Characterisation and Soil Pollution in Agrarian Floodplain of Ibadan Peri-Urban in South Western Nigeria

Abstract

Ibadan metropolis in Nigeria has population of about 6millons people. There is increasing concern about lowland soils around Ibadan periurban where most of the industrial wastes transported  majorly by River Ona were deposited. These soils are used for dry season farming and  contribute to food security. This research was carried out to characterise and  determine the vulnerability of periurban lowland  soils to industrial pollution . The area was studied using 50mx50m  grid. Surface samples were taken at 50m interval. Representative profile pits were dug and described using USDA method. Particle size analysis and chemical analyses including Phosphorus, Nitrogen , exchangeable Cations (Ca, Mg, Na, K,),  Mn and heavy metals such as Pb. Cu, Zn, Cr, Fe, Cd determinations were carried out. The results shows that the surface soil of the flood plain was fertile with high N (0.35cmol/kg), P (51.25 cmol/kg), K (0.61 cmol/kg) with very high to toxic levels of phosphorous in the soil which range between 28.99 to 87.70 ppm. Average lead concentration was (34.30 mg/kg), Zn (171.20 mg/kg), Fe (83.97 mg/kg), Cu (19.11 mg/kg), Mn (31.10 mg/kg), Cr (0.69 mg/kg), Cd (0.3 mg/kg). The predictions from soil-plant heavy metal transfer coefficient (Pb:35-343; Cr:0.46-4.6; Zn:171-1712; Cu:19-191; Fe:83-840; Mn:31-281; Cd:0.1-10)  shows that there might be toxic level in crops in the area but the high yield and health of plant from field evidence and farmers interaction indicate that the  high level of P (28.99-87ppm) must have inhibited uptake of some metals such as Pb, Zn and Cu.

Keywords: Fadama, Urban waste, Heavy metals, Soil pollution, Peri-urban farming