A Comparison of The Levels of Heavy Metals in Cabbages Irrigated With Reservoir and Tap Water

A study was carried out in Malawi to determine the levels of heavy metals in cabbages grown in gardens irrigated with reservoir and tap water. The concentrations of cadmium, lead and chromium were determined in the leaf and in the corresponding soils in order to assess whether the amounts in the soils reflected the accumulation of heavy metals in plants. The results showed that the levels of the heavy metals in both the cabbages and soils irrigated with reservoir water were generally low. The concentration of cadmium in reservoir water irrigated cabbages was significantly higher (p<0.05) than that in tap water irrigated cabbages. The concentration of cadmium in both the dam water and tap water irrigated cabbages was much higher than the levels (0.2ppm) recommended by the European Union for leafy vegetables. The trend was opposite for lead; the amounts in reservoir water irrigated cabbages were lower than in tap water irrigated ones although the two were not statistically different. The higher concentrations in the leaf from both sites (p<0.05) compared to those in the soils could be an indication of hyper accumulation in the leaf. In contrast to cadmium, the concentration of lead in tap water irrigated cabbages was higher than that recommended by the European Union (0.3ppm) for leafy vegetables. There was no significant difference in the concentration of chromium in dam and tap water irrigated cabbages. The significantly higher concentration of chromium in the cabbages than in the soils for both dam and tap water irrigated fields could also be indicative of bio-accumulation of the metal in the leaf.