Heavy Metal Contamination and Ecological Risk Assessment of Soils Around Mzedi Municipal Dumpsite, Blantyre, Malawi: Implications for Food Safety in Subsistence Farming Areas
Jul 2026· Resources Environment and Information Engineering· Vol 8, pp. 464-477· 0 citations· 22 references
Abstract
Uncontrolled disposal of municipal solid waste is a growing environmental concern in developing countries, contributing to heavy metal accumulation in surrounding soils and water. This study assessed the concentrations, spatial distribution, and ecological risks of heavy metals around the Mzedi municipal dumpsite in Blantyre, Malawi. Composite soil samples were collected at 0 m, 50 m, 250 m, 400 m, and 650 m from the dumpsite, while surface water samples were taken from a nearby stream receiving runoff. Samples were analyzed for cadmium (Cd), zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), lead (Pb), and cobalt (Co) using atomic absorption spectrophotometry. Contamination and risk levels were evaluated using the Contamination Factor (CF), Geo-accumulation Index (Igeo), Enrichment Factor (EF), and Potential Ecological Risk Index (PERI). Soil metal concentrations decreased with distance from the dumpsite in the order Fe > Mn > Zn > Cu > Pb > Cd > Co. Cadmium exhibited the highest contamination levels, with CF (70.00), Igeo (5.54), and EF (19.17) at 0 m indicating extremely polluted conditions and severe anthropogenic enrichment. PERI values ranged from 2,181 at 0 m to 117 at 650 m, shifting from very high to low ecological risk. Cadmium contributed > 96% of the total ecological risk, confirming it the dominant contributor to ecological risk. In surface water, Cd (0.006–0.008 mg/L) and Pb (0.025–0.030 mg/L) exceeded WHO drinking water guidelines, confirming leachate-driven contamination of the adjacent stream. While crop metal concentrations were not directly measured, the elevated soil cadmium levels indicate potential for plant uptake and possible human exposure. However, without direct crop analysis, we cannot confirm the extent of food chain transfer, quantify dietary exposure, or assess compliance with food safety standards. This highlights the critical need for targeted crop monitoring studies to validate the inferred human health risks. This study provides the first comprehensive quantitative assessment of ecological risk at the Mzedi dumpsite using multiple contamination indices and robust statistical analysis. The findings support precautionary management measures, including restrictions on farming directly on the dumpsite, upgrading of waste disposal infrastructure, and community awareness programs.
Aim: This study assessed the ecological risk posed by six heavy metals [lead (Pb), zinc (Zn), nickel (Ni), copper (Cu), chromium (Cr), and cadmium (Cd)] in soils and surface waters.
Study Design: Soil samples were collected at two depths (0–15 and 15–30 cm) from 12 stations across Onna, Mkpat Enin, Eastern Obolo, and Uyo in Akwa Ibom State. Surface-water samples were also collected, and Uyo served as the reference location.
Methodology: Composite soil samples were collected using a stainless-steel soil auger. Following acid digestion, metal concentrations were determined by atomic absorption spectrophotometry (AAS). The contamination factor (CF), degree of contamination (C-deg), geoaccumulation index (Igeo), single-metal ecological risk factor, and comprehensive potential ecological risk index (RI) were calculated using average-shale background values and the methods of Müller and Hakanson.
Results: Except for nickel at Onna Station 3 (57.5 mg/kg), which exceeded the adopted agricultural and residential soil guideline values, soil-metal concentrations were below the relevant limits. In surface water, lead and nickel exceeded the adopted WHO guideline values at all four locations, whereas chromium and cadmium exceeded the guidelines at two locations. Most CF and Igeo values indicated low contamination, although cadmium showed the greatest relative enrichment at several stations.
Conclusion: Although several stations, including the reference location, showed moderate-to-considerable single-metal risk from cadmium, RI remained below 150 at all soil stations, indicating low overall potential ecological risk. The results provide baseline information for environmental monitoring and remediation prioritisation in the studied oil-producing areas.
