HEAVY METAL CONTAMINATION AND ASSOCIATED HUMAN HEALTH RISKS IN DRINKING WATER, SOIL, AND EDIBLE VEGETABLES IN NIGERIA: A SYSTEMATIC REVIEW

Systematic review of the health risks of waste related heavy metals and toxic chemicals among vulnerable populations in low- and middle-income countries

In developing countries, poor waste management causes widespread heavy metal and toxic chemical contamination, threatening vulnerable populations. This systematic review of the health risks of waste-related heavy metals and toxic chemicals among vulnerable populations in low- and middle-income (LMICs) countries synthesizes multifaceted exposure pathways, clinical biomarker data, and localized risk thresholds. PubMed, Scopus, ScienceDirect, and ProQuest databases were searched for peer-reviewed studies published in English between 2012 and 2025. Out of the 731 records identified, two independent reviewers extracted data and appraised the quality of 21 eligible studies using Joanna Briggs Institute (JBI) Critical Appraisal Checklist, with initial variances successfully resolved via a formal consensus protocol. Primary contaminants identified were Pb, Cd, Cr, As, Hg, and Ni. Exposure pathways included soil and dust ingestion, inhalation of contaminated emissions, dermal absorption, occupational contact. Pediatric cohorts face extreme risks through ingestion and inhalation; mean blood lead reached 60.43 µg/L, breaching the World Health Organization 50 µg/L threshold, and correlated with a Full-Scale IQ decline (β= − 18.42, p < 0.05). Risk modeling showed pediatric non-carcinogenic vulnerabilities exceeded the US EPA Hazard Index baseline of 1.0 (e.g., Mn HI = 1.69), while total carcinogenic risk reached concerning level (10–5). Occupational biomarkers tracked hair mercury up to 10.8 mg/kg in miners and mean blood cyanide at 400 µg/L. Toxic waste exposures drive severe, unequal neurological, renal, hepatic, and carcinogenic burdens across LMICs. Mitigating these risks requires operationalized policies including enforcement of the Basel convention, mandatory provision of N95/P100 respirators and nitrile gloves, annual blood lead screenings, and formalizing labor contracts via Extended Producer Responsibility models.

A systematic review on the sources and health risk of heavy metal contamination in environmental and food systems in Uganda

This study systematically reviewed research on heavy metal contamination in environmental and food systems in Uganda using the PRISMA 2020 data reporting method and the PICOS framework. An extensive literature search of published papers on heavy metal contamination in Uganda's environment and food systems was conducted in PubMed, Web of Science, and Scopus databases up to May 21, 2024. Boolean operators (AND/OR/NOT) were applied to develop search strategies tailored to each database. Following duplicate removal, title and abstract screening, and full-text assessment using the Rayyan platform, 39 articles were included in the final review. Data were extracted from each study using a standardized template that captured metal type, contamination source, concentration levels, affected food or environmental matrix, geographic location, and toxicological impact. Data were synthesized using a descriptive and narrative approach. Key sources of contamination include industrial and municipal waste, agricultural practices, and emissions from transport and manufacturing. Among the metals, lead was the most mentioned across studies. Regional analysis revealed that Central Uganda had the highest reports on heavy metals, while Northern Uganda remains critically understudied. Ecologically, heavy metals threaten soil fertility, aquatic biodiversity, and agricultural sustainability. Contamination of staple foods with lead, cadmium, and mercury poses significant public health risks, particularly for children and pregnant women. Strengthened environmental monitoring, targeted regional investigations, and improved food safety surveillance within a One Health framework are urgently recommended.

Evaluating the Health and Ecological Risks of Toxic Elements in the Agricultural Soil of China using Traditional and Advanced Techniques: A One Health Approach

