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Development of Analytical Method for Assessment of Selected Toxic Trace Elements in Fresh Fruits from Turabah Valley by ICP-OES

Awad Abdalla Momen1,2*, Mohamed Hesham Hassan Mahmoud3,4, Dafaalla Mohammed Hag Ali1,5, Malik Abdalla Elsheikh1,5 and Mohammed Awad Ali1,6

1Department of Chemistry, Turabah University College, Saudi Arabia

2Department of Chemistry, College of Science, University of Bahri, Sudan

3Department of Chemistry, College of Science, Taif University, Saudi Arabia

4Central Metallurgical Research and Development Institute, Helwan, Egypt

5Department of Chemistry, College of Science, Sudan University of Science and Technology, Sudan

6Department of Chemistry, College of Science, University of Khartoum, Sudan

*Corresponding Author:
Awad Abdalla Momen
Department of Chemistry
Turabah University College, Saudi Arabia
Tel: +96654103638
E-mail: aamomena@yahoo.com

Received Date: 23/02/2019; Accepted Date: 07/03/2019; Published Date: 08/03/2019

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Abstract

The contents of selected toxic trace elements (TTEs) namely, Al, Ni, Co, Mn, Cr, Pb, As, and Cd were assessed in fresh fruit samples from Turabah Valley. These samples include date palm (rutab), cantaloupe melon, watermelon, lemon, mandarin, grape, pomegranate and tomatoes. The dried powdered samples were digested by a microwave using a 1:2.5 mL mixtures of H2O2 and HNO3 and TTEs levels were analyzed by using inductively coupled plasma-optical emission spectrometry (ICP–OES). The developed analytical method was validated in terms of linearity, accuracy, precision, detection and quantification limits that provided satisfactory results in all cases. It was found that Al, Mn, Pb, As, and Cd were detected in most analyzed samples, while other analytes were below the detection limits of the method. A considerable variation were observed with regard to TTEs concentrations in different studied fruit samples. TTEs contents of fruits were compared with those of soil and well water used for irrigation in the same area. The estimated contents of studied elements were within the critical safety levels specified by the FAO/WHO/SASO. This indicated that the residents may not face any public health harmful effects due to fruit consumptions, in spite of that some regular monitoring were need both at the farm and the table. Some physico-chemical properties such as moisture contents (%), ash contents (%) and total solid contents (%) of fruits were also estimated and compared with the reference values. Student t-test, ANOVA test, and Microsoft excel were employed to estimate the significance of values obtained.

Keywords

Analytical Method, Toxic Trace Elements, Fresh Fruits, ICP-OES, Health Harmful Effects, Turabah Valley

Introduction

The effect of toxic trace elements (TTEs) contamination of fruits cannot be underestimated, as this food source is an important component of human diet. Different elements are present in the human diet that are necessary for good health; however, others may cause acute toxicity. For instance, Ca is necessary for the proper development of bone and teeth and plays an important role in glucose and protein absorption [1]. The toxicity of some elements like Pb and Cd can reduce mental and central nervous function and damage many organs. For this reason, a large number of studies have been undertaken to identify the potential risk factors with TTEs in different food matrices [2,3].

Fruits are important edible crops and are an essential part of the human diet. They are rich in nutrients required for human health, and are an important source of carbohydrates, vitamins, minerals, and fibers. Furthermore, fruits can potentially be contaminated with toxic elements from water and/or soil by using fertilizers and pesticides, through air by vehicles and/or generators exhausts, also by mining and industrial activities [4].

A great effort has been expended on developing analytical methods for determination of TTEs in food matrices [5,6]. Many studies in literature were attempt to assess the nutritional benefits and potential risks arising from the consumption of fruits. For example, Yami et al. [4]. have studied selected nutrients and toxic metals in fruits from Ethiopia. Radwan and Salama [7] have reported heavy metal content in fruits and vegetables in Egypt. Sager [8] was able to determine the main and trace element contents of tomatoes grown in Austria. Todea et al. [9] have studied the level from major–to–trace elements in different apple cultivars in Romania. Abdrabo et al. [10]. have determined a total of 23 elements in Spanish palm dates. Basha et al. [3] have reported trace elements in vegetables and fruits cultivated in India. Taharn et al. [11] have investigated the concentration of major to trace elements in tomato varieties economically grown in the northeast of Thailand. Mausi et al. [12]. have conducted a study on the assessment of selected heavy metal concentrations in selected fresh fruits in Kenya. Fernanda et al. [13]. have determined the trace element concentrations in tomato samples at different stages of maturation in Brazil. Igwegbe et al. [14]. have reported a survey of heavy metal contents of selected fruit and vegetable crops in Nigeria. Mohamed and Khairia [15] have studied the content of heavy metals in fruits from Saudi Arabian markets. Aldjain et al. [16]. have determined the concentration of heavy metals in the fruit of date palm growing at different locations of Riyadh (Saudi Arabia).

