Comparative biotolerance of water spinach, Ipomoea aquatica, to heavy metal pollution in the Agodi Reservoir and the Ogunpa River, Oyo State, Nigeria

Abstract

The biotolerance of water spinach (Ipomoea aquatica) to heavy metals was investigated in the Agodi Reservoir and its supplying source, the Ogunpa River, to examine the impact of aquatic pollution. I. aquatica was collected monthly from the Ogunpa River and the Agodi Reservoir. Atomic absorption spectrophotometry was used to analyse the concentration of heavy metals in the samples. A box plot was used to evaluate the tolerance of the plants to heavy metals and ecological risk quotients (ERQ) were calculated to indicate the threat to human health and environment. The concentrations of cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni) and zinc (Zn) in the plants were below standard thresholds, but cadmium (Cd), iron (Fe), manganese (Mn) and lead (Pb) were present in higher than permissible levels. The ERQ of Cd in I. aquatica in the Ogunpa River was at an elevated ecological risk level in January (3.450), May (3.125), June (8.175), August (1.900) and September (2.025). The ERQ of Co, Cr, Cu and Ni in plants from both the reservoir and the river were less than one. The ERQ and biotolerance of heavy metals in this study indicated that I. aquatica is effective in binding heavy metals.