1.      Introduction:

Soil plays an important role in maintaining environmental health and agricultural productivity. Because it supports plant growth, which in turn feeds humans and animals, soil is extremely vital to the environment. However, as a result of human activity, soil becomes contaminated with a variety of pollutants, including fertilizers, pesticides, particulates, etc. [1]. In recent years, environmental and health issues have gained significant international attention [2]. Municipal solid waste, hospital waste, overuse of pesticides, fertilizers, and herbicides, ponding of industrial effluents, and the discharge of industrial solid waste on open land are the main causes of soil contamination. Because heavy metals are toxic and pose a hazard to both human health and the environment, soil pollution with these contaminants is a serious concern [3].  Heavy metals can accumulate in soil, plants, and water after being introduced into the environment. They do not biodegrade; whether inhaled, ingested, or absorbed via the skin, they remain and present serious health dangers [4,5]. Acute exposure can cause rashes, gastrointestinal problems, nausea, and vomiting. Extended exposure can harm the nervous system and lead to conditions like Parkinson's and Alzheimer's [6] and can harm essential organs, including the kidneys, liver, and lungs. Human health depends on trace metals like Cu, Se, and Zn, yet high concentrations can be hazardous [7].

Soil plays an important role in maintaining environmental health and agricultural productivity. Because it supports plant growth, which in turn feeds humans and animals, soil is extremely vital to the environment. However, as a result of human activity, soil becomes contaminated with a variety of pollutants, including fertilizers, pesticides, particulates, etc. [1]. In recent years, environmental and health issues have gained significant international attention [2]. Municipal solid waste, hospital waste, overuse of pesticides, fertilizers, and herbicides, ponding of industrial effluents, and the discharge of industrial solid waste on open land are the main causes of soil contamination. Because heavy metals are toxic and pose a hazard to both human health and the environment, soil pollution with these contaminants is a serious concern [3].

Heavy metals can accumulate in soil, plants, and water after being introduced into the environment. They do not biodegrade; whether inhaled, ingested, or absorbed via the skin, they remain and present serious health dangers [4,5]. Acute exposure can cause rashes, gastrointestinal problems, nausea, and vomiting. Extended exposure can harm the nervous system and lead to conditions like Parkinson's and Alzheimer's [6] and can harm essential organs, including the kidneys, liver, and lungs. Human health depends on trace metals like Cu, Se, and Zn, yet high concentrations can be hazardous [7].

2.    Materials and Methods:

2.1. Study Area: 

The study was conducted in 10 different sites in Sulaymaniyah province. The area was selected to examine soil quality, the level of heavy metals in soil, and the effects of industrial activity on soil contamination, as well as to assess the risks of soil pollution to human health. 

Fig 1. Map showing sampling locations.

2.2. Soil Sampling:

Soil samples were collected during September 2024, situated from ten different sites (the samples were obtained from 0-15 cm using a steel auger). Following sample collection, soil samples were packaged in plastic bags and labeled, and then transported to the laboratory. In the laboratory, soil samples were air dried in a clean, dust-free environment at room temperature, 25˚C, for 3 to 5 days. Next, sieved soil samples using a 2mm sieve to prepare samples for digestion and analysis.

Table 1. Description of Sample Locations.

2.3. Soil Analysis:

Soil samples were analyzed at the University of Salahaddin, College of Science, Environmental Science and Health department for chemical properties of soil to determine essential elements of soil. Heavy metals (Zn, Pb, Cd, Cu and Co) were analyzed by using the acid digestion method 1 g of soil was placed in a 250 ml volume trick flask of digestion at first samples heat on at 95 ˚C with 10 ml of 50 % HNO₃ without boiling after cooling samples were added slowly 10 ML of 30 % H₂O₂ after the mixture boiled with 10 ml 37% HCl at 95 ˚C for 15 minutes. After cooling, the digested solution obtained was filtered with a 0.45µm M membrane paper, then diluted to 100ml with deionized water and stored at 4˚C [11]. The Apric and Elmer optimum of 4300 DV inductively coupled plasma optical emission spectrometer. ICP- OES was used to determine metals. Nutrients like calcium and magnesium were quantified using the EDTA method as determined by [12]. Potassium was determined using a flame photometer instrument as determined by [13].

2.4. Statistical analysis: 

SPSS was used to conduct statistical analysis of data; the experimental design was one-way ANOVA to compare between locations and the correlation between metals. The significance level was set at P⩽0.05.

