This study was conducted at the district of Jhansi, a known historic place in Uttar Pradesh State of India. The city has a historical background because the empress “Rani Lakhsmi Bai” ruled this city in the mid-19th century. This study area is situated between 25°07” to 25°57″ N and 78°10” to 79° 25″ E, in Jhansi city, which has an elevation above the mean sea level of 284 m. The average annual rainfall of this city is 885 mm and type of climate is sub-humid with hot and dry summer and cold winter (CGWB, 2017). Seven sampling sites were chosen for collection of samples on the basis of exposure to vehicular emission from the entire study area (Figure 1). A total of three national highways including NH-27 (from Porbandar to Silchar), NH-44 (from Srinagar to Kanyakumari), and NH-39 (from Jhansi to Ranchi) passed through the city. NH-27 adjoins the Jhansi to Kanpur which is a major financial and industrial center of North India and also called the ‘Leather City of the World’. The vehicles coming from NH-44 and NH-39 pass through the selected sampling points to Kanpur.

The soil and vegetable samples (coriander, onion, and tomato) were collected during spring and summer seasons from seven farmers’ fields near the national highway NH-27, Jhansi city, as depicted in Figure 1. The vegetable samples were collected on the basis of availability in all farmers’ fields at the same time. First of all, the soil samples were randomly collected in triplicate at a 0–15 cm depth using a spade from all selected sampling points. Then, the collected subsamples were mixed together to attain a 1 Kg of representative sample. Finally, soil samples were taken into labeled zippered polyethylene (PE) bags to prevent them from further contamination and immediately taken to the laboratory for further analysis. Similarly, the vegetable samples (edible parts) were also collected from same fields in triplicates and stored in pre-labeled zippered PE bags and taken to the laboratory for further processing. Details of vegetable samples are given in Table 1.

The soil samples were dried in air at room temperature to attain a constant weight and ground using mortar and pestle to obtain fine-textured powder. However, in case of vegetables, the collected edible parts were first cut into small pieces using a pre-cleaned stainless steel knife and then dried in the laboratory oven at 75°C for 3 days. The dried vegetable samples were uniformly ground using mortar and pestle to fine-textured powder. The grounded fine-textured samples were stored in clean PE bags at room temperature for heavy metals and other parameters analysis. The heavy metals contents were analyzed by atomic absorption spectrometry method using Perkin-Elmer AAnalyst 400, USA model after digestion of samples. The digestion (wet oxidation) process for soil and vegetables samples was done with the help of solution which was prepared by mixing one part of perchloric acid (HClO₄) and three part of conc. Nitric acid (HNO₃) (Guo et al., 2006; Singh and Praharaj, 2017).

The analysis of samples was done for quality control and assurance. The analytical-grade chemicals and reagents were used during entire analytical procedures. Double distilled water (DDW) was applied to prepare the required reagents, standards, and analytical samples processing and dilution. Calibration curves were produced for each investigated heavy metal. Blanks were also analyzed frequently to ensure analytical quality. Procedural washing at regular intervals was done using DDW during the entire analysis to avert any contamination in the equipment. The values of instrumental detection limit (IDL) were lower than the values of method detection limit (MDL) and method quantification limit (MQL) which signaled the good sensitivity of the instrument (atomic absorption spectrophotometer) for heavy metals estimation.

BCF of heavy metals from soils to vegetables was assessed by computing the ratio of the concentration of each heavy metal in vegetable’s edible parts and the concentration of corresponding heavy metals in the respective soil. If BCF is less than 1, it suggests less movement of heavy metals from soil to vegetables. Conversely, BCF of more than one indicate the higher uptake of heavy metals by tested vegetable from soil (Sharma et al., 2018). It was assessed by following Eq. 1. B i o − c o n c e n t r a t i o n   ( B C F )   =   C V C S . (1) Where, C_v is the amount of heavy metals in vegetables on dry weight (DW) basis (mg/kg dw), while C_s is the amount of heavy metals (mg/kg dw) in soil samples.

The evaluation of possible level of any potentially harmful health effects occurring over a specified time period is known as “risk assessment” (Mohammadi et al., 2019). Based on the assessment of risk level, it can be categorized into carcinogenic and non-carcinogenic risks (Wongsasuluk et al., 2014). Carcinogenic risk assessment is a method of estimating the incremental probability of developing cancer over an individual’s lifetime due to exposure to a potential carcinogenic metal (USEPA, 1991). According to IARC (2014), Cd, Ni, and Co were considered as carcinogenic metals in this study that have the potential to cause cancer when an individual is exposed to them for a lifetime (70 years). However, quantitative assessment of carcinogenic risk from oral exposure to these metals was not performed under the Integrated Risk Information System (IRIS) program (USEPA, 2021). Therefore, the carcinogenic risk assessment was not performed due to non-availability of oral slope factor (SF_O) for these metals.