Agricultural soil quality is critical for sustainable food production, yet contamination by toxic elements (TEs) may pose ecological and human health risks. This study assessed the concentrations, ecological impacts, and potential health risks of five TEs (Cr, Cu, Cd, Pb, and Zn) in agricultural soils across China by combining traditional pollution indices, health risk models, and machine learning. A total of 1131 georeferenced samples compiled from published studies, representing 6 plantation types, food crop, fruit, vegetable, tea, medicinal, and others, were analyzed. Spatial mapping, Pearson correlation analysis, and the United States Environmental Protection Agency (USEPA) health risk framework were used to characterize contamination levels and estimate exposure. Among the plantation types examined, food crop plantations showed the highest contamination levels, with Pb and Zn most prominent, whereas Cd contributed most to ecological risk. Pollution index classification identified several regional hotspots warranting further monitoring. Estimated hazard indices remained below the threshold of concern for both adults and children, although they were consistently higher in children, and carcinogenic risks fell within acceptable limits for both groups. Of the three models tested, Random Forest performed the best (R2 = 0.99, 0.98, 0.96, 0.92, and 0.89 for Cu, Cd, Pb, Zn, and Cr, respectively), outperforming CatBoost and support vector regression. Feature importance and partial dependence analyses identified pH, magnesium, clay content, and total phosphorus as the most influential predictors of TE distribution. Interpreted within a One Health framework, these findings support continued monitoring and targeted management of agricultural soils in China.

Concentrations, Human Health Risks, Household Knowledge and Awareness of Heavy Metal Contamination in Ogbanokwute Spring Water, Enugu State, Nigeria

Heavy metal contamination of drinking water poses significant environmental and public health concerns due to the persistence, toxicity, and bioaccumulation of these pollutants. Consequently, the objective of this paper was to evaluate the Concentrations, Human Health Risks, Household Knowledge and Awareness of Heavy Metal Contamination in Ogbanokwute Spring Water, Enugu State, Nigeria using appropriate standard methods including structured questionnaire administered to 360 households. Chromium, lead, arsenic, and silver were not detected, while cadmium, aluminium, and zinc concentrations were within the World Health Organization (WHO) permissible limits. Heavy Metal Pollution Index (HPI) values (19.80 and 58.92), Metal Index (MI) values (0.658 and 1.537), and Degree of Contamination (Cd) values (−6.342 and −5.463) indicated low levels of contamination. Hazard Quotient (HQ) and Total Hazard Index (THI) values were below 1, indicating negligible non-carcinogenic health risks. Respondents demonstrated low-to-moderate knowledge and low awareness of the health effects of heavy metal contamination despite their heavy reliance on untreated spring water. Although the spring water is currently safe for consumption, inadequate public awareness may increase future vulnerability should contamination occur. Overall, Ogbanokwute Spring Water is presently safe for drinking with respect to heavy metal contamination. However, continuous water quality monitoring and community-based environmental health education are recommended. By integrating water quality assessment, human health risk evaluation, and community perception, this study provides evidence to support informed drinking water management and public health interventions.

Human Health Risk Assessment of Heavy-metal Exposure in Soil and Water from Oil-producing Communities of Delta State, Nigeria: An Audited Reassessment

Heavy-metal contamination in oil-producing environments may create human-health concerns through ingestion, inhalation and dermal exposure. This study reassessed non-carcinogenic and carcinogenic risks associated with Ni, Cr, Cu, Co, Pb, Cd, Fe, Mn, As and Zn in soil and water from the Apkai and Umusedege communities, Delta State, Nigeria, while auditing inconsistencies between thesis narrative summaries and numerical appendices. Concentrations were determined using atomic absorption spectrometry, with X-ray fluorescence used to validate soil results. Risk was evaluated using average daily intake, hazard quotient, hazard index and excess lifetime cancer risk for children and adults. The audit confirmed soil hazard indices of 2.51 for children and 1.29 for adults. Recalculation of water components yielded hazard indices of 0.02 for children and 12.31 for adults, producing corrected overall values of 2.53 and 13.60, respectively. For carcinogenic risk, an exponent error in the adult soil total was corrected to 1.85×10⁻⁶. Corrected total excess lifetime cancer risks were 7.18×10⁻⁶ for children and 2.40×10⁻⁶ for adults, both below the adopted 1×10⁻⁴ upper screening level. Soil ingestion dominated non-carcinogenic soil risk, whereas ingestion was the principal carcinogenic pathway. The unusually large adult water dermal hazard quotient of 12.04 requires independent verification. Overall, the audited results identify non-carcinogenic risk as the main modelled health concern.

From environment to human: systematic assessment of heavy metal contamination and exposure in a typical karst agricultural area