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Assessment of heavy metals and radionuclides pollution in an agro-mining river system: implications for environmental and human health

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
Open access Jul 2026

Predicting Cadmium and Arsenic Accumulation and Soil-Exposure Health Risks in Agricultural Soils Below the Risk Screening Values: A Refined Flux Balance Model

Less attention has been paid to soils with potentially toxic elements (PTEs) below agricultural land risk screening values, even though they continue to accumulate these elements. In this study, four typical areas in Ningxia were selected to determine the concentrations of cadmium (Cd) and arsenic (As) in 176 samples collected from 130 sampling sites across seven matrices. A refined mass balance model was developed by partitioning irrigation input into suspended-solid and supernatant phases and crop removal into grain and straw components. The model was used to analyze the contributions of various input and output factors and to predict future soil Cd/As concentrations and their related health risks via soil exposure. The input fluxes of Cd and As in the four regions ranged from 1.31 to 3.25 g·ha−1·yr−1 and 71.43 to 146.99 g·ha−1·yr−1, respectively, mainly contributed by irrigation water (40~64%), especially suspended solids in irrigation water, and atmospheric deposition (23~40%). The output fluxes of Cd and As were 0.89~1.43 g·ha−1·yr−1 and 13.81~33.86 g·ha−1·yr−1, respectively, dominated by crop harvesting (36~82%). The differences in input and output fluxes were mainly caused by the regional industrial structure and agricultural planting structure. The predicted results showed that soil Cd and As concentrations in all regions would not exceed regulatory limits after 100 years in the current scenario. A health risk assessment based on soil ingestion, dermal contact, and inhalation showed that the hazard indices for Cd and As were negligible, but their total carcinogenic risk reached notable levels. Over time, Cd-specific carcinogenic risk for children increased in several scenarios and transitioned from negligible to notable risk, with soil ingestion being the dominant exposure pathway. According to the results, targeted mitigation strategies, including the regulation of atmospheric deposition, optimization of irrigation water quality, and adoption of straw off-field practices, show potential to effectively limit the accumulation of potentially toxic elements in agricultural soils.

Ting-Ting Fan, Feiyang Xia, Da Ding et al. · 0 citations
Open access Aug 2026

Geochemistry, sources, human health and ecological risk of trace elements in soil from the Mirsarai export processing zone, southeastern coast of Bangladesh

Rapid industrial growth in Export Processing Zones (EPZs) has intensified concerns regarding trace element accumulation in soils and its environmental consequences. This study quantified twelve trace elements in soils from the Mirsarai Export Processing Zone using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) to evaluate contamination status, spatial distribution, potential sources, and associated ecological and human health risks. The results revealed significant enrichment of all trace elements except Fe, with pollution indices and spatial analysis indicating considerable contamination and heterogeneous distribution across the study area. Pearson correlation and principal component analysis (PCA) suggested that elevated trace element concentrations were primarily associated with industrial waste inputs. Ecological risk assessment identified Se as the dominant contributor (ER = 601.40), followed by As (149.85) and Hg (106.45). An innovative Source-Pathway-Receptor (SPR) model linked industrial activities with contaminant transport and environmental risks, identifying textile dyeing, leather processing, electroplating, battery manufacturing, metal finishing, and electronics industries as the principal sources of As, Cr, Cu, Zn, Pb, Cd, Ni, and Co. Non-carcinogenic risk assessment showed that Co posed the highest risk to children (HI = 8.54), followed by Mn (2.62), Cr (2.05), and As (1.45), whereas only Co exceeded the acceptable threshold for adults (HI = 2.25). Children experienced approximately 3.1-fold higher carcinogenic risk than adults, with Ni, Cr, and As exceeding the USEPA acceptable limit (1.0E−04). Monte Carlo simulation further confirmed a mean total carcinogenic risk of 1.58E−04 for children, highlighting the urgent need for pollution control and sustainable environmental management in rapidly industrializing EPZs.

M. S. Rahman, M. Uddin, M. Moniruzzaman et al. · 0 citations
Open access Aug 2026

Refining source-oriented ecological-health risk assessments of soil potentially toxic elements using region-specific geochemical baseline values in a high geological background region.

