Accumulation of selected metals in the fruits of medicinal plants grown in urban environment of Islamabad, Pakistan

2.1 Study area

The wild edible fruits and relevant soil samples were collected from urban areas of Islamabad, the capital city of Pakistan. It is located at 33.43°N & 73.04°E in the northwest of the country against the backdrop of Margalla Hills. The city extends over 906 km² and it has an estimated population of more than one million. The climate is tropical with two diverse seasons, viz. winter (October-February) and summer (March-September); average temperature ranges from 13 °C in January to 38 °C in June (Shah and Shaheen, 2007).

2.2 Sample collection

Composite samples of the wild edible fruits of Carrisa opeca, Phyllanthus emblica, Solanum nigrum, Zizyphus nummularia, Zizyphus mauritiana, Physalis minima, Opuntia dillenii and Phoenix dactylifera were collected from various urban areas of Islamabad during October 2010-April 2011 (Table 1). The plant identification and verification were carried in the Herbarium of Quaid-i-Azam University, Islamabad, Pakistan, where the voucher specimen for each plant was submitted. The plant species were collected from different urban localities along with the soil sample. Most of the samples were collected in the vicinity of medium to high traffic density areas. The fresh fruit samples were carefully collected in clean polyethene bags and transported to the laboratory for further analysis. About 18–20 composite fruit samples of each medicinal plant were collected from the study area. Composite soil samples (0–30 cm, top layer) were also collected from the place of the collection of fruit samples. Three composite soil samples were collected from the locality of each plant, and each composite sample consisted of 3–5 sub-samples that were mixed in equal proportions. About 500 g of the soil samples was collected in polyethene bags and labelled and transported to the laboratory for further analysis (Radojevic and Bashkin, 1999).

2.3 Sample preparation

The fresh weights (FW) of the fruit samples were recorded just after sample collection. The samples were then washed with distilled water and dried at 70–80 °C for 48 h in an electric oven. The dried samples were ground into fine powder by porcelain mortar and pestle. The powdered samples were placed in tightly closed clean/labelled sample bottles and stored at room temperature in desiccators until further analysis. Afterwards, about 1.0 g of the powdered sample was digested using 20 mL HNO₃ and 10 mL HClO₄. The mixture was heated to obtain clear solution and the final volume (50 mL) was adjusted with 0.1 M HNO₃. Along with each batch of five samples, a blank (containing all the reagents except the fruit sample) was also processed through the same procedure in order to maintain the accuracy of results (Radojevic and Bashkin, 1999).

In the case of soil samples, large items such as stones, grass, and pieces of wood were manually removed and samples were dried in an electric oven at 70–80 °C for 48 h to achieve the constant weight. Dried samples were ground to smallest possible size and stored in desiccators until further processing (Guvenc et al., 2003). Every precaution was taken to avoid contamination during the sampling, drying, grinding and storage. For digestion, the exactly weighed quantity of the soil sample (∼1.000 g) was taken in the digestion vessel, to which 15 mL of freshly prepared aqua-regia was added and left for 16 h. Then the vessel was placed on heating block and continued heating at 50 °C for 30 min. Afterwards, the temperature was raised to 120 °C and continued the heating for 2 h. Then the vessel was cooled and 10 mL of 0.25 M HNO₃ was added. The solution was filtered and the filtrate transferred to a 50 mL flask and made up to the mark with 0.25 M HNO₃. Blank samples were also processed in the similar manner along with each batch of five samples (Radojevic and Bashkin, 1999).

2.4 Instrumental analysis

The quantitative measurement of selected metals (Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Pb, Sr and Zn) in the digested fruits and soil samples was performed on flame atomic absorption spectrophotometer (Model: AA-670 Shimadzu, Japan) using optimum analytical condition (Table 2). Standard stock solutions (1000 mg/L) were used to prepare the working standard for each metal. The working standards were prepared afresh on the day of analysis by successive dilutions. Accuracy of the quantified results was also checked by analysing the standard reference materials of plant (NIST SRM-1515, USA) and soil (NIST SRM-2711a, USA) origin and the recoveries were 98 to 101% as shown in Table 2. Some of the samples were also analysed at an independent laboratory for cross comparison and the results were found to be within ±2.5%. All the reagents used were of ultrahigh purity (certified >99.99%) procured from E-Merck and BDH.