Sample digestion is of great importance for obtaining desirable results. Wet and/or dry ashing procedures are quite slow making it difficult to follow consistently [17]. Recently, microwave techniques have become more popular in the digestion of various food samples. Since they provide simple and rapid dissolution of the sample matrices allowing for the powerful extraction of elements from samples. In addition, they require low oxidizing reagent volumes, cause less contamination, and prevent the volatilization of elements.

In literature, different techniques have been reported for the analysis of trace elements in different food matrices including fruits. There are many factors affecting the choice for an analytical technique. These include the susceptibility to matrix effects, the detection limits, and the suitability for the matrix of interest. Historically, atomic absorption spectrophotometers (AAS) have been the instruments of choice for most fruit analysis, but recently, inductively coupled plasma-optical emission spectrometry (ICP–OES) has been used frequently by many authors because it provides fast, rugged, and multi–element analysis in a single solution [17].

Based on many behaviors like the probability of potential toxicity effects by TTEs in human diets because of the consumption of fruits. This requires an excessive assessment of fruit contents to ensure that their levels meet the standards that are agreed by local and international authorities like the Food and Agriculture Organization and World Health Organization (FAO and WHO) and Saudi Arabian Standard Organization (SASO). Therefore, the aims of the present work were undertaken for the first time to determine and to compare the concentration of selected eight TTEs (Al, Ni, Co, Mn, Cr, Pb, As and Cd) found in the edible parts of selected fresh fruits from Turabah Valley (Saudi Arabia). Also, in this work we focused to understand the ecological and the environmental relationship between TTEs contents in fruits with those found in agricultural soil and well water from the same area especially the presence of high concentration of Al in soil [4,18]. In addition, some comparative study of for physico-chemical properties such as moisture contents (%), ash contents (%) and total solid contents (%) were also estimated and compared by the reference values for nutritive purposes.

Experimental

Thin layer chromatography was run on silica gel-G and visualization was done using UV light or iodine. IR spectra were recorded by Perkin-Elmer 1000 instrument in KBr pellets. 1H-NMR spectra were recorded in CDCl3 or DMSO-D6 solvent using trimethylsilane as the internal standard by the 300 MHz spectrometer. By Jeol-JMS D-300 spectrometer, mass spectra were recorded. Starting materials which were used in this chapter were obtained from commercial sources and used as such.

Materials and Methods

Instrumentation and Apparatus

A microwave digestion system (Model MARS-5, CEM corporation, Matthews, USA) programmable for time and power between 800-1600 Watts, equipped with 12 high pressure Teflon vessels (Model Easy Prep xp-1500 plus, CEM corporation, Matthews, USA) were used for sample digestions. The heating programs of the digestion system were shown in Table 1. In addition, a quadruple Elan DRC II (PerkinElmer Life and Analytical Sciences, Shelton, CT, USA) ICP-OES (Perkin Elmer Model Optima 2100 DV, USA) with CCD detector was used in this study for standards and samples analysis. The operating conditions of ICP-OES were indicated in Table 1. These conditions were carefully selected and well optimized in order to maximize the sensitivity for the desired elements and to obtain the best precision and accuracy. Moreover, some instrumental operating conditions of MARS-5 and ICP-OES were set according to manufacturer guidelines.

Heating program of MARS-5 Instrumental conditions of the ICP-OES
Parameters Conditions Parameters Values
Temperature 220 (OC) RF incident power 1600 (Watts)
Pressure 800 (pis) Frequency 40.68 (MHz)
Ramp time 25 (min) Nebulizer argon flow rate 0.60 (L min-1, Argon)
Holding time 10 (min) Plasma argon flow rate 15.0 (L min-1, Argon)
Ventilation 10 (min) Auxiliary argon flow rate 0.2 (L min-1, Argon)
Acid/oxidant mixture 2 mL H2O2 (30%)/5 mL HNO3 (65%) Pump flow rate 2.0 (mL min-1)

Table 1. Heating program of MARS-5 for digestion of fresh fruit samples and the instrumental conditions of the ICP-OES.

