Heavy metal accumulation and food safety of lettuce ( L.) amended by bioslurry and chemical fertilizer application.

The accumulation of heavy metals in soil and plant tissue is a serious concern since it impacts both soil quality and food safety. This study evaluated the accumulation of heavy metals and the food quality of lettuce as a result of the application of chemical fertilizer (CF) and bioslurry (BS). The treatments were CF (158 kg ha NPS and 200 kg ha urea), BS (5 ton ha), and control with no fertilizer, laid out in a randomized complete block design with three replications. Soil samples were analyzed for their physico-chemical characteristics. The concentrations of 10 heavy metals (As, Pb, Zn, Cd, Cu, Ni, Co, Fe, Mn, and Cr) in the agricultural soil, bioslurry, and lettuce tissue were determined. Both the BS and CF reduced the concentrations of most heavy metals in the agricultural soil, particularly As, Pb, and Cd. Only the mean concentration of Cd in the agricultural soils exceeded the threshold level set by WHO/FAO (2011) for agricultural soils. Similarly, the concentration of As, Pb, and Cd in lettuce tissue grown in BS-treated soils and the concentration of As in agricultural soils surpassed the limit set for vegetables. Given the toxicities of As, Cd, and Pb, as well as the effect on food safety, human health, and the environment, it is unsafe to cultivate lettuce using either the agricultural soil or BS in the study area.