Microbial and chemical contamination of water, sediment and soil in the Nakivubo wetland area in Kampala, Uganda

Abstract

The reuse of domestic and industrial wastewater in urban settings of the developing world may harm the health of people through direct contact or via contaminated urban agricultural products and drinking water. We assessed chemical and microbial pollutants in 23 sentinel sites along the wastewater and faecal sludge management and reuse chain of Kampala, Uganda. Water samples were examined for bacteria (thermotolerant coliforms (TTCs), Escherichia coli and Salmonella spp.) and helminth eggs. Physico-chemical parameters were determined. Water, sediment and soil samples and edible plants (yams and sugar cane) were tested for heavy metals. Water samples derived from the Nakivubo wetland showed mean concentrations of TTCs of 2.9 × 10(5) colony-forming units (CFU)/100 mL. Mean E. coli was 9.9 × 10(4) CFU/100 mL. Hookworm eggs were found in 13.5% of the water samples. Mean concentrations of iron (Fe), copper (Cu) and cadmium (Cd) were 21.5, 3.3 and 0.14 mg/L, respectively. In soil samples, we found a mean lead (Pb) concentration of 132.7 mg/L. In yams, concentrations of Cd, chromium (Cr) and Pb were 4.4, 4.0 and 0.2 mg/L, while the respective concentrations in sugar cane were 8.4, 4.3 and 0.2 mg/L. TTCs and E. coli in the water, Pb in soil, and Cd, Cr and Pb in the plants were above national thresholds. We conclude that there is considerable environmental pollution in the Nakivubo wetland and the Lake Victoria ecosystem in Kampala. Our findings have important public health implications, and we suggest that a system of sentinel surveillance is being implemented that, in turn, can guide adequate responses.

Fig. 1

Map of Kampala showing the study area, including detailed maps of the four sampling systems with the specific sampling points (Nakivubo channel, Nakivubo wetland, community areas and Inner Murchison Bay in Lake Victoria)

Fig. 2

Box-and-whisker plot of the concentration of BOD₅, COD, ammonia-N and total solid suspended in the four sampling systems along the Nakivubo channel, in Kampala, Uganda (sampling period: 15 October to 5 December 2013). Red line: maximum acceptable concentrations of TTCs (NEMA 1999) and E. coli (WHO 2006). Ls surface and Lb bottom samples taken within the Inner Murchison Bay of Lake Victoria

Fig. 3

Box-and-whisker plot of the concentration of thermotolerant coliforms (TTCs), E. coli and Salmonella spp. in the four sampling systems along the Nakivubo channel, in Kampala (sampling period: 15 October to 5 December 2013). Red line: maximum acceptable concentrations of TTCs (NEMA 1999) and E. coli (WHO 2006). Ls surface and Lb bottom samples taken within the Inner Murchison Bay of Lake Victoria