.265342) of Sur, a district of Diyarbakır, Türkiye. It is assumed that tree roots at depths of 30, 60, and 90 cm take up plant nutrients and that micro, macro, and toxic elements are transported to the plant through the roots at these depths. Therefore, generally, when analyzing the soil of fruit trees, the soils at these depths are analyzed separately. The collected fruits were divided into the skin, pulp, and seeds. To remove moisture, the pulp, skin, seed, and leaves were dried in the oven (Mipro) at 65°C for 24 hrs and then ground into small particles with the mill (Perten 3303). Furthermore, soil samples were prepared for elemental and physical analysis. A microwave digestion unit (Milestone Start D, Italy) was used for the digestion of the samples, and ICP OES (Thermo Fisher Scientific ICAP 6000, England) was used for elemental determination.

2.2. Methods

3.1. Major elements

Calcium: Russian olive’s seed had the highest Ca concentration among the plant parts, followed by the skin and pulp. It is clear that the ground Russian olive seed and fruit can be a beneficial source of Ca, and on average, plants contain 1000 to 10000 mg/kg of Ca, according to WHO [33]. Furthermore, soil samples and leaves were unable to identify Ca content, leading to no evaluation. Table 6 and Figure 1 show Ca values.

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Figure 1.

Radar graphic representation of major element distribution in plant and soil.

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Magnesium: When looking at the Mg results, it was found that they were mostly in the soil that was taken at a depth of 60 cm. The soils taken from 30 and 90 cm depths also showed high concentrations and proximity to each other. The leaves and seeds were the most commonly found plant parts, followed by the skin and pulp. Moreover, FAO/WHO [34] reports that plants contain an average of 1000 to 4000 mg/kg of Mg.

Sodium: The plant’s leaves had the highest Na values, but the soil, pulp, skin, and seed had similar ones.

Potassium: The K levels in the pulp and skin were similar to the K levels in the 60-cm-deep soil sample. The K level in the leaf was very similar to the value in the 30 cm depth soil sample, and the K level in the skin was similar to the value in the 90 cm depth soil sample. According to WHO [33], the average K level in plants is between 10,000 and 50,000 mg/kg.

Phosphorus: P wasn’t found in the leaves, but the seeds had the highest P value of all the plant parts. The P values in the soil were similar but still very low compared to the plant parts. Table 6 displays the results. Figures 1-3 provide examples of radar graphics that clearly show the prominent elements in plant and soil samples.

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Figure 2.

Radar graphic representation of essential trace element distribution in plant and soil.

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Figure 3.

Radar graphic representation of potentially toxic trace elements in plant parts and soil.

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Humans and other species require heavy metals in specific quantities. Nevertheless, elevated exposures to heavy metals might potentially harm living organisms. The primary heavy metals that can induce toxicity include Zn, Cu, Ni, As, Cd, Pb, and Cr. Heavy metals in soil and water are frequently detrimental as they are assimilated by organisms and enter the food chain. They can exhibit bioaccumulation at that level. A significant quantity of hazardous chemicals accumulates inside the food chain. Life may be adversely impacted. In addition to living situations, hereditary factors, food habits, and environmental contaminants contribute to the development of numerous diseases. Details regarding several metals have been provided below.

3.2. Essential trace elements

Iron: Plant parts contain less iron than the soil, despite the soil’s abundance. Iron is a very prominent element because it is an essential trace element that plays a significant role in many metabolic activities, especially in anemia. According to WHO [33], the maximum permissible concentration of iron in soils is 5000 mg/kg, and in plants, it is 1000 mg/kg. Excessive Fe levels can lead to liver failure, dizziness, and gastrointestinal disorders [35].

Copper: Approximately 10 times more Cu was found in the soil parts than in the plant parts, and it was identified mostly in the seed and skin parts of the plant, followed by the leaves. Cu is also an important trace element for metabolism; the maximum permissible value of Cu in soils is 36 mg/kg, while the maximum permissible value in plants is 10 mg/kg [33]. Copper is essential for hair, skin, bone, and some internal organs, promoting significant growth. However, it serves as a fundamental building component and may lead to gradual development, greying of hair, reduced body warmth, and potential brain damage [36].

