SECOLOGICAL RISK OF HEAVY METALS IN SURFACE WATER, SEDIMENT AND DOMINANT FISH SPECIES FROM TUNGAN KAWO RESERVOIR, KONTAGORA, NIGER STATE, NIGERIA

Abstract

ABSTRACT Developing countries like Nigeria are faced with increased in generation of domestic, industrial and agricultural wastes that found their way into the surrounding water bodies which are slowly contaminating the water. This study was aim to evaluate ecological risk of heavy metals in surface water, sediment and dominant fish species from Tungan Kawo Reservoir, Kontagora, Niger State, Nigeria. Physico-chemical parameters and heavy metals in surface water, sediment and three commercially important fishes were determined in the reservoir water using standard methods from July 2018 – February 2019 at four different sampling stations of human activities around the water. A total of five heavy metals were selected [lead (Pb), copper (Cu), manganese (Mn), iron (Fe) and chromium, (Cr)] in the surface water, sediment and fish species. The results from physio-chemical parameters showed that, nitrate (3.2 – 7.5 mg/L), temperature (27 – 32.4 0C), dissolved oxygen (2.4 – 5.2 mg/L), electrical conductivity (81 – 125 µS/cm), biochemical oxygen demand (1.9 – 4.4 mg/L), alkalinity (16 – 34 mg/L) and total dissolved solids (117 – 198 ppm) were within standard for drinking water and survival of fishes, however, the pH (6.3 – 9.8) and phosphate (0.4 – 2.5 mg/L) was above the standard for FEPA and NESREA for drinking water but can fairly support aquatic life. The results obtained from heavy metals showed that iron (Fe) and (Cr) had the highest concentration with mean of 6.18 mg/kg and 1.45 mg/kg in surface water and 7.08 mg/kg and 1.54 mg/kg in sediment respectively, followed by Mn with 1.36 mg/kg (sediment) and 0.09 mg/L (water) while Cu had the lowest concentration of 0.03 mg/kg in the Surface water and 0.99 mg/kg in the sediment respectively. Lead was detected in the sediment in low concentration with a mean value of 0.01 mg/kg in Stations 1, 2 and 4 respectively. However, Pb was not detected throughout the time of the study from surface water. In the three fish species examined, iron was the most highly concentrated value (0.64±0.072 mg/kg) in Synodontis clarias while lead (0.01±0.013 mg/kg) was the lowest found in Oreochromis niloticus and Coptidon zillii (formerly Tilapia zillii). The bottom feeders were found to accumulate more of these heavy metals. This indicates the good health status of the reservoir for aquatic biota. The values obtained from risk indices were very low when compared with the background values and target for Hakanson risk index of a standard soil and have not constitute any risk to Tungan Kawo Reservoir. This current finding indicates that the water is safe for both aquatic life and domestic purpose but not suitable for direct human consumption without being properly treated. However, there is the need for regular monitoring of the heavy metals load in this water body and the aquatic organisms because of the long-term effects.