U. U. Ubong, A. D. Akpan, U. G. Isotuk· Asian Journal of Physical an...· 0 citations
Municipal open dumpsites are major sources of heavy metal contamination, posing significant risks to agricultural soils and food safety in developing countries. This study evaluated the seasonal distribution, soil to tuber translocation, contamination indices and human health risks of Pb, Zn, Ni, Cu, Cr and Cd in soils and cocoyam (Colocasia esculenta) cultivated around three municipal dumpsites in Akwa Ibom State, Nigeria. Composite soil samples were collected at three depths (0–10, 10–20, 20–30 cm) from each dumpsite and a control site, in both dry and wet seasons, to assess vertical and seasonal metal variation. Cocoyam tubers were also harvested at each location. Metals were determined by Atomic Absorption Spectrophotometry after digestion. Transfer factor (TF), contamination factor (CF), degree of contamination (Cdeg), hazard quotient (HQ) and hazard index (HI) were computed to assess metal mobility and health risk. Metal concentrations generally decreased with soil depth, showing surface accumulation from waste deposition. The highest concentrations occurred at Ikot Ekpene (13.50 and 88.50 mg/kg in Pb and Zn, dry season), while Pb increased to 37.50 mg/kg in wet season. Transfer factors exceeded unity for Pb at Eket (TF = 1.22, dry season), and for Pb at Uyo (TF = 1.27) and Cr at Eket (TF = 1.43) in the wet season, indicating high translocation into tubers. Soil contamination was highest at Ikot Ekpene (Cdeg = 18.36 dry season; 37.77 wet season), while tubers recorded Cdeg values of 22.40–24.67 (dry season). Hazard indices exceeded the US EPA threshold (HI > 1.0) at all dumpsites, peaking at 11.29 (Ikot Ekpene, wet season), with Pb the major contributor to risk. Cocoyam cultivated around municipal dumpsites carries a high heavy metal exposure risk. Improved waste management and restrictions on food crop cultivation in contaminated areas are recommended.
A. D. Akpan, U. U. Ubong, Aniefiok E. Ite et al.· International journal of re...· 0 citations
This study investigated the accumulation and ecological risk of heavy metals in soils surrounding a major open dumpsite adjacent to the New Abattoir in Akerebiata Harmony Estate, Ilorin, Southwestern Nigeria. Ten representative soil samples were collected at 9 m by 45 m intervals and analyzed using Atomic Absorption Spectroscopy (AAS) to determine concentrations of Copper (Cu), Zinc (Zn), Chromium (Cr), Iron (Fe), Cadmium (Cd), Cobalt (Co), Arsenic (As), Lead (Pb), Silver (Ag), and Mercury (Hg). Environmental impact was evaluated through the calculation of the Geo-accumulation Index (Igeo), Contamination Factor (CF), Pollution Index (PI), Enrichment Factor (EF), Hazard Quotient (HQ), Hazard Index (HI), and Cancer Risk (CR). Results indicated that while absolute concentrations remained below current regulatory limits, the site is moderately to strongly polluted (PI = 3.37) due to significant anthropogenic inputs. Igeo values showed that the area is uncontaminated regarding Cr, Hg, and Cd, but moderately contaminated with Co and As. The HQ and HI values for all metals were below 1.0 for both children (HI = 0.0016) and adults (HI = 0.0002), indicating no immediate non-carcinogenic risk via soil ingestion. Total cancer risk (CR = 2.08 × 10⁻8 for children) fell within the acceptable range (< 10⁻⁶). However, trends in As, Co, and Hg contamination factors warrant precautionary monitoring. Principal Component Analysis (PCA) attributed PC1 (34.73% variance) primarily to geogenic Fe–Cr inputs and PC2 (24.52%) to anthropogenic Cu-As loading. These findings suggest that the current open dumping system poses a growing risk to the local ecosystem and public health. The study recommends the implementation of engineered sanitary landfills, regular environmental monitoring, and remediation strategies to mitigate future heavy metal accumulation.
Durga Ruth Panchalingam, M. Adisa· Discover Environment· 0 citations
Lavonnonkaha dam reservoir serve as vital source of water for local farmers. However, ecological and economic zone, has been heavily impacted by the discharge of agricultural waste, leading to significant heavy metal contamination. Ten (10) sediment samples from dam were examined for heavy metals contents in objective potential ecological risk status. their heavy metals concentrations were determined using Atomic Absorption Spectrometry (AAS). Ecological risk assessment was carried out using single (contamination factor, geo-accumulation index, enrichment factor) and multi-elemental (contamination degree, pollution index and modified pollution index) standard indices. The assess ment based on these methods demonstrated that sediments were polluted with Cd and the sediments quality guidelines confirmed these results. The mean concentration of heavy metals (mg/kg) of sediments are as follows: Cu (15,78), Cd (0,89), Zn (6), Al (45535,42), Cr (0,53) et Pb (0,006). The contamination factor (CF) and geo-accumulation index (Igeo) revealed that the all of sediment samples are highly polluted with Cd. The enrichment factor (EF) values ranged from 1,61 to 22,16, with Cd (EF = 15,67) and Cu (EF = 2,04) showing significant anthropogenic enrichment. The modified degree of contamination (mCd) results indicated a moderate degree of contamination in 50% of sites. calculated pollution index (PI) and modified pollution index (MPI) revealing that all the samples were severely polluted. Finally, the risk assessment showed that Cd in the sediments presented a very high potential ecological risk.
