Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 6, 1875-1883 2025 Publisher: Learning Gate DOI: 10.55214/25768484.v9i6.8265 © 2025 by the authors; licensee Learning Gate © 2025 by the authors; licensee Learning Gate History: Received: 16 April 2025; Revised: 20 May 2025; Accepted: 23 May 2025; Published: 21 June 2025 * Correspondence: letlotloletuka@gmail.com Assessment of heavy metals and health risks of street vended foods in the Mangaung metro municipality, free State, South Africa Ponts’o Letuka1*, Sebolelo Jane Nkhebenyane1, Zikhona Tywabi-Ngeva2 1Department of Environmental Health, Central University of Technology, Bloem-fontein 9301, South Africa; letlotloletuka@gmail.com (P.L) snkheben@cut.ac.za (S.J.N.K.). 2Department of Chemistry, Nelson Mandela University, Port Elizabeth, South Africa; Zikhona.Tywabi-Ngeva@mandela.ac.za (Z.T.N.). Abstract: Street food vending is part of the informal sector that plays a significant role in improving the socio-economic status of vendors and the food security of consumers but faces safety challenges mostly due to anthropogenic activities and the lack of regulation. This study aimed to evaluate heavy metal contamination in commonly vended foods—pap, chicken, pork, and moroho/salads—in the Free State, South Africa, and assess the associated health risks to consumers. Shapiro-Wilk’s normality test and Kruskal-Wallis H tests were used to compare means. Results indicated heavy metal contamination in all analyzed samples. The overall median and IQR in descending order: Fe 4.365(4.424), Zn 3.605(3.711), As 2.653(2.971), Pb 1.095(1.266), Cu 0.271(0.326), Cr 0.212(0.117), and Zn 0.023(0.027) mg/kg. A significant difference (p < 0.05) was found for As between all pairs, while other heavy metals showed some variations without statistical significance. The EDI values of all sample types were below the recommended dietary values, suggesting that the heavy metals may not pose a public health risk. The health risk assessment through ICLR and Hazard Index (HI) indicated potential cancer and non- cancer risks from heavy metals in street-vended foods, as ICLR ≥ 10-3 and HI > 1. This implies that habitual consumers are at risk of non-carcinogenic health conditions. Keywords: Cancer risk, Heavy metals, Non-cancer risk, Street vended foods. 1. Introduction Street food vending contributes to food security and social justice by nourishing communities, empowering vendors, and fostering cultural resilience. However, this sector faces safety challenges mostly due to anthropogenic activities. Studies have highlighted the prevailing contamination of various food substances and some street vended foods with heavy metals and various conditions leading to this contamination [1-3]. Some of the metals found in street vended foods in their reports include Pb, Cd, Hg, Sb, Mn and Al. Although consumers are advised to visually inspect food before purchasing, contamination of food with heavy metals which are present in parts per million (ppm) cannot be seen with the naked eye [4]. Food may intentionally (through adulteration) or unintentionally be contaminated with trace metals before, during or after processing. Throughout the street food production and vending processes, the unintentional contamination with toxic metals can occur and influenced by numerous factors including environmental conditions during growth to post harvest handling, storage and preparation of meals, selection of raw materials and even the vending sites [5]. Heavy metal contamination may also arise from poor packaging, vehicular exhaust emissions, indiscriminate waste disposal, industrial pollutants and other environmental pollutants in the vicinity of the vending stalls Ankar-Brewoo, et al. [6] further adds that metals used for food processing equipment material may contribute to leaching of toxic metals into food. https://orcid.org/0000-0003-0699-9751 https://orcid.org/0000-0002-9245-387X https://orcid.org/0000-0002-5290-6942 1876 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 6: 1875-1883, 2025 DOI: 10.55214/25768484.v9i6.8265 © 2025 by the authors; licensee Learning Gate Street vended food have also been found to have the potential to greatly contribute to the daily intake of essential trace elements otherwise known as essential minerals [7]. However, data on bioavailability of these essential minerals is not widely known. Sufficient intake of essential minerals throughout the human