Seasonal variation of heavy metal speciation in soil and stream sediments from hospital waste dumpsite in Ilesa, Southwestern Nigeria

A speciation study of selected heavy metals in soil and stream sediments around a hospital waste dumpsite was investigated. Sequential extraction procedure was used to fractionate the metals into 4 fractions: Exchangeable and bound to carbonate, oxyhydroxide of Fe and Mn, organic matter and the residual fraction. Speciation analysis of Fe, Mn, Zn, Cu, Cd and Pb in soil revealed that a major portion of the metals were associated with the residual fraction. The exchangeable and carbonate fraction was the most important fraction for Mn(Dry/Wet) and Zn(Dry/Wet) with an average of (27%, 35.6%) Mn and (20.8%, 27.3% ) Zn. Cd, Fe and Cu were associated with the oxyhydroxide of Fe and Mn fraction with an average of (61%, 44.2%) Cd(Dry/Wet), (41%, 21%) Fe(Dry/Wet) and (25.3%, 22.5%) Cu(Dry/Wet). A significant amount of Pb(Dry/Wet) (10.7%, 21.8%) was bound to  organic fraction during dry and wet season respectively. In sediments, Mn(Dry/Wet) occurred mainly in exchangeable and carbonate fraction (45.2%, 29.3%), Fe(Dry/Wet) and Cd(Dry/Wet) in the oxyhydroxide of Fe and Mn fraction were (41%, 31.2%) and (26.6%, 93.6%) respectively and the amount of Pb(Dry/Wet) bound to the organic fraction was (86.9%, 27.3%). A significant amount of Cu(Dry/Wet) (20.8%, 29.4%) was bound to the organic fraction and Zn(Dry/Wet) (35.5%, 73%) was retained in the residual fraction. In soil and sediments, Mn was potentially more bioavailable.  However, the level of lead in organic matter fraction of soil suggest that it may be remobilized under oxidizing condition, hence, bioavailable.   Keywords: Speciation, hospital waste, heavy metal, sediments, soil.