Reagents and Materials

All reagents were of the highest commercially available purity grade. Ultrapure deionized distilled water (UDDW), (18 MΩ/ cm) was obtained from a Milli-Q Plus water purification system (Millipore Inc., Paris, France) and used throughout the experiments. 30% H2O2 (d=1.11 kg L-1) and 65% HNO3 (d=1.40 kg L-1) (Merck, Germany) were used as received for digestion of fruit samples. High-purity grade V (Atomic Spectroscopy Standard Solution) consist of Pb (2 mg L-1), Cd (5 mg L-1), As and Cr (10 mg L-1), Mn (15 mg L-1), Ni (40 mg L-1), Co (50 mg L-1) and Al (200 mg L-1) was purchased from PerkinElmer, Shelton, CT, USA). This solution was used for preparing standards for calibration curves and spiking of some samples for recovery test. The purity of argon and nitrogen gases used in this study were greater than 99.99 (v/v). All laboratory glassware were soaked in 10% (v/v) HNO3 for 24 hours, rinsed several times with UDDW and dried in a microwave oven (isik, GORKEM Co., Ltd, Turkey).

Sampling and Preservation

A total of 42 fresh fruit samples, namely date palm (rutab, wet stage of fruit), cantaloupe melon, watermelon, lemon, mandarin, grape, pomegranate and tomatoes were collected from the vegetable and fruit markets in Turabah Province (Saudi Arabian). The detail informations of the studied fruit samples were indicated in Table 2. Samples were collected in clean polyethylene containers according to their types. Surface contaminants of the fruits were washed first with tap water, rinsed UDDW and dried with tissue paper, then preserved in the refrigerator prior to processing for drying. After a while, each sample was cut separately with clean stainless steel knife into small pieces (2-3 mm size), well mixed and dried at 90°C in microwave oven until constant weight was achieved [19]. Three dried samples of each type were mixed and subsequently grounded into a fine powder and homogenized using a clean commercial kitchen grinder (Philips, Indonesia). The grounded samples were properly labeled and stored in polyethylene containers at -20°C until needed for analysis.

Fruits (English name) Fruits (Scientific name) Part investigated Number of samples (Sps)
Date palm (rutab) a Phoenix dactylifera L. Edible tissues 9
Cantaloupe melon Cucumis melo L. Edible tissues 3
Watermelon (i) b Citrullus lanatus L. Edible tissues 3
Watermelon (ii) c Citrullus lanatus L. Edible tissues 3
Lemon Citrus limonum L. Whole 6
Grapes (i) d Vitis vinifera L. Whole 3
Grapes (ii) e Vitis vinifera L. Whole 3
Mandarin Citrus reticulate L. Edible tissues 3
Pomegranate Punica granatum L. Edible tissues 3
Tomatoes Solanum lycopersicum L. Whole 6
Total of Sps=42

Table 2. Details of the studied fresh fruit samples that collected from Turabah Valley.

Digestion of Fruits

For determination of moisture content (%), a apportion from each sample was weighed accurately using 0.01 mg sensitive weighing analytical balance in a clean dried porcelain crucible, then dried at 90°C in a microwave oven (ISIK GORKEM Co. Ltd., Turkey) until constant weight was obtained [19]. For sample digestions, about 0.5 gm of each dried sample was weighed accurately into dry clean PTFE digestion vessel and inserted directly into a dry and clean Teflon separate microwave assisted digestion vessel. 2 mL H2O2 (30%) and 5 mL HNO3 (65%) in the ratio of 1:2.5 were added drop wise to each sample. The contents were shaken carefully, then the digestion vessels were closed and the selected heating programs were followed (Table 1). After digestion, clear solutions were cooled down to room temperature and reactors were opened to eliminate nitrous vapors. Then, the interior walls of the vessels were washed down with UDDW and vessels were swirled through the digestion to keep the wall clean and to prevent the loss of the samples. Then, the contents of the vessels were quantitatively transferred to 50 mL volumetric flask and diluted to the mark with UDDW. This procedure was partly modified from that recommended by Bressy et al. [20], with minor modifications in reagent volumes and sample weights. Several analytical blanks consisting of UDDW/H2O2/HNO3 were also prepared in the same way as the samples and analyzed to characterize instrumental drift. The digests were prepared three times (n=3) for each sample. To avoid cross-contamination, all vessels were carefully cleaned with 10% (v/v) HNO3 solution before to proceed with the sample digestion. In addition, for safety purposes, sample and blank solutions were prepared in a Class-100 laminar flow hood. The optimizations were based on production of clear solutions, shorter digestion time and minimum reagents.

