A Multivariate and Geographic-Information-System Approach to Assess Environmental and Health Hazards of Fe, Cr, Zn, Cu, and Pb in Agricultural Soils of Western Saudi Arabia

Abstract

This study evaluates the environmental and health hazards associated with the presence of Fe, Cr, Zn, Cu, and Pb in agricultural soils from the Makkah region in western Saudi Arabia. Soil samples were collected from 32 farms predominantly cultivating dates and vegetables and analyzed for heavy metals (HMs) using inductively coupled plasma-atomic emission spectrometry (ICP-AES). Multivariate statistical analysis, Geographic Information Systems (GIS), and various contamination indices were employed. The average HM concentrations were arranged in descending order as follows: Fe (35.138 mg/kg), Zn (69.59 mg/kg), Cu (55.13 mg/kg), Cr (47.88 mg/kg), and Pb (6.09 mg/kg). Contamination indices indicated considerable enrichment of Cu and deficient to minimal enrichment for the other HMs, though a few individual samples showed higher enrichment factor (EF) values. Risk assessments revealed a low-level risk associated with HMs in Makkah soils. Multivariate analyses suggested that the HMs primarily originated from natural geological processes, with anthropogenic contributions particularly evident for Cu. Hazard index (HI) values ranged from 0.0003 to 0.0691 for adults and 0.003 to 0.6438 for children, remaining below the threshold of 1.0, which indicates no significant non-carcinogenic risk. Lifetime cancer risk estimates for Pb were below 1 × 10⁻⁶, while those for Cr ranged from 1 × 10⁻⁶ to 1 × 10⁻⁴, indicating tolerable carcinogenic risk levels with a few exceptions for Cr in children. This study is significant as it provides critical baseline data on HM contamination in agricultural soils in the Makkah region, offering insights into natural and anthropogenic contributions to soil pollution. The findings contribute to the broader understanding of environmental risk assessments and serve as a foundation for developing sustainable agricultural practices and targeted mitigation strategies to minimize health risks in regions with similar environmental conditions.

1. Introduction

The presence of harmful heavy metals (HHMs) in soil is a major issue in developing nations since it has enduring health consequences. Human activities have caused metal concentrations to grow in several environmental media [1,2]. Anthropogenic activities are the main contributors to localized pollution, including abandoned industrial sites, poor waste disposal, unregulated landfills, excessive use of agrochemicals, spills, and similar accidents. Unregulated mining and smelting practices are a significant cause of HM contamination in many locations throughout the world [3,4,5].

In addition, the presence of aromatic hydrocarbons and toxic metals, which are often found in oil products, contributes to the occurrence of localized pollution [6,7]. Soils in close proximity to roads often show elevated concentrations of HHMs, polycyclic aromatic hydrocarbons, and other contaminants [8,9,10]. Specific crucial trace elements such as Co, Cu, F, Mn, Mo, Ni, and Zn are essential in small amounts for diverse biological processes. Nevertheless, an overabundance of these vital HHMs might have detrimental effects on plant growth, potentially compromising the integrity and functionality of cellular structures [11,12]. In contrast, non-essential metals such as Pb, Cd, Hg, As, Cr, Ag, and Sb are harmful to both eukaryotic and prokaryotic life. The excessive accumulation of HHMs in the environment frequently results in substantial pollution of soil and water, giving rise to considerable worldwide environmental issues [13,14].

The western region of Saudi Arabia is distinguished by a multitude of Wadis, which are created by the runoff of transitory streams that originate in the mountains of the Arabian Shield and flow towards the Red Sea. The alluvial deposits found in these Wadi channels are crucial for providing a local source of groundwater [15,16]. The studied region is mostly defined by Torriorthents soil, which is a type of Entisols. This soil is primarily found in residuum or colluvium on slopes that are actively eroding, as well as in materials that are resistant to weathering. The soils in question are often shallow and consist of several types of soil, such as loamy sand, fine sandy loam, sandy loam, loam, or clay loam. Additionally, there are also gravelly variations in these soils [17,18].

Geographic Information Systems (GIS) (ArcGIS 10.8, QGIS 3.28) and multivariate statistical analysis are essential tools for evaluating the health and environmental risks posed by heavy metals (HMs) in agricultural soils. To determine possible HM sources, differentiate between anthropogenic and natural contributions, and find temporal and spatial trends in contamination levels, multivariate techniques like Principal Component Analysis (PCA), Cluster Analysis (CA), and correlation analysis are frequently employed [19]. By breaking down complicated statistics into digestible insights, these techniques can identify important pollutants for additional research and help comprehend the correlations between variables. By combining environmental, health, and socioeconomic data for thorough risk evaluations, mapping risk zones, and spatially displaying pollution patterns, GIS enhances these analyses [20]. Researchers can evaluate exposure pathways, estimate pollutant dispersion, and forecast possible effects on ecosystems and human health by combining GIS with multivariate methods. When combined, these techniques offer a strong foundation for focused mitigation plans and evidence-based policymaking to protect public health and agricultural output [21].

