Heavy metal contamination in agricultural soils and potential human health risks

Heavy metal contamination in agricultural soils is a growing concern due to potential human health risks via ingestion, dermal contact, and inhalation. However, data on fertiliser-related contamination in rural Tanzanian settings remain limited. This study assessed contamination levels and associated health risks in Kibwabwa village, Iringa, Tanzania. A total of 48 soil samples were collected from eight farms at a depth of 0–15 cm. Concentrations of Cu, Zn, Ni, Cd, Cr, and Pb were determined using Atomic Absorption Spectroscopy (AAS). Health risks were evaluated using chronic daily intake (CDI), hazard quotient (HQ), hazard index (HI), and carcinogenic risk (CR) models for ingestion, dermal contact, and inhalation pathways in both adults and children. Mean concentrations (mg/kg) were 8.58 for Cu, 1.07 for Zn, 5.98 for Ni, 0.26 for Cd, and 9.67 for Cr, while Pb was not detected. All measured values fell within the permissible limits established by the FAO/WHO and the Tanzania Bureau of Standards (TBS). Correlation analysis showed that Cu correlated negatively with Cd (r = –0.629, p = 0.05) and positively with Cr (r = 0.650, p = 0.05). Ingestion was the main exposure pathway for adults, whereas dermal contact posed the highest risk for children. Inhalation was the least significant route for both groups. HQ values were below 1, and CR values ranged from 1E–06 to 1E–04, indicating low non-carcinogenic and carcinogenic risks, respectively. Children, however, exhibited greater vulnerability, particularly to Cr and Cu exposure. This study provides new insights into the health implications of fertiliser-related soil contamination in Tanzania. Although current heavy metal levels remain within safe limits, regular monitoring is recommended to prevent future accumulation and protect public health, especially that of children.