Calibrations

Standard solutions were prepared in HNO3 (65%) by diluting a multi-elemental standard solution containing the analyte elements. Reagent blanks were prepared in the same manner as standards. Under the optimized conditions, seven concentrations (mg L-1) of working standards within the linear dynamic range of ICP-OES were measured, and calibration curves for each analyte element were plotted.

Chemical Analyses of Fruits

The moisture contents (%) and the total sold contents (%) of fruits were determined after drying in a microwave oven at 90°C until constant weight [19]. In addition, the ash contents (%) of fruits were also determined after ashing in a muffle furnace (Ninther band) set at 550°C for 2 hours. Standard solution was diluted with UDDW for calibration standards. All standards and sample solutions were analyzed three times on a simultaneous Varian 710 ES axial ICP-OES with CCD detector. A Cetac auto sampler with 15 mL sample tubes was connected to the peristaltic pump. A Burgener Teflon Mira Mist-nebulizer (SCP Science) and glass cyclonic spray chamber were used for sample introduction. The operating conditions of ICP-OES were indicated in Table 1. The instrument detection limits were determined by measuring the emission intensities of seven blanks.

Statistical Analysis

The results were statistically evaluated by ANOVA test and Student t-test, (P=0.05), in addition, Microsoft Excel and Origin software’s were also used. The obtained concentrations were expressed as average value ± confidence interval (at 95% confidence interval). All statistical analysis were based upon triplicate measurements (n=3).

Validation of Method

To evaluate the analytical method proposed for the TTEs analysis of fruits by ICP-OES based techniques, some analytical figures of merit were estimated, such as spectral emission lines (wavelengths), linearity, accuracy and precision, limits of detection (LOD) and limit of quantification (LOQ). The spectral lines (nm) for the target elements were selected in terms of high sensitivity and absence of spectral interferences. The linearity as a square correlation coefficient (R2) for each analyte was determined by preparing the calibration curve using non-weighted least-squares linear regression line. The accuracy of the method as a recovery (%) was determined by spiking some fruit samples with different concentration levels of standard solution (before and after digestion steps) and passed through the same digestion procedure. The precision of the method was estimated by means of the relative standard deviation (RSD). The RSDs were calculated from the elemental concentrations obtained after the analysis of the five independent replicates of each sample.

Results and Discussion

Analytical Figures of Merit

The selected spectral lines that gives high sensitivities and maximum emission intensities under the optimal ICP-OES operating conditions were described in Table 3. Moreover, the calibration curve of each analyte that measured using the selected analytical line was suitable and had good linearity (R2>0.9990 or better). This confirmed the linearity of the analytical method followed in accordance with criteria that specified by Association of Official Analytical Chemists (AOAC) [21,22]. The method accuracy of each analyte was calculated as a recovery (%), and it was found to be within the acceptable range (100 ± 8 for all estimated elements) (Table 3). This indicate that there were no significant losses or gained for analytes by the followed analytical technique. In addition, the precision of the ICP-OES method was calculated as a relative standard deviation (RSD) of five independent replicates of each sample. It was found to be below 4% (Table 3). Furthermore, this value confirmed that was good precision of the following method. Moreover, the LODs and LOQs methods for the tested elements were determined by analyzing seven portions of standard solutions simultaneously following the general procedure. The LOD and the LOQ of each analyte were calculated as follows [23]:

image While,image

Whereas: LOD is the limit of detection, LOQ is the limit of quantification, σ is the standard deviation of the intensity of seven blanks and m is the slope of the calibration curve for each element.

The LODs (mg kg-1) of the elements were ranged between 0.0005-0.0556 mg L-1 for Mn and Al respectively, while LOQs (mg kg-1) were ranged between 0.003 mg L‑1 for Co and 0.174 mg L-1 for Al (Table 3). The values of LODs and LOQs clearly demonstrate the high sensitivity and the linear range of ICP-OES method.