2.5. Calculation of indices: 

2.5.1. Contamination Factor (Cf): The level of contamination of heavy metals in soil expressed in contamination factor terms, calculated as follows, 

C f = CD(sample concentration) / CR(Bachground concentation)    .....(2.1)

CD is the measured concentration of heavy metal CR is the background value of heavy metal in soil Cf is the contamination coefficient [14]. The grading standard and classification of Cf values are shown in Table 2.

Table 2. The grading standard level of contamination factor (Cf) in soil

2.5.1.     CCME soil quality index (SoQI):

The Canadian Council of Ministers of the Environment (CCME), soil quality index is an additional tool that tends to focus more on determining the relative risk through comparing pollutant concentration levels with the suitable soil quality guidelines. The SQoI for contaminated sites was developed by using three factors, namely, F1 (Scope), F2 (Frequency), and F3 (Amplitude) [15]. The CCME soil quality index is an additional tool that tends to focus more on determining the relative risk through comparing pollutant concentration levels with the suitable soil quality guidelines. The SoQI for contaminated sites was developed by using three factors, namely: F1 (Scope), F2 (Frequency), and F3 (Amplitude) [15]. 

F¹= Number o f f ailed contaminants / Total number o f contaminants ×100       .....(2.2)

F² = Number o f f ailed tests / Total number o f tests ×100       .....(2.3)

Excursion¹ = Failed Test Vaue / Guideline −1      .....(2.4)

For the cases in which the test value must not fall below the guideline: 

Excursion² =  Guideline / Failed Test Value −1       .....(2.5)

ase = ∑ ⁿ_i=1 excursion / #o f f ailed tests      .....(2.6)

F ³ =  ase / 0.01 ase+0.01       .....(2.7) 

SoQI = 100 − √ F1² +F2² +F3²  / 1.732    .....(2.8)

2.6 Health Risk Assessment (Non-Carcinogenic):

Through ingestion, the population’s health risk for the nearby soils was evaluated. The United States Environmental Protection Agency’s (USEPA) health risk assessment techniques were used in this investigation [16]. Three indices were used to assess non-carcinogenic health risks associated with heavy metal consumption: the hazard index (HI), the target hazard quotient (THQ), and the estimated daily intake (EDI). These techniques were based on research [17] to evaluate possible risks to human health.

2.6.1 Estimated Daily Intake (EDI):

EDI for heavy metal ingestion through was calculated for each element in (mg/kg/day) by using equation (2.11). The exposure parameters used for heavy metal ingestion are shown in Table 4.

EDIing = Csoil ×IngREF ×ED / BW AT ×10⁻⁶        .....(2.9)

parameters and input assumtions for HMs ingestion in soil is shown in Table 4. 

2.6.2 Hazard Quotient (HQ): 

The non-carcinogenic risk associated with individual heavy metals was assessed using the hazard quotient (HQ). If the  Hazard Quotient (HQ) is less than 1, the local population is considered safe. If the HQ is one or higher, it is considered unsafe for human health [17]. Each metals has different reference dose as shown in Table 5. 

HQ = EDI / R f D    .....(2.10)

Table 3. Concern levels of the soil quality index.

2.6.3 Hazard Index (HI): 

The risk to human health is higher when there are several heavy metals than when there is only one. We use the total hazard index (HI), which shows the cumulative non-carcinogenic risks related to exposure to various heavy metals, to assess the overall health impact of these metals. The following is the formula (2.11).

Table 4. Parameters and input assumptions for HMs ingestion in soil.

HI = ∑^m _j=1 HQi        .....(2.11) 

A HI score larger than one (>1.0) implies a very high risk of harm to human health, whereas a value less than one (<1.0) suggests no obvious non-carcinogenic damage to the human body [19].

Table 5. Reference dose values for metals [18].

