Levels of heavy metals in tobacco leaves, tobacco waste and tobacco growing soils from Eastern and Western blocks of Kenya
Wangoli, Panyako Asman
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Globally 1.1 billion people are involved in smoking. Nearly 5 million premature deaths were caused in the year 2000 alone as a result of cigarette smoking. The main cause of death attributable to smoking are cardiovascular diseases (1.7 million deaths), chronic obstructive pulmonary disease (1 million) and lung cancer approximately 850,000 deaths. Numerous other health hazards including respiratory diseases, peptic ulcers, complications of pregnancy, chronic bronchitis and emphysema, heart diseases and stroke causes about 1.5 million deaths which is attributed to tobacco smoking. In Kenya, 27% (six million) of the population is addicted to tobacco and about ten billion cigarettes are smoked in one year. This is more than 330 cigarettes for one Kenyan in a year. This shows that a significantly high percentage of Kenyan population remain at risk of exposure to tobacco toxins and tobacco related diseases. Some of these diseases are associated with heavy metals like Pb, As, Se, Hg and Cd. This study investigated the levels of Hg, As, Pb, Cd and Ag in both fresh and cured tobacco leaves, tobacco waste and soils from the tobacco growing blocks of Eastern and Western Kenya. The study aimed at establishing if the concentrations of these heavy metals are above the FAO/WHO recommended levels in tobacco. A comparative study of the levels of these metals was carried out using atomic absorption spectroscopy (AAS) and differential pulse anodic stripping voltammetry (DPASV). A good correlation between these two analytical methods (AAS and DPASV) was obtained. The analysis was done on weighed samples, which were air or oven dried up to 70°C for mercury (Hg) and at 100°C for lead (Pb), cadmium (Cd), arsenic (As) and silver (Ag) analysis. The wet ashing process involved digesting the weighed samples with high purity 70% HN03 and 70% HC104 acids. The cold-vapour technique for Hg and hydride generation for arsenic was employed. The mean concentration ranges of these metals in pg/g in fresh leaves, cured leaves and soil were: Lead; 7.16 - 11.79, 6.26 - 10.14, 9.04 -28.91, cadmium; 0.62 - 2.62, 1.13 - 2.22, 1.77 - 3.26 and arsenic; 0.83 - 1.48, 0.82 - 1.53, 0.86 - 2.35 respectively. For mercury and silver the AAS technique was used. The concentration in mg/g in fresh leaves, cured leaves and soil were; mercury; 0.052 - 0.089, 0.046 - 0.069, 0.063 - 0.099 and silver; 0.24 - 0.49, 0.26 - 0.52, 0.24 - 0.55 respectively. Concentrations of all the studied metals were found to be within the FAO/WHO recommended tolerable intake limits. The presence of all these toxic elements in tobacco could have synergistic toxic effect especially for those who smoke cigarettes for many years since these metals are cumulative toxins. There was a good correlation between levels of these metal concentrations in tobacco leaves and in soils where it is grown.