Elements Wavelengths (nm) Correlation coefficients (R2) RSDs (%) Spiking recoveries (%) LODs (mg kg-1) LOQs (mg kg-1)
Al 308.212 0.9993 3.15 106 ± 4 0.0556 0.174
Ni 231.604 0.9991 NC 106 ± 5 0.0011 0.004
Co 238.892 0.9997 NC 95 ± 3 0.0008 0.003
Mn 257.61 0.9993 2.22 108 ± 6 0.0005 0.006
Cr 267.716 0.9996 2.11 100 ± 4 0.0012 0.042
Pb 220.353 0.9997 2.98 98 ± 5 0.0062 0.086
As 188.979 0.9998 1.01 102 ± 5 0.0054 0.016
Cd 226.502 0.999 2.83 104 ± 3 0.0007 0.019

Table 3. Analytical figures of merits of ICP-OES method.

Moisture content (%)

The total water component of a sample is described as the moisture content (%) of the food sample. It is used to determines the storage capacity and the quality of food sample. For moisture content (%) determination a three crucibles were oven dried at 90°C for 30 min and transferred into desiccators to cool down. After cooling, 5.0 g of each of the samples were weighed in the crucible and then oven dried at 90°C to a constant weight. The percentage values for the moisture contents (%) calculated using the formula [19]:

image

Whereas: W1, W2 and W3 are the weight of crucible, weight of crucible and sample before drying and weight of crucible and sample after drying respectively.

The moisture content (%) of fruits obtained in this study and those found in literature were indicated in Table 4. It was observed that moisture content (%) was lower for date palms (rutab) and higher for tomatoes, but the differences were not significant because all the fruits were still fresh when purchased from the market. Moisture content (%) influences the activities of microorganisms during storage. The higher the moisture content (%), the more susceptible the sample will be to microbial attack. In addition, increase in moisture content (%) reduces the proximate principles such as fat, protein and carbohydrate. thereby decreasing the energy value [24]. The obtained results were generally comparable to those reported in literature previously with some variations related to fruit variety and agro-climatic and environmental conditions.

Fruits Moisture contents (%) Ash contents (%)
Found in this study Literature values Found in this study
Date palm (rutab) 21.8 ± 0.69a 21.9[25], 22.8[26] 3.8 ± 0.7a
Cantaloupe melon 90.0 ± 1.34b 92.5[27], 87.5[28] 1.2 ± 0.2b
Watermelon (i) 93.1 ± 1.90b 95.4[27], 89.6[28] 1.3 ± 0.3b
Watermelon (ii) 92.3 ± 1.03b 95.4[27], 89.6[28] 1.5 ± 0.3b
Lemon 88.5 ± 1.98b 85.1[29] 0.6 ± 0.03b
Grape (i) 85.4 ± 1.76b 83.0[4], 89.1[22], 90.4[27] 0.57 ± 0.04c
Grape (ii) 84.6 ± 1.81b 83.0[4], 82.5[22], 79.15[27] 0.72 ± 0.06c
Mandarin 87.2 ± 1.56b 88.4[4], 88.0[22] 0.42 ± 0.02c
Pomegranate 83.0 ± 1.88b 89.6[24], 79.80-80.5[30], 84.6[31] 0.46 ± 0.02c
Tomatoes 94.5 ± 1.49 93.6[32] 0.65 ± 0.05c

Table 4. Proximate moisture and total solid contents (%) of fresh fruit samples.

Total Solid Content (%)

The total solid content (%) is a measure of the amount of material remaining after all the water has been evaporated. The percentage values for the total solid contents (%) calculated using the formula:

Total Solid Content(%) =100-Moisture content(%)

As can be seen in Table 4, the total solid contents (%) is the lowest for tomatoes (5.5%). and the highest for date palm (rutab) (88.2%). The order of total solid contents (%) in the fruits is date palm (rutab)>grape (ii)>grape (i)>mandarin>lemon>cantaloupe melon>watermelon (ii)>pomegranate>watermelon (i)>tomatoes. These values are approximately comparable with literature values.

