The study area, which is one of the largest districts in Ashanti and makes up around 5.4% of the Ashanti Region’s total land area, is situated within latitudes 6˚ North: 7˚ North and longitudes 2˚ West and 3˚ West. It covers an area of roughly 1364 square kilometers, as seen in Figure 1.

The district has significant gold mineralization and extensive artisanal and small-scale gold mining (ASM) activity.

Tontokrom, Datanor, Keniago, Watreso, Dunhura, and Asamang are some of the major communities engaged in artisanal mining. Major crops like cassava, yam, cocoyam, and some vegetables were once grown in these communities, providing food for Kumasi and the surrounding area. In order to buy food for their livelihood, the local population prefers to walk to nearby villages that have not been impacted by the spread of ASM activities, which have contaminated the environment and reduced soil fertility.

Figure 1. Location of Amansie West District; Source: Authors’ own construct.

The district has a humid, semi-equatorial climate, which is characterized by a bimodal rainfall pattern with major and minor wet seasons. There are two rainfall peaks during the main rainy season, which runs from March to July. September through November are the off-peak months for the wet season. The annual rainfall ranges from 855 mm to 1,500 mm. The average annual number of rainy days is between 110 and 120. Generally speaking, December through March are dry months with high temperatures and chilly, rainy, and foggy mornings [13].

The soil is predominantly Orthic Ferralsol (highly weathered, iron-rich soils) and Dystric Fluvisol (acidic, alluvial soils) soil types.

According to Agricultural Extension Officers of the Ministry of Food and Agriculture (MOFA), six agricultural communities were badly affected by the ASM operations. These communities used to be agricultural communities in the district, which served Kumasi and its environs with foodstuffs. Unfortunately, with the advent of ASM activities, these communities have been badly affected by chemical pollution, and topsoil, which contains nutrients, has been removed as a result of this menace. The communities were Tontokrom, Datanor, Keniago, Watreso, Dunhura, and Asamang. Therefore, the focus of this study was on these communities.

A total of 90 composite soil samples and 60 edible vegetable (tomato, cabbage, and onion) samples were collected from active farming plots within the six mining-impacted communities during the dry season (January-February 2023). For each of the six communities, 15 composite soil samples were randomly collected from agricultural plots at 0 - 20 cm depth using a stainless-steel auger, while 10 composite vegetable samples per species were collected from the same farming areas. The vegetables were harvested by uprooting them manually from the soil and separated into roots and edible portions using sharp scissors. The samples were then kept in well-labelled Ziploc bags and transferred to the laboratory for analysis.

Soil samples were air-dried, ground, and sieved through a 2 mm mesh sieve. Soil pH was measured using a 1:2.5 soil-to-water suspension with a calibrated pH meter following standard procedures [14]. Additionally, vegetable samples were rinsed with deionized water, oven-dried at 65˚C for 72 h, ground, and sieved. Individual vegetable (tomato, cabbage and onion) samples were analyzed separately for community- and species-specific PTE concentrations and transfer calculations. Where applicable, samples were subsequently composited for community-level risk assessment. This enabled us to calculate bioconcentration factors and health risk indices (carcinogenic and non-carcinogenic) for each community.

Aqua regia (1 HNO₃:3 HCl) was prepared and used to digest about 1.0 g of each sample (soil and vegetable), allowed to cool, filtered, and decanted after 30 minutes. Atomic Absorption Spectrophotometry (AAS) (Model: Agilent 200) was then used to measure the concentrations of arsenic (As), lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), copper (Cu), and zinc (Zn) in the soils and vegetables. Additionally, a vapor generation accessory (VGA) and AAS were used to measure mercury in both samples. The Global Soil Laboratory Network (GLOSOLAN) certified reference standards were used for instrument calibration, and procedural blanks were added to guarantee analytical accuracy.

To ensure data reliability, duplicate samples, reagent blanks, and certified reference materials (GL0-10 for soil) were added to the samples and analyzed. The percentage recovery and the relative standard deviation of target metals were estimated using the relation: Quality Assurance and Quality Control (QA/QC)

And

The accuracy and effectiveness of an analytical method in measuring metals in a sample are estimated by the percentage recovery [15].

