Comparative Evaluation of Heavy Metals Bioconcentrations in Spinach Grown on Cow Dung-Enhanced and NPK-Enhanced Soils

This study compares heavy metal bioconcentrations in spinach (Spinacia oleracea) cultivated in soils enhanced with cow dung and NPK (15:15:15) fertilizer. Soil samples from agricultural fields around Wukari, Nigeria, were analyzed for physicochemical properties, revealing an alkaline pH, moderate organic carbon, and high nitrogen content, which are conducive to plant growth. Spinach plants were grown under controlled greenhouse conditions with different nutrient treatments: cow dung alone, NPK alone, a combination of both, and no enhancement. After a 37-day growth period, heavy metal concentrations, specifically Pb, Fe, Zn, and Cr, in plant roots and shoots were quantified using atomic absorption spectrophotometry and compared against WHO/FAO permissible limits. The result showed significant difference (P≤0.05) in the heavy metals accumulation in the plant under study indicating that NPK and cow dung amendments influenced heavy metal uptake, with elevated levels of Pb and Zn observed in tissues, particularly in NPK-enhanced spinach, where Pb in NPK-enhanced shoots (0.617 mg/kg) exceeded WHO limits (0.3 mg/kg). BCF for Pb reached 2.0 in cow dung-NPK enhanced soil, suggesting a potential health risk. Bio-concentration and translocation factors revealed spinach's capacity to accumulate Pb and Zn, highlighting the risk of heavy metal transfer through the food chain. The findings underscore the importance of selecting appropriate soil amendments to mitigate heavy metal uptake, recommending integrated nutrient management practices that minimize health risks while sustaining crop productivity. Overall, the study emphasizes the need for ongoing monitoring and sustainable fertilization strategies in vegetable cultivation to ensure food safety.