CHEMICAL FRACTIONATION AND MOBILITY OF HEAVY METALS IN ALLUVIAL FLOODPLAINS OF SOME RIVERS IN EKITI STATE, SOUTHWEST NIGERIA

Abstract

Floodplains are agro zone for most vegetables worldwide and incidentally they are sinks for pollutants especially heavy metals. The total concentration of metals is not a good indicator of mobility/bioavailability or potential risk assessment hence more preferred elemental geochemical environment. This study is therefore aimed at investigating the geochemical environment of some potentially harmful elements in the agro zone flood plains of some rivers in Ekiti State, Southwest Nigeria. Bulked soil samples of 0-10cm, 10-20cm and 20-30cmdepth were collected at 5m, 25m and 45m perpendicular distances to the river course. Soil samples were air-dried in the dust free open laboratory, disaggregated, sieved through 2mm BS mesh and sequentially fractionated using Tessier’s method. The result shows that a large proportion of the fractions were found in the non-mobile fractions bound to organic matter (F4)and residual (F5), implying that the metals may not be readily available for plant uptake. The mobility factor for the metals at Irintan floodplain, (Ogbese) Omi-Eye floodplain (Erio) and Egbigbu floodplain (Ayetoro),were respectively in the order Pb>Zn>Cr>Cu>Fe>Cd, Cd>Fe>Cu>Zn>Pb>Cr and Cd>Zn>Cr>Fe>Cu>Pb. This suggests that cadmium has the highest mobility factor at both Omi-Eye and Egbigbu floodplains than other metals. This portends danger as the metal is known to be potentially toxic to ecosystem. It is hereby recommended to regulatory authorities to carry out a more detailed assessment of the floodplains for potentially toxic metals contamination to forestall transfer to human through plant uptake.