life is necessary- about 1-2500 mg per day depending on the mineral- is essential for immune functions and biochemical processes that facilitate growth and chronic disease prevention [8, 9]. The essential minerals are divided into two classifications, namely, macrominerals and microminerals. Macrominerals are those that are required in greater quantities and these include calcium, magnesium, potassium and sulphur, while micronutrients are those that are only necessary in smaller amounts, these include zinc, iron, selenium, manganese, copper, chromium, and boron [10]. These implies that the insufficient supply of macronutrients or over consumption of micronutrients could be problematic to human health and development. The objective of this study was to assess the level of heavy metals in ready-to-eat street vended foods in MMM, Free State, South Africa. 2. Materials and Methods 2.1. Food Sample Characterization A variation of 4 different food samples were collected around marketplaces and taxi ranks in the 7 towns within the Mangaung Metropolitan Municipality (MMM), namely: Thaba Nchu, Bloemfontein, Botshabelo, Wepener, Soutpan, Van Stadensrus and Dewetsdorp. These samples consisted of pap, chicken, pork and moroho/salads. Samples were collected from 6 vendors in each town, thereby resulting in 168 food samples in total. Table 1. Types of food samples collected. Food sample Composition and preparation Pap Maize meal cooked to a stiff consistency with water. Sometimes salt is added for taste Chicken Seasoned chicken portions/cuts grilled on an open flame, often using coal or wood. Pork Seasoned pork portions/cuts grilled on an open flame, often using coal or wood Moroho/ salads Fried green vegetables such as kale, with spices, or varied mixtures of raw vegetables such as lettuce, tomatoes, onions etc 2.2. Sample Preparation The concentration of HMs in the street-vended samples was determined using ICPE (ICPE-9820, Shimadzu, Japan) and sample preparation was done following the method of Kaushik, et al. [11]. All reagent solutions were prepared using analytical-grade reagents dissolved in deionized water. The samples (168) were dried at 105 °C for 3–4 h in a hot-air oven, followed by manual crushing using a mortar and pestle and sieving. A sample of 0.5 g was then digested using a closed vessel microwave digestion method (model to be confirmed) with a mixture of 65 % HNO3, 36 % HCl, and 30 % H2O2. The digestion parameters were as follows: 130 °C for 10 min, 150 °C for 5 min, 180 °C for 5 min, and 210 °C for 15 min, with a power of 400 w. After digestion, the sample was filtered, and the volume was adjusted to 50 mL without further dilution. 2.3. Determination of Heavy Metals USING ICP-OES The amount of arsenic, cadmium, chromium, lead, iron, copper and zinc in prepared solutions was then determined using inductively coupled plasma optical emission spectrometer (ICP-OES), IRIS Interpid II XSP Model and using five standard solutions (10, 50, 100, 500 and 1000 μg L–1) for each heavy metal. 2.4. Health Risk Assessment To determine the health risk posed by the heavy metals, concentrations of carcinogenic and non- carcinogenic metals obtained from various food samples were used. Oral reference doses (RfD) of heavy metals were obtained from United States Environmental Protection Agency (US EPA) and the Agency 1877 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 6: 1875-1883, 2025 DOI: 10.55214/25768484.v9i6.8265 © 2025 by the authors; licensee Learning Gate for Toxic Substances and Disease Registry [12, 13]. The health risk assessment was done following methods by Muhammad, et al. [14]; Bamuwamye, et al. [15] and Onyele and Anyanwu [16]. The presumption was made that the amount of contaminant ingested equals the dose adsorbed, and cooking was considered to have no impact on the toxicity of the heavy metals in the street vended foods. Table 2. Oral reference doses of heavy metals. Metal RfD (mg/kg/day) Arsenic 0.0003 Cadmium 0.0005 Chromium 0.0003 Copper 0.04 Lead 0.0035 Iron 0.007 Zinc 0.3 Source: United States Environmental Protection Agency (USEPA) [12] and Agency for Toxic Substances and Disease Registry (ATSDR) [13]. 2.5. Estimated Daily Intake The estimated daily intake depends on the metal concentration, ingestion/consumption rate and body weight. The EDI was determined using equation 1: 𝐸𝐷𝐼 = 𝐶𝑚𝑒𝑡𝑎𝑙 × 𝐷𝑓𝑜𝑜𝑑 𝑖𝑛𝑡𝑎𝑘𝑒 𝐵𝑊𝑎𝑣𝑒𝑟𝑎𝑔𝑒 (1) Where C is the metal concentration in food (mg/kg) and D represents the daily intake of food in kg per person, and BW is the average body weight in kg (70 kg for adults). 