Makkah city is situated in the southwestern region of the Al Hijaz province within the Kingdom of Saudi Arabia. The area lies between the flat coastal plain (Tihamat Al Hijaz) and the steep slopes of the Sarawat mountains, which were formed by tectonic activity associated with the splitting of the Red Sea [22]. The Wadis of Makkah exhibit intricate and interconnected patterns as they traverse the mountain ranges, a characteristic feature of dry landscapes. These intersecting alluvial zones provide valuable insights into the morphotectonic evolution of the region. Geologically, Makkah is underlain by late Proterozoic volcanic and volcaniclastic rocks of the Arabian Shield, which include the Milh complex, Ju’Ranah complex, Zibarah group, Samaran group, and Fatima group [23]. These rocks have undergone multiple phases of deformation, metamorphism, and igneous intrusion. Additionally, the geological makeup encompasses Tertiary formations such as the Shumaysi, Sita, and Khulays Formations, along with Quaternary deposits including talus, fluvial, alluvial, and sabkha sediments [24].

Due to its volcanic and volcaniclastic origins, Makkah’s geological makeup contains naturally elevated concentrations of heavy metals like Fe, Cr, Zn, Cu, and Pb [25,26]. In addition, tectonic activity associated with the Red Sea rifting has caused multiple deformation phases and igneous intrusions, which have likely contributed to geochemical anomalies in the area [27]. Prolonged weathering and erosion of these rocks release trace metals into the surrounding environment, particularly into the Wadi systems that traverse the region. The region’s farming activities, predominantly in Wadi systems, rely heavily on soil and water resources influenced by natural processes and anthropogenic activities. The combination of the area’s complex geological background and its use for agriculture raises the potential for HM accumulation in the soil, either from natural geological sources or human-induced factors.

Understanding the extent of HM contamination in this area is critical for assessing environmental and health risks, ensuring sustainable agricultural practices, and protecting food safety in a region where agriculture plays a vital role. Multiple research studies conducted in Saudi Arabia have focused on analyzing the levels of soil contamination, identifying the sources of contamination, and assessing the overall pollution status [28]. However, these studies lacked knowledge of metal mobility and bioavailability and solely relied on the total concentration of HHMs in the soil samples, ignoring geographical variability. Methods like as factor analysis, Cluster Analysis, and Principal Component Analysis (PCA) can be used to determine and differentiate between anthropogenic and geogenic origins of HHMs [14]. Correlations between metal concentrations and particular environmental or human activities are also disclosed by these analyses. Spatial patterns of metal distribution can be visualized by combining GIS mapping with geostatistical techniques. This can draw attention to pathways and hotspots for pollution in the Wadi systems [29,30]. Furthermore, it is possible to quantify contamination levels in relation to background concentrations and evaluate ecological risk by utilizing indices like the enrichment factor (EF), geoaccumulation index (Igeo), and risk index (RI) [31].

This study aims to (i) assess the concentrations of Fe, Zn, Cr, Pb, and Cu in agricultural soils, emphasizing the broader implications of HHM contamination for global food security and sustainable agricultural practices; (ii) evaluate the potential environmental hazards posed by these HHMs, highlighting their contribution to transboundary environmental challenges and the global ecosystem; and (iii) examine the health risks associated with HHMs in soil, considering ingestion, dermal contact, and inhalation pathways, while underlining the universal relevance of soil contamination to public health and its impact on global populations, particularly vulnerable groups such as children. This evaluation emphasizes the interconnectedness of environmental and public health risks in a globalized world, where contamination in one region can affect international food trade, biodiversity, and collective human well-being.

