Long term effect of municipal solid waste amendment on soil heavy metal content of sites used for periurban agriculture in Ngaoundere, Cameroon

Abstract

An assessment of the impact of amendment using untreated municipal solid wastes on the trace element contents of periurban areas soils was carried out in  Ngaoundere. Waste samples were collected in November and soil samples were collected in November, January, April and July. Heavy metal total concentrations in urban wastes differed significantly among sites and ranged from 0.48 to 7.64 mg/kg for Cd, 38.3 to 236 mg/kg for Cu, 44.06 to 58.03 mg/kg for Ni, 117 to 528 mg/kg for Pb and 270 to 2110 mg/kg for Zn. These levels were out of the critical level for agricultural use at Camp prison (for Pb and Zn), Norvegien (for Cd, Cu and Zn), and Sabongari Gare site (for Cd, Cu and Zn). The levels of Ni in urban wastes from all sites and the levels of all heavy metals in urban wastes from Douze Poteaux site were lower than the critical level. The results revealed that the soil total  concentrations of Cu, Zn, Cd and Pb were below the typical agricultural soil critical level for the soil control and out of the critical level for amended soils. The levels of Ni were found to be within the normal range at all sites. The highest available  concentration of Zn (139.17 mg/kg) was found in November, Fe (843.23 mg/kg) and Pb (38.82 mg/kg) in January and Cu (19.09 mg/kg) and Ni (8.98 mg/kg) in July.  The available concentrations of Cd did not differ among periods. The highest   bioavailable factor (BF) of Zn, Ni and Pb was found at Douze Poteaux site and of Cd and Cu at Sabongari Gare site.

Key words: Heavy metals, soils, municipal solid wastes, amendment, bioavailability factor.