Trace Metals in Rice Grains and Their Associated Health Risks from Conventional and Non-Conventional Rice Growing Areas in Punjab-Pakistan

Abstract

Rice (Oryza sativa L.) is cultivated and consumed worldwide, but the contamination of rice grains with trace metals (TMs) could cause adverse impacts on human health. The aims of this study were to determine the concentrations of TMs in different rice varieties available for sale in local markets and to determine whether consumers are likely to be at risk via the consumption of these rice cultivars. For this purpose, samples of rice grains were collected from 12 rice growing districts (administrative units) in Punjab, Pakistan. These districts were further classified based on rice growing methods due to specific soil type. In conventional districts, the puddling method was used, while direct seeding was used for rice cultivation in non-conventional districts. The samples were collected and analyzed for the determination of essential (Cu, Fe, Zn, and Mn) and non-essential (Cd, Ni, and Pb) TMs using an atomic absorption spectrophotometer (AAS). The results showed that the maximum respective concentrations of Cd, Ni, and Pb (0.54, 0.05, 1.10 mg kg−1) were found in rice grains in conventional areas, whereas values of 0.47, 0.20, and 1.20 mg kg−1 were found in non-conventional rice growing areas. The maximum concentrations of essential TMs (Cu, Fe, Mn, and Zn) were 4.54, 66.01, 4.82, and 21.51 mg kg−1 in conventional areas and 3.76, 74.11, 5.66, 19.63 mg kg−1 in non-conventional areas. In the conventional rice growing areas, Fe and Zn concentrations exceeded the permissible limits in the 27 and 7% samples, respectively. In the non-conventional rice areas, the concentrations of Cu, Fe, and Mn exceeded the permissible limits in the 15, 26, and 3% samples, respectively, while its Zn concentration was found within the permissible limits. The estimated weekly intake (EWI) and maximum tolerable dietary intake (MTDI) values for all studied metals were found within the permissible values set by WHO, except for Fe, in both sampled areas. It was concluded that no health risks were associated by utilizing the rice grains. However, the mean values of TMs were found considerably higher in collected rice samples from non-conventional areas than the conventional areas. Therefore, the concentrations of TMs should be monitored properly.