Assessment of potential health risks from heavy metal pollution of surface water for drinking in a multi-industry area in Mali using a multi-indices approach

The Niger River, Bamako's population's primary drinking water source, is threatened by human activities. This study examines the Niger River pollution trend using heavy metals pollution indexes and Bamako's population's non-carcinogenic and carcinogenic related health risks. Parameters were monitored at fifteen sampling locations in low and high flow seasons. pH (7.30-7.50) and fluoride (0.15-0.26 mg/L) were within the normal drinking water range. Among seven heavy metals (copper, zinc, cadmium, nickel, iron, manganese, and lead), the latter three were above the drinking water standard. The degree of contamination was negative, pointing to better water quality. However, the heavy metal evaluation index (HEI) was below the mean (5.88), between the mean and twice the mean, indicating a low and medium degree of pollution. Besides, heavy metal pollution indexes (HPI) were above the standard value (100), explaining a low-medium pollution level. High values of HPI could be explained by the industrial units' intensive activities coupled with the runoff effect. The hazard index (HI) indicated a low and medium non-carcinogenic health risk for adults and children. The probability of cancer risk (PCR) of nickel showed a cancer risk. Therefore, the river was polluted with trace elements and could not be used for drinking water without any treatment.