Assessment of Water Pollution Indices of Two Anthropogenic Impacted Rivers in Southern Nigeria

Freshwater ecosystems afford essential needs and services to humans and have not been spared the effects of anthropogenic pressures exacerbated by increasing urbanization and industrialization. The study was undertaken in two southern inland rivers in Edo State, Nigeria, following concerns that the increasing human population in the region, coupled with indiscriminate discharges into rivers could erode water quality and elevate metal concentrations above allowable limits. Water samples were collected and analyzed for heavy metal concentrations using standard procedures. The results showed that metal concentrations were generally within national and international limits for drinking water with exceptions in cadmium and lead. Water pollution indices showed metal pollution index for cadmium (1037, 757) and lead (503, 379) in Ovia and Ossiomo Rivers respectively. These values far exceeded the critical level of 100 with a high contamination index (>6) of cadmium in both rivers. Water quality index from physico-chemical analysis indicated poor conditions in Ossiomo River relative to very poor water conditions in Ovia River. The study demonstrated that cadmium and lead were the major contributors to the adverse environmental conditions in both rivers. Thus, incessant anthropogenic pressures adversely affected water quality of these rivers rendering them unsuitable for human use. This would potentially have serious ecological and human health implications as chronic effects may be unquantifiable. Keywords: Ovia and Ossiomo Rivers, heavy metal, water quality index, contamination inde