Plant ability to accumulate the metals from soil can be estimated using the bioaccumulation factor (BAF), which is defined as the ratio of metal concentrations in the fruits samples to that in soil (Kovacik et al., 2012; Gebrekidan et al., 2013):

2.5 Statistical analysis

Statistical analysis of the analytical data was carried out using STATISTICA software version 6.0 (StatSoft, 1999). Basic statistical parameters and correlation coefficients were calculated for the metal data of fruits and soil. Multivariate analysis may be particularly valuable when there is a huge volume of experimental results and sometime they provide insight into the multidimensional patterns in the data that might be overlooked with univariate analysis (Shtangeeva et al., 2009). Multivariate principal component analysis was performed using varimax normalized rotation on the data set. It is generally used for the pattern recognition and apportionment of the variables.

2.6 Ecological risk assessment

Potential ecological risks associated with the concentrations of selected metals in the soil were assessed using contamination factor (CF) and degree of contamination (C_deg). The CF is calculated using the following equation as suggested by Hakanson (1980):

In this study, mean concentrations of the metals in background soil of Islamabad (Iqbal et al., 2015) were used as reference values.

Enrichment factor (EF) can be used to assess the extent of metal pollution in soil and represents the contamination level in the soil and is a good tool to differentiate among the anthropogenic and natural sources of the metals. Enrichment factor is usually taken as double ratio of the target element and a reference element in soils and earth crust:

2.7 Health risk assessment

A detailed door-to-door survey with open response and multiple-choice questions was administered to the adults in local population. Information acquired included the fruiting season, the consumption duration, the intake rate, the number of family members and the source of the fruits. A total of 351 respondents participated in the survey. The average daily intake of each fruit by an adult in a year was then calculated (Cherfi et al., 2014). Risk to human health was evaluated by computing the health risk index (HRI) which depends on daily intake of the metals through consumption of the fruits (C_n × D_n) and then compares them to the prescribed reference oral dose (Abbasi et al., 2013; Li et al., 2012). This index was calculated using following relationship:

Target hazard quotient (THQ) is used to assess the non-carcinogenic risks to humans from food consumption (Abbasi et al., 2013; Cherfi et al., 2014). The method to estimate THQ was provided in USEPA Region III Risk-Based Concentration Table (USEPA, 2006):

The hazard index (HI) can be expressed as the sum of the hazard quotients for all metals (USEPA, 2006):

3.1 Metal concentrations in the fruits

Distribution of selected metal levels (mg/kg, dry weight) in the fruits of medicinal plants is shown in Table 3. It is clear from the results that Ca and Mg were the most abundant elements in the fruit samples. Highest average concentration of Ca was noted for O. dillenii (6.62%), followed by Z. nummularia (0.48%), Z. mauritiana (0.28%), P. emblica (0.19%), C. opeca (0.18%), P. dactilifera (0.14%), S. nigrum (0.05%), and P. minima (0.05%). Exceptionally higher concentration of Ca found in fruits of O. dillenii indicated the uptake and enrichment of the metal in this plant, which may be used as a food supplement to overcome the Ca-deficiency. High concentration of Ca is considered important in medicinal plants because of its role in maintaining healthy bones and teeth (Rihawy et al., 2010). Like the previous case, Mg contents were the highest (0.21%) in O. dillenii, while lowest concentrations (0.05%) were noted in P. emblica. Mg along with K is essential electrolyte for maintaining normal fluid balance in cells. Moreover, normal cardiac rhythm is maintained and increase in blood pressure is prevented by a delicate balance of these two elements (Desideri et al., 2010).