Ash content (%)

The fruit ash was determined as total inorganic matter (residue) that remains after organic matter has been burnt off [19]. Different studies have shown the variations in ash contents (%) in different fruits. High total ash content (%) for a food material signifies the presence of adulterants [24]. For determination of ash contents (%), crucibles were dried in a microwave oven at 90°C until constant weight, and were transferred into the desiccators to cool down. Then 5.0 g of each of the samples were weighed into the crucible and heated in a muffle furnace set at 550°C for 2 hours after which the crucibles were transferred into desiccators then cooled and weighted. The percentage values for the ash contents (%) calculated using the formula [19]:

image

Whereas: W1, W2 and W3 are the weight of crucible, weight of crucible and sample before ashing and weight of crucible and sample after ashing respectively.

The ash content (%) of a biological material is the organic residue that remains after organic matter has been burnt. Ash contents (%) were determined to assess their nutritive value of fruits. The obtained values in this study and those found in literature were shown in Table 4. It was observed that ash (%) was lower for date palm (rutab) and higher for tomatoes. The obtained results were generally comparable to those reported in literature previously with some variations related to fruit variety and agro-climatic and environmental conditions.

TTEs contents (mg kg-1)

The analytical method employed was that of inductively coupled plasma-optical emission spectrometry (ICP-OES). The digestion method using H2O2/HNO3 was applied for the determination of Al, Ni, Co, Mn, Cr, Pb, As and Cd in ten varieties of the most commonly fresh fruits in Turabah Province and other regions in Saudi Arabia. The average concentrations (mean ± SD, mg kg-1 dry wt.) of TTEs were described in Table 5. In the whole, TTEs contents of the analyzed samples showed highest amount of Al in cantaloupe melon (0.917 ± 0.072 mg kg-1) and watermelon (i) (0.878 ± 0.091), while Al was not detected (ND) in watermelon (ii), lemon, grape (ii) and tomatoes due to below the LOD of the ICP-OES method. Furthermore, Mn was detected in tomatoes (0.016 ± 0.004 mg kg-1) and grape (ii) (0.024 ± 0.006), but ND in other samples due to below the LOD of the ICP-OES method. Cr was detected in very low concentrations in grapes (ii) only at 0.005 ± 0.001 mg kg-1. Moreover, Co and Ni were ND in all studied samples because they are below the LOD of the ICP-OES method. As unexpected Cd, As and Pb were found in most studied fruit samples but with very low concentrations (~0.031 ± 0.001 mg kg-1, ~0.049 ± 0.005 mg kg-1 and ~0.039 ± 0.006 mg kg-1 respectively). Furthermore, moderately highest concentrations of TTEs were recorded in watermelon (i), grape (i) and mandarin, while the lowest one were recorded in lemon. Figure 1 showing an illustrating graph for bar plot of the TTEs average contents in fruits under study. Moreover, our results (Table 5) reveal that a considerable variations were observed with regards to element concentrations in different studied fruits. The differences were significant for different samples at 95% confidence level. In general, our results were in close agreement with those of reported in literature [4-25]. In addition, FAO/WHO/SASO has set a limit for heavy metal intake based on body weight for an average adult (60 Kg body weight). It was found that our estimated concentrations of all studied elements were within the critical levels specified by the FAO/WHO/SASO. The variation in TTEs concentrations in the different fruits samples may be related to variation in texture, structure, chemical and mineral composition of soil. In addition, the morphology of fruits influence the dust deposition and hence different patterns were observed for elemental concentrations in plant tissues and their fruits. The bioaccumulation of trace elements in the fruits of the plants is the combined result of the uptake processes via the roots from the soil.

