Contamination profile of major rivers along the highways in Ondo State, Nigeria

I. A. Ololade¹* and A. O. Ajayi²

¹Department of Chemistry and Industrial Chemistry, Adekunle Ajasin University, P. M. B.  001, Akungba-Akoko, Ondo State, Nigeria.

²Department of Microbiology, Adekunle Ajasin University, P. M. B. 001, Akungba-Akoko, Ondo-State, Nigeria.

*Corresponding author. E -mail: olisa200@yahoo.com. Tel: +234 8077812009

Accepted 20 August, 2009

   Abstract

The quality of major rivers (Oluwa, Owena, Ogbese and Ose) along the highways in Ondo state, Nigeria were investigated using water, surface sediment and African catfish, Clarias gariepinus, as environmental indicators. Results from the study revealed that some of the water quality constituents exceeded the World Health Organization (WHO) standards for drinking water and water meant for other recreational uses. Of the four metals (Cd, Cu, Pb and Zn) determined, only Cd was recorded at toxic level in both water and sediment based on WHO and sediment quality guidelines respectively. Elevated concentrations of some pollutants detected in surface sediments and water are attributable to run-off from agricultural site and commercial activities. The pH, EC, TDS and PO₄^3- of the water displayed significant positive correlation with Pb (p = 0.05) and Zn (p = 0.01) while Cl^- equally showed correlation with all the metals. The index of geoaccumulation (I_geo) seems to be a more objective tool for assessing contamination. Highest and least microbial load were (439 × 10⁶ cfu/100 ml) and least (259 × 10⁶ cfu/100 ml) respectively. In the fish, the highest and least bioaccumulation factors (BAF) were recorded for Pb and Cu respectively. The bioaccumulated heavy metals in the tissues of C. gariepinus were above the acceptable limits stipulated by international codes of practice, implying critical pollution in the biota.

Key words: Anthropogenic input, heavy metals, seasonal changes, sediment, pollution.