dissertation
Humans are exposed to heavy metals mainly through ingestion from different sources such
as foods, water, air, and occupational settings. It is estimated that millions of people are
exposed to heavy metals in different countries globally. Heavy metals toxicity can result to
both carcinogenic and systemic health effects to human body. Artisanal small-scale
mining activities are found to be a significant source of heavy metals contamination in
crops and environmental. This study aimed to evaluate levels of selected heavy metals
(Mercury, Lead and Arsenic) contamination in irrigation water and vegetables grown
around small scale mining sites in Geita, Tanzania. The study also evaluated the effects of
washing, chopping and cooking on the heavy metal concentrations in the selected
vegetables. The study revealed that 10% of irrigation water samples were contaminated
above recommended safe limit of 5 mg/L for Lead while 80% were having total Arsenic
concentration above recommended safe limit of 0.1 mg/L. For leafy vegetables samples,
23% were contaminated with lead above the recommended safe limit of 0.3 mg/kg and
60% of the samples were contaminated with total Arsenic above the maximum limit of 0.1
mg/kg. Despite the fact that some vegetable samples were contaminated with heavy metal
above safe limits, their Non carcinogenic health risk index was found to be below one (1)
implying that there will be no immediate obvious health risk upon consumption of these
vegetables. None of the samples were found to have cancer risk value (C R ) that was
categorized as risk or very high risk to cause cancer. Twenty seven percent of the
vegetable samples were found to have very low risk while the remaining 73% were found
to have moderate carcinogenic risk. Washing, chopping and cooking of the vegetables,
following traditional method of cooking significantly reduced the amount of mercury and
total arsenic by 84% and 34% of the originally present quantities in the spinach samples;
and 70% and 40% for amaranth samples respectively.
Tanzania Drugand Medical Devices Authority (TMDA)