Assessment of Heavy Metal Concentrations in Selected Nigerian-Grown Rice Grains: Implications for Public Health

Abstract

Contamination of the food chain by heavy metals poses a serious threat to human health and disrupts sustainable agriculture. This study aims to evaluate heavy metal contamination in locally grown rice from selected states across Nigeria. Rice and soil samples were collected from rice paddy fields in Ogun, Kwara, Ekiti, Edo, Jigawa, and Kano. Atomic absorption spectrophotometry was employed to evaluate the elemental composition of rice and soil samples. Toxic metals such as Pb, Ni, Cd, and As were detected in some of the local rice varieties sampled. Notably, Pb (0.040±0.00) and Cd (0.277±0.02) were found in Ofada rice from Ogun state. Higher concentrations of Ni were found in Igbemo rice from Ekiti, with the lowest levels observed in Umza rice from Kano. Variations in As levels in the rice types followed the order: Ofada rice, Ogun > Sese rice, Edo > Pategi rice, Kwara > Costus rice, Kano > Igbemo rice, Ekiti > Umza rice, Kano. In soil samples, variations in Pb levels followed the order: Kwara soil > Kano soil > Ogun soil > Edo soil. Cadmium (Cd) levels were highest in Kwara soil (0.856±0.11) and lowest in Jigawa soil (0.119±0.01). However, the lifetime cancer risk (LCR) assessment for rice samples from different regions reveals that most of the samples exceed the US EPA LCR acceptable upper limit is 1.0 × 10⁻⁴, suggesting a substantial danger of exposure to life cancer risk throughout a lifetime. Hence, underscoring the need for continuous monitoring and stringent control measures in vulnerable regions.