Fruits Concentration (mg Kg-1 dry wt., edible portion)
Al Cd As Pb Mn Cr Co Ni
Date palm (rutab) 0.118 ± 0.054 a 0.033 ± 0.002 a 0.068 ± 0.005 a ND ND ND ND ND
Cantaloupe melon 0.917 ± 0.072 b 0.030 ± 0.001 a 0.084 ± 0.006 a ND ND ND ND ND
Watermelon (i) 0.878 ± 0.091 b 0.029 ± 0.001 a 0.081 ± 0.004 a 0.077 ± 0.005 a ND ND ND ND
Watermelon (ii) ND 0.032 ± 0.002 a ND 0.083 ± 0.006 a ND ND ND ND
Lemon ND 0.030 ± 0.001 a ND 0.031 ± 0.001 b ND ND ND ND
Grape (i) 0.947 ± 0.088 b 0.032 ± 0.001 a ND 0.043 ± 0.003 b ND 0.005 ± 0.001 ND ND
Grape (ii) ND 0.032 ± 0.001 a ND ND 0.024 ± 0.003 a ND ND ND
Mandarin 0.935 ± 0.074 b 0.033 ± 0.001 a 0.063 ± 0.003 a 0.098 ± 0.006 a ND ND ND ND
Pomegranate 0.258 ± 0.051 a 0.030 ± 0.001 a 0.092 ± 0.005 a ND ND ND ND ND
Tomatoes ND 0.033 ± 0.002 a ND 0.162 ± 0.075 c 0.016 ± 0.002 a ND ND ND
AC in fruits (Sps=10) 0.579 ± 0.085 0.031 ± 0.001 0.039 ± 0.006 0.049 ± 0.005 NC NC NC NC

Table 5. Average concentrations of TTEs in ten varieties of fruit samples.

chemistry-average-contents

Figure 1. Illustrating graph showing bar plot of the TTEs average contents in fruits.

Comparison of TTEs Contents

Plants are long-lived organisms, which can take up trace elements from the soil, water or air, and retain them for a long time. These elements may enter the human body through consumption of fruits grown in contaminated soil. Therefore, the average contents of TTEs of soil (mg Kg-1) and irrigation water (mg L-1) samples from the same area were compared with our results (Table 6) [2,27]. Figure 2 illustrates graph for bar plot of the TTEs average contents in fruits compared with those found in agricultural soil and wells water samples from the same area. As expected, Al had the highest concentrations in fruit, agricultural soil, and well water samples, while the opposite was observed for all the other elements. Therefore, the presence of Al in this area must be strictly revised in coming future. Cd is readily available for uptake by plants as there is a clear association between Cd concentration in soil and the plants grown on the soil. The guideline value for Cd in soil from plant uptake is 1 mg kg-1 dry soil weight [33]. As Pb is not being translocated readily in plants, it could be suggested that Pb found in different samples originated from atmospheric deposition. This may also be due to the vehicular lead emission could be likely source of lead pollution in areas close to agricultural fields. On contrary, in all fruit samples, the uptake and accumulation of Mn is relatively low. However, generally speaking, we can say that the concentration of studied TTEs in fruits from Turabah Valley were below the permissible concentrations given for fruits.

Samples Concentration (mg Kg-1 dry wt., edible part of fruit, mg Kg-1 dry wt. of soil and mg L-1 of water) References
Al Cd As Pb Mn Cr Co Ni
Fruits (Sps=10) 0.579 ± 0.085 0.031 ± 0.001 0.039 ± 0.006 0.049 ± 0.005 NC NC NC NC Present study
Soil (Sps=10) 55.26 ± 3.05 NC 0.043 ± 0.006 0.047 ± 0.004 3.01 ± 1.13 0.24 ± 0.06 NC 0.147 ± 0.034 [2]
Wells water (Sps=15) 0.015 0.006 0.032 0.015 NC NC NC NC [2,32]

Table 6. Average concentrations of TTEs in fruit, agricultural soil and wells water samples.

chemistry-agricultural-soil

Figure 2. Illustrating graph showing bar plot of the TTEs average contents in fruit, agricultural soil and wells water samples.

Conclusions

Finally, we can conclude that, the results obtained for fresh fruit samples were within the recommended limits for the FAO/ WHO/SASO. The elevated level of Al may not cause harmful effects to human health. In addition, the presence of Cd, As and Pb in some fruits indicates there may be a translocation of those elements from the irrigation water or from atmosphere (vehicle and generator exhaust), since the agricultural soils were approximately free from Cd and Pb. However, we can also recommend that the main source of TTEs (soil, water, air …etc) in the Turabah Valley should be strictly monitored for protecting the health of riverine ecosystems along with fruits. In addition, the obtained results for the moisture contents (%), the ash contents (%) and the total solid contents (%) of fruits were generally comparable to those reported in literature previously with some variations related to fruit variety and agro-climatic and environmental conditions.

Acknowledgments

The authors gratefully thank the Dean of the Deanship of Scientific Research, Taif University, Saudi Arabia, for sponsoring this project (Project Number: 5552-438-1). In addition, we thank the Dean of Turabah University College and all the individuals who kindly participated in this study.

References