Abstract
<title>Abstract</title> <p> <italic>The reuse of untreated slaughterhouse wastewater for agricultural irrigation can enhance crop production by supplying nutrients but may also introduce potentially toxic elements (PTEs) into agricultural soils and edible crops. This study investigated the occurrence, soil–plant transfer, and potential human health risks associated with chromium (Cr), copper (Cu), iron (Fe), lead (Pb), and zinc (Zn) in green leafy vegetables cultivated using slaughterhouse wastewater in Ikwiriri Ward, Tanzania. Twelve samples each of Vigna unguiculata, Ipomoea sp., and Cucurbita sp., together with corresponding soil and wastewater samples, were collected and analyzed. Samples were subjected to matrix-specific acid digestion procedures using nitric acid (HNO₃), sulfuric acid (H₂SO₄), and perchloric acid (HClO₄) for solid samples and nitric acid–hydrogen peroxide digestion for wastewater samples. Metal concentrations were determined using microwave plasma atomic emission spectrometry (MP-AES; Agilent 4200). All investigated metals were detected in vegetable tissues, indicating the transfer of contaminants within the wastewater–soil–plant system. Iron was the most abundant element in vegetables, ranging from 15.543 to 96.109 mg kg⁻¹ dry weight, followed by Zn (2.933–7.740 mg kg⁻¹), Cu (1.212–2.307 mg kg⁻¹), Cr (0.182–0.437 mg kg⁻¹), and Pb (0.073–0.158 mg kg⁻¹). Wastewater samples contained Fe at the highest concentration (2.098 mg L⁻¹), followed by Zn, Pb, Cr, and Cu. Although individual metal concentrations in vegetables were below established international guideline values, the combined exposure assessment revealed hazard index (HI) values above unity for V. unguiculata (1.650) and Cucurbita sp. (1.533), suggesting potential long-term non-carcinogenic health concerns. The findings demonstrate that untreated slaughterhouse wastewater may represent a persistent pathway for metal entry into agricultural food systems and highlight the need for wastewater treatment, routine monitoring, and improved management practices to safeguard food safety and public health.</italic> </p>