Quantifying Levels of Selected Metals in Different Rice Brands

This research focused on assessing the levels of selected metal contamination in seven different rice brands (Jasmine, Basmati, Mapembe, Morogoro, Shinyanga, Mbeya, and Cheju). Cheju rice was obtained from local producers from the Cheju area in Zanzibar, while the remaining rice brands namely, Jasmine, Basmati, Mapembe, Morogoro, Shinyanga, and Mbeya were randomly taken from local markets at Darajani and Mwanakwerekwe in Zanzibar. Samples were prepared in accordance with applicable Safe Operating Procedures (SOPs) and laboratory SOPs using information provided by field sample preparation. The samples were ground to fineness and an aliquot of about 10.0 g was measured on the beam balance and mounted on the sample holders for laboratory analysis. An Energy Dispersive X-Ray Fluorescence (EDXRF) technique with a Rigaku NEX CG EDXRF model spectrometer was used for metal analysis. The study revealed that the percentage of metal contamination varied considerably from one rice brand to another, with Basmati and Jasmine rice each exhibiting a contamination level of 50%, while Shinyanga, Mbeya, Mapembe, and Cheju rice showed a level of 25% each. Notably, Morogoro rice had no observable heavy metal contamination. Additionally, a significant positive correlation was observed between several metal pairs: Au and Cr (r² = 1.00), Au and Ti (r² = 0.613), Cr and Ti (r² = 0.613), Ni and Pb (r² = 0.748), Ni and Hf (r² = 0.660), Pb and Hf (r² = 0.656), and Ti and Sn (r² = 0.671). The individual occurrence (percentage) for metals across all rice brands were as follows: 71.42% for Sn, and 28.57% for Hf, Ni, Pb, and Ti, while traces of Au, Cr, and Y each had an occurrence level of 14.28%. While Morogoro rice showed no metal discernible analyzed heavy metal contamination, the other rice brands were observed to have a considerable heavy metal contamination trend. The patterns of metal occurrence in each rice brand were observed as follows: Basmati: Sn > Ti > Au > Cr; Jasmine: Sn > Hf > Ni > Pb; Shinyanga: Sn > Pb; Mbeya: Sn > Hf; Mapembe: Sn > Ti; Cheju: Ni > Y. The patterns, then yield the ranking of metal contamination across all seven rice brands from lowest to highest is as follows: Morogoro < (Mapembe, Cheju, Mbeya, Shinyanga) < (Jasmine, Basmati). Furthermore, the data analysis indicated that the concentrations of Cr (1.08 mg/Kg), Ni (4.65 mg/Kg), and Pb (3.05 mg/Kg) detected in the samples surpassed the maximum permissible limits established by WHO/FAO which were 1.0 mg/Kg, 0.10 mg/Kg and 0.20 mg/Kg respectively. Consequently, the study concludes that Morogoro rice is the most superior and considered the safest choice for consumption, while Jasmine and Basmati rice are associated with higher levels of metal contamination. Thus, it is highly recommended that Tanzania intensify its rice cultivation efforts to reduce reliance on rice imports from other nations.