2. Materials and Methods

2.1. Sampling and Analytical Methods

Soil samples were collected from 32 farms located in the Makkah region of western Saudi Arabia (Figure 1). Samples were collected using a hard-plastic hand trowel at a depth of less than 10 cm. This depth is important for biological relevance, ecological and human exposure, nutrient cycling, and organic matter, and it is suitable for assessing surface pollution, where contaminants frequently concentrate [32]. Three subsamples were combined to make a composite sample, which was then sealed in plastic bags and kept in an icebox to create a representative sample. To guarantee a consistent particle size, all samples were dried at 100 °C and crushed; many were sieved to 63 µm. The farms that were analyzed mostly focused on growing vegetables (farms 1, 11, 18, 23, 26, 29, 31, 32), citrus fruits (farms 2, 12, 16), clover (farms 3, 7), and date trees (farms 4, 8, 9, 10, 13–15, 17, 19–22, 24, 25, 27, 28, 30).

An investigation of the elements Fe, Zn, Cr, Pb, and Cu was conducted at the ALS Geochemistry Lab in Jeddah, Saudi Arabia, utilizing inductively coupled plasma-atomic emission spectrometry (ICP-AES; Thermo Fisher iCAP 6500, Waltham, MA, USA, and the PerkinElmer Optima series, Norwalk, CT, USA). Iron was chosen as a target material due to its critical role as a plant micronutrient essential for soil fertility and crop production. However, excessive Fe levels can harm soil quality, affect plant health, and influence the behavior of other heavy metals, intensifying environmental risks. Globally, Fe contamination from industrial activities and waste disposal underscores the need for monitoring to address shared challenges in agricultural productivity, food safety, and environmental sustainability [33].

In total, 1.5. mL of concentrated nitric and perchloric acids are used to digest the prepared sample (nominal weight 0.25 g), which is then followed by concentrated hydrofluoric acid. After being heated to 185 °C until it begins to dry out, 50% hydrochloric acid is used to leach the mixture, and then weak HCl is added to dilute it to volume. After that, the findings of the analysis of the final solution are adjusted for spectral inter-element interferences. Certified multi-element standards with known concentrations that were generated in an acid matrix comparable to the soil samples were used to calibrate the ICP-AES. To confirm the accuracy of the approach, the samples were evaluated alongside Certified Reference Materials (CRMs) that were matrix-matched to soil and had known compositions. In order to guarantee accuracy and repeatability, duplicate samples or splits were also examined.

2.2. Multivariate Tools and Contamination Indices

Multivariate statistical approaches, specifically correlation matrix (CM) and Principal Component Analysis (PCA), were used to determine the possible origins of HHMs in the soil being studied. We utilized the SPSS software (IBM SPSS Statistics 29 and OriginPro 2023b software) for this investigation. The assessment of HM pollution in soil samples involved the use of many indices, including the enrichment factor (EF), contamination factor (CF), potential ecological risk index (RI), and pollution load index (PLI) [31,34,35,36].

EF = (M/Fe) sample/(M/Fe) background

(1)

CF = Co/Cb

(2)

PLI = (CF1 × CF2 × CF3 × CF4… × CFn)1/n

(3)

Eri = Tri × Cfi

(4)

RI = ∑(Tri × Cfi)

(5)

The (M/Fe) sample indicates the proportion of metal to iron concentrations in the sample, while the (M/Fe) background refers to the proportion of metal to iron concentrations in the Earth’s crust. Co denotes the metal concentration in the soil sample, whereas Cb represents the typical background level of the metal. CF denotes the degree of contamination. Eri symbolizes the ecological risk potential of a specific element, Tri represents the biological toxicity response factor of a specific element, and Cfi displays the contamination factor for each unique element. The toxicity ranking for metals is as follows: Zn = 1, Cr = 2, Cu = Pb = 5 [31]. The contamination indices used in this study are classified in Table S1 [34].

In addition, a comprehensive evaluation of health risks was conducted using chronic daily intake (CDI), hazard index (HI), cancer risk (CR), and total lifetime cancer risk (LCR) assessments. The evaluations were conducted using the equations provided by [37,38,39,40].

CDIing = (Csoil × IngR × EF × ED)/(BW × AT) × CF

(6)

CDIinh = (Csoil × InhR × EF × ED)/(PEF × BW × AT)

(7)

CDIderm = (Csoil × SA × AFsoil × ABS × EF × ED)/(BW × AT) × CF

(8)

HQ = CDI/RfD

(9)

HI = ∑HQ = HQing + HQderm+ HQinh

(10)

Cancer risk = CDI × CSF

(11)

LCR = ∑Cancer Risk = Cancer risking + Cancer riskderm + Cancer riskinh

(12)

Table 1. Exposure factors used in estimation of chronic daily intake (CDI) for non-carcinogenic risk from agricultural soil in western Saudi Arabia [38,39].

