Phosphorus and nitrogen speciation in waters and sediments highly contaminated by an illicit urban landfill: The Akouedo landfill, Côte d’Ivoire

Abstract

Phosphorus and nitrogen pollution in groundwater, surface and marine waters results in tremendous economic, environmental and human health issues. This study examined phosphorus and nitrogen fate in sediments and the landfill leachate around the Akouedo landfill, the only landfill of the megacity Abidjan (Cote d’Ivoire, West Africa). The reactive phosphorus (255 ± 22.3 mg/L as PO43−-P) and ammonium (49 ± 4.2 mg/L as NH4+-N) concentrations in the leachate were significantly high and relatively low compared with the literature, respectively. The reactive phosphorus made up 60% of total phosphorus in the leachate, while inorganic nitrogen (nitrate + nitrite + ammonium) concentrations represented 80% of total nitrogen. All phosphorus and nitrogen forms showed a decreasing gradient along the leachate, a decreasing trend with sediment depth, and a sharp peak at the 0–20 cm depth. The leachate pollution and water quality indexes revealed that the Akouedo landfill has a substantial impact on groundwater quality. NO3− contributed to 97% of inorganic nitrogen in the sediments. Very high iron-bound (82%) and very low calcium-bound (5%) phosphorus were found in the sediments. The results from this study suggest that highly contaminated sediments adjacent to the Akouedo landfill are significant sources of bioavailable phosphorus to groundwater and surface waters.