2.6. Carcinogenic Risks To assess both the cancer and non-cancer risk presented by exposure to heavy metals, the Chronic Daily Intake (CDI) was calculated following equation 2. However, the probable cancer risk associated with exposure to a measured dose of a heavy metal can be estimated using Incremental Lifetime Cancer Risk (ILCR). The ICLR was worked out using the Cancer Slope Factor (CSF), which is considered as the risk produced by lifetime average dose of 1 mgkg-1 BWday-1 and is contaminant specific. ICLR was calculated for As, Cd, Pb and Cr using respective slope factors (mgkg-1day-1) following equation 3 [15, 17]. CDI = CW x IR x EF x ED BWx AT (2) ICLR = CDI x CSF (3) Table 3. Parameters used for calculating CDI and ICLR. Factor/parameter Symbol Units Adult Exposure duration ED Years 30 Lifetime Years 70 Exposure frequency EF days/year 365 Average time AT: Lifetime x 365 or ED x 365 Days 25 550 or 10 950 Body weight Bw Kg 70 Oral Cancer Slope Factor CSF (mg/kg/day)^-1 As- 1.5; Cd- 0.38; Cr- 0.5; Pb-0.0085 Ingestion rate IR: Pap Chicken Pork Moroho/salad kg/day 0.366 0.105 0.105 0.252 1878 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 6: 1875-1883, 2025 DOI: 10.55214/25768484.v9i6.8265 © 2025 by the authors; licensee Learning Gate 2.7. Non Carcinogenic Risk 2.7.1. Hazard Quotient HQ values were used to determine the potential for non-carcinogenic health risk that could occur as a result of heavy metal oral exposure. The HQ was determined using equation 4 as the human exposure to a metal of interest (mg/kg/day) divided by its reference dose (mg/kg/day) [18]. 𝐻𝑄 = 𝐶𝐷𝐼 𝑅𝑓𝐷𝑜 (4) The chronic hazard index (HI) was calculated as a sum of all hazard quotients (HQ) calculated for individual heavy metals for a particular exposure pathway [19]. This was to allow for evaluation of potential risk to consumer health as a result of exposure to more than one heavy metal. The HI was determined using equation 5. 𝐻𝐼 = 𝐻𝑄1 + 𝐻𝑄2 + ⋯ + 𝐻𝑄𝑛 (5) It is assumed that the overall impact on human health increases in direct proportion to the sum of different heavy metals on is exposed to [20]. According to standards, the population is considered safe when HI<1 and at risk when HI>1 [21]. 2.8. Statistical Analysis Quantitative data was captured on excel in preparation for statistical analysis. Various statistical analyses were carried out on the quantitative data using computer-based SPSS software version 26. A normality test was performed for the continuous variables in order to ascertain which methods would be appropriate for analyzing the variables. Visual inspection i.e., looking at the histogram and Q-Q plots, was used to investigate normality of the data. However, since the visual inspection may not be reliable, the Shapiro-Wilk’s normality test was also used to establish whether the data followed a normal distribution. The Kruskal-Wallis H tests was carried out to evaluate differences between mean of different heavy metals in different food types and sampling areas. Subsequently, the Pairwise Comparison with significance values having been adjusted for by the Bonferroni correction for multiple tests was done for both food types and sampling areas. The significance level was 0.05. Data did not have a normal distribution and the assumption of equality of variance was not fulfilled, hence the need to use non-parametric test. 3. Results and Discussions The test for normality indicated that all the data sets were not normally distributed (p< 0.01). Therefore, the median and interquartile range have been reported on. The results obtained indicated that there was heavy metal contamination in all analysed samples. The overall median and IQR from all food samples were as follows: of As, Cd, Cr, Cu, Fe, Pb, and Zn were As-2.653(2.971), Cd-0.023(0.027), Cr0.212(0.117), 0.271(0.326), 4.365(4.424), 1.095(1.266), and 3.605(3.711) mg/kg respectively. Iron had the highest overall concentration, 4.365(4.424) mg/kg, while cadmium had the lowest concentration 0.023(0.027) mg/kg. Furthermore, a Kruskal-Wallis test was done and results showed that there was a statistically significant difference in the amount of As, Cd and Cu where p<0.001 between different food types. However, no statistically significant differences were observed among different food types for Cr, Fe, Pb and Zn. Table 