The recovery percentages of the various PTEs were Pb (85% - 112%), As (88% - 115%), Cd (110% - 119%), Cu (89% - 97%), and Zn (85% - 115%). All values fell within the acceptable limits (80% - 120%) specified by the USEPA [15] guidelines, depending on the specific PTE. The lowest detectable limits for all the PTEs established were Pb: 0.0100 mg/kg, As: 0.0030 mg/kg, Cd: 0.0020 mg/kg, Hg: 0.0020 mg/kg, Cu: 0.0030 mg/kg, and Zn: 0.0010 mg/kg. With a correlation coefficient of 0.994 to 0.998, the calibration lines were linear. All analyses were conducted in triplicate, the average taken, and the results were expressed in mg/kg on a dry weight basis. Additionally, the data were subjected to descriptive analysis using OriginPro version 2022b (Origin Lab Corporation of Northampton, USA), in which mean values were determined.

We also used the Shapiro-Wilk test to make sure the data had a normal distribution before performing the various tests. In this case, variables were assumed to have a normal distribution if P > 0.05 but not if P < 0.05. Differences among communities were evaluated descriptively using the reported community-level concentrations and ranges. Because inferential statistical testing was not performed, differences are not interpreted as statistically significant.

The accumulation of potentially toxic elements (PTEs) by the roots and edible parts of the vegetables was calculated using the bioaccumulation coefficient (BAC) and Bioconcentration Factor (BCF), respectively. BAC measures the transfer of PTEs from soil to edible plant parts (shoots), while BCF measures the transfer from soil to roots. Both indices measure the ability of a plant to accumulate heavy metals from soil into its edible parts [16][17]. This is given by the relation:

This evaluates how efficiently the vegetables absorb PTEs from soil into their edible parts (shoot system), helps identify hyperaccumulator species for phytoremediation, and assesses bioavailability of metals in soil [16][17]. According to Yoon et al. [16] and Zhuang et al. [17], if BAC is greater than one (1), it implies that a high concentration of PTEs is accumulated in the edible part of the vegetables and BAC less than one (1) also implies that the vegetables absorb less of the metal relative to soil concentration. Similarly, BCF values greater than one (1) indicate high root accumulation. Both BAC and BCF are employed in this study to represent soil-to-plant transfer of potentially toxic elements (PTEs).

Health risk assessment was performed using the United States Environmental Protection Agency (USEPA) risk assessment guidelines [18][19]. There are three routes of exposure of PTEs to adults and children: Oral ingestion, dermal contact and inhalation [20]. In the six communities of the Amansie West District, oral ingestion and dermal contact were the common routes of exposure; therefore, human health risk assessment was estimated through consumption of contaminated vegetables (oral ingestion) and dermal contact with contaminated soil [20].

2.6.1. Non-Carcinogenic Health Risk Assessment

The Hazard Quotient (HQ) and the Hazard Index (HI) are two measures used to evaluate the potential health risks posed by exposure to environmental contaminants, as well as non-carcinogenic risk. They are commonly used in environmental health risk assessment and toxicology to assess the potential effects of exposure to contaminants in the environment, and in combination with other measures to assess the potential health risks posed by exposure to environmental contaminants [21]. The Hazard Quotient is a measure of the potential health risk posed by exposure to a single contaminant, and by a single contamination pathway or the hazard quotient (HQ) measures the total non-carcinogenic hazards associated with heavy metal intake from regular consumption of contaminated vegetables. It is calculated by dividing the estimated exposure dose of a contaminant by its reference dose, which is the level of long-term exposure considered safe for human health [21][22].

The Hazard Index is a measure of the potential health risk posed by exposure to multiple contaminants. It is calculated by the summation of the Hazard Quotients for all contaminants of concern in a particular exposure pathway. The HI is useful in evaluating the overall health risk posed by exposure to multiple contaminants [23]. It is assumed that an adverse health effect exists when HQ and HI are above 1, whilst adverse health effects are unlikely at HQ and HI of less than or equal to 1 [21][22].

In Ghana, tomato, cabbage, and onion are often eaten raw as salad or cooked as stew [24], and some are also consumed by individuals to boost their nutritional health status. Then we first calculated the Estimated Daily Intake (EDI) of possible oral ingestion of the PTEs in mg/kg bodyweight/day:

where C = metal concentration in vegetables (mg/kg);

IR = ingestion rate (200 g/day for adults; 100 g/day for children);

EF = exposure frequency (365 days/year);

ED = exposure duration (30 years for adults; 6 years for children);

BW = body weight (70 kg for adults; 15 kg for children);

AT = averaging time (non-carcinogenic: ED × 365; carcinogenic: 70 × 365).

