Heavy metals pollution, distribution and associated human health risks in groundwater and surface water: a case of Kampala and Mbarara districts, Uganda

Abstract Groundwater and surface water quality is of great significance for humanity as they serve as the primary drinking water sources globally. Due to population growth and the need to provide people with necessities that depend on water as an essential resource, these bodies of water are becoming more polluted. The present study involved the collection of groundwater and surface water samples from Kampala and Mbarara districts in Uganda during the dry and wet seasons. Also, concentrations of lead (Pb), manganese (Mn), cadmium (Cd), copper (Cu), and iron (Fe) were analyzed in order to evaluate the toxicity of metals, identify potential sources, and determine the health risk associated with their presence in water. Results showed that metals were observed with higher concentration during the wet season than the dry season. The concentrations of Fe (8.646 ± 0.00 mg/L), Mn (2.691 ± 0.01 mg/L) and Cd (0.090 ± 0.41 mg/L) measured in groundwater were significantly higher than those measured in surface water. However, only Cu was observed with higher concentration (0.322 ± 0.06 mg/L) in surface water during the wet season. Furthermore, the degree of contamination (Cd) and the heavy metal pollution index (HPI) were evaluated for both the wet and dry seasons. Results showed that few samples were found in the category of portable drinking water while majority are within the “poor” and “very poor” classes which require proper treatment before consumption. The oral hazard index (HIoral) results showed that none of the samples are suitable for consumption; therefore, cause potential non-carcinogenic health issues to the consumer (HIoral > 1). Moreover, children are more at risk than adults in the study districts (higher HI values in both seasons). This study recommends frequent monitoring of quality of water and also effluent waste treatment by the major source of pollution.