3. Results and Discussion: 
3.1 Soil Fertility Assessment:

The analysis of soil samples from different sites (S1-S10), provided insights into the nutrient distributions, including potassium (K), magnesium (Mg), manganese (Mn), calcium (Ca), and molybdenum (Mo) as shown in Table 6. Mean concentration of K ranged from 45.8 mg.kg⁻¹ (S4) to 179 mg.kg⁻¹ (S6). According to the recommended nutrient value for soils as shown in (Table 7), several samples, such as S1, S2, S3, S5, S6, S7, S9, and S10, exhibited concentrations within the optimum range (100-200) mg.kg⁻¹ indicating adequate potassium for plant growth. while others like S4 and S8 were categorized as low (<50 mg.kg⁻¹ ), which could limit plant productivity, as K is critical for water regulation and enzymatic activity, photosynthesis, carbohydrate transport, and protein synthesis in plants [8]. Mg levels were consistently within the ptimal range (177.667-235.4) mg.kg⁻¹ across all samples. The highest mean value was observed at S6 (253.667) mg.kg⁻¹ , suggesting a relatively homogeneous distribution with no alarming deficiencies or excesses and ensuring sufficient chlorophyll formation and enzymatic activation for plant growth [20]. The concentration of Mn varied significantly, ranging from 22.333 mg.kg⁻¹ (S4) to 43.409 mg.kg⁻¹ (S10). All the samples were within the high range (20-50) mg.kg⁻¹ , indicating sufficient availability for plant growth without reaching toxicity levels. Manganese is important for photosynthesis [21]. Calcium is a  structural component of plant cell walls [8]. Calcium concentrations displayed considerable variability, ranging from 3688.967 mg.kg−1 (S9) to 8246.667 mg.kg⁻¹ (S7), most samples exceeded the extremely high threshold (>3000) mg.kg⁻¹ , particularly S6, S7, and S10, indicating potential concerns about Ca accumulation in these areas. High Ca can interfere with the absorption of Mg and K, leading to deficiency despite their presence in soil. Additionally, elevated Ca can increase soil alkalinity, reducing the availability of micronutrients like Mn, and Zn. Molybdenum concentrations ranged from 0.145 mg.kg⁻¹ (S4) to 0.469 mg.kg⁻¹ (S10). All the samples exceeded the optimum range (0.2-0.3 mg.kg⁻¹ ), with S10 showing an extremely high concentration. An elevated concentration of Mo could impact soil microbial activity and plant health, particularly nitrogen fixation [22]. This may indicate anthropogenic inputs such as fertilizer, industrial contamination, or localized geologic inputs. The correlation matrix Figure 1 illustrates the relationship among various metals and nutrients. Potassium shows a positive correlation with all parameters except for Pb (r = -0.063) and Cd (r = -0.030) which shows a negligible relation. Mg shows a weak correlation with all metals and nutrients except a moderate relation with Ca (r = 0.55). While, Mo shows a strong correlation with Mo (r = 0.882), a negative correlation with Cu, and a weak or negligible correlation with others. Cadmium shows a positive correlation with nutrients and metals except for Pb (r = -0.29) and Cd (r = - 0.080). while Mo, shows a negative correlation with Cu and positive with others. The moderate and strong positive correlations like Mg and Ca and Mn and Mo, may result from their co-occurrence in geochemical cycles, similar environmental behavior, or synergistic roles in biological and soil processes. Weak correlations suggest limited interaction due to differing geochemical behavior, solubility or environmental availability. Negative correlations indicate distinct sources, minimal overlap in environmental pathways, or limited shared uptake mechanisms.

Table 6. Nutrient concentrations in soil samples.

*Different letters (a, b, c, d) indicate statistically significant difference among sites at p-value < 0.05 according to one-way ANOVA followed by post-hoc test.

3.2 Heavy Metal Concentrations and WHO Comparison:

According to the data from Table 8, the mean of Zn concentrations in the samples range from 53.74 mg.kg−1 (S2) to 102.88 mg.kg−1 (S9). The World Health Organization (WHO) set the guidelines for Zn as 50 ppm Table 8 in soil, according  to this norm all samples exceeded the limit. In S 9, the Z and concentration surpass 100 mg.kg−1 , suggesting potential contamination, particularly if related to industrial activities or waste. A similar finding was reported by [24]. However, this location may be subject to more industrial or agricultural activities, as Zn is often associated with fertilizers and metal processing. Zn is an essential micronutrient for plants, critical for enzyme function and growth [25], so moderate levels, may still support planned health without posing toxicity risks. These findings stand with [23]. (Table 7). The post-hoc analysis has shown that the Zn is significantly different among the studied soil samples (P = 0.001). The correlation matrix Figure 2. It has been demonstrated that Zn has a positive relationship with all elements except for Mn (r = 0.042) and  Mo (r = 0.093) indicating no relation. The Pb concentrations range from 2.26 mg.kg−1 (S1) to 114.02 mg.kg−1 (S9). Lead at (S9) exceeded the acceptable limits of WHO (85 mg.kg−1) (Table 8). the lower Pb concentration is recorded by [26]. where Pb concentration was lower than the WHO permissible limit. Elevated Pb levels can result from anthropogenic activities such as vehicular emissions, industrial waste, and the use of contaminated fertilizers [27]. High pb concentrations in soils are particularly concerning due to their potential to harm human health through the food chain. Pb contamination may reduce plant growth, affect microbial activities, and pose risks to soil quality and plant safety [28]. There is a significant difference in Pb content between all sites with S9 (p-value = 0.002). The correlation matrix Figure 2, shows that Pb has a moderate positive correlation with Zn, and Cd, and a negative correlation with Cu, Co, K, and Ca. Cadmium concentration, the mean values range from 0.97 mg.kg−1 (S5) to 3.26 mg.kg−1 (S9), S9 showing the highest Cd content, this raises alarms due to their extreme toxicity, even at low concentrations. A similar result was recorded by [29]. where Cd was recorded as high as 2.74 mg.kg−1 , exceeding the WHO limit. Cd can accumulate in plants, especially in roots, leaves, and grains ultimately affecting food safety [25]. given the widespread use of phosphate fertilizers, which often contain Cd, its presence in soil is frequently associated with agricultural inputs, [30].

