Abstract
We have determined the levels of five heavy metals (Cu, Hg, Mn, Pb, Zn) in outer tissue washings, outer tissues, and inner tissues of different vegetable samples (beans, cabbage, capsicum, carrot, cauliflower, cucumber, eggplant, green pepper, pea, and tomato) from the Qassim region of Saudi Arabia. Instead of using the customary dried tissue power, we conducted all the analysis directly in the wet tissues following microwave digestion; the levels of heavy metals being reported in wet as well as dry tissue using the water-content factor. Pb was absent in the washings but present in most of the vegetables in the range of 0.013-0.25 mu g/g wet tissue (0.201-5.055 mu g/g dry tissue). Although traces of Hg (5.994-6.520 ng/g wet tissue) were present in the washing, this metal was not detected in the vegetable tissues. Cu was observed in the range of 0.079-1.785 mu g/g wet tissue (1.104-22.919 mu g/g dry tissue), whereas the range of Mn was found to be 0.239-3.263 mu g/g wet tissue (4.626-47.036 mu g/g dry tissue). Only in the outer tissues of peas were Cu levels found to be slightly higher (22.919 mu g/g dried tissue) than the recommended upper limit of 20 mu g/g. Zn was detected only in the beans, green pepper, and peas; its concentration was much higher in outer (552.77 mu g/g) and inner (686.71 mu g/g) tissues of green pepper than the recommended upper limit of 100 mu g/g. The lower limits of detection (LOD) and quantification (LOQ) for Hg were found to be 0.81 and 1.61 ng/kg, respectively. The LOD and LOQ for the remaining heavy metals were as follows: Cu (1.28 and 4.27 mu g/kg), Mn (0.23 and 0.77 mu g/kg), Pb (7.56 and 24.79 mu g/kg), and Zn (5.98 and 19.96 mu g/kg). Our findings suggest that the analysis of heavy metals directly in the wet samples provides a quick alternative for screening of heavy metals as this method can determine the heavy metals well below their toxic limits. The presence of heavy metals in the washings of the outer tissues of vegetables points toward the importance of thoroughly washing vegetables before consumption.