Manganese: Total Mn content in the soil was close to each other and very high compared to the plant, whereas in the plant’s parts, Mn was detected in leaves more than in other parts, followed by seeds, skin, and pulp. Mn is an important essential trace element. The maximum permissible value of Mn in soils is 1000 mg/kg, while in plants it is 100 mg/kg [34]. Elevated levels of Mn are associated with Alzheimer’s disease [37]. Manganese has been associated with mitochondrial disruption and is significant in the death of central nervous system cells, as described [38].

Zinc: While soil samples contained much more Zn, seeds and leaves exhibited the highest concentration, followed by pulp and skin. Zinc is a crucial trace element for hormonal balance and metabolism, and the maximum permissible value for Zn in soils is 300 mg/kg, while in plants it is 100 mg/kg [34]. Zinc concentrations over 3 mg/L in water result in numerous health issues [39]. Zinc, ulcers, pulmonary edema, and irritation of mucosal membranes and respiratory pathways induce airway irritation [40]. Additionally, experimental mice were utilized to assess the impact of Zn in a study examining its carcinogenicity and effects on patient behavior [41].

Chromium: The pulp contained the least Cr, while the seed contained the most. On the other hand, the soil samples showed very high Cr levels compared to the plant parts. In addition, it is stated that Cr is involved in the insulin mechanism, and the maximum permissible value for Cr in soils is 100 mg/kg, while in the plants it is 1.3 mg/kg [33]. Chromium poses a health risk when consumed within the established daily dosage limits. Excessive inhalation of Cr can lead to upper respiratory tract diseases, asthma, and hemorrhages resulting from nasal damage reported [42].

Cobalt: It was not detected in pulp but was found in the skin, seeds, and leaves in tiny amounts compared to soil. The maximum permissible Co value in plants is 0.5 mg/kg, whereas the soil has a value of 10 mg/kg [33]. Cobalt dissolves in the lungs and subsequently enters the bloodstream and urine [43]. Inhalation of Co absorbed into the body induces lung cancer and detrimental effects on DNA structure [44].

Nickel: The leaves exhibited the highest concentration of nickel, while the skin showed the least amount. However, concentrations were close to each other and higher than the plant in soil samples. The maximum permissible Ni value in plants is 10 mg/kg, while in the soil it is 80 mg/kg [33]. Excessive Ni consumption beyond the threshold can lead to diarrhea, vomiting, respiratory constriction, liver and kidney damage, and chronic Ni toxicity, perhaps resulting in allergic reactions [45].

Selenium: Se was not detected in soil samples, but in plant parts, it was only detected in pulp (0.22 mg/kg). Moreover, Se plays an important role in many metabolic events, and the maximum Se content in soils and plants generally varies between 0.1 and 2 ppm. On average, the Se content in soils was 0.31 ppm. Although Se is a micronutrient that can be beneficial for plants at low concentrations, high doses can lead to toxic effects. Therefore, it is important to carefully monitor the selenium content in plants and soils [46].

Tin: It was found to be higher in all plant parts than in soil samples, except for the seeds, and close values were detected in the soil. The Turkish Food Codex determined that the maximum residue amount for Sn is 50-200 mg/kg [47].

Vanadium: The plant’s seed contained the highest amount of V, while leaves, pulp, and skin also showed similar levels. In soil samples, it was detected at quite high levels and close to each other compared to the plant. Table 6 and Figure 2 display the results. The average V content of soils around the world ranges from 18 mg/kg to 115 mg/kg, while the V content of plants ranges from 0.06 mg/kg to 3 mg/kg [48].