These values were used and reported in previous studies [23][25].

Hazard quotient (HQ) was then estimated using the formula:

where RfD is the PTE oral reference dose as reported by Li et al. [21], and Shen et al. [26]. (Pb = 0.0035, Cd = 0.001, As = 0.0003, and Hg = 0.0001 mg/kg/day). The value of Hg was reported by Mawari et al. [27]. The RfD is the oral ingestion of a daily substance that will not harm a person throughout his/her lifetime. RfD is critical in the EPA’s evaluation of non-carcinogenic health risks [28].

The Hazard Index (HI) is therefore estimated using the following relation:

2.6.2. Carcinogenic Health Risk Assessment

Assessing the risk of carcinogenic soil to human health is a critical component of environmental and public health management. Conducting a risk assessment involves evaluating the exposure to these carcinogens and determining the likelihood of adverse health effects.

The estimated cancer risk (ECR) was calculated as:

where CSF is the cancer slope factor (mg/kg/day). CSF of the selected metals was reported in USEPA [19] (Pb = 0.0085, Cd = 0.3800, As = 0.6700, Hg = N/A). The cancer slope factor is an estimate of the probability that an individual will develop cancer if exposed to a chemical substance for a lifetime of 70 years [29]. ECR above 0.0001 is viewed as unacceptable; risks below 0.000001 are not considered to have significant health effects, and risk lying between 0.0001 and 0.000001 is considered an acceptable range [24][30].

Although the USEPA provides a cancer slope factor for cadmium (Cd) (USEPA, 2011), carcinogenic risk was assessed only for arsenic (As) and lead (Pb), as these elements were identified as the primary carcinogenic contaminants of concern in the study area [24][29].

Table 1 shows the levels of potentially toxic elements (PTEs) in agricultural soils in six communities affected by ASM. The PTE concentrations showed notable differences among the six communities. Tontokrom, Datanor, and Keniago typically had high levels of the potentially hazardous elements, probably due to artisanal small-scale mining activities. Tontokrom had the highest concentration of iron (Fe) at 16418.00 mg/kg, which was below the 20,000 mg/kg reference value [31].

Pb, As, Cd, and Hg, the most critical contaminants, were present in high concentrations in Tontokrom, 9.42 mg/kg for Pb, 8.16 mg/kg for As, 2.55 mg/kg for Hg, and 0.78 mg/kg for Cd in Datanor. Pb was above the local tailings background levels of 4.53 mg/kg, despite being below the global soil average of 10 mg/kg [32], implying anthropogenic input.

Tontokrom, Datanor, and Keniago had arsenic concentrations above the typical global background concentration of 5.0 mg/kg [33]. However, these values remain below the cited Dutch Target Value of 29 mg/kg [34]. Similarly, lead concentrations were highest in Tontokrom (9.42 mg/kg), followed by Datanor (8.66 mg/kg) and Keniago (5.83 mg/kg), while substantially lower concentrations were recorded in Dunhura (1.49 mg/kg) and Asamang (0.17 mg/kg). Furthermore, in the same communities, mercury levels exceeded the global soil mean (0.5 mg/kg) and the FAO/WHO permissible level (1.0 mg/kg), indicating widespread contamination brought on by ASM operations.

Table 1.Mean concentrations of PTEs in soil samples (mg/kg).

Values are means of analytical replicates. Standard deviations are not reported as the study focused on community-level mean concentrations for comparative risk assessment.

Across the six artisanal small-scale mining (ASM) communities, there were notable differences in the bioaccumulation coefficient (BAC) of Pb, Cd, As, and Hg in tomato, cabbage, and onion (Figure 2).

Figure 2.Bioaccumulation coefficient (BAC) of potentially toxic elements in tomato, cabbage and onion in the six ASGM communities. The red lines represent a BAC = 1, above which it indicates effective transfer of toxic elements from soil to edible plant parts.

