Occurrence and Risk Evaluation of Trace Metals in Infant Nutrition Sources in Rural and Urban Multan, Pakistan

Lead (Pb), cadmium (Cd), nickel (Ni) and other toxic trace metals pose risks to infants due to their rapidly developing organ systems and limited capacity to detoxify contaminants. These metals can be found in breast milk and commercially sold infant formulas, which often serve as sole nutritional source in early life. This first-of-its-kind cross-sectional study in Pakistan analyzed trace metals in breast milk from lactating mothers and 62 commercial infant formula brands in Multan. Infants were grouped by age (0–3.5 and 3.6–7 months) and dwelling (urban/rural). Zinc (Zn), Iron (Fe), Nickel (Ni), Lead (Pb), and Cadmium (Cd) were detected using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Risk was assessed via Estimated Daily Intake (EDI), Target Hazard Quotient (THQ), Hazard Index (HI), and Target Cancer Risk (TCR), with statistical analysis through t-tests, effect sizes, correlation, and PCA. Rural samples showed higher Zn and Fe concentrations, while urban samples exhibited elevated Pb and Cd. Cumulative HI exceeded 1 in both regions (rural: 2.30 ± 2.70; urban: 4.18 ± 3.13), with urban HI significantly higher (p = 0.0128). TCR values for Ni, Pb, and Cd surpassed the 10⁻⁴ threshold in both areas, with urban cumulative TCR (0.00205) exceeding rural (0.00161). PCA identified Pb, Cd, and HI as principal risk drivers; effect size analysis highlighted Cd as a large contributor (d = 1.05). This study documents rural–urban disparities in infant metal exposure and introduces carcinogenic and non-carcinogenic risk frameworks as tools for public health advocacy on infant nutrition in South Asia.