TOE-Bi Kizito Katel Kahou, Kpan Oulai Jean-Gautier, Djeya Kouamé Leger et al.· GSC Advanced Research and Re...· 0 citations
Automobile mechanic activities can introduce potentially toxic metals into surrounding soils through the disposal of spent engine oil, metallic scraps, batteries and other vehicle-related wastes. This study assessed heavy metal contamination, ecological risk and potential human-health risks in soils from automobile mechanic villages at Coal Camp and Emene, Enugu State, Nigeria. Soil samples were digested using a nitric acid–perchloric acid mixture and analysed for Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn using Atomic Absorption Spectrophotometry (AAS). Contamination and ecological risks were evaluated using the contamination factor (CF), pollution load index (PLI), degree of contamination (Cdeg), modified degree of contamination (mCd), geo-accumulation index (Igeo) and potential ecological risk index (PERI). Human-health exposure was evaluated through dermal contact and soil ingestion using estimated average daily dose (ADD), hazard quotient (HQ), hazard index (HI) and incremental lifetime cancer risk (ILCR). Zinc recorded the highest concentrations at Coal Camp (1.2338 mg/kg) and Emene (1.2327 mg/kg), whereas mercury exhibited the highest contamination and ecological-risk contribution. The highest CF values were recorded for Hg at Coal Camp (10.075) and Emene (7.280), while Igeo values of 2.748 and 2.279 indicated moderate-to-strong Hg pollution, respectively. Coal Camp recorded higher Cdeg (11.270), mCd (1.127), PLI (0.0133) and RI (436.52) than Emene, which recorded Cdeg (8.417), mCd (0.842), PLI (0.0124) and RI (322.98). All HQ and HI values were below 1, indicating low non-carcinogenic risk through soil ingestion. Total ILCR values ranged from 4.882 × 10⁻⁷ to 1.359 × 10⁻⁶, with children showing higher estimated risks than adults. Overall, the soils exhibited low overall metal pollution based on PLI, but Hg represented the principal contaminant of concern and contributed substantially to ecological risk. Improved management of automobile wastes and regular monitoring of mechanic-village soils are recommended.
E. Ugwu, P. I. Udeozo, O. P. Nsude et al.· Asian Journal of Physical an...· 0 citations
This study assessed heavy metal (Cu, Ni, Pb, Zn and Cd) and radionuclide (²²⁶Ra, ²³²Th and ⁴⁰K) pollution and associated risks in the Likuyu River system, Tanzania. Surface water and sediments were collected from five sites along a 22.7 km river stretch, while soils and leafy vegetables were sampled from adjacent farms. Heavy metals were analysed by atomic absorption spectrometry and radionuclides by high-purity germanium gamma spectrometry. Risk assessment used contamination factor (CF), geoaccumulation index (Igeo), pollution load index (PLI), bioaccumulation factor (BAF), non-carcinogenic risk, carcinogenic risk (CR), annual effective dose (AED), radium equivalent activity (Raeq), annual ingestion dose (Ding) and excess lifetime cancer risk (ELCR). Heavy metals in river water were below detection limits and complied with WHO drinking-water limits: The Zn, 3–5 mg L⁻¹; Cd, 0.003 mg L⁻¹; Ni, 0.07 mg L⁻¹; Cu, 2.0 mg L⁻¹; and Pb, 0.0135 mg L⁻¹. The Ni in sediments at Sites A and E reached 32.1 ± 26.90 and 35.97 ± 6.51 mg kg⁻¹, respectively, exceeding the threshold effect concentration of 22.7 mg kg⁻¹ but remaining below the probable effect concentration of 48.6 mg kg⁻¹. Pollution indices indicated generally low sediment contamination, with CF values mostly below 1, Igeo values from −5.49 to −0.40, and PLI values from 0.077 to 0.251, although slight Zn enrichment occurred at Site A (CF = 1.14). Soils were weakly polluted, with PLI values of 0.078–0.105; however, Site SOD showed localized Ni enrichment, with CF = 1.577 and Igeo = +0.07, reaching 107.2 ± 1.40 mg kg⁻¹, exceeding the TBS limit of 50 mg kg⁻¹. Bioaccumulation results showed strong Zn uptake in napa cabbage (BAF >12), cowpea (BAF ~8) and okra (BAF ~6), and Pb accumulation in okra (BAF ~6) and cowpea (BAF ~5), whereas Ni and Cd had BAF
Charles D. Kadala· 0 citations
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