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Mapping and quantifying the spatial and temporal composition of waste piles in informal settlements of urban Malawi
Summary
A longitudinal drone and transect survey of informal waste piles in urban Malawi found that plastics — predominantly Low-Density Polyethylene — were the largest non-organic waste component by volume, concentrated along rivers and streams. This documents a direct plastic-to-waterway pathway in Sub-Saharan Africa where waste management data have historically been scarce, highlighting a major underreported source of riverine microplastic pollution.
Solid waste pollution is a multifaceted global challenge affecting the environment, economy, and human health, yet our understanding of environmental solid waste dynamics, such as waste type, weight(W), and volume(V), which inform waste management initiatives and policy frameworks remains limited in Sub-Saharan Africa. In this longitudinal study, we mapped informal waste disposal sites using transect-walks and drones in urban Malawi. Monthly characterisation of selected individual waste piles was undertaken for 12 months. Sampling (200L/waste pile) included both surface and compacted sections. (60 cm depth), which were characterised by weight(kg/m2), volume(m3), and individual counts of plastic items(m2). Three-way ANOVA and a linear mixed-effect model were used to predict percentage recovery for the interactions between month, waste pile depth, and waste type as fixed factors. Fourteen out of 56 waste piles received detailed temporal characterisation. Waste piles were located along rivers(50%), streams(29%), and open-dumping spaces(21%). Soil (W:60%, V:19%), organic material (W:22%, 33%), and plastics (W:8%, V:24%) were the highest components by weight, and volume, making plastics the highest non-organic category of waste. Seven plastic polymer types were identified, with Low-Density Polyethylene being the most common (83% plastic items/m2). Seasonality, waste pile depth, and waste type (F(171, 4284) = 11.44, p < .001, η2 = .31) significantly affected percentage recovery of waste items, indicating their effect on waste pile dynamics. Sustainable waste management initiatives need to account for seasonal changes, material characteristics, and waste pile stratification to effectively improve waste management systems and the public health implications of waste piles.