Investigation of Heavy Metal Concentration in Cabbage Leaves (Brassica oleracea) Using Atomic Absorption Spectroscopy
Yusuf Ismail Koleleni *
Department of Physics, Muslim University of Morogoro, P.O.Box 1031, Morogoro, Tanzania.
*Author to whom correspondence should be addressed.
Abstract
Heavy metal accumulation in leafy vegetables is a food safety concern, particularly where agricultural production occurs under differing environmental conditions. This study investigated the concentrations of selected heavy metals, namely Zinc (Zn), Copper (Cu), Lead (Pb) and Cadmium (Cd), in cabbage leaves (Brassica oleracea) collected from three regions of Tanzania: Iringa (Sample A), Tanga (Sample B) and Morogoro (Sample C), using Flame Atomic Absorption Spectroscopy (FAAS). Samples were washed, dried, homogenised, and digested using a mixture of nitric acid (HNO₃) and hydrogen peroxide (H₂O₂) prior to analysis. The results showed that Zinc recorded the highest concentration among all analysed metals, ranging from 15.00 ppm in Sample A to 46.00 ppm in Sample C, followed by Copper (0.80 to 4.10 ppm) and Lead (0.01 to 0.40 ppm). Cadmium was not detected in Samples A and B but was recorded at 0.11 ppm in Sample C. In all cases, concentrations increased progressively from Iringa to Tanga to Morogoro, suggesting that agricultural practices, irrigation water quality, and industrial and urban activities influenced heavy metal accumulation in cabbage leaves. Comparison of the results with WHO/FAO permissible limits showed that Zinc, Copper, and Cadmium concentrations were within the recommended safety limits in all three samples. However, the Lead concentration recorded in the Morogoro sample (0.40 ppm) exceeded the WHO/FAO permissible limit, indicating a potential health risk to consumers if such cabbage is consumed regularly over a long period. The study concludes that cabbage grown in Iringa and Tanga was generally safe for human consumption with respect to the metals analysed, while cabbage grown in Morogoro requires closer monitoring due to its elevated Lead concentration. The study recommends regular monitoring of irrigation water quality, controlled application of agrochemicals, and continued surveillance of heavy metal levels in vegetables grown in peri-urban and industrial-adjacent areas in order to safeguard public health.
Keywords: Heavy metal concentration, leafy vegetables, food safety, cabbage leaves, irrigation