Heavy metal and pesticide toxicity in agricultural soils across a farming intensity gradient in Central Zambia

Routine pesticide applications are an under‑recognized pathway for heavy metal accumulation in agricultural soils, particularly in sub‑Saharan Africa where synthetic pesticide use is expanding rapidly but systematic monitoring remains limited. This study investigated the co‑occurrence of heavy metals and pesticides in soils across farming landscapes of Central Province, Zambia, focusing on Chibombo and Mkushi Districts. Four metals (Cd, Pb, Cu, Zn) and twelve pesticides; acetamiprid, acifluorfen, chlorpyrifos, clodinafop propargyl, lambda cyhalothrin, cypermethrin, emamectin benzoate, fomesafen, haloxyfop methyl, lufenuron, profenofos, glyphosate, and its metabolite AMPA, were assessed in commercial, emergent, and smallholder farming systems using pollution indices (enrichment factor and ecological hazard index) and correlation analysis. Results showed significant differences in the accumulation of Cu, Cd, and Zn across farming systems, with commercial farms exhibiting higher Cd and Cu concentrations than emergent and smallholder systems, and heavy metals being significantly enriched in topsoils (0-20 cm) compared to deeper layers. Smallholder farms had high insecticide residues, especially chlorpyrifos (1494-5961 µg/kg), emergent farms showed elevated insecticide and herbicide levels, notably cypermethrin and fomesafen, while commercial farms were dominated by herbicides including acifluorfen, fomesafen, glyphosate, and AMPA. Correlation analysis revealed significant associations between metals and certain pesticides, with chlorpyrifos and profenofos residues showing consistent negative correlations with all metals except Cu. Comparative analysis against international soil quality standards indicated heavy metals remained below WHO limits except for Cu and Cd in some commercial farms. These findings underscore significant ecological and food safety risks, highlighting the urgent need for systematic monitoring and integration into policy frameworks.