At Tontokrom, BAC values greater than 1 were observed for several crop-PTE combinations. The strongest transfer was observed for Hg in cabbage (BAC = 4.03), As in cabbage (3.15), As in onion (2.54), and Pb in onion (2.17). Moderate accumulation was seen in tomatoes, especially for Cd (BAC = 1.2). Similarly, in Datanor, tomatoes accumulated higher levels of Pb (BAC = 1.8) and Cd (BAC = 1.4), while cabbage showed higher accumulations of Hg (BAC = 4.0) and As (BAC = 2.8), surpassing the threshold of 1.0.

In Keniago, cabbage showed higher As uptake (BAC = 1.2), and onion showed markedly higher Pb accumulation (BAC = 1.9). While the majority of the metals in Watreso had BAC values below 1.0, selective uptake was evident in the accumulation of Hg (BAC = 1.1) and As (BAC = 0.9) in cabbage and onions, respectively.

Dunhura recorded BAC near-threshold accumulation for almost all the PTEs, with tomato (Cd = 1.1) and cabbage (Pb = 1.0; As = 1.1) showing slight exceedances of the safe limit. In Asamang, all metals showed BAC values below 1.0, except onion, which approached the threshold for Hg (BAC = 0.9), suggesting relatively lower transfer efficiency in this community.

In comparison to Pb and Cd, As and Hg consistently showed BAC values above 1.0 in the majority of crops, particularly in onions and cabbage, indicating their greater translocation and bioavailability. This pattern suggests that communities affected by mining are at higher risk of dietary exposure to arsenic and mercury.

The vegetables from each community were composited, dried, ground, and analyzed for PTEs. The resulting concentrations were used to estimate health risk factors for adults and children. To assess the potential health risk to adults and children in the six communities from vegetable consumption, the estimated daily intake of PTEs (EDI), hazard quotient (HQ), and hazard index (HI) were calculated. The calculations were made using Equations (3), (4), and (5), respectively, from which non-carcinogenic and carcinogenic health risks were calculated and the results presented.

3.3.1. Estimated Daily Intake (EDI)

Table 2presents the estimated daily intake (EDI) of PTEs through vegetable consumption for adults and children. Children had higher EDI values due to lower body weight and similar ingestion rates.

Table 2.Estimated daily intake of potentially toxic elements (PTEs) via vegetable consumption.

Child EDI values are based on the stated exposure parameters (IR = 100 g/day, BW = 15 kg, ED = 6 years). The child/adult ratio of 2.33 is a mathematical consequence of these parameters.

3.3.2. Non-Carcinogenic Risk (Hazard Quotient and Hazard Index)

Table 3 presents the Hazard Index (HI) values for adults and children across the six communities. The HI values, which were derived from the summed HQs of individual metals, exceeded the safe threshold of 1.0 for children in all six communities, with the highest values occurring in Tontokrom (2.96) and Datanor (2.63). For adults, HI exceeded 1.0 in Tontokrom (1.27) and Datanor (1.13) but remained below 1.0 in the other four communities. These elevated HI values were driven primarily by arsenic (As) and mercury (Hg), indicating potential non-carcinogenic health concerns, particularly for children.

Table 3.Hazard Index (HI) across communities.

3.3.3. Carcinogenic Risk

Cancer risk (CR) values for As and Pb exceeded the USEPA acceptable limit of 1 × 10⁻⁴ in Tontokrom and Datanor, especially among children (Table 4). For Pb, CR values exceeded the limit only in Tontokrom (1.1 × 10⁻⁴ for adults, 0.5 × 10⁻⁴ for children).

Table 4.Carcinogenic risk (CR) values for As and Pb Across Communities.

The findings indicated that PTE concentrations, including those of arsenic (As), lead (Pb), mercury (Hg), and cadmium (Cd), in soils from mining communities in Amansie West were much higher than background levels and the WHO/FAO-recommended limits for agricultural soils [17]. Communities such as Tontokrom and Datanor recorded elevated As concentrations relative to the cited global background level; however, the reported values remained below the Dutch Target Value of 29 mg/kg [34]. The widespread use of mercury amalgamation in ASM operations and the geological diversity of the Birimian rocks in gold-bearing arsenopyrite minerals are the causes of these elevated levels [5]. Mercury and arsenic tend to remain in the environment and become immobilized in the soils with low pH and organic matter [12]. The mobility of these PTEs increases under acidic soil conditions (pH < 5), enhancing their uptake by plants [35].