3.3. Potentially toxic trace elements

Silver: Silver content was higher in all plant parts than in the soil samples. The pulp of the plant contained the highest concentration of silver, while the soil at a depth of 90 cm had the lowest. While there is no universally accepted maximum concentration for silver in plants from FAO or WHO, concentrations above 0.1 to 1 mg/kg are generally considered harmful [49]. Accordingly, Ag values were found to be well above the limit values in plant parts. Due to anthropogenic activity, Ag is progressively functioning as a pollutant, resulting in the contamination of ecosystems and soils with numerous silver compounds (nanoparticles, oxides, sulfides, etc.). As agricultural crops absorb trace elements from irrigation water and soil, direct contact between Ag nanoparticles and plant roots may result in their uptake and translocation to shoots, stems, and leaves. Silver nanoparticles can infiltrate plant organs from the soil through various mechanisms. The initial method involves diffusion into seeds, followed by absorption into the root, and ultimately translocation to various plant organs. The other method involves absorption by plant roots, followed by migration to other organs. The third method involves direct migration to plant organs and localization inside the epidermal or xylem cells. The pathways for Ag nanoparticles to enter plant cells from soil or water are contingent upon their size, concentration, and physicochemical properties, in addition to the features of the crops and soil structure. Nevertheless, insufficient research exists to evaluate the impact of Ag and its nanoparticles on plants, as most studies are undertaken during the early stages of plant development.

Arsenic: Only the seed contained 0.62 mg/kg of the substance. Furthermore, in the soil samples, the highest value was 3.81 mg/kg. According to FAO, the maximum permissible value in soils is 20 mg/kg, whereas the average amount of As that can be found in foods is 0.1–2.0 mg/kg [50], and the maximum permissible value in foods is 0.02 mg/kg [51]. Arsenic induces hepatomegaly, anemia, and the development of brown spots on the skin, along with several dermatological conditions. Elevated As concentrations have been demonstrated to impact bone health and have been associated with respiratory system malignancies [45].

Barium: Plant parts primarily involved leaves, with seed, skin, and pulp following closely behind. Furthermore, the soil samples revealed high levels of Ba. To sum up, regulatory bodies have not set a clear maximum concentration for Ba in plants. However, concentrations above 200 mg/kg are usually thought to be harmful, while lower levels are typically okay and don’t cause any problems [52].

Cadmium: Although the soil contained very little cadmium, plant parts contained more of it. Pulp had the highest amount, followed by skin, leaves, and seeds. According to FAO/WHO [34], the maximum permissible value for Cd in soil is 3 mg/kg, whereas it is 0.2 mg/kg in foods. Table 6 and Figure 3 present the results. Cadmium, osteoporosis, and tooth problems are the primary sources [53]. Research indicates that persistent Cd poisoning can lead to lung and prostate cancer associated with the condition [54].

Lead: The seed contained the highest amount of lead, followed by leaves, skin, and pulp. The maximum permissible value for lead in soils is 100 mg/kg, while for plants it is 2 mg/kg [33]. Despite Pb being the first metal utilized since antiquity, it has been assimilated into human metabolism. Lead is a significant heavy metal that is extremely detrimental [55]. Excessive Pb levels in the human body that disseminate to bones and other organs result in harm to the kidneys, brain, and nervous systems [56].