The data obtained from the experimental analysis was simplified through principal component analysis (PCA) to speculate the sources of heavy metals in the vegetables of the study area. It was analyzed by the software, Statistical Package for Social Sciences (SPSS, Version 20.0). PCA involves extracting linear composites of observed variables. It allows the dataset for dimension reduction while keeping a maximum amount of information.

The concentration levels of heavy metals in soil showed a higher inequality. The average amount of heavy metals in soil decreased in the sequence of Zn > Ni > Pb > Mn > Cu > Co > Cd (Table 2). The levels of Ni, Pb, Cu, and Zn were noted under the safe limit of India’s standards as reported by Awasthi (2000) and USEPA (2002). However, Cd concentration was exceeding USEPA (2002) standards but under the India’s standards as reported by Awasthi (2000) for agricultural soils. It is also worth noting that the average contents of Ni, Co, Cu, and Mn were less than the background values of soil of India while Cd, Pb, and Zn contents were higher than the background values of soil of India (Table 2). The Cd, Co, and Cu concentrations were highest at sampling site three whereas the accumulation of Zn and Pb was greatest by the soil of sampling site 5. Furthermore, the accumulated amount of Ni and Mn was richest in the samples picked up from sampling site 2 and 1, respectively. The maximum concentrations of Cd and Cu correspond with the results reported in a previous study (Ashraf et al., 2021). The concentration of Pb may be high due to the accumulation of pollutants from vehicles. The use of lead arsenate pesticides can also increase the concentration of Pb in the soil. The mean concentration of Pb, Co, Cu, and Ni attained in the present study was higher than those from the values reported by Muhammad et al. (2021) for agricultural soil samples. In contrast, it was very much lesser than the values reported by Moghtaderi et al. (2018) (Table 3).

The sequence of average concentrations of heavy metals in coriander exhibited the following pattern: Zn > Mn > Cu > Pb > Ni > Co > Cd. The concentration of Cu was observed highest at sampling site S5 and lowest at sampling site S4. The results of this study were several folds lower than the results obtained by Sharma et al. (2016) and Tefera and Teklewold (2021) for coriander leaves and seeds, respectively. In the present study concentration of Mn was found lower (21.65 mg/kg dw) than the value reported by Ramesh and Murthy (2012). The Cd concentration obtained in the current study (0.23 mg/kg dw) exceeded the permissible limit at all sites. When compared with the previous research findings, the Cd values obtained in this study were less than the values reported by Sharma et al. (2016). However, it was higher than that of values reported by Kladsomboon et al. (2020). In our study, Pb concentration was found much higher at all sites than the permissible limit of 0.1–0.3 mg/kg dw compared to the value reported by Gebeyehu and Bayissa (2020). However, the present study results resembled the results obtained by Khan et al. (2018). The Ni content in coriander samples at all sites was found well within the allowable limit of 10 mg/kg dw reported by Gebeyehu and Bayissa (2020) for vegetables. Baig et al. (2018) reported that Ni concentration ranged from 6.14–9.43 mg/kg dw in the coriander leaves collected from Punjab, Pakistan (Khan et al., 2018). The mean value of Co was found to be 0.47 mg/kg dw. Sharma et al. (2016) reported the Co concentration up to 69 mg/kg dw in coriander from Punjab, India.

In onion, heavy metals concentration was exhibited in the order of Zn > Mn > Cu > Pb > Ni > Co > Cd. The concentration of Cu ranged between 2.64 and 13.42 mg/kg dw with a mean value of 6.25 mg/kg dw. Filimon et al. (2021) reported a Cu concentration of 3.94 mg/kg dw in onions collected from a copper mining area in Eastern Serbia. The concentration of Mn in onion in the present study (20.15 mg/kg dw) is very much higher than reported in Romania (0.33–4.07 mg/kg dw) (Manea et al., 2020), Ghana (0.07–0.015 mg/kg dw) (Ametepey et al., 2018); Eastern Serbia (9.96 mg/kg dw) (Filimon et al., 2021), and Nigeria (4.26 mg/kg dw) (Muhammad et al., 2021). The range of Zn concentration in the present study was close to the results (11.4–25.5 mg/kg dw) obtained by Amin et al. (2013). The greatest amount of Zn in the present study was noticed at S6. The average concentrations of Cd in both seasons were much higher than the permissible limit of 0.05 mg/kg dw set by FAO/WHO (2019) for bulb vegetables. In the present work, the range and mean values of Cd in onion were in line with the work done by Islam et al. (2016), where the range of Cd was 0.06–0.25 mg/kg dw with an average value of 0.14 mg/kg dw. The concentrations of Pb in onion at all sites exceeded the allowable limit of 0.1 mg/kg dw prescribed by FAO/WHO (2019) for bulb vegetables. The mean values of Pb obtained in the present study resemble the results obtained by Islam et al. (2016). Contrary to this, the concentration of Ni was several folds lower than reported in France (4.74 mg/kg dw) (Cherfi et al., 2016). The mean concentration of Co obtained in the present study (0.32 mg/kg dw) was much lesser than the results reported by Muhammad et al. (2021).

