One of Qatar’s most remarkable characteristics is its arch surface expression. Another notable characteristic is that the peninsula is covered with pebbles and sand that have detached from outcropped limestone (Peng et al., 2016; Al-Sulaiti et al., 2017). While there is insufficient knowledge about lithological events in Qatar, the country’s exterior predominately rests on layers of clay and limestone (Alsafran et al., 2021; Fourniadis, 2010). Earlier studies on metal(oid) remediation in Qatar’s natural soil have found that the concentrations of some elements were below detection limit (Usman et al., 2019; Al-Thani and Yasseen, 2020). Therefore, no proof suggesting that the lithological events magnify metal concentrations exist. This research used irrigated, open farms located in central and northwestern Qatar (Figure 1). From January to April 2020, 70 km away from the center of Doha, 10 different locations were chosen to collect 150 vegetable samples (50 each for rocca, coriander, and parsley). The locations of the samplings were randomly chosen (Figure 1) and their coordinates were documented (Supplementary Table S1). The vegetables cultivated from the locations included mint, parsley, vegetable silk, spinach, silk, lettuce, coriander, dill, onion, and rocca. Imported soil, peat moss, and compost manure were commonly used to improve the fertility of the soil.

The edible parts of the vegetable samples (rocca, coriander, and parsley) were collected into pre-cleaned and sterilized separate polyethylene bags for plant samples. About 1 kg of each of the vegetables was separately collected from five randomly selected subsampling sites and pooled together to form a composite. The rotten portions were removed, and the remaining samples were carefully packed and immediately transported to the laboratory for further processing and analysis.

In the laboratory, the samples were treated with acid (0.01% HCl) and thoroughly washed with tap and distilled water to remove soil and particulate matter. To facilitate drying, the cleaned samples were chopped into small pieces using a plastic knife. Subsequently, the samples were air-dried in a hot air oven at 50–60°C for 24 h to remove moisture and maintain constant mass. The dried materials were grounded into a fine powder using a mortar and pestle and passed through a 2 mm mesh size sieve. The sieved samples were finally stored in polyethylene bags and kept in desiccators until digestion and analysis.

Analytical grade hydrochloric acid (HCl), nitric acid (HNO₃), and hydrofluoric acid (HF) were used to prepare the samples for the microwave-assisted digestion process. Before digestion, all glassware were washed with HCl and deionized water. These samples were gradually agitated and moved into a Microwave Digestion System MARS 6 (CEM Corporation, USA) at rotating temperatures. At the end of digestion cycles, the digests were transferred into 150 ml flasks, cooled, and filtered. Lastly, deionized water was used to produce 150 ml of each of the samples.

After digestion, the concentrations of potential toxic metal(oid)s were determined by interpolating specimens into an Inductively Coupled Plasma (ICPMS) NexIon 300D, (PerkinElmer, USA). Conforming to the USEPA classifications, along with previous reports (Peng et al., 2016; Al-Thani and Yasseen, 2020), public health risks were considered when choosing the type of analyses to do (Usman et al., 2019; Usman et al., 2020b). In order to ensure valid, quality, controlled results, the National Institute of Standards and Technology for apple leaves 1515, laboratory duplicates at every 10th sample, and reagent blanks were used. The % recovery of the quantified metal(oid)s in the certified material were between 94.5 and 102%. For reagent blanks and lab duplicates, the concentrations (mg/kg) were below the detection limit and corresponded to that of the samples (±0.94 mg/kg), respectively.

The metal(oid) mean concentrations of three leafy vegetables (rocca, coriander, and parsley), as well as the estimated daily consumption of the vegetables (g), was used to calculate the element's estimated daily intake (EDI) using the equation described by Gebeyehu and Bayissa (2020). E D I = E f × E d × F i r × C m × C f B w × T a × 0.001   , where E_f = exposure frequency (365 days/year); E_d = exposure period (for men 77 years, women 81 years), which is equivalent to the average life span; F_ir = average vegetable consumption (240 g/person/day), as defined by the World Health Report (WHO, 2002) for low fruit and vegetable intake. C_m = metal concentration (mg/kg dry weight); Cf = concentration conversion factor for fresh vegetable weight to dry weight (0.085) (Arora et al., 2008); B_w = body weight (85.9 kg for men, 74 kg for women); and T_a = average exposure period (Ed 365 days/year), and 0.001 stands for unit conversion factor.