Zinc is known to be involved in immunomodulatory functions and its deficiency in diet could be extremely detrimental to human health (Alexander et al., 2006). In the present study, its concentration varied from 3.61 mg/kg in Z. mauritiana to 125 mg/kg in Z. nummularia. Significant concentrations of Zn were found in P. dactylifera (81.5 mg/kg) and O. dillenii (45.7 mg/kg). FAO/WHO recommended 27.4 mg/kg of Zn as the permissible limit in edible plants (FAO/WHO, 1984). Average concentrations of Zn found in S. nigrum, P. emblica, C. opeca, P. minima and Z. mauritiana during the present study were within the FAO/WHO limit, while Z. nummularia, O. dillenii and P. dactylifera revealed elevated levels than the recommended limit. However, the daily intake of Zn associated with the consumption of these fruits was well below the maximum limits of 21 mg/day (USEPA, 2002; Bagdatlioglu et al., 2010). Somewhat consistent levels were noted for Fe in the fruit samples, ranging from 24.9 mg/kg in Z. nummularia to 65.5 mg/kg in Z. mauritiana. Appreciably higher Fe levels were noted in the fruits of P. minima (63.2 mg/kg), P. dactylifera (57.5 mg/kg) and P. emblica (55.0 mg/kg). The average daily intake of Fe through the fruit consumption was found to be within the WHO provisional maximum tolerable daily intake limits of 56 mg/day (Goldhaber, 2003; Bagdatlioglu et al., 2010). Similarly, cobalt was measured in the fruits samples at almost comparable levels ranging from 27.8 mg/kg in P. dactilifera to 38.4 mg/kg in Z. mauritiana. However, relatively large variations in the Sr levels were observed in the fruit samples ranging from 2.03 mg/kg in S. nigrum to 61.4 mg/kg in O. dillenii. Like Ca and Mg, O. dillenii depicted highest concentrations of Sr. Although there are no known physiological effects of Sr at low concentration, its accumulation in the body could be detrimental to health (Desideri et al., 2010).

Among the fruits, C. opeca depicted highest concentrations of Cr (19.0 mg/kg), followed by P. dactilifera (18.7 mg/kg), Z. mauritiana (17.3 mg/kg), P. minima (16.3 mg/kg), O. dillenii (15.7 mg/kg), S. nigrum (15.7 mg/kg) and P. emblica (14.6 mg/kg). Most of the fruits samples showed significant uptake of Cr, except Z. nummularia which showed lowest average levels at 2.33 mg/kg. The permissible limit for Cr in edible plants was set by FAO/WHO (1984) at 0.02 mg/kg. In the present study, all fruit samples contained Cr far above than this limit. The elevated Cr levels in the fruits samples may be attributed to the anthropogenic sources of Cr in the urban areas from where the samples were collected (Shah and Shaheen, 2007; Shah et al., 2012). The environmental risks of Cr are not considered very high since most of the Cr in soil exists in form of Cr³⁺ which is not toxic and also relatively immobile due to strong sorption by soil (Moodley et al., 2012). Significantly high concentrations of Pb were noted in all fruit samples except O. dillenii (3.24 mg/kg); however, highest concentration of Pb was observed in the fruits of Z. mauritiana (41.7 mg/kg), followed by S. nigrum (37.8 mg/kg) and C. opeca (36.1 mg/kg). According to WHO, the permissible limit of Pb for medicinal plants based on acceptable daily intake (ADI) is 10 ppm (WHO, 1992). Thus, the medicinal plants under investigation accumulated the metal at a significantly higher level compared to the permissible level, except O. dilleni. The weekly intake of Pb through the consumption of these fruits was also found to be considerably higher than the FAO/WHO provisional tolerable weekly intake limit of 1.750 mg/week (FAO/WHO, 1999; Bagdatlioglu et al., 2010). Higher accumulation of Pb in the fruits samples may be associated with various anthropogenic sources of the metals in the local urban environment (Shah and Shaheen, 2007; Shah et al., 2012). It is recognized as the most toxic environmental contaminant which accumulates in the skeleton, predominantly in bone marrow. It is a neurotoxin, retard intelligence and mental development and causes behavioural abnormalities (Oymak et al., 2009).