In tomato, heavy metals accumulation was found in order of Zn > Mn > Cu > Ni > Pb > Co > Cd as shown in Table 2. However, Cd concentrations exceeded the allowable limit of 0.05 mg/kg dw as notified by FAO/WHO (2019) for fruit vegetables. The amount of Pb and Ni was found to exceed the allowable limit, as described by Gebeyehu and Bayissa (2020). Co and Mn concentrations were observed many folds less than the permissible limit of FAO/WHO (2019). The level of Zn in tomatoes varied from 7.81 to 23.92 mg/kg dw. In this investigation, Zn in tomatoes was found higher than the value (3.57–9.25 mg/kg dw) reported in Algeria by Bounar et al., 2020. The value for Zn was slightly lower than that reported in Iran (29.80 mg/kg dw) by Zafarzadeh et al., 2018. The Cu concentration in all samples was well within the prescribed limit of 0.5 mg/kg dw.

Overall, the ranking of heavy metal concentrations investigated vegetables was as follows: coriander > onion > tomato. It is worth noting that the leafy vegetable coriander has accumulated more amounts of heavy metals followed by onion bulbs and tomato fruits. Similar trends were also reported by Letshwenyo and Mokokwe (2020), Gan et al. (2017), Sharma et al. (2016), and Zhou et al. (2016).

A comparison of the concentrations of Cd, Pb, Ni, Co, Zn, Cu, and Zn in soil and vegetables grown in the present study area with those reported in the literature shows that the heavy metals contents in the study area were lower than those collected from industrial areas or irrigated with wastewater. In contrast, the levels of heavy metals in the study area were higher than those collected from non-industrial areas and local market (Table 3). The heavy metals concentrations in vegetable samples collected from local market might be less due to the fact that local markets have the vegetables from different areas.

The heavy metal BCF is directly proportional to heavy metals in vegetables and their accumulation efficiency. However, it is vice versa (inversely proportional) in the case of soil. Therefore, a BCF less than 0.1 suggest that a vegetable eliminates the respective heavy metal from its tissues (leaf, stem, root, fruit, and seed) (Bounar et al., 2020). However, the BCF ≥0.5 indicates that the soil and vegetables have been started to get contaminated by anthropogenic activities.

BCF of heavy metals were observed in decreasing order of Mn > Zn > Cu > Cd > Pb > Ni > Co with the highest and lowest values of 1.42 and 0.05 in coriander (Figure 2). The BCF of Cd, Pb, Ni, and Co was ≤0.2 in coriander at all sampling sites. In contrast, BCF of Cu at sampling site 2 (0.52) indicates that the site has been started to get contaminated by anthropogenic activities. Hence, it needs an attention to lower the heavy metals concentration in the area. However, the BCF of Mn and Zn has surpassed the value of one at almost all selected locations, revealing that the accumulation of heavy metals in coriander was greater than the accumulation in soil.

BCF of heavy metals in the onion bulbs were found in reducing order of Mn > Zn > Cu > Cd > Pb > Co > Ni. It is worth noting that for the onion samples at all sampling sites, BCF values for Cd, Pb, Ni, and Co were <0.1 (Figure 2). However, the accumulation of Mn in onion was higher than the accumulation in the soil at all sampling sites except S3 and S4. The bio-concentration factor for Zn was higher than 0.50 at all sites except S3 which reveals that accumulation of Zn has been initiated in onion. Whereas BCF of Cu was less than 0.50 at all sites except S5 and S6. The BCF of heavy metals in tomato were ranked as Mn > Zn > Cu > Cd > Ni > Pb > Co (Figure 2). However, BCF of all heavy metals were below the value of one which signifies less accumulation of these heavy metals in tomato. The research findings revealed that heavy metals accumulation varies in these vegetables. However, it was found that leafy vegetable coriander accumulates greater amounts of heavy metals than the onion bulb and tomato fruits.

