Risk Assessment on Trace Metals in Groundwater and Springs in Urban Environment of Zanzibar Island

Abstract

Urban-west region is the most highly populated region of Zanzibar. More than half of the Zanzibar populations reside at this region. Groundwater is the main resource of drinking water in this area, and currently there is no drinking water treatment plant; hence, the suitability and appropriateness of groundwater resources for drinking and other domestic uses is of public and scientific concern. In this study, groundwater samples were collected from 30 sites in urban areas of Zanzibar Island in December 2012. Measurements, and investigation of the levels of trace metals in water including Cd, Co, Cr(III), Cu, Fe, Li, Mn, Mo, Sb, Se, Ti, and Zn were measured in thirty locations in Zanzibar urban west region using Inductively Coupled Plasma Emission Spectroscopy (ICP-OES). The paper also highlights and depicts the estimate of the degree of metal contamination (C d ), hazard quotient which yields hazard index (HI), heavy metal evaluation index (HEI), and heavy metal pollution index (HPI). Using the four heavy metals (Cd, Zn, Cu, and Fe), the degree of contamination (C d ) in all water sources were less than 1, thus they fall in to the category of low degree of contamination. The general trend of the average daily dose (ADD) of Zn, Cu, Fe, and Cd in water sources was Zn ˃ Cu ˃ Fe ˃ Cd. As the severity of metal toxicity is governed by several factors, such as dose, nutrition, age, and even life style. Therefore, this trend might not guarantee the absence of human health risk. Generally, from risk assessment on trace metals using risk indices (C d , HPI, HI and HEI), the analyzed water sources might not be at the alarming health risk. However, due to an increasing level of environmental pollution, water sources might be potential sink of contaminants; this is significant reason that makes the treatment of drinking water and monitoring implementation inevitable.