Assessment of Heavy Metal Accumulation in Aquatic Macrophytes of the Osun River, Osun State

Aquatic macrophytes accumulate heavy metals from polluted water bodies and can serve as biomonitors and phytoremediators in contaminated river systems. This study assessed the accumulation of cadmium, lead, copper, zinc, and iron in three abundant aquatic macrophyte species in the Osun River, Osun State, South West Nigeria, at sites upstream, midstream, and downstream of Oshogbo city effluent discharge zones. Eichhornia crassipes, Ceratophyllum demersum, and Nymphaea lotus were collected from each site, acid-digested, and analysed by atomic absorption spectrophotometry. Corresponding water and sediment samples were also analysed. The bioconcentration factor and translocation factor were calculated for each metal and species combination. Results showed that all three species accumulated heavy metals above ambient water concentrations. Eichhornia crassipes had the highest bioconcentration factor for lead (BCF = 412) and cadmium (BCF = 318), indicating excellent hyperaccumulation potential. Metal concentrations increased significantly from upstream to downstream sites for lead, cadmium, and copper, consistent with urban effluent loading. Ceratophyllum demersum was the most effective biomonitor for dissolved metals due to its entirely submerged growth habit. Translocation factors above 1.0 for zinc in all three species indicated efficient root-to-shoot transfer. The study concludes that Eichhornia crassipes has strong phytoremediation potential for heavy metal-polluted sections of the Osun River and recommends piloting managed macrophyte phytoremediation units below major effluent discharge points.

Keywords: aquatic macrophytes, heavy metals, bioconcentration factor, Osun River, phytoremediation