Ecological Risk Assessments of Heavy Metal Contamination in Water, Sediment and Biota of Otamiri and Imo Rivers, Nigeria

Heavy metals pollution of the environment is a serious concern because of the hazardous effects they pose to human health, ecosystems and other biological receptors. The aim of this study was to assess the ecological risk of exposure to heavy metals and physicochemical parameters around Otamiri and Imo rivers in Etche and Oyibo Local Government Areas of Rivers State. Water, sediment, arrow head plant (Sagittaria latifolia) and christmas bush Plant (Ceratopetalum gummiferum), tilapia fish samples (Oreochromis niloticus) and cat fish (Clarias gariepinus) were collected at different points from five sample stations for wet and dry seasons. These samples were analyzed quantitatively to assess the levels of contamination in the samples using the ecological risk assessment models associated with exposure to these contaminants. The results of the heavy metal analysis show that the Estimated Daily Intake (EDI) for biota samples ranged from 0.000 – 1.254 mg/kg/day while water ranged from 0.000 -0.322 mg/kg/day. The target hazard quotient (THQ) ranged from 0.000 – 69.228 for both biota and river water samples for Otamiri and Imo rivers The hazard index values indicated significant public health risk with values of 1.42 was recorded for Tilapia and 33.14 for Christmas bush plant. Cancer risk due to heavy metals exposure had a peak value of 1.04 x10-1 for wet season. The bioaccumulation of the metals showed that the pollution load index values ranged from 2.467- 5.822 in wet season and 9.708 – 99.853 in dry season. The presence of these heavy metals above threshold values suggest that the aquatic life that inhabit such rivers risk bioaccumulation which may affect the human population that depends on Otamiri/Imo rivers for fishing, drinking or irrigation. These poses a danger if bioaccumulation was to take place over a long period of time.