4 below depicts the mean concentrations of heavy metals obtained from the street vended foods in MMM. 1879 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 6: 1875-1883, 2025 DOI: 10.55214/25768484.v9i6.8265 © 2025 by the authors; licensee Learning Gate Table 4. Means of heavy metal concentration (mg/kg) in MMM street vended foods. Heavy Metals Food type Pap Chicken Pork Moroho/salad As 2.034±0.037 6.117±1.011 1.022±0.529 4.367±0.645 Cd 0.018±0.013 0.168±0.218 0.022±0.012 0.028±0.023 Cr 0.2±0.061 0.197±0.079 0.227±0.124 0.196±0.076 Cu 0.208±0.062 0.172±0.072 0.577±0.223 0.423±0.174 Fe 4.467±2.402 4.477±2.454 4.529±2.518 4.325±2.568 Pb 1.2±0.707 1.108±0.693 1.192±0.699 1.141±0.673 Zn 3.678±1.972 3.574±2.072 3.519±1.987 3.458±2.021 A Kruskal-Wallis Test (one-way non-parametric ANOVA) was done on the concentration of heavy metals present in the different food types. For this test, a comparison between groups based on the mean rank of the dependent variable (heavy metal concentration) was done. The null hypothesis stated that concentration distributions across different food types is the same. The multiple pairwise comparisons between different food types is presented in Table 5. For As, there was a statistically significant difference (p <0.05) between all pairs. However, for Cd, a significant difference was observed only among the following pairs: pap and chicken, pork and chicken, and moroho/salad and chicken. Copper concentrations were significantly different only among the following pairs: chicken and moroho/salad, chicken and pork, pap and moroho/salad, and pap and pork. Notably, no significant differences (p>0.05) were observed among all pairs for Cr, Fe, Pb and Zn concentrations. This analysis suggests that for some heavy metals, there is a real and meaningful difference in the levels of contamination between the compared food samples. Considering the location of the sampling areas (urban areas with busy traffic), this difference can be attributed to various anthropogenic activities such as industrial activities, motor vehicle emissions, choice of cooking utensils, as well as some environmental factors [22]. 3.1. Health Risks To quantitatively evaluate the likely health risks posed to street vended food consumers within the Mangaung Metro Municipality, a health risk assessment was carried out. The results of which are presented in Tables 6 to 9 below. Table 6. EDI of heavy metal for adults through consumption of street vended foods (mg/kg/day). Table 6 shows the Estimated Daily Intake (EDI) of heavy metals for adults with a body weight of 70kg. The EDI of As ranged between 0.0002 and 0.02 mg/kg/day with the highest value being obtained from mohoro/salad. The EDI of Cr and Cd from the street foods was highest in pork (0.003) mg/kg/day). Moroho/salad, among all other food types, had the highest EDI of both Cu and Fe, 0.002 and 0.02 mg/kg/day respectively. Daily intake rate of Pb and Zn ranged from 0.002 to 0.006 mg/kg/day and 0.005 to 0.02 g/kg/day respectively. These results indicate that the EDI values for the examined food samples are below the recommended dietary values. Therefore, the heavy metals assessed in this study through the consumption of the selected food samples do not pose a public health risk. Food type As Cd Cr Cu Fe Pb Zn Pap 0.01 0.0007 0.001 0.001 0.02 0.006 0.02 Chicken 0.0002 0.0002 0.001 0.0003 0.007 0.002 0.005 Pork 0.002 0.003 0.003 0.0009 0.007 0.002 0.005 Moroho/salad 0.02 0.00009 0.0007 0.002 0.02 0.004 0.01 Recommended daily dose (mg/kg/day) 0.13 [23] 0.062 [24] 0.035 [25] 2-3 [26] 18 [27] 0.21 [23] 14-20 [26] 1880 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 6: 1875-1883, 2025 DOI: 10.55214/25768484.v9i6.8265 © 2025 by the authors; licensee Learning Gate Table 7. The Chronic Daily Intake of heavy metals in adults (mg/kg/day). Heavy Metal Food type Pap Chicken Pork Moroho/salad Copper 0.001 0.0003 0.0001 0.002 Iron 0.023 0.007 0.007 0.016 Zinc 0.019 0.005 0.005 0.013 Arsenic 0.011 0.009 0.002 0.016 Cadmium <0.0000 0.0003 <0.0000 0.0001 Chromium 0.001 0.0003 0.0003 0.0007 Lead 0.006 0.002 0.002 0.004 Table 7 indicates the CDI of heavy metals which was used to calculate the ICLR. The CDI data obtained suggests that regular consumption of these ready-to-eat foods could result in cumulative exposure to heavy metals, thereby warranting continuous monitoring and control measures. According to USEPA, a one in a million chance of cancer over