Trace Metal Concentrations in Local and Imported Rice Consumed in Southeast Nigeria

Abstract

Rice (Oryza sativa L.) is a staple for half the world’s population and a major component of the Nigerian diet. As domestic production lags behind rising demand, Nigeria increasingly relies on rice imports, raising food safety concerns. This study aims to determine and compare concentrations of Zn, Pb, Cr, Cu, and Cd in 36 rice samples (20 imported, 16 locally grown; short- and long-grain) collected from markets across five southeastern Nigerian states. Additionally, health risks from rice consumption were assessed. Samples were processed and analysed by atomic absorption spectrometry. The objectives were to quantify trace metal levels in local and imported rice, evaluate differences by grain size and location, assess potential health risks, and compare results with FAO/WHO limits and literature. Results showed a decreasing concentration trend: Zn > Cd > Cu > Pb > Cr. Mean concentrations (±SD) were 1.24±1.15 mg/kg (Zn), 0.58±1.55 mg/kg (Cd), 0.24±0.17 mg/kg (Cu), 0.18±0.23 mg/kg (Pb), and 0.12±0.27 mg/kg (Cr). All metals except Cd were below FAO/WHO maximum limits, but some samples exceeded the 0.2 mg/kg Cd threshold. Locally produced rice contained significantly higher Zn (3.6×), Pb (2.0×), and Cd (18×) than imported rice. Short-grain rice had higher Zn, Pb, and Cd than long-grain. Notably, rice from Ebonyi State (a known Pb-Zn mining region) showed extreme Cd (1.89±3.27 mg/kg), suggesting geogenic contamination. Health risk assessments indicated estimated daily intakes and hazard quotients below harmful levels for adults and children. Our findings provide important baseline data and highlight the need for continued monitoring of trace metals in rice for food safety in Nigeria. The findings suggest that rice consumed in southeastern Nigeria is generally safe, though residents of Ebonyi State who frequently consume locally produced rice may be at risk of increased cadmium accumulation. Regular monitoring of food products for metal contamination remains essential for public health protection. This study thus contributes critical baseline data to guide food safety policy and monitoring efforts in Nigeria.