Russian olive parts and soil samples were analyzed, and the results were tabulated in Table 6. The study looked at the differences in element concentrations between different parts of the plant. The leaf had higher concentrations of Mg, Ba, Mn, Na, and Ni than the other parts. Khan et al. [57] studied the leaves of Russian olives and found that the amounts of Cu, Ni, Cr, Pb, Cd, Zn, and Co were 0.072±0.0009, 0.016±0.001, 0.002±0.0011, 0.006±0.0007, 0.009±0.0004, 0.780±0.0011, and 0.008±0.0034 mg/kg, respectively. These values are significantly lower than those found in the present study. The study by Hambaba et al. [58], on the other hand, discovered that the leaves of E. angustifolia had Pb levels ranging from 1.05 ± 0.22 to 5.47 ± 4.65 mg/kg, Cd levels ranging from 0.01 ± 0.01 to 0.24 ± 0.23 mg/kg, Ni levels ranging from 2.13 ± 0.59 to 6.61 ± 3.75 mg/kg, Fe levels ranging from 30.8 ± 11.84 to 237 ± 76.62 mg/kg, Cu levels ranging from 4.18 ± 0.49 to 19.42 ± 15.89 mg/kg, Zn levels ranging from 45.0 ± 7.50 mg/kg to 58.5 ± 17.91 mg/kg, and Mn levels ranging from 162.35 ± 30.81 mg/kg to 253.3 ± 14.83 mg/kg. On the other hand, the element concentrations that Khan et al. [57] observed were different from their values. To clearly identify these differences would require a huge amount of work. However, to summarize briefly, soil structure, texture, and other physicochemical properties of the countries may explain these differences, as well as the methods of analysis, chemicals, and equipment used. On the other hand, climate and environmental factors (such as applied fertilizers, pesticides, vehicle exhaust, industrial chimneys, and waste) may cause these differences. Moreover, in the study of Yildirim et al. [59] on E. angustifolia, Cu, Fe, and Mn amounts in leaf samples were determined by atomic absorption spectrophotometer (AAS), and the values found for Cu, Fe, and Mn were 25.39, 26.37, and 11.70 mg/kg, respectively. It was observed that Cu contents were considerably higher than the values of the current study, but Fe and Mn contents were significantly lower than the values of the present study. According to Noreen et al. [60], the amounts of N, P, K, Ca, and Mg in dry Russian olive leaves were 37,500, 5580, 43,700, 24590, and 7690 mg/kg, respectively. Whereas Motsara and Roy [61] reported that optimal N, P, K, Ca, and Mg ranges in plants were for N between 20000-50000, for P between 2000-5000, for K between 10000-50000, for Ca between 1000-10000, and for Mg between 1000-4000 mg/kg. The study found that the skin part had higher concentrations of Co, K, and Sn elements than other components (Table 6). The seed, on the other hand, had more As, Ca, Cr, Cu, Fe, Pb, V, Zn, and P than the other parts of the plant. This finding suggests that different parts of the plant accumulate different elements in different ways, with some elements being more concentrated in certain parts of the plant. These findings have implications for understanding the distribution of essential and non-essential elements in plants and their potential impact on human health. These results suggest that the leaf samples of Russian olives have sufficient levels of macro and trace elements for healthy growth.

3.4. The mineral ratio and mineral safety index of Russian olive parts

Mineral ratios are more important than minerals alone. These important ratios play an important role in the balance of metabolism and in the prevention and detection of certain diseases. In contrast, overloading some body elements can disrupt the uptake and mechanism of others. Therefore, these important element ratios and safety indices were tabulated (Tables 7 and 8) and evaluated. Ca/K, Ca/P, Na/K, Ca/Mg, Na/Mg, Zn/Cu, Fe/Cu, Ca/Pb, Fe/Pb, Zn/Cd, Fe/Co, K/Co, and the milliequivalent ratio of [K/(Ca + Mg)]; the mineral safety index (MSI) of Na, Mg, P, Ca, Fe, Cu, Zn, and Se was also calculated according to Eq. (1) [62-65].

To calculate MSI,

RAI is the recommended adult intake, while CV in the table will represent the calculated value of the calculated MSI from research results. The differences between the standard MSI and the MSI of the samples were also calculated [62].

Table 7 depicts the MSI of the Russian olive part samples. Table 7 also presents the standard MSI values for the elements. Na (4.80), Ca (10.0), Mg (15.0), Zn (33.0), Fe (6.70), Cu (33.0), P (10.0), and Se (14.0) [65].