Parameter	Units	Adults	Children
Ingestion rate (IngR)	mg/day	100	200
Inhalation rate (InhR)	m3/day	20	7.6
Exposure frequency (EF)	days/year	350	350
Exposure duration (ED)	year	24	6
Body weight (BW)	kg	70	15
Average time for non-carcinogenic risk (ATnc)	days	8760	2190
Average time for carcinogenic risk (ATc)	days	25,550	25,550
Particulate emission factor (PEF)	m3/kg	1.36 × 109	1.36 × 109
Skin surface area (SA)	cm2	5700	2800
Adherence factor (AF)	mg/cm	0.07	0.2
Dermal absorption factor (ABS)	-	0.001	0.001
Conversion factor (CF)	kg/mg	10−6	10−6
Concentration of heavy metal(loid)s (C)	mg/kg	-	-

displays the exposure parameters used to calculate the CDI for non-carcinogenic risk [37,38]. The absence of RfDinh and RfDderm values for Fe is the reason why

Table 2. The reference dose (RfD) and the cancer slope factors (CSFs) for HHMs from agricultural soil of western Saudi Arabia [38,39,40].

RfDinh	RfDderm	RfDing	HMs
2.86 × 10−5	6 × 10−5	3 × 10−3	Cr
1.2 × 10−2	4.02 × 10−2	4 × 10−2	Cu
-	-	7 × 10−1	Fe
3 × 10−1	6 × 10−2	3 × 10−1	Zn
3.52 × 10−3	3.25 × 10−4	3.5 × 10−3	Pb
CSFinh	CSFderm	CSFing	HMs
42.0	20.0	0.50	Cr
0.042	-	0.0085	Pb

does not provide a CDI value for Fe. The lack of information may be due to inconsistencies in the published data or the inability to accurately track back to the original study for the reference value [40]. The potential effects of Pb on humans through direct skin contact are still not fully understood; hence, the values of the cancer slope factors (CSFs) for skin exposure to Pb were infrequently mentioned in Table 2 [40].

3. Results

3.1. Distribution and Environmental Hazards

The levels of HMs in this study are outlined in Table S2. The average values of the HHMs (dry weight, mg/kg) were in the order of Fe (35,138 mg/kg), Zn (69.59 mg/kg), Cu (55.13 mg/kg), Cr (47.88 mg/kg), and Pb (6.09 mg/kg). The average concentrations of Cr, Zn, and Fe in our study were below the global average [41], as well as the background value established by [42]. Our soil samples showed higher concentrations of HHMs compared to the average levels seen in soils worldwide [41]. In some cases, the HHM levels significantly exceeded the natural background values [42]. For example, sample 1 (Cr, Cu, Fe, Pb, and Zn); sample 2 (Cu); samples 3, 10, and 11 (Fe); sample 13 (Cr, Fe, and Zn); sample 14 (Zn); sample 15 (Cr, Cu, Fe, and Zn); sample 16 (Cu and Fe); sample 17 (Cr, Cu, Fe, and Zn); sample 19 (Cr, Fe, and Zn); sample 20 (Cr, Cu, Fe, and Zn); sample 25 (Fe and Zn); and sample 30 (Cr, Cu, Fe, and Zn).

Figure 2 presents the spatial distribution of Fe, Cr, Zn, Cu, and Pb per sample location. In total, 40.6% of samples exceed the guideline value of Cr (<50 mg/kg), especially in the southern and somewhat northern parts of the study area, indicating possible localized Cr contamination. The normal background levels of Cu are usually <100 mg/kg, whereas sample 2 in the northern part indicates significant contamination with Cu (656 mg/kg), possibly from geogenic, agricultural, or industrial activities. Low Pb concentrations generally <10 mg/kg, align with non-polluted soils, except sample 1, which indicates significant contamination. Concentrations range between 40.00 and 122.00 mg/kg, with some exceeding 100 mg/kg (e.g., samples 1, 13, 17, 22, 26). Elevated Zn levels could indicate anthropogenic sources such as fertilizers and other agricultural practices.

The enrichment factor (EF) is a useful tool for distinguishing components that are affected by human activities from those that occur naturally in the Earth’s geology [35]. The EF values in this investigation showed substantial enrichment for Cu and deficient to low enrichment for the other HHMs (

Table 3. Minimum, maximum, and average values of the contamination indices for HHMs from Makkah agricultural soil.

