Assessment of heavy metals concentrations, soil-to-plant transfer factor and potential health risk in soil and rice samples from Ezillo rice fields in Ebonyi State, Nigeria

Abstract

This study examined the level of heavy metals (Pb, Ni, Cd and Cr) concentrations in soil and rice samples from two paddy fields (field 1 and 2) located in Ezillo, Ebonyi State by means of flame atomic spectrophotometer. Topsoil soil samples at depths 0–4 cm and 4–8 cm were collected before planting (BP), after planting (AP) and during harvesting (DH) stages. The concentrations of the metals in soil from field 1 at depth 0–4 cm decreased in this order of Cr > Ni > Pb > Cd (BP), Ni > Cr > Pb > Cd (AP) and Cr > Ni > Cd > Pb (DH) while at depth 4–8 cm, the orders were Ni > Cr > Cd > Pb (BP), Cr > Ni > Pb > Cd (AP) and Ni > Cr > Pb > Cd (DH). In field 2, at depth 0–4 cm, the order Cr > Ni > Pb > Cd was found in all the farming stages while at depth 4–8 cm orders were Cr > Ni > Cd > Pb (BP), Cr > Ni > Pb > Cd (AP) and Ni > Cr > Pb > Cd (DH). In the rice samples, the orders were Cr > Ni > Pb > Cd in field 1 and Cr > Ni > Cd > Pb in field 2. The levels of the metals in both soil and rice samples were relatively low when compared with permissible limits of some regulatory agencies. The estimated average daily intake (ADI), hazard quotients (HQ) and total hazard index (THI) of the metals in both soil and rice indicate higher values in children than the adult group. The HQ and HI values were below the permissible safe limits of 1.0. This is an indication that the selected metals in the paddy soil and rice present no appreciable threat to food safety. Therefore, with respect to the investigated metals, the rice produced from these fields is safe for human consumption.