Significant difference among sites is obvious for Cd content with (P-value = 0.00002) the correlation matrix Figure 2, shows that Cd has a moderate positive correlation with Pb and Zn. Mg, and negative correlation with Co and K. Copper, concentrations are highly variable, ranging from 27.38 mg.kg-1−1 (S9) to 191.30 mg.kg−1 (S7). The high concentration of Zn, Pb, and Cd at site 9 maybe, attributed to intensive anthropogenic activities, including high traffic density, improper disposal of solid waste, use of phosphate fertilizer, and proximity to commercial or small-scale industrial activities. Copper concentrations have exceeded the limit of WHO (35 mg.kg−1 ) at S2, S4, S5, S6, S7, and S10. While Cu is necessary for plant metabolism, the mean content of Cu as observed in S7 can cause soil toxicity and reduce beneficial microbial populations. Elevated Cu concentration in soils are often associated with the use of fungicides and other Cu-based chemicals in agriculture, industrial activities, waste disposal containing electronic and industrial waste, or maybe due to the geochemistry of Cu-rich parent material [27]. Cu concentrations can also impair nutrient absorption in plants, particularly iron and phosphorus due to antagonistic interactions [31]. The opposite result is gained through the study conducted by [32], where Cu concentration was 28.7 mg/kg. Significant difference is also found among sites for Cu content with (P-value = 0.002). Cu has a moderate positive correlation only with Ca, and a negative correlation with Mo, Mn and Pb. Cobalt concentrations are relatively consistent, ranging from 5.31 mg.kg−1 (S1) to 16.34 mg.kg−1 (S6), with (S6) having the highest concentration. However, all soil samples’ Co content was within acceptable limits (40 mg.kg−1) by [33].

Though essential for nitrogen vexation in legumes, the excessive limit of Co in soil may reduce overall soil fertility [27]. Co-toxicity can inhibit plant growth, particularly in nonluminous plants, where its excessive presence can disrupt enzyme activity and reduce crop yields [34]. A concentration of 13.44 mg.kg−1 was recorded by [32]. Significant variation among sites for Co content (P-value = 0.00004) exists. Cobalt has shown a moderate correlation with Ca and a negative correlation with Pb and Cd Figure 1. The positive correlation between metals indicates a common source for these environmental elements. Meanwhile, a negative correlation suggests opposing trends between these metals. The elevated heavy metal concentrations in certain areas, particularly Pb, Cu, and Cd in S9 and S10, indicate potential pollution hotspots. 

Table 7. Recommended values for soil nutrients.

3.3 Soil Quality Index (SoQI):

In this study, the Canadian soil quality index was used because it is an important measure for assessing soil health and productivity for agriculture and its relation to human health. The highest soil quality index value indicates preferable soil quality and lower environmental concern. Data as shown in Table 10 indicated that the minimum and maximum values of SQoI ranged between 36.680 in S7 and 78.030 in S1. The highest SQoI value categorizes the low level of concern, which shows that the S1 has the minimal risk for environment and it is considered a healthy and suitable soil for agriculture or planting. Medium concentration concerns were recorded at S3 and S8. This level has no high risk to the environment or health; however, it should focus on good monitoring to prevent pollutant sources and control and maintain good soil fertility. While the lowest SQoI index value which recorded at S2, S3, S4, S5, S6, S7, S9, and S10 those level categorize the high concentration of concern as shown Table 3 this level indicates low soil management low fertility and high contamination as well as cues to decreasing nutrients in soil at this extent recommended to remediate soil by natural compounds such as green Nano technology or woody biochars to control soil contamination and remediate to good fertility, and high soil management which can use to agriculture those results are similar to those results reported by [35] used the SQoI index to inform decision making for remediation. Their results of the index were ranged between 39.9 and 49.1, respectively, which indicated that all s sites had a high-level concern for pollutants and were required to use the best method for remediation of soil. 