Naturally mineralized regions exhibit elevated geochemical backgrounds of soil potentially toxic elements (PTEs). However, the use of uniform geochemical baseline values (GBVs) frequently leads to misclassification between natural enrichment and anthropogenic contamination, hindering accurate source identification and risk control. To address this issue, this study established a region-specific GBV framework and integrated multi-receptor models with the Geo-detector and Partial Least Squares Structural Equation Modeling (PLS-SEM) to achieve source-oriented comprehensive risk assessments and elucidate underlying driving mechanisms in a high geological background region of northwestern China. Results showed that soil PTE enrichment was governed by four distinct pathways, including soil parent material characterized by Cr, Ni, and Co (A-F1: 26.61%), grazing-related inputs characterized by Cu and Zn (A-F2: 21.09%), mineralization-related background anomalies dominated by Hg (A-F3: 16.09%), and domestic emissions characterized by Pb and As (A-F4: 7.62%). PLS-SEM further demonstrated that soil PTE enrichment resulted from interactions among geological background (0.894, p < 0.001), climatic regulation, and anthropogenic modification (0.448, p < 0.001), revealing hierarchical mechanisms linking environmental drivers, source formation, and PTE accumulation. Meanwhile, low and moderate potential ecological risks occurred in 99.6% and 0.4% of the area, respectively. The risk was mainly driven by mineralization-related anomalies, which accounted for 67.41% of the ecological risk. The total non-carcinogenic health risks were generally within acceptable levels (Total hazard index < 1.00). Deterministic assessment indicated unacceptable carcinogenic risk (Total carcinogenic risk > 1.00 × 10⁻4) in 6.0% (children) and 3.9% (adults) of the study area, whereas probabilistic Monte Carlo simulation revealed higher exceedance probabilities at the 95th percentile (25.97% for children). Natural geogenic sources (A-F1 and A-F3) dominated the non-carcinogenic risk, contributing 65.48% and 68.36% of the THI for adults and children, respectively. Carcinogenic risk was driven by both soil parent material (A-F1: 44.34% for adults, 36.32% for children) and anthropogenic inputs (A-F2 and A-F4: 46.88% for adults, 56.48% for children) of the TCR. Among the characteristic PTEs, Cr and Ni primarily represented concentration-driven risks, whereas Hg posed toxicity-driven risks despite its relatively low concentrations. These findings demonstrate that ecological-health risks in high geological background regions are commonly controlled by source characteristics, elemental toxicity, and exposure pathways rather than contamination levels alone. They provide a scientific basis for source-oriented risk management under region-specific geochemical backgrounds.

Shi-Ming Yang, Zi-Hao Fan, Qiong Han et al. · 0 citations
Open access Aug 2026

Spatial Distribution, Source Apportionment, and Source-Specific Ecological Risk Assessment of Heavy Metals in Farmland Soils of the Ningxia Yellow River Irrigation Area

To characterize heavy metal accumulation, potential sources, and source-specific ecological risks in farmland soils of the Ningxia Yellow River Irrigation Area, 537 topsoil samples were analyzed for As, Hg, Cd, Pb, and Cr. positive matrix factorization (PMF) was coupled with the potential ecological risk index to quantify source-specific mass and ecological risk contributions. Cd and Hg showed the strongest enrichment relative to regional background values, with mean concentrations of 2.38 and 2.02 times the respective background values. PMF resolved four factors interpreted as an agricultural input-related source, a parent material-dominated natural source, an urban industrial- and combustion-related atmospheric deposition source, and a Yellow River alluvial–hydrological natural background source. The mean potential ecological risk index calculated from PMF reconstructed concentrations was 168.45, closely matching the observed value of 168.77. Source-specific mass and ecological risk contributions were clearly decoupled: the two natural source factors contributed 71.19% of the modeled heavy metal mass but only 24.21% of the ecological risk, whereas the two anthropogenic source factors contributed 28.81% of the mass but 75.80% of the risk. The atmospheric deposition and agricultural input-related sources contributed 47.27% and 28.53% of the ecological risk, respectively. Site-level bootstrap resampling and alternative allocation procedures retained the source risk ranking. These findings indicate that risk-based management should prioritize Hg-related atmospheric deposition and Cd-related agricultural inputs rather than total heavy metal mass alone.

Xiangyu Liang, Yu-Jie Zhao, Jian-Jun Ma et al. · 0 citations
Aug 2026

Cadmium in global topsoil: Spatial distribution, associated factors, and cropland exposure screening.

Soil cadmium (Cd) pollution is a persistent concern for soil quality, crop production, and food safety. Despite global concerns, spatial predictions of topsoil Cd remain challenging due to limitations in model accuracy, covariate representation, and nonlinearity handling. This study addresses these gaps by integrating 59,328 topsoil Cd samples worldwide to map global Cd exceedance probability and concentration distribution using classification and regression machine-learning models, with AUC of 0.90 and R² of 0.72, respectively. Variable importance analysis identifies climate factors (39.00%) and soil properties (34.01%) as the dominant factors associated with Cd exceedance probability, followed by geology (13.22%), topography (5.01%), and vegetation (4.58%), while anthropogenic contributions appear more localized at the global scale. High-resolution (1 km) maps of global soil Cd exceedance probability and predicted concentration distribution are generated. Under the moderate screening scenario, approximately 0.14% of global cropland (23,130 km²) overlapped with acidic high-soil-Cd-risk zones, mainly in China (15,201 km²), the UK (4956 km²), and Ireland (1382 km²). Approximately 1.24% of rice, 0.33% of wheat, and 0.22% of maize production were located in areas classified as high soil-Cd-risk zones, indicating priority areas for monitoring rather than direct evidence of grain Cd exceedance. These findings provide a spatially explicit basis for preliminary screening, targeted monitoring, and soil Cd management.

Rui-Xing Huang, Zhentao Xiao, Chengxue Ma et al. · 1 citation

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