Health risk analysis of toxic metals in soils and vegetables from Tatsawarki Farms in Kano State, Nigeria

Abstract

This study evaluated the concentrations of toxic metals in soils and vegetables, as well as the environmental and health risks in selected Tatsawarki Farms. Physico-chemical parameters, including pH, Electrical Conductivity (EC), and particle size, were analyzed, and Atomic Absorption Spectrophotometry (AAS) was used for metal concentration assessment. Pollution indices (Geo-accumulation Index (Igeo), Enrichment Factor (EF), Contamination Factor (CF), Ecological risk Factor ( $${\text{E}}_{r}^{i}$$ ), Ecological Risk Index (RI), and Pollution Load Index (PLI)) were calculated. Additionally, Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) were used to trace contamination sources. Health risks were assessed using (EDIM), target hazard quotient (THQ), Health Risk Index (HRI) and, transfer factor (TF) calculations to analyze metal accumulation. Soil pH samples ranged from 7.30 to 8.20. The concentrations of Cd, Cr, and Zn in soil ranged from 0.25 to 17.50 mg/kg, 8.25 to 194.50 mg/kg, 6.00 to76.75 mg/kg, respectively, while levels in vegetables were 0.00–13.50 mg/kg, 1.50–82.25 mg/kg, and 0.00–92.25 mg/kg, respectively. Pollution indices indicated Cd posed the highest contamination risk, followed by Cr, while Zn had the least pollution impact. PCA and HCA classified the toxic metals into two groups, indicating that both human activities and parent material significantly contributed to the contamination of Cd, Cr and Zn. Cd and Zn may originate from anthropogenic sources, whereas Cr may originate from lithogenic-anthropogenic sources. Cadmium concentrations were 9.06 ± 0.72 mg/kg, 10.08 ± 0.92 mg/kg and 8.53 ± 0.13 mg/kg from F1, F2 and F3 Farms, respectively. However, the concentration of Cr was significantly higher in F3 compared to F1 and F2. There was no significant difference in the concentrations of Cd and Zn in the soil samples from the three farms (Post-hoc, p > 0.05). Heavy metal concentration followed the pattern: soil > vegetables. Zinc had the highest transfer factor (TF = 1.20), followed by Cr (0.88) and Cd (0.74). Health risk assessments (EDIM, THQ, HRI) revealed Cd exposure exceeded safe limits, posing greater risks for children and adults. The study reveals that excessive toxic metal concentrations in vegetables could pose serious health risks to consumers, necessitating continuous environmental monitoring. The concentrations of Cd and Cr in some vegetables were above the FAO/WHO permissible levels. Effluents discharged into water used for irrigating vegetable samples are local pollution Sources. Pollution indices indicated toxic metal contamination. Cluster analysis showed anthropogenic and lithogenic sources of pollution. Transfer factor showed the mobility of toxic metals from soil to vegetables. Estimated daily intake of metal (EDIM), target hazard quotient (THQ) and Health Risk Index (HRI) indicated that Cd poses a potential health risk.