Principal component analysis by varimax rotation method was applied on the data set of seven heavy metals to assume the sources of these metals in vegetables. The data extracted from PCA is given in Table 4, including component matrix, rotated component matrix, extraction sum of squared loadings, rotation sums of squared loadings, and initial eigenvalues. The first three principal components (PCs) accounted for 81.83% of the total variability. The first PC (PC-1) explained 36.61% with significant + ve loadings of Mn (0.99), Cu (0.61), Zn (0.61), and Ni (0.59). The contamination of Cu can occur due to the friction material used in the brake system of vehicles (Adamiec et al., 2016). However, tire wearing and corrosion of galvanized parts might contribute to the raised concentration of Zn (Taylor and Kruger, 2020). Currently, Zn is preferred for making wheel balancing weights to avoid leaded-wheel balancing weights. Besides the vehicular emission, a manufacturing unit of Portland cement (Mycem) is also situated in the study area which might be responsible for an elevated content of Cu, Ni, Co, and Pb. The cement plants use these metals as catalysts, modifiers, and dryers in the manufacturing process (Jan et al., 2010). In addition to this, a single super phosphate fertilizer industry is also located in the study area which might be responsible for the increased concentration of Zn and Pb in the study area. These facts signify that these heavy metals exist in the vegetables due to human-induced activities. It may include frequent chemical fertilizers and pesticides, vehicular emission, industrial discharge, etc. The contribution of PC-2 was 27.73% to the total variance with high + ve loadings of Co (0.68) and Pb (0.64). Contrary to this, PC-2 was negatively loaded with Zn and Ni. However, the data showed that Cd and Co had a mixed source of origin in the study area (Figure 3).

The order of heavy metals with respect to EDI in coriander and onion is Zn > Mn > Cu > Pb > Ni > Co > Cd. However, for tomato, EDI of heavy metals was found in order of Zn > Mn > Cu > Ni > Pb > Co > Cd (Table 5). The results revealed that EDI of Cd, Pb, Zn, and Cu for coriander, onion, and tomato were within the provisional maximum tolerable daily intake (PMTDI) values as notified by FAO/WHO (2019). The highest and lowest EDI of Cu, Mn, Zn, Cd, Pb, Ni, and Co in coriander were 3.86E-03 at S2 and 2.11E-03 at S6, 1.41E-02 at S2 and 6.77E-03 at S6, 2.42E-02 at S7, and 1.49E-02 at S1, 1.63E-04 at S2 and 7.95–05 at S6, 2.07E-03 at S4 and 4.31E-04 at S5, 7.70E-04 at S2 and 2.56E-04 at S3, and 5.65E-04 at S2 and 3.54E-05 at S5, respectively (Figures 4A,B). It is worth noting that the EDI of all metals was highest at S2 except Zn and Pb in coriander which indicated the maximum involvement of human activities in the area. However, the EDI of Cu, Mn, Zn, Cd, Pb, Ni, and Co in onion were varied from 3.23E-03–8.68E-03, 9.11E-03–2.47E-02, 1.1. E-02–2.75E-02, 4.18E-06–1.73E-04, 2.00E-04–1.32E-03, 1.58E-04–8.93E-04, and 4.14E-05–6.13E-04, respectively (Figures 5A,B)It is worthy to note that the sequence of EDI of heavy metals in coriander and onion was similar, but the contribution was different. The maximum and minimum EDI values for Cu, Mn, Zn, Cd, Pb, Ni, and Co, of tomato, was 7.10E-03 at S2 and 2.75E-03 at S7, 1.80E-02 at S2 and 1.05E-03 at S1, 1.93E-02 at S3, and 8.52E-03 at S4, 2.43E-04 at S1 and 2.36E-05 at S5, 1.34E-03 at S2 and 3.81E-05 at S7, 3.38E-03 at S7 and 1.64E-04 at S5, and 5.45E-04 at S2 and 1.85E-05 at S6, respectively (Figures 6A,B).

The THQ of heavy metals resulting from coriander leaves intake was found to follow decreasing order of Pb > Mn > Cd > Zn > Ni > Co > Cu. In onion intake THQ of heavy metals was followed similar trends as Mn > Pb > Cd > Zn > Ni > Co > Cu. However, the sequence of THQ of heavy metals in tomatoes followed a pattern in the order of Mn > Cd > Pb > Zn > Ni > Cu > Co (Table 6). The THQ of Mn was highest in onion samples. It is noticeable that the highest THQ value was noted for Mn in onion. Despite the highest THQ of Mn in onion, it was not exceeding the safe value of 1. THQ of all analyzed heavy metals in coriander, onion, and tomato was under the safe value of 1, indicating that the vegetable consumption in these areas will not have any significant non-carcinogenic effects on humans.

The HRI value reflects the cumulative effects of various heavy metals in coriander, onion, and tomato consumption. Thus, it is evident from HRI that coriander, onion, and tomato consumptions are risk-free in the study area (Table 6). However, HRI value in coriander was slightly higher than the safe limit of one at S3 and S4 with their respective values of 1.03 and 1.01. Hence, it needs urgent attention to lower the heavy metals concentration in these sampling sites; otherwise, it may pose serious health hazards to humans in the near future.