Assessment of metallic pollution status of surface water and aquatic macrophytes of earthen dams in Ilorin, north-central of Nigeria as indicators of environmental health

The functional quality of an aquatic ecosystem is a reflection of the health of the environment. Therefore, the present study evaluates the trace metal contamination (Pb, Cd, Ni and Mn) of water and aquatic macrophytes in Asa, Agba, Unilorin and Sobi (Moro) earthen dams, north-central Nigeria to evaluate the level of anthropogenic impact on the immediate environment. The concentrations of trace metals in samples of water and available macrophytes from the earthen dams were determined by Atomic Absorption Spectrophotometry. Trace metal contamination of surface water in the earthen dams was assessed using metal index (MPI) and metal pollution index (HPI). The biological accumulation factor of trace metals in the aquatic macrophytes was extrapolated from trace metal concentrations in the water and macrophyte samples. The results of the MPI revealed gross metal contamination of the surface water by Pb and Cd (>6.0 for both metals) in the four earthen dams; while Agba and Sobi dams were slightly contaminated by Ni (MPIs = 1.43 and 1.14 respectively). All the earthen dams were considered safe from Mn contamination (MPI < 1.0). Considering the HPI, the four earthen dams fall within the critical pollution threshold for trace metals (HPI > 100), but Asa dam (HPI = 2682.4) was the most contaminated. The biological accumulation factor of Mn in the macrophytes indicated Ceratophyllum demersum, Pycreus lanceolatus and Pistia stratiotes as moderate accumulators of Mn, and can be used as bioindicators in monitoring Mn pollution of aquatic ecosystem. The obtained results in this study showed that the earthen dams are polluted by Pb, Cd and Ni which pose human health risks to the inhabitants through drinking water.