OCCURRENCE OF ARSENIC, LEAD, THALLIUM AND BERYLLIUM IN GROUNDWATER

The occurrence of carcinogenic and heavy metals in groundwater sources in Urban-west region of Zanzibar Island is an issue that is not very well known. This could be also coupled with the absence of drinking water treatment plants. This study for the first time reports on the occurrence and the levels of three carcinogenic metals-Arsenic (As), Beryllium (Be) and lead (Pb) in thirty groundwater samples collected from Zanzibar’s Urban/West region. The levels of alkalinity, Magnesium (Mg) and Thallium (Tl) were also determined. The concentrations of As, Be, TI and Pb in the water samples were determined by the Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). Palintest photometry procedures were used to determine the levels of total alkalinity and magnesium. Be, As, Tl and Pb were not detected (nd) in some water samples. The ranges of concentrations of Be, As, TI and Pb in the samples were; nd to 6100 ng L^-1, nd to 6600 ng L^-1, nd to 11600 ng L^-1 and nd to 31400 ng L^-1 respectively. The levels of total alkalinity varied from 38 to 380 (mg L^-1 as CaCO₃). The proportions of water samples contaminated with Be, Tl, As and Pb were 43.3, 66.7, 70 and 96.7% respectively. About 23% of the water samples had Pb concentrations beyond WHO limits for safe drinking water, while 30 and 56.67% of the samples had Be and Tl concentrations beyond the US EPA’s maximum limits. The concentration of arsenic in each water sample was within WHO limits. The occurrence and the levels of carcinogenic metals in water sources could be a potential cause of cancer cases in Zanzibar. Therefore, prompt action is required to control the levels of these hazardous metals, and other possible contaminants in Zanzibar’s domestic water systems.