a 70 year lifetime period (ICLR=10-6) is considered acceptable, while ICLR of or greater than 10-3 (one in a thousand) is said to be serious and is a cause for remediation [28]. In this study, cancer risk was computed as 2.44x10-2 for highest and 3.17x10-3 for lowest risk for moroho/salad and pork respectively. Cumulatively, all ICLR was found to be equal to greater than what is considered to be increased risk of cancer (10-3) as reflected in Table 8. The chronic exposure to low concentrations of heavy metals such as Pb, As and Cd has the potential to result in many forms of cancers and other toxic effects [29, 30]. For chromium, its toxicity is dependent on its chemical composition. The health effects of chromium exposure can include, but are not limited to respiratory problems, lung cancer and skin effects [31]. Table 8. ICLR for the adult population of MMM through the consumption street vended foods. Heavy Metal Food type Pap Chicken Pork Moroho/salad Arsenic 1.65x10-2 1.35x10-2 3.00x10-3 2.40x10-2 Cadmium 0 1.14x10-4 0 3.80x10-5 Chromium 5.00x10-5 1.50x10-4 1.50x10-4 3.50x10-4 Lead 5.10x10-5 1.70x10-5 1.70x10-5 3.4x10-5 ∑ICLR 1.66X10-2 1.38x10-2 3.17x10-3 2.44x10-2 Table 9. The Hazard Quotient of Heavy Metal for Oral Ingestion in Adults. Aina, et al. [32] describes hazard quotient as “a proportion of the probable exposure to an element or chemical at such a level with no expected negative impacts when the quotient is less than 1, but an indication of potential health risks resulting from and exposure, when it is greater than 1”. The hazard quotients (HQ) were worked out to determine the non-cancer risk for all metals evaluated in this study and presented in table 9. The HQ in decreasing order or As, Fe, Pb, Cr, Zn, Cu and Cd for pap; As, Fe, Cr, Cd, Pb, Zn and Cu for chicken; As, Fe, Cr, Pb, Zn, Cu, and Cd for pork and As, Cr, Fe, Pb, Cd, Cu, Heavy Metal Food type Pap Chicken Pork Moroho/salad Copper 0.025 0.008 0.003 0.05 Iron 3.286 1 1 2.286 Zinc 0.063 0.017 0.017 0.043 Arsenic 36.67 30 6.67 53 Cadmium <0.001 0.6 <0.001 0.2 Chromium 0.33 1 1 2.33 Lead 1.71 0.57 0.57 1.14 HI=∑HQ 42.085 33.195 9.261 59.019 1881 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 6: 1875-1883, 2025 DOI: 10.55214/25768484.v9i6.8265 © 2025 by the authors; licensee Learning Gate and Zn for moroho/salad. The HQ was less than 1 in 86% (6 out of 7) of the heavy metals in chicken and pork, with As being the only heavy metal with a HQ >1. Similar observations were reported by Bamuwamye, et al. [15]. The hazard index (HI) for individual food types was calculated and the results in descending order were as follows:  HIΣmoroho/salad 50.019, HIΣpap 42.085, HIΣchicken 33.195 and HIΣpork 9.261. The HI of all sampled food types as per their daily ingestion rate indicated that consumers were at a significant non- carcinogenic health risk. From table 4.11, it can be noted that As THQs are the major contributors to the very high HI in all food types. Contrary to the findings of this study, Kaushik, et al. [11] reported a target hazard quotient and hazard index of <1 for all analyzed metals, which was indicative of health risks being lower. 4. Conclusions All food samples analysed in this study tested positive for all heavy metals tested. Although some of the metals are essential trace elements, exposure to them in concentrations exceeding safety standards can be detrimental to the health of consumers. The estimated daily intake obtained for all heavy metals was below recommended limits, thereby indicating no real risk to public health. The results portrayed by the incremental lifetime cancer risk indicate a necessity for remediation. Moreover, the hazard index of different food types was high (HI>1). This implies that habitual consumers are at risk of non- carcinogenic health conditions. The high HI observed could be a result of various reasons such as low RfD and the cumulative exposure to multiple heavy metals. Funding: This research was funded by the Central University of Technology Research Fund and the Lesotho Manpower Development Secretariat. The APC was funded by Central University of Technology Research Fund. Transparency: The authors confirm that the manuscript is an honest, accurate and transparent account of the study that no vital features of the study have been omitted and that any discrepancies from the study as planned have been explained. 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