Heavy metal toxicity in the water column and benthic sediments of a degraded tropical stream.

Agriculture and other anthropogenic activities on riparian corridors pose a great ecotoxicological risk to freshwater ecosystem and human health. Using the atomic absorption spectroscopy, concentrations of heavy metals (Cd, Cu, Fe, Zn, Pb and As) in the water column and benthic sediments of a degraded tropical stream (Opa Stream, Ile-Ife, Nigeria), were assessed with a view to determining the stream's health status. Three metals (Cu, Pb, and As) showed significant positive correlations between concentrations in the water column and the benthic sediments. All but one heavy metal (i.e. Zn) had reached disturbing concentrations in the stream's water column and exceeded their recommended limits in surface freshwaters. The geo-accumulation index (Igeo) and contamination factor (CF) indicated that the stream was moderately contaminated with Cd (0 <Igeo< 1; CF much closer to 1). This study concludes that the stream was impacted with heavy metals in its water column and slightly impacted with Cd on its bed, thus raising health concerns for plankton, benthic organisms and all users of the surface water. More conservation attention by relevant stakeholders through monitoring and regulation of human activities in river basins, is recommended for the sustenance of tropical freshwater ecosystem and human health.