The measured levels of Mn in the fruits samples ranged from 3.90 mg/kg in P. dactelifera to 44.6 mg/kg in O. dillenii. Permissible limit set by FAO/WHO (1984) for Mn in edible plant is 2 mg/kg. Comparison of the present results with the proposed limit revealed that all the medicinal plants accumulated Mn in their fruits higher than the limit. Copper has critical biological functions in plant as a micronutrient; nonetheless, higher concentration in plant tissues could be toxic (Kubova et al., 2008). In the present study, highest concentration of Cu was observed in fruits of P. minima (14.4 mg/kg), while the fruits of P. emblica exhibited lowest contents (0.50 mg/kg). The permissible limit for Cu in edible plants was set by FAO/WHO (1984) at 3 mg/kg; hence, most of the samples in present study exceeded the limit except S. nigrum and P. emblica. Nonetheless, the average daily intake of Cu through the fruit consumption in the present study was found within the WHO maximum limit of daily intake (35 mg/day) (Goldhaber, 2003; Bagdatlioglu et al., 2010).

Highest average concentrations of Cd were noted in the fruits of O. dillenii (3.49 mg/kg) and P. minima (3.48 mg/kg), followed by Z. nummularia (3.01 mg/kg), C. opeca (2.52 mg/kg), P. dactilifera (1.73 mg/kg), and Z. mauritiana (1.30 mg/kg). All these fruits showed Cd concentrations exceeding the limit of 0.3 mg/kg recommended for medicinal plants (WHO, 2005). Nevertheless, fruits of P. emblica (0.250 mg/kg) and S. nigrum (0.010 mg/kg) exhibited Cd concentrations within the permissible limit. The weekly intake of Cd through the consumption of these fruits was noticeably higher than the FAO/WHO provisional tolerable weekly intake limit of 490 µg/week (FAO/WHO, 1999; Bagdatlioglu et al., 2010). Excessive accumulation of Cd in the fruits samples can be linked with various anthropogenic activities in the urban areas (Shah and Shaheen, 2007; Shah et al., 2012). Environmental risks of Cd are of major concern because it showed adverse effects on brain metabolism and other severe effects such as prostate cancer, liver, kidney, lungs and bone damage (Baldwin and Marshall 1999).

3.2 Metal concentrations in the soil

The distribution of selected metal levels (mg/kg, dry weight) in the soil samples is shown in Fig. 1. An examination of the metals data in soil revealed relatively broad distribution for Sr, Pb, Zn, Cu and Cd while relatively narrow ranges were observed for Fe, Cr, Co, Mn, Mg and Ca. Among the metal dominant mean levels were shown by Ca (2.01%), Fe (0.83%) and Mg (0.14%), followed by Mn (520 mg/kg), Sr (510 mg/kg), Zn (73 mg/kg), Cr (43 mg/kg), Cu (43 mg/kg), Pb (35 mg/kg), and Co (29 mg/kg), while Cd showed the lowest average concentration (5.12 mg/kg). Consequently, the soil in the study area was mostly calcite in nature (showing comparatively higher concentrations of the alkaline earth metals) and almost similar results were reported in an earlier study (Iqbal and Shah, 2011). Soil samples collected from the sites of S. nigrum showed lowest concentrations of Ca and Sr while the highest concentrations were found in the samples collected from the vicinity of P. minima. Highest concentration of Mg (0.34%) was recorded in the soil samples related to P. datylifera, while its lowest concentration (0.09%) was present in soil samples related to S. nigrum.

Close

Figure 1

Distribution of selected metal levels (mg/kg, dry weight) in the soil samples.