The calculated MSI for Na ranged in plant parts from 3.55 to 9.48, with discrepancies between the table values (TV) and the calculated values (CV) ranging from 0.04 to -4.68. The zinc pulp (26.4) and skin (18.4) were below the standard value. Nonetheless, the output exceeding the acceptable value in the leaf (41.8) and seed (50.97) indicates a substantial uptake that could interfere with the Cu and Mn content necessary for metabolism. Elevated Zn levels are detrimental as they can impede the absorption of other metals, such as Cu and Fe. Iron is crucial for optimal growth, healthy blood cell formation, and hemoglobin production; its lack is linked to diminished cognitive performance [62]. A 2143% Fe excess was detected in the leaf. The finding indicates a potential risk of excessive indebtedness. Conversely, all plant components contain elevated levels of Fe compared to the usual value. Calcium, P, and Se values could not be available in the leaf and could not be calculated. On the other hand, there were positive differences in Na, Cu, Zn, and Se in the pulp, while negative differences were observed in Ca, Mg, P, and Fe. In addition, in pulp and skin, negative differences were observed in other elements except Cu and Zn, but Se could not be measured. In the seed, negative changes were observed in elements other than Na and Cu; also, Se could not be measured. The fact that Cu is positive differences in plant parts is a beneficial result for Fe, Mn, and Zn metabolism. However, high amounts of Cu can disrupt Fe, Mn, and Zn metabolism. On the other hand, the fact that Mg shows negative differences in all plant parts meant that it could overload the consumer by 1457% in leaves, 29.8% in pulp, 65.3% in skin, and 308% in seeds.

The minerals’ ratios are sometimes considered more important than their absolute levels. The chosen mineral ratios showed a satisfactory balance between these elements and provided information about what might happen if the connections between them are messed up. This disruption may affect disease conditions and physiological and developmental factors, along with the effects of nutrition and pharmaceutical drugs [63].

Table 8 shows the mineral ratios. The 6th and 7th columns of the table displays the ideal ratio and the acceptable ratio, respectively. The leaf did not have a Ca/K ratio, but the pulp, skin, and seed ratios were significantly lower than the standard ratio (4.0). Furthermore, the Ca/P ratio could not be determined in the leaf, but it was found that it was above 0.50 and below the acceptable value (2.6) in other plant parts. When it comes to optimal calcium absorption in the intestine and bone formation, higher Ca/P ratios would lead to faster bone growth because they allow for better absorption. Numerous animals have demonstrated that the Ca/P ratio influences blood calcium levels [66]. Na and K are needed to keep the osmotic balance in body fluids, keep the pH level stable, control the absorption of glucose, and help cells keep the right amount of protein as they grow [62]. All plant parts have a Na/K ratio well below the standard, which favors the non-enhancement of high blood pressure. Additionally, the Na/K ratio in food sources should be approximately 0.6. The WHO [67] recommended a Na/K ratio of less than 1 as an advantageous strategy for hypertension management. The Ca/Mg ratios in plant parts ranged between 2.78 and 4.21, exceeding the threshold of 1.0 but below the acceptable value of 7.0; the Ca/Mg ratio could not be measured in leaves. The Ca/Mg ratio aids in the regulation of blood glucose levels. Mg deficiency and an elevated Ca/Mg ratio cause excessive insulin release, resulting in a decrease in blood sugar levels. The [K/Ca+Mg]* milliequivalent ratio could not be determined in the leaf but was above the standard value (2.2) in pulp and skin and well below the standard value in seed. The report of Marton and Andersen [68] showed that the milliequivalent of [K(Ca+Mg)] must be less than 2.2 to prevent hypomagnesaemia. On the other hand, all plant parts showed a Na/Mg ratio significantly lower than the standard value (4.17). The Zn/Cu ratio was below the standard value in all plant parts. The Fe/Cu ratio was much higher than the standard value in all plant parts. The Fe/Cu ratios surpassed the advised threshold of 0.9. The elevated Fe/Cu ratio is due to the higher concentration of Fe compared to the lower amount of Cu. The ratios of Ca/Pb and Fe/Pb exceeded the acceptable ranges. Ca/Pb value could not be determined in leaves, but it was found to be much higher than the standard (84) in other plant parts. Likewise, the Fe/Pb ratio was well above the standard (4.4) in all plant parts. However, the Zn/Cd ratio was much lower than the standard value in all plant parts. This is not a desired situation either. On the other hand, Fe/Co and K/Co ratios could not be determined in the pulp but were found to be much higher than the standard value in other plant parts. This result is a desired situation.