HMs	Indices	Min.	Max.	Aver.
Pb	EF	0.15	1.99	0.44
	CF	0.15	1.85	0.35
Zn	EF	0.52	2.01	1.00
	CF	0.42	1.28	0.74
Cr	EF	0.33	1.03	0.71
	CF	0.22	1.03	0.54
Cu	EF	0.68	21.9	2.27
	CF	0.4	14.6	1.59
Fe	CF	0.51	1.00	0.75

). Nevertheless, sample 2 demonstrated a significant concentration of Cu. Based on the EF categories shown in Table 1, it can be concluded that all HMs found in the soil of Makkah were naturally occurring, with only a few cases of little human influence resulting in increased levels in certain samples. Because of their volcanic and volcanoclastic origins, the underlying Proterozoic rocks of the Arabian Shield in the Makkah region are known to naturally contain elevated quantities of copper. A baseline increase in Cu concentrations could result from the long-term weathering and erosion of these rocks, which could add Cu to the nearby soil and Wadi sediments [25,26]. Furthermore, because Cu-based insecticides, fungicides, and fertilizers are widely used, Cu pollution is frequently linked to agricultural operations [43,44].

The contamination factor (CF) revealed a low level of contamination for the nine HMs in the soil of Makkah, with the exception of Cu, which exhibited a moderate level of contamination. Sample 2 showed a significantly high contamination factor (CF = 14.58), suggesting the presence of a localized source of Cu pollution, while sample 1 had a moderate contamination factor for Pb, samples 1, 13, 17, 22, 26, and 30 had a moderate contamination factor for Zn, sample 27 had a moderate contamination factor for Cr, and sample 27 had a moderate contamination factor for Fe. The pollution load index (PLI) and risk index (RI) are employed to evaluate the level of HM pollution at specific soil locations [34]. The pollution load index (PLI) ranged from 0.34 in sample 5 to 0.69 in sample 2 within the study region. The average PLI was 0.48, suggesting that the soil in the area is not polluted [45]. The risk index (RI) values ranged from 12.09 in sample 7 to 91.38 in sample 2, with an average value of 21.11. These results indicate a minimal risk for the presence of the nine HMs in the current soil [46].

The correlation matrix (CM) presented in

Table 4. Correlation matrix for HHMs of soil samples from Makkah agricultural soil.

	Cr	Cu	Fe	Pb	Zn
Cr	1
Cu	−0.033	1
Fe	0.795 **	−0.037	1
Pb	0.215	0.027	0.314	1
Zn	0.447 *	0.074	0.426 *	0.349 *	1

**. Correlation is significant at the 0.01 level (2-tailed). *. Correlation is significant at the 0.05 level (2-tailed).

shows the strength and direction of linear relationships between HHMs in soil samples. A strong positive correlation between Cr-Fe (r = 0.795) suggests that areas with high Cr concentrations also tend to have elevated Fe levels. This could be due to shared geogenic origins or similar chemical behavior in the soil environment [47,48]. A moderate positive correlation between Cr and Zn (r = 0.447), implying some association, possibly linked to contamination from common sources such as fertilizers [49]. Pb and Cu have a weak relationship with all other metals, indicating they might have distinct origins, such as localized pollution from lead and copper-containing products [49].

Principal Component Analysis (PCA) reduces the dimensionality of datasets while retaining most of the variance, making it a useful tool for identifying patterns and potential sources of HM contamination in soils [50]. Three PCs were extracted, accounting for 51.94%, 18.05%, and 12.83% of the total variance, respectively (

Table 5. Loading matrix of PCs and the total variance explained by each PC for HHMs from Makkah agricultural soil.

	Component
	PC1	PC2	PC3
Cr	0.741	−0.319	0.400
Cu	0.149	0.829	0.490
Fe	0.897	−0.347	0.175
Pb	0.516	0.234	−0.532
Zn	0.643	0.156	−0.160
% of Variance	51.94	18.05	12.83
Cumulative %	51.94	69.99	82.82

). The PC1 captures the most significant trends in the dataset and shows strong loadings and associations for Cr, Fe, Pb, and Zn. This suggests PC1 reflects geogenic factors, such as the natural weathering of metal-rich minerals, which often co-mobilize these metals. Fe’s dominance supports its role as a marker for lithogenic contributions [51,52]. PC2 exhibited strong loadings for Cu, with moderate negative contributions from Cr and Fe. This likely reflects anthropogenic influences such as agricultural inputs [53]. In PC3, Pb shows a notable negative loading (−0.532), differentiating it from the others. This could indicate specific localized sources of Pb, and agricultural practices.

3.2. Health Hazards

Specific HHMs, including Zn, Cd, Ni, and Fe, have crucial functions in nutrition and are necessary in small amounts [54]. Nevertheless, prolonged exposure to these HHMs can be detrimental to health and result in serious illnesses [55].