Export to PPT

Uptake of Fe by plant at very high concentration could be toxic and may inhibit their growth. In the present study, Fe showed highest levels (0.91%) in the soil samples related to S. nigrum while it showed minimum levels (0.69%) in the soil sample related to P. minima. Although Fe concentration in the soil samples was relatively high only a small fraction was taken up by the plants. Cobalt concentrations in soil samples were restricted to narrow range, lowest of 21.1 mg/kg to the highest of 30.8 mg/kg in the soil samples taken from the vicinity of Z. mauritian and P. dactylifera, respectively. Soil samples related to Z. nummularia exhibited highest concentration of Zn (133 mg/kg), while soil sample collected from the vicinity of S. nigrum showed very high levels of Cu (148 mg/kg). The permissible levels for Zn and Cu in agricultural soil are 150–300 mg/kg and 50–140 mg/kg (Kabata-Pendias and Pendias, 2001). Zn contents in all soil samples were within the permissible limit; however in case of Cu, the metal levels were below the permissible levels except the soil samples related to S. nigrum.

Highest concentration of Cr (52.9 mg/kg) was found in the soil samples related to Z. mauritiana, while its lowest concentration (35.6 mg/kg) was noted in the soil sample related to Z. nummularia. Under moderately oxidizing/reducing conditions and neutral pH values, Cr shows low mobility and Cr⁶⁺ adsorption decreases with increasing pH while that of Cr³⁺ increases with increasing pH (Gowd et al., 2010). Highest concentration of Cd (8.77 mg/kg) was noted in the soil sample taken from vicinity of O. dillenii. The permissible level for Cd in agricultural soil is 1–3 mg/kg (Kabata-Pendias and Pendias, 2001). Present results revealed that most of the soil samples contained Cd contents above this limit; it may be attributed to the anthropogenic activities in the urban environment. Highest concentration of Pb (54.0 mg/kg) was found in the soil samples related to O. dillenii, followed by those related to C. oppeca (47.6 mg/kg), S. nigrum (44.1 mg/kg), Z. nummularia (42.6 mg/kg), P. emblica (27.2 mg/kg), P. dactylifera (26.0 mg/kg), P. minima (18.0 mg/kg) and Z. mauritiana (17.7 mg/kg). In the present study, most of the soil samples were found to be slightly basic in nature showing mean pH value of 8.01.

Concentrations of the selected metals in the atmosphere from the study area have been reported by Shah et al. (2012); mean levels of Cd, Co, Cr, Cu, Fe, Mn, Pb and Zn in the air of the study area were reported at 3.43, 12.2, 7.18, 38.1, 1343, 38.8, 63.5 and 3325 ng/m³, respectively. Overall, Pb, Cd, Zn, Co, Cr and Cu were mainly associated with the anthropogenic enrichment in the atmospheric particulates of Islamabad, Pakistan (Shah and Shaheen, 2007; Shah et al., 2012).

