SPATIO-TEMPORAL CHARACTERISTICS OF METALS AND SELECTED PERSISTENT ORGANIC POLLUTANTS IN FLOODPLAIN SOILS OF LOWER REACHES OF THE RIVER NIGER, NIGERIA

Abstract

In Nigeria, floods are common attributes during the rainy period (May – October), occurring naturally on the floodplains when water in the rivers and their tributaries overflow their banks. These floods are usually restricted to the river floodplains which are the low flat, periodically flooded lands adjacent to rivers, lakes and oceans and subject to geomorphic (land shaping) and hydrological (water flow) processes (Osakwe 2014). Flood water contains significant loads of suspensions and nutrients, as well as large amounts of organic compounds which are often toxic. This contamination by flood water is washed away from roads, football fields, warehouses and petrol stations, mechanic workshops, laundry places, places where solvents and pesticides are disposed, landfills and domestic septic tanks that collect household sewage (Tomasz et al 2014). Pollution carried by flood water can be divided into two major groups: the first group are primarily inorganic substances that contain heavy metals and nutrients, which are retained by physical or chemical sorption during the process of migration into the soil profile and finally enriching the flooded soil (Maliszewka-Kodyrbash,et al 2012). The other group consists of  organic compounds present in the form of  pre-decomposed remains of plant and animal tissues derived from municipal waste and organic matter contained in compost, manure, slurry tanks, and septic tanks as well as organic compounds that might have toxic properties (Kluska 2004,Kluska et al 2014). In addition, these water contain compounds belonging to the group of persistent organic pollutants (POPs) (Witt, Siegel 2000). Soil and sediment act as sinks for heavy metals, and fluvial processes are the primary mechanisms for transportation and redistribution of heavy metals (Graf 1990 et,al, Miller  1997). Metals combine with sediment or particulate matter in aquatic environments by attaching to sediment particles (Graf 1990 et,al, Miller 1997). Since these particles follow the same transportation paths in streams and rivers as other sediments, geomorphologic processes and channel sedimentation play a role in understanding these sediment-associated metals (Witt, Siegel 2000, Miller,1997, Macklin 1996).