The cancer risk (CR) presented to human health by individual potential carcinogenic metals was calculated. Then, the cumulative cancer risk (TCR), which may promote carcinogenic effects depending on exposure dose, was then calculated from ingestion of metal(oid)s (Cr, Ni, As, Pb, and Cd). C R = E D I × C S F , TCR = ∑ n = 1   i C R n ;   i   =   1 ,   2 ,   3 , ....... n , where CR = cancer risk over a lifetime by individual heavy metal ingestion, EDI = estimated daily metal intake of the population in mg/day/kg body weight, CSF = oral cancer slope factor in (mg/kg/day), and n is the number of heavy metals considered for cancer risk calculation. The CSF values of Cr, Ni, As, Pb, and Cd were 0.5, 1.7, 1.5, 0.38, and 0.01 mg/kg/day, respectively (Gebeyehu and Bayissa, 2020). For single carcinogenic metals and multi carcinogenic metals, the permissible limits are 10⁻⁶ and < 10⁻⁴, respectively (Tepanosyan et al., 2017).

The effects of local farm location (10 sites), vegetable crops (three crops), and their interactions on the metal(oid) concentrations were examined using the analysis of variance of a factorial experiment. Paired mean comparisons were performed using Tukey’s test when the F-test indicated significant effects at the level of p < 0.05. The relationship of elemental concentrations in plant samples was investigated by the means of principal component analysis (PCA). All observation data were mean-centered and standardized prior to PCA, and only principal components with eigenvalues > 1 were considered (Kaiser and Rice, 1974). All statistical analyses were performed using Minitab Computer Software ver. 17.

Since vegetables are valuable components of the everyday human diet, it is critical to maintaining their quality. If grown in a contaminated environment, they can accumulate high metal(oid) concentrations that could negatively affect human health after consumption (Alam et al., 2003). Potential toxic metal(oid)s accumulate more quickly in edible portions of vegetables, particularly leafy vegetables, than in fruit and grain crops (Mapanda et al., 2005). Their concentrations vary between vegetables due to their differential vegetable absorption ability for different elements (Singh et al., 2010). The levels of metal(oid)s in vegetable samples (rocca, coriander, and parsley) grown in the farmlands in different municipalities in Qatar were examined, and the findings are summarized in Table 1.

The contents of V, Cr, Ni, Cu, As, Cd, and Pb in rocca varied from 0.65 to 50.95, 1.33 to 15.20, 0.00 to 9.50, 7.34 to 20.45, 0.19 to 37.11, 0.10 to 1.90 and 0.94 to14.37 mg/kg, respectively; in coriander 1.06 to 48.52, 1.49 to 17.82, 0.00 to 10.82, 9.16 to 22.64, 0.32 to 43.24, 0.00 to 1.93, and 1.11 to 13.09 mg/kg, respectively; in parsley 1.03 to 44.05, 1.33 to 14.77, 0.00 to 8.84, 11.20 to 25.62, 0.00 to 41.81, 0.00 to 5.13 and 1.31 to14.29 mg/kg, respectively (Table 1). Overall, the mean concentrations of V, Cr, Ni, Cu, As, Cd, and Pb in rocca are17.09, 6.41, 1.70, 13.04, 14.72, 0.90, and 6.36 mg/kg, respectively; in coriander are 15.91, 6.03, 1.38, 15.30, 16.86, 0.43, and 5.00 mg/kg, respectively; and in parsley are 16.25, 6.26, 2.19, 17.97, 16.60, 0.51, and 5.46 mg/kg, respectively. The overall accumulation of metal(oid)s were as follows for rocca: V > As > Cu > Cr > Pb > Ni > Cd; coriander: As > V > Cu > Cr > Pb > Ni > Cd; and parsley: Cu > As > V > Cr > Pb > Ni > Cd. The mean levels of V, Cr, As, Cd, and Pb in the studied vegetables were found to be higher than the recommended value proposed by the WHO/FAO, indicating that they are potentially unsafe to consume. Consistent with our findings, other studies involving different leafy vegetables (Kananke et al., 2014) including coriander (Souri et al., 2018), and parsley (Delbari and Kulkarni, 2014) found that the levels of As, Cd, Cu, and Cr were significantly higher than the recommended safe limits.

Our results are further supported by the findings of Gupta et al. (2021), Chang et al. (2014), Luo et al. (2011), and Zhuang et al. (2009), all of which clearly showed that leafy vegetables accumulate potential toxic elements, and to a greater degree than non-leafy vegetables. Due to the large surface areas of their leaves, the leafy vegetables were often exposed to metal(oid)s by indirect means such as dust and rainwater. Leafy vegetables could absorb higher concentrations than typical plants due to their high growth rates (Khan et al., 2013). The elements accumulation in vegetable samples may be due to chemical fertilizer usage or the discharge of untreated solid and/or fluid waste from factories in the surrounding areas (Alsafran et al., 2021). Toxic levels of these metal(oid)s in the vegetables studied may harm the health of the residents who stay nearby. As a result, vegetables grown in suburban areas are heavily contaminated with these elements, both noncarcinogenic and carcinogenic, harmful to human health. As a result, it is recommended that their contents in this area’s food crops be monitored and assessed regularly.

