Heavy metal concentrations in surface water, sediments and fish and their potential toxicity in highly degraded multipurpose peri-urban Eleyele Lake, Ibadan City, Oyo State, south-western Nigeria

Abstract Metal concentrations in water, sediments and gills and edible stomach muscle tissues of two fish species, African Sharptooth mud catfish (Clarias gariepinus) and the Nile Tilapia (Oreochromis niloticus) in Eleyele Lake, Nigeria, were assessed in the rainy season (April), mid-dry spell time (July) and dry period (November) in 2017 to evaluate the potential ecological risks they pose to aquatic organisms. The concentrations of Fe, Co, Pb, Ni and Zn were significantly (p < 0.05) high in water and sediments and in some cases exceeded Nigerian Standards for Drinking Water Quality and World Health Organization guideline values. Study results highlight no significant spatial variation of all metals in the water and sediment phases and tissues for both fish species in the lake. Significant temporal variation in metals noted in the water and sediment phases most likely relate to the seasonal heterogeneity of catchment anthropogenic sources such as domestic sewer and fertilisers and pesticides from farming and backyard aquacultural enterprises. High Co, Cd and Zn concentrations recorded in tissues of the ecologically dichotomous two fish species corroborate with high metal levels in water and sediments. All pollution indices detected metal contamination in sediments whereas Ni posed a serious ecological risk to the fish (and possibly the fish consumers) in the lake indicating that nutrient retention especially within sediments is central to the pollution dynamics of Eleyele Lake and must inform management of the system.