Assessment of heavy metal contamination in irrigation water and its impact on maize crops: a case study of Peshawar, Pakistan

Abstract Soil contamination with heavy metals from irrigation systems is a growing environmental problem in agriculture areas of Pakistan that impacts soil quality, food safety and food security. Little information is available regarding the transfer dynamics from irrigation water to soil and maize in the Peshawar area for cadmium (Cd), chromium (Cr) and lead (Pb). This study provides a baseline assessment of Cd, Cr, and Pb concentrations in irrigation water, soil, and maize tissues collected from three agricultural sites: Mera Kachori, Tarnab Farm, and Haider Khan Garhi. Results indicated that Cd concentrations in irrigation water (0.02–0.05 µg mL⁻¹) exceeded WHO permissible limits at all sites, while Cr and Pb remained within safe limits. Although the concentration of Pb in the irrigation water may be low, repeated use can cause the progressive accumulation of Pb in the soil matrix due to the binding of Pb to the clay particles and organic matter, and once bound to soil, the Pb can be available for root uptake, thus resulting in higher levels of Pb in the roots and shoots even if the source water is within the limits. Soil metal concentrations were below FAO/WHO guideline values, indicating no immediate soil contamination risk. In maize, Cd and Pb accumulation was observed in vegetative tissues, with occasional exceedance of permissible limits in leaves, roots, and shoots, whereas Cr remained within safe thresholds across all plant parts. However, grain samples consistently remained within safe limits for all metals. The results indicated minimal, short-term human health threat from grain exposure, but elevated levels in the vegetative tissues indicated potential threats to livestock exposure and long-term environmental loading. Continuous monitoring and improved irrigation management strategies are recommended to mitigate potential risks to the soil–plant system.