3.3 Correlation study

Inter-relationships among selected metals in the fruits and soil samples were computed in terms of correlation coefficients (r), which revealed very strong relationships (p < 0.001) between following metal pairs in the fruits: Ca-Mn (r = 0.98), Ca-Sr (r = 0.95), Pb-Cd (r = 0.93), Mg-Mn (r = 0.92), Ca-Mg (r = 0.90), Mg-Sr (r = 0.79), Sr-Mn (r = 0.76), Fe-Pb (r = 0.70), Cu-Cr (r = 0.56) and Pb-Cu (r = 0.55). Some significant inverse associations were also observed as shown by negative correlations among various metal pairs: Pb with Ca (r = −0.76) & Mg (r = −0.74), Fe-Mn (r = −0.63), Co-Cr (r = −0.58), Fe-Ca (r = −0.57), Co-Cu (r = −0.52) and Fe-Sr (r = −0.46). These results indicated mutual relationships among Ca, Mg, Sr and Mn in the fruits samples while inverse associations of these metals were noted with Pb and Fe which showed common associations in the fruit samples. This aspect would be further explored by multivariate statistical analysis. Very strong positive correlations (p < 0.001) in the soil samples were noted between Mn-Sr (r = 0.89) and Ca-Sr (r = 0.80), followed by significant positive relationships between Mg-Cd (r = 0.70), Fe-Mn (r = 0.63), Ca-Mg (r = 0.59), Mg-Sr (r = 0.52) and Mn-Cd (r = 0.49). The correlation study thus indicated common variations of these metals in the soil. Some significantly negative correlations among the metals were also noted: Sr with Fe (r = −0.74) & Pb (r = −0.64), Fe with Ca (r = −0.70) & Zn (r = −0.65), Mn with Ca (r = −0.54) & Pb (r = −0.77), and Pb with Cd (r = −0.62). The inverse relationships among these metals revealed their divergent variations in the soil samples. Although very complex in nature, the correlation study suggested that Ca, Mg and Sr find their way through common sources in soil while Fe and Mn constitute another common group based on mutual distribution.

3.4 Bioaccumulation factor

Accumulation of the metals in the plants was assessed by bioaccumulation factor (BAF) which helps in comparing the ability of different plants in taking up metal from soil (Kovacik et al., 2012; Gebrekidan et al., 2013). In the present study most of the fruits species revealed relatively low BAF values (on the average) which showed limited ability of the plants to accumulate the metals (Table 4). Highest accumulation of Ca, Mg and Mn was observed in O. dillenii while S. nigrum and P. dactylifera revealed maximum BAF for Cr and Zn, respectively. Maximum accumulation of Co, Sr and Pb was observed in Z. mauritiana, whereas P. minima showed comparatively higher accumulation of Cd, Cu and Fe from the soil. Most of the metals exhibited relatively lower BAF values (below 1.0) in the fruits except Co and Pb, which showed somewhat higher BAF values (above 1.0 in most of the cases). Consequently, the bioaccumulation of Co and Pb indicated uptake and storage of the metals in the fruits samples of the plants grown in the urban environment. Overall, based on the average BAF of all fruit samples, plants were most efficient in taking up Co (1.204), followed by Pb (0.978), Mg (0.753), Zn (0.522), Ca (0.489), Cd (0.432), Cr (0.337), Cu (0.282), Sr (0.431), Mn (0.0291) and Fe (0.005).

3.5 Ecological risk assessment

The ecological risks associated with the metal levels in the soil were evaluated in terms of the contamination factor (CF) and degree of contamination (C_deg) and their results were interpreted as proposed by Hakanson (1980): CF < 1 = low contamination, 1 ≤ CF < 3 = moderate contamination, 3 ≤ CF < 6 = considerable contamination, 6 ≤ CF = very high contamination, C_deg < 8 = low degree of contamination, 8 ≤ C_deg < 16 = moderate degree of contamination, 16 ≤ C_deg < 32 = considerable degree of contamination, 32 ≤ C_deg = very high degree of contamination. The CFs of the metals in the soil are shown in Fig. 2 which revealed that Mg and Fe showed low contamination while Ca, Cr, Mn, Co, Zn and Sr exhibited moderate to considerable contamination. However, Cu and Pb showed considerable to very high contamination and Cd demonstrated very high contamination in the soil samples. The C_deg was also calculated and it showed a range of 15–155 with a mean value of 53; thus, it fluctuated from moderate degree of contamination to very high degree of contamination but on the average basis it indicated very high degree of contamination in the soil.

Close

Figure 2

Contamination factors of selected metals in the soil samples.

