Demographics, insufficient wastewater infrastructure, and electronic waste recycling imperil urban tropical rivers

Urban rivers in the Global South face under-researched pollutant pressures, unlike some of the extensively studied rivers of the Global North. Differences in climatic cycling, demographics, agriculture, and industries limit the extrapolation of findings from published studies of temperate-climate rivers to conservation in the tropics. To address this knowledge gap, we measured the presence of contaminants at eight surface and four groundwater sites along the Odaw River in Accra, Ghana, across both dry and wet seasons. Using established protocols, triplicate samples were assessed for nutrients, organic matter, hormones, and heavy metals. A congruent spatial pattern emerged, whereby downstream sites had the highest contaminant loads, often exceeding WHO drinking water guidelines. Temporal trends were less pronounced as dry and wet seasons have become less distinct due to climate change. The high concentrations of nutrients and especially estrone suggest that the lack of an adequate wastewater treatment infrastructure prevents the removal of these pollutants prior to entering aquatic habitats. Electronic waste recycling contributed to high concentrations of copper and chromium at downstream sites. Despite Ghana's phase-out of leaded fuel, lead in many samples highlights soils as a reservoir for contamination. Groundwater, used primarily for cooking and washing, but also for drinking among the poorest, was less affected by contamination. Together, these data document differences in pollutant sources and fates in tropical rivers compared to temperate regions. This study highlights the importance of establishing baselines for pollutant sources, presence, and fate in tropical urban rivers, as well as developing wastewater treatment infrastructure, as population growth and changing climatic conditions are likely to exacerbate threats to water quality.