Table 6. The CDI (mg/kg/day), HQ, and HI for non-carcinogenic risk in adults and children for HHMs from Makkah agricultural soil.

HMs	Adults
	CDIIng	CDIDerm	CDIInh	HQIng	HQDem	HQInh	HI
Cr	6.62 × 10−5	2.64 × 10−7	9.75 × 10−10	0.0221	8.81 × 10−5	3.25 × 10−7	0.0222
Pb	9.47 × 10−6	3.78 × 10−8	1.39 × 10−10	0.0027	1.08 × 10−5	3.98 × 10−8	0.0027
Cu	9.82 × 10−5	3.92 × 10−7	1.44 × 10−9	0.0026	1.06 × 10−5	3.90 × 10−8	0.0027
Zn	9.63 × 10−5	3.84 × 10−7	1.42 × 10−9	0.0003	1.28 × 10−6	4.72 × 10−9	0.0003
Fe	0.0546	-	-	0.0688	-	-	0.0688
HMs	Children
	CDIIng	CDIDerm	CDIInh	HQIng	HQDem	HQInh	HI
Cr	0.00062	1.23 × 10−6	4.55 × 10−9	0.206	0.00041	1.52 × 10−6	0.207
Pb	8.84 × 10−5	1.76 × 10−7	6.50 × 10−10	0.025	5.04 × 10−5	1.86 × 10−7	0.025
Cu	0.00092	1.83 × 10−6	6.74 × 10−9	0.025	4.93 × 10−5	1.82 × 10−7	0.025
Zn	0.00089	1.79 × 10−6	6.61 × 10−9	0.003	5.97 × 10−6	2.20 × 10−8	0.003
Fe	0.4497	-	-	0.6425	-	-	0.643

presents the results of chronic daily intake (CDI), hazard quotient (HQ), and hazard index (HI) regarding non-carcinogenic risks linked to HMs through different pathways for both adults and children in the soil examined.

When it comes to non-carcinogenic hazards, the adult CDI values (mg/kg/day) varied from 9.468 × 10⁻⁶ (Pb) to 0.048 (Fe) by ingestion, from 3.778 × 10⁻⁸ (Pb) to 2.644 × 10⁻⁷ (Cr) through dermal contact, and from 1.392 × 10⁻¹⁰ (Pb) to 1.445 × 10⁻⁹ (Cu) through inhalation. The CDI for children ranged from 8.837 × 10⁻⁵ (Pb) to 0.450 (Fe) through ingestion, from 3.778 × 10⁻⁸ (Pb) to 1.829 × 10⁻⁶ (Cu) through skin contact, and from 6.498 × 10⁻¹⁰ (Pb) to 6.741 × 10⁻⁹ (Cu) through inhalation. The average CDI from the three pathways in children shows a notable rise in comparison to adults, implying that children are more prone to being exposed to non-carcinogenic substances. Children have a higher risk of ingesting HHMs through soil during outdoor play activities, which can be ascribed to their increased sensitivity to exposure [56]. Increasing awareness and education, creating secure play zones, advocating for vegetative barriers, implementing soil amendments and stabilization, and enclosing contaminated sites are preventive strategies to mitigate children’s exposure to polluted soil [57].

The hazard index (HI) values for HMs in adults were ranked in descending order as follows: Fe (0.0688), Cr (0.0222), Pb (0.0027), Cu (0.0027), and Zn (0.0003). In contrast, the sequence of concentration in children was as follows: Fe (0.6425), Cr (0.2066), Pb (0.0253), Cu (0.0248), and Zn (0.0030). Figure 3 and Figure 4 show spatial distribution maps of HI values in soil samples for HMs in both adults and children. These maps indicated higher values in the northeast and central regions for Cr and Zn, in the northeast and southeast regions for Fe, and eastern part for Pb and Cu. It is worth mentioning that the HI for HMs was considerably greater in children than in adults in relation to the risk of non-carcinogenic effects (Figure S1 and Table S3), reflecting their greater vulnerability to heavy metal exposure due to lower body weight and higher rates of ingestion or absorption. Importantly, no heavy metal in this study has an HI > 1, meaning no significant non-carcinogenic risk for either adults or children. However, Cr and Fe for children show elevated HI values in specific samples (e.g., samples 27 and 19 for Cr; sample 27 for Fe [47,49]. Nevertheless, it is crucial to emphasize that children, as a result of their oral and finger habits, are more prone to health consequences and exhibit a significant susceptibility to the impacts of HMs [58,59,60].