In order to interpret their multivariate relationships and to classify their potential sources, the metal(oid) concentration in the vegetables was subjected to the principal component analysis (PCA). The PCA components such as eigenvalue, variance (%), cumulative (%), and PCA biplot of the elements in all vegetables are presented in Figure 2 and Supplementary Table S2. The PCA of the metal(oid) concentrations in the vegetable samples revealed seven principal components (PCs), two of them showed eigenvalues > 1.00, which is considered significantly important. These two principal components (PCs) explained 65.4% of the overall variability (Figure 2; Supplementary Table S2). PC1 accounted for 40.4% of the overall variability, and data showed a significant positive correlation of PC1 with the following elements; V, Cr, Ni, As, Cd, and Pb. The strongest one was V (0.511), followed by Ni (0.474), and Cd (0.431), which indicates an anthropogenic source, which in part, and could be due to active oil and gas production. Past research has implied that the concentrations of these elements in Qatar vary across the country, which can be attributed to the most active human activities of the surrounding areas (Usman et al., 2019; Al-Thani and Yasseen, 2020; Usman et al., 2020b). In contrast, PC1 exhibited a weak negative linkage with Cu. PC2 accounted for 25% of the overall variability, presented a moderate negative one with Cr and Pb, while a significant association with As (0.561), which may be released from the emissions created by human undertakings (Ying et al., 2016; Zhang et al., 2018).

The dietary exposure approach to vegetable consumption is a valid method for examining a population’s diet regarding nutrient, bioactive component, and contaminant intake levels, providing critical information regarding potential nutritional deficiencies or food contamination exposure (WHO, 1985). Because of the increasing awareness of the connection between diet and human health, people are eating more green vegetables than ever before. Food safety and sustainability have become critical issues due to the rapid cultivation and use of green plants (Rahmdel et al., 2018). The metal(oid) mean concentration in each vegetable, and their respective consumption rates were used to calculate the EDI. The results for men and women are presented in Table 2. The mean EDI values for men of V, Cr, Ni, Cu, As, Cd, and Pb through the consumption of rocca were 4.06 × 10⁻³, 1.52 × 10⁻³, 4.04 × 10⁻⁴, 3.10 × 10⁻³, 3.50 × 10⁻³, 2.14 × 10⁻⁴, and 1.51 × 10⁻³ mg/day/kg bw, respectively; coriander were 3.78 × 10⁻³, 1.43 × 10⁻³, 3.28 × 10⁻⁴, 3.63 × 10⁻³, 4.00 × 10⁻³, 1.01 × 10⁻⁴, and 1.19 × 10⁻³ mg/day/kg bw, respectively; while the corresponding values in parsley were 3.86 × 10⁻³, 1.49 × 10⁻³, 5.21 × 10⁻⁴, 4.27 × 10⁻³, 3.94 × 10⁻³, 1.20 × 10⁻⁴, and 1.30 × 10⁻³ mg/day/kg bw, respectively (Table 2). The EDI of individual metals for men due to the consumption of rocca were in the following order V > As > Cu > Cr > Pb > Ni > Cd; coriander As > V > Cu > Cr > Pb > Ni > Cd; and in parsley Cu > As > V > Cr > Pb > > Ni > Cd. Similarly, for women the EDI values for V, Cr, Ni, Cu, As, Cd, and Pb due to the consumption of rocca were 4.71 × 10⁻³, 1.77 × 10⁻³, 4.69 × 10⁻⁴, 3.59 × 10⁻³, 4.06 × 10⁻³, 2.48 × 10⁻⁴, and 1.75 × 10⁻³ mg/day/kg bw, respectively; coriander were 4.39 × 10⁻³, 1.66 × 10⁻³, 3.81 × 10⁻⁴, 4.22 × 10⁻³, 4.65 × 10⁻³, 1.18 × 10⁻⁴, and 1.38 × 10⁻³ mg/day/kg bw, respectively; and in parsley were 4.48 × 10⁻³, 1.73 × 10⁻³, 6.04 × 10⁻⁴, 4.95 × 10⁻³, 4.58 × 10⁻³, 1.39 × 10⁻⁴,and 1.50 × 10⁻³ mg/day/kg bw, respectively (Table 2). The EDI of individual metals for women as a result of consumption of rocca were in the following order V > As > Cu > Cr > Pb > Ni > Cd; coriander As > V > Cu > Cr > Pb > Ni > Cd; and in parsley Cu > As > V > Cr > Pb > Ni > Ni > Cd. The total EDI values for all metal(oid)s of interest as a result of rocca, coriander, and parsley consumption for men were found to be 1.43 × 10⁻², 1.45 × 10⁻³, and 1.55 × 10⁻² mg/day/kg bw, respectively, while for women, the values were found to be 1.66 × 10⁻², 1.68 × 10⁻² and 1.80 × 10⁻² mg/day/kg bw, respectively (Table 2).