Daily variation of heavy metal contamination and its potential sources along the major urban wastewater channel in Kampala, Uganda
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Heavy metal pollution from untreated industrial wastewater has become a major concern to the environment and public health in many rapidly growing cities in low-income countries. Previous studies on heavy metals of urban wastewater systems have focused on long-term (weekly or seasonal) variations, while only few studies investigated short-term (daily) variation to capture potential bulk discharges. To monitor and enforce wastewater discharge regulations and reduce industrial pollution, a better understanding of the short-term variation of these pollutants and industrial discharge practices is needed. The aim of this study is to assess the daily variation of heavy metals and physicochemical parameters along the major urban wastewater system in Kampala, Uganda. Over 1 week, daily water samples were collected at 16 locations and analyzed for lead (Pb), mercury (Hg), copper (Cu), and chromium (Cr) and a range of physicochemical parameters. Additionally, 25 key informant interviews with industries were administered to investigate their potential to contaminate the environment. Among 78 water samples, 29 exceeded the national standards for Pb (> 0.1 mg/L) and one for Hg (> 0.01 mg/L). High daily variation and peak concentrations were detected which are likely due to industries retaining their effluents and discharging them irregularly. Although 24 industries used heavy metals in their manufacturing processes and are likely to discharge heavy metals, only ten industries had a wastewater treatment system in place. Our results show that repeated measurements of heavy metals over short time intervals are needed to capture their high daily variation in an urban wastewater system. Furthermore, there is an urgent need to register industries and to assess their effluent composition in order to select appropriate wastewater management measures.
KeywordsEnvironmental pollution Industrial wastewater Lead Mercury Chromium Nakivubo Channel
This work was funded by the Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH (grant number 81194938). We want to thank the German Development Cooperation (GIZ) for their thrust and support for this study.
Special thanks go to Catherine, Sammy, and Simon for their diligent work in the field and to Dean for his flexibility with the analysis of the samples. Further, we want to express our gratitude to all people from the Directorate of Water Resources Management (DWRM), the National Water and Sewerage Corporation (NWSC), and the Kampala Capital City Authority (KCCA) for our fruitful interactions.
SF, DD, and GC initiated and elaborated the design of the study in interaction with partners in Uganda. DD, SF, and EM conducted the water sampling in the field in collaboration with MB and AA. EM mapped industries and conducted the key informant interviews. DD and SF undertook data analysis and wrote the manuscript. All the co-authors provided inputs to the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare no personal, financial, or other conflict of interest.
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