Figure 2. Correlation matrix among the studied parameters.

3.4 Pollution Indices:
3.4.1 Contamination Factor Cf: 

Contamination factor index is used to assess the toxic level of elements in soil. Data in Table 11 indicated that the Zn value ranged between 2.057 and 1.074, showing the contamination was moderate in all locations, if compare to guidelines as show in (Table 2) which is not critically harmful for agriculture, but probably should control the pollutant sources of Zn in soil. Pb values ranged between 1.341 and 0.026, low in all sites that had not been environmentally effective or harmful to soil fertility and management. Cd values ranging between 4.075 and 1.212 indicated contamination levels in the moderate to critical range of contamination recommended to prevent pollutant sources near those locations. Exceptions of S9 are considered a strong contamination level by Cd. Cu values ranged between 5.313 and 0.760 contamination level of Cu is considered moderate in all locations, except S7, which is considered to have a strong contamination level of Cu. Co values ranged between 0.265 and 0.817, considering no contamination in all locations. Results indicated Co concentrations were within acceptable limits and safe to the environment, agriculture, and human health. In general, the results of contamination factor CF indicated most of levels are medium to moderate of Zn and Pb, while the high level contamination were by Cd and Cu especially in S7 and S9 recorded highest level contamination which pose risks to human health luck soil fertility, as well as cues bioaccumulation of metals in agriculture crops, those results similar to [36] results indicated the study area polluted by Cd, and the contamination level of the other heavy metals were medium to moderate in more locations.

Table 9. The WHO has set the following permissible limits for heavy metals in soil.

Table 10. CCME Soil Quality Index (SQoI).

Table 11. Contamination factors (CF) of heavy metals.

3.5 Human Health Risk Assessment (EDI, HQ, and HI):

The estimated daily intake (EDI) values for the metals via soil ingestion Table 12 were generally low, with Zn and Cu showing relatively high values due to higher soil concentrations. Hazard quotient (HQ) for all metals Table 13 at all sites was below 1, indicating no risks to humans. if compare to guidelines as show in Table 5 Notably, Pb at S9 contributed the largest HQ value among all metals, which corresponds to the high level of Pb at this site. The hazard index, which represents the cumulative risk Table 13, ranged from 0.028 to 0.078, also below 1, which indicates that combined exposure to these metals through soil ingestion poses minimal or no health risks. The non-carcinogenic risk of heavy metals arranged from highest to lowest is as follows: Co > Pb > Cu > Cd > Zn. So, although cobalt concentrations did not exceed permissible limits, its relatively low reference dose resulted in higher HQ values compared to other metals. This indicates that toxicity potential, rather than concentration alone, governs health risk outcomes of cobalt concentration despite low risk levels at those sites. Periodic monitoring is recommended, especially for Pb and Co, as localized hotspots could pose long-term health concerns.

Table 12. Estimate daily intake for metals.

Table 13. Hazard quotients and hazard index for metals.

4.  Conclusion:

This study provides an integrated evaluation of soil nutrient status, heavy metal contamination, soil quality, and associated non- carcinogenic health risks in selected areas of Sulaymaniyah Province. The results indicate that while several essential nutrients were generally sufficient to support plant growth, imbalances in certain elements and elevated concentrations of specific heavy metals were detected in some locations, reflecting the influence of anthropogenic activities on soil quality. Soil quality assessment indices revealed that most sites fall within medium to high levels of environmental concern, suggesting reduced soil management practices. Although the health risk assessment showed no immediate non-carcinogenic risks to the local population through soil ingestion, it highlighted the importance of preventive measures to avoid long-term environmental and health impacts. Overall, the study emphasizes the necessity of continuous monitoring, effective pollution control, and sustainable soil remediation strategies to improve soil quality, protect human health, and ensure environmental sustainability in the study area.