Bioaccumulation patterns from the field samples showed that leafy vegetables such as cabbage, tomato, and onion accumulated high levels of As, Pb, and Cd—consistent with prior findings in mining-affected zones in Ghana and Nigeria [36][37]. The calculated Bioaccumulation Coefficients (BACs) exceeded 1 for many of these PTEs in multiple communities, indicating active transfer from soil to plant tissue.

Vegetables grown in Datanor and Tontokrom registered BAC values for As and Hg above 1.2, confirming their phytoremediation potential but also pointing to significant health risks if consumed regularly. Such high transfer values are particularly high when plant uptake is not matched by environmental regulation or soil immobilization of metals, which again highlights the absence of proper soil management and nutrient buffering in these communities [33].

Health risk assessments based on United States Environmental Protection Agency (USEPA) models [19] indicated Hazard Index (HI) values exceeding the safe threshold of 1.0 in most cases for children in all six communities. This outcome suggests a potential for adverse non-carcinogenic health effects, particularly due to exposure to arsenic and mercury. For adults, HI exceeded 1.0 in Tontokrom (1.27) and Datanor (1.13). In these communities, although individual HQ values were below 1 for some metals, cumulative exposure from multiple PTEs resulted in HI values surpassing the threshold. In the remaining communities (Keniago, Watreso, Dunhura, and Asamang), adult HI values remained below 1.0.

Carcinogenic risks (CR) calculated for As and Pb frequently exceeded the acceptable USEPA limit of 1 × 10⁻⁴, especially in children, a group highly susceptible to long-term toxicological effects. Chronic ingestion of arsenic-contaminated vegetables could potentially lead to skin, bladder, and lung cancers, while lead exposure is strongly associated with developmental disorders, particularly in children under 6 years of age [9].

The health risk assessment results revealed marked differences in susceptibility between adults and children exposed to potentially toxic elements (PTEs) through vegetable consumption in the ASM-impacted communities. Children consistently exhibited higher hazard quotients (HQ) and hazard indices (HI) compared to adults, owing to their lower body weight, higher food intake per unit body mass, and greater sensitivity to toxicants [19][38]. For example, the Hazard Index exceeded the safe threshold of 1.0 for children in all six communities, with the highest values in Tontokrom (2.96) and Datanor (2.63), indicating significant non-carcinogenic risks. For adults, HI exceeded 1.0 only in Tontokrom (1.27) and Datanor (1.13), while adult values in the other four communities remained below the threshold. This suggests that children in mining-affected households face a greater likelihood of developing adverse health effects such as impaired growth, cognitive deficits, and organ dysfunction linked to chronic exposure to metals like As, Pb, and Hg [39][40].

Furthermore, carcinogenic risk (CR) values for arsenic (1.4 × 10⁻⁴ - 2.3 × 10⁻⁴) surpassed the USEPA acceptable limit of 1.0 × 10⁻⁴, implying a potential lifetime cancer risk for both adults and children, though children remain at greater long-term risk due to early-life exposures. Chronic exposure to arsenic has been associated with skin lesions, respiratory problems, and increased incidence of internal cancers [41]. Mercury, another prevalent contaminant in the district, poses risks of neurological and developmental disorders, particularly in children, where early exposure may result in irreversible cognitive impairment [42].

For adults, although HI values were generally below the safe threshold, continuous dietary exposure could still lead to cumulative health effects, including kidney dysfunction (from Cd), cardiovascular disorders (from Pb), and neurological effects (from Hg). In contrast, children are more vulnerable to immediate and long-term impacts, raising urgent concerns about food safety in these communities.

The findings underscore the urgent need for dietary advisories, soil remediation, and health surveillance programs to safeguard vulnerable populations. Targeted interventions should prioritize children, who face disproportionately higher risks, while also protecting adults whose prolonged exposure may result in chronic diseases that burden community health systems.

The findings of this study emphasize the need for sustained environmental health interventions in communities affected by ASM activities. Priority measures may include the following; routine monitoring of PTEs in agricultural soils and food crops, targeted risk communication and public-health interventions in high-risk communities, and appropriate soil-management and remediation strategies.

These actions are important to safeguard food security and public health in mining-impacted areas and for supporting progress toward the Sustainable Development Goals (SDGs 3, 6, and 15).