The average carcinogenic risk (CR) values for Cr and Pb in both children and adults, taking into account the three pathways, show that the risk of Cr is higher than that of Pb (

Table 7. Average CRs and LCR for Cr and Pb from Makkah agricultural soil.

HMs	Adults				Children
	CRIng	CRDerm	CRInh	LCR	CRIng	CRDerm	CRInh	LCR
Cr	3.31 × 10−5	1.32 × 10−7	4.87 × 10−10	3.33 × 10−5	0.00031	6.17 × 10−7	2.27 × 10−9	0.00031
Pb	8.05 × 10−8	-	1.18 × 10−12	8.08 × 10−8	7.51 × 10−7	-	5.52 × 10−12	7.53 × 10−7

). Under certain circumstances, particularly when oxidized, Cr shows increased environmental mobility, increasing its bioavailability in soil, water, and air. This raises CR levels by increasing exposure through the skin, inhalation, and ingestion. The risk contribution from ingestion and inhalation channels is decreased by lead’s tendency to create relatively stable compounds that are more firmly attached to soil particles and less bioavailable. The highest CR values for adults and children by ingestion and inhalation pathways are as follows: 3.314 × 10⁻⁵–0.00031 for adults and 4.873 × 10⁻¹⁰–2.274 × 10⁻⁹ for children, respectively. The findings indicate a significantly greater risk in children compared to adults, highlighting that children are more vulnerable to exposure to harmful substances due to their behavioral patterns, particularly hand-to-mouth activity, outdoor play, and closer ground proximity [44,61].

The lifetime cancer risk (LCR) is a probabilistic measure to estimate the likelihood of developing cancer due to lifetime exposure to carcinogenic agents. Levels of LCR for Cr and Pb were greater in children than in adults at all the sites examined (Table S4). The LCR values for Cr varied from 3.33 × 10⁻⁵ to 0.00031, while for Pb they ranged from 8.08 × 10⁻⁸ to 7.53 × 10⁻⁷ in adults and children, respectively (Table 7). The ingestion pathway made a large contribution to the LCR, representing 99.50% in adults and 99.80% in children.

In contaminated environments, the most common route to be exposed to HHMs is through direct or indirect intake of soil. It is possible for both adults and children to consume soil particles through contaminated food, water, or hand-to-mouth contact [62]. Because of the comparatively greater amounts consumed, this route contributes more to LCR than inhalation or dermal absorption. For HHMs like chromium and lead, the dermal route has a lower bioavailability than ingestion. Because the skin acts as a natural barrier, HHM absorption is restricted. Due to the limited resuspension of soil particles and the comparatively lower amounts of dust inhaled in comparison to swallowed dirt, the inhalation pathway also makes a negligible contribution. The spatial distribution of the LCR for Cr and Pb at each sample location indicated a comparable trend for both children and adults, with higher values observed in children (Figure 5). Children exhibit higher LCR values compared to adults for the following reasons: children engage in frequent hand-to-mouth activity, particularly during outdoor play, increasing their ingestion of contaminated soil and dust. This leads to higher exposure compared to adults. Samples 27 and 19 in the northeast and central regions exhibited an elevated concentration of Cr, whereas sample 1 in the eastern part exhibited an elevated concentration of Pb. The Proterozoic rocks of the Arabian Shield, which are naturally rich in minerals including chromium, provide the foundation of Makkah’s northeast and center areas. As these chromium-rich rocks weather, the surrounding soils may have higher quantities of Cr. Additionally, the sampling sites might cross over into Wadi systems, where heavy metals like Cr are gradually concentrated in sediment deposits by alluvial processes [25,26,27]. Regarding LCR values, both adults and children did not encounter substantial health risks from Pb (LCR ˂ 1 × 10⁻⁶) and Cr (from 1 × 10⁻⁶ to 1 × 10⁻⁴), indicating a tolerable level of risk, except for Cr in children [61].

4. Discussion

The findings of this study provide insight into the spatial distribution and potential sources of HHMs in the soil of Makkah. While the average concentrations of Cr, Zn, and Fe were below the global average, localized samples demonstrated elevated levels, suggesting a mix of geogenic and anthropogenic influences [46,47]. The significant contamination of Cu in sample 2 aligns with mixed geogenic enrichment and agricultural practices [27]. Similarly, elevated levels of Zn and Pb in specific samples could be attributed to the use of fertilizers and natural enrichment from the weathering of basement rocks in the study area [25,26].

