Ecological and Health Risk Assessment of Heavy Metals and Organochlorine Pesticides in Water and Sediments from Otamiri River in Imo State, Nigeria

Ecological and health risk of selected heavy metals and Organochlorine pesticide residues (OCPs) were assessed in Water and Sediments from Otamiri River in Imo state, Nigeria. Water and sediment samples were collected during rainy and dry periods from three different points and mixed together to form a composite sample. Pesticide residues and heavy metals were analysed using gas chromatography-mass spectrometry and atomic absorption spectrophotometer respectively. The concentration of heavy metal during rainy and dry season ranged from ND to 1.56 mg/l and ND to 3.61 mg/l for water samples, 0.005 to 1.8 mg/kg, and 0.008 to 1.0 mg/kg for sediments respectively. The geo-accumulation index Igeo(x) of heavy metals on sediment ranged from 0 to 0.7 while the values of pollution index were greater than one, signifying heavy metal pollution status of the river. The ecological risk index showed that Nickel and Cadmium had moderate to considerable ecological risk ranging from 129.9-348. The OCP residues concentration ranged from ND to 6.35 mg/l and ND to 4.55 mg/l for water samples, ND to 3.22 mg/kg and ND to 3.5 mg/kg for sediments during rainy and dry season respectively, with predominance of BHCs, DDTs and heptachlor epoxide in water and sediment matrixes. The pesticide residues found in the present study were generally below the maximum residues limit (MRL) set by FAO/WHO bodies. Ecological risk using the Risk quotient was found to be (RQ ≥1) during both seasons and shows higher risks for β-HCH, endosulphan sulfate and p,p′-DDT. The non-carcinogenic risk hazard index (HI) values of both exposure routes were less than one. Conversely, the estimated carcinogenic risk by OCPs through ingestion exposure ranged from 8.142E−9 to 1.20E−7 and 6.36E-7 to 6.44E-4 while dermal range from 3.4E-11 to 2.14E-8 and 7.14E-7 to 8.6E-4 for adults and children respectively, showing considerable carcinogenic risk associated to p,p′-DDT, heptachlor epoxide, α- HCH and aldrