Heavy metals seasonal variation and uptake pattern in rice grown in Kano State, Nigeria

Abstract

The contamination of rice by heavy metals (HMs) has been assessed and investigations have uncovered that the concentrations of heavy metals such as lead, chromium, manganese, and cadmium in rice samples have exceeded the permissible thresholds in many locations across the world including Nigeria. This study aimed to determine the pattern of Zn, Pb, Cd, Ni, Co, Cu, Cr and Hg accumulation in the roots and grains of rice samples collected from 10 different locations across the Kano River Irrigation Project during wet and dry season production and compare the metal concentrations with the permissible limits recommended by FAO/WHO. Also, to use Translocation Factors and study Zn, Pb, Cd, Ni, Co, Cu, Cr and Hg uptake patterns in rice during wet and dry growing seasons. Rice grain and root samples were collected from 10 different locations across the irrigation scheme during the 2022 wet season and 2023 dry season. Samples were prepared using standard laboratory methods and subjected to metal analysis using an atomic absorption spectrophotometer. The results show that the accumulation of HMs in rice grain samples follows this order Zn>Cu>Pb>Ni>Cr>Co>Cd for both wet and dry seasons with higher accumulation reported in dry season production. It was only the mean concentration of Zn that exceeded the permissible limit during the wet season. The concentrations of Pb and Cd were also observed to exceed permissible limits in addition to Zn during dry season production. Hg was not detected in all the samples. Wet season production provides a safer rice grains with lesser heavy metals contamination.