Assessment of groundwater pollution in Singida urban and Manyoni districts

Abstract

The quality of groundwater in Tanzania has over the years remained poorly understood, hence posing risks to human health and the environment. In this study, the quality of groundwater sources used for drinking purpose in Singida Urban and Manyoni districts were investigated with a view to explore how the end users could be safeguarded from water borne diseases. Water samples from 30 boreholes and 28 shallow wells were randomly collected during dry and wet seasons. Water quality assessments were conducted following recommended guidelines by Tanzania Bureau of Standards (TBS) and international standards (WHO) for drinking water. Twelve physicochemical parameters were assessed using standard methods for water and wastewater from American Public and Health Association (APHA). Microbial water quality (TC, FC, and E.coli) were examined using membrane filtration technique while toxic metals were determined using Inductively Coupled Plasma Optical Emission Spectrometer. Nitrate source identifications were done using Elemental Analyzer/ isotope ratio mass spectrometry techniques. Results showed that shallow wells recorded significant higher turbidity (p<0.0001) compared to boreholes. The water samples collected during wet season had significantly higher microbial contamination compared to those collected during dry season. Additionally, the wells were buckets are used to draw water had significantly higher TC, FC and E.coli (n=11, p≤ 0.01), also wells without covers (n=15, p≤0.01) had significantly higher feacal coliform bacteria than those which motor or hand pump were used in both seasons. Concentration of toxic metals was significantly higher (p<0.05) during the dry season than in the wet season and 40- 66% of all samples had an elevated level of Mn, Cr, Pb, and Al above the recommended standards by World Health Organization (WHO) and Tanzania Bureau of Standards (TBS), hence unsafe for drinking. Nitrate sources identification revealed that, most nitrate contamination were originated from sewage effluents and/or organic wastes such as manure. The study recommends that water from shallow wells should be treated either by boiling, chlorination, or use of low cost technologies such as sand filter before consumption. In addition, the proper sitting of the wells based on the recommended standards by TBS has to be enforced in order to prevent further contamination from human activities.