The correlation matrix supports the notion that Cr and Fe may share common geogenic origins, as evidenced by their strong positive correlation [46]. Iron and chromium are commonly associated with Proterozoic rocks, particularly ultramafic and mafic formations such as those in the Arabian Shield beneath Makkah. These rock types’ naturally occurring iron oxides and Cr-bearing minerals (such as chromite) decompose and release Cr and Fe into the surrounding soil. Minerals that are rich in Cr and Fe weather naturally over time, releasing these metals into soils and sediments simultaneously. This geogenic mechanism can account for the observed high positive correlation. The moderate correlation between Cr and Zn hints at contamination from overlapping sources, such as fertilizers [47]. Zinc is commonly added to agricultural fertilizers to encourage plant development, even though some phosphate-based fertilizers may have Cr contamination as an impurity. The simultaneous application of both nutrients in agricultural soils may result in a modest relationship between Cr and Zn. Even though geogenic processes predominate in the distribution of Cr, it is also possible that Zn comes from natural sources, such as the weathering of Zn-containing minerals, which could account for the apparent link. However, the weak correlations of Pb and Cu with other metals suggest distinct and localized origins, potentially from industrial or consumer products containing these metals [47]. Pb has a limited association with other metals, which highlights its dispersed distribution and specific sources of pollution, like garbage dumping and agricultural practices. Furthermore, Cu comes from anthropogenic rather than geogenic origins, as seen by its weak association with other metals.

Principal Component Analysis (PCA) reinforces these findings, with PC1 reflecting geogenic factors influencing Cr, Fe, Pb, and Zn, and PC2, highlighting the anthropogenic impact on Cu levels [49]. The differentiation of Pb in PC3 underscores specific localized sources, potentially linked to agricultural or residential activities [51]. The natural weathering of Proterozoic rocks, which raises the amounts of Cr and Fe, is one of the geogenic variables that PC1 captures. Because Pb and Zn are naturally enriched in the nearby bedrock, their existence in this component indicates a partial geogenic contribution. The impact of human activity on Cu concentrations is shown in PC2. The main causes of Cu pollution are industrial processes, agricultural uses, and the application of insecticides containing copper. The Cu separation into PC2 indicates that it comes from a different source than the geogenic metals in PC1. PC3 emphasizes the localized sources of lead, which might be caused by past or ongoing human actions, like the usage of lead-based products in certain places. The Pb separation into a distinct component is consistent with its poor association with other metals and emphasizes the significance of locating the sources of contamination locally [52,53].

The health risk assessment underscores that children are more vulnerable to the adverse effects of HHMs due to their behavioral patterns and physiological differences [57,59]. While the HI values for all metals remained below the threshold of concern, the elevated HI and LCR values for Cr in children suggest a need for targeted interventions in specific hotspots [60]. This aligns with findings from previous studies emphasizing children’s susceptibility to heavy metal exposure [61,63]. Despite the tolerable levels of carcinogenic and non-carcinogenic risks, continuous monitoring and risk mitigation strategies are essential to minimize potential health impacts, particularly in areas where anthropogenic activities contribute to elevated metal concentrations [63]. Future research should explore the long-term effects of such exposures and develop sustainable management practices to limit human and environmental risks.

5. Conclusions

The present work highlighted the existence of Fe, Cr, Zn, Cu, and Pb and their potential environmental and health hazards in agricultural soil in Makkah, western Saudi Arabia. The average HM concentrations had the order of Fe ˃ Zn ˃ Cu ˃ Cr ˃ Pb. The contamination indices revealed that the tested soil had either little or minimal accumulation, low pollution, and a low level of risk associated with HHMs. However, several individual samples showed higher values. The Proterozoic rocks on the Arabian Shield, which have high concentrations because of their volcanic and volcaniclastic origins, are the main source of the HM concentrations in Makkah’s soil, according to PCA. HM concentrations in surrounding soil and Wadi sediments may increase as a result of these rocks’ weathering and erosion. Furthermore, because Cu-based fertilizers, fungicides, and pesticides are commonly employed, agricultural practices may be connected to Cu contamination in particular regions. The order of HM concentrations in adults and children, based on their HI values, was as follows: Fe > Cr > Pb > Cu > Zn. The HI values for HMs in Makkah soil were below 1.0, indicating the absence of significant non-carcinogenic risk. The lifetime cancer risk values (LCR) for Pb were below 1 × 10⁻⁶, while for Cr they ranged from 1 × 10⁻⁶ to 1 × 10⁻⁴, which suggests that the level of carcinogenic risk is within an acceptable range.