Export to PPT

Enrichment factors (EFs) of selected metals were considered to assess the anthropogenic intrusions of the metals in the soils. If EF approaches unity or less, the element is considered crustal in origin; however, the element with EF higher than 20 is considered to originate primarily from anthropogenic sources (Sutherland, 2000). Fig. 3 shows the minimum, mean and maximum values of EFs for the metals in soil samples. Average EFs of the metals were as follows: Cd (557) > Pb (40) > Sr (23) > Co (19) > Zn (17) > Cu (12) > Mn (8.9) > Ca (7.9) > Cr (6.9) > Fe (2.4). These values were interpreted as suggested by Sutherland (2000) and Loska et al. (2004); EF < 2 showed deficiency to minimal enrichment; EF = 2–5 indicated moderate enrichment; EF = 5–20 exhibited significant enrichment; EF = 20–40 demonstrated very high enrichment; and EF > 40 revealed extremely high enrichment. In the present study, mean values of EF for Cd and Pb were greater than 40 indicating extreme enrichment of these metals in the soil samples which may be linked with excessive anthropogenic uses and uncontrolled emissions of the metals in urban environment. The metals were mainly contributed by traffic emissions and other anthropogenic activities, such as industrial emissions, fertilizers, waste incineration and fossil fuel burning. Both metals are relatively volatile, and thus can also undergo long-range transport (Dragovic and Mihailovic, 2009). Among rest of the metals, soil samples were found to be significantly enriched by Ca, Cu, Co, Cr, Mn, and Zn, whereas highly enriched by Sr. Therefore, EFs revealed significant anthropogenic enrichment of most of the metals in the soil samples from local urban areas.

Close

Figure 3

Enrichment factors of selected metals in the soil samples.

Export to PPT

3.6 Principal component analysis

Multivariate principal component analysis (PCA) was applied to the metal data pertaining to the fruit samples using varimax normalized rotation of the data set and the results are presented in Table 5. Three significant principal components (PCs) with eigenvalues greater than 1.0 were obtained explaining more than 90% variance of the data. First PC explaining highest variance of the data (43.89%) showed significantly elevated loadings for Ca, Mg, Mn and Sr while PC 2 exhibited maximum loadings for Cd, Cr, Cu and Zn. Third PC revealed significant loadings in favour of Pb, Fe and Co. First PC was mostly contributed by the crustal materials and hence predominantly natural in origin. These findings are well supported by the CF and EF results discussed above. Second PC indicated mixed contributions of natural and anthropogenic sources such as fertilizers, pesticides and domestic wastes. The third PC was mostly derived from anthropogenic activities such as automobile/industrial emissions and domestic wastes. Although Fe is one of the major constituents of the soil most of its lithogenic form is not bioavailable while the anthropogenic contributions are generally bioavailable and plants can assimilate them readily. A mutual PC of Fe with Pb and Co indicated the anthropogenic contributions of Fe in the soil as also supported by the EFs in the previous section. Overall, multivariate PCA revealed significant anthropogenic contributions of some metals in the fruit samples which may be of concern to the consumers.

3.7 Health risk assessment

The calculated values of health risk index (HRI), target hazard quotient (THQ) and hazard index (HI) for the metal levels in the fruits of medicinal plants are shown in Table 6. The HRI values of Mg, Sr, Fe, Zn, Cu, Cr and Cd in each fruit species were less than unity (1.0), which is considered to be safe for human consumption. Nonetheless, the HRI values for Pb, Co and Mn were greater than unity for majority of the plant species; therefore, the consumers are at risk with respect to these metal contents in the fruits, which may be associated with adverse health effects (Abbasi et al., 2013). The HRI value of Ca was also below unity for most of the plant species except O. dillenii which exhibited significantly higher HRI value. The health protection standard of lifetime risks for THQ and HI is 1.0 (USEPA, 2006). As shown in Table 6, the THQ values for all of the metal levels in the medicinal plants were substantially lower than the permissible limit (1.0); therefore, the present study revealed that the consumption of these fruits would not result in any significant non-carcinogenic risks related to these metals to the consumers. A significantly lower value of HI (0.0112) demonstrated that the consumption of these fruits was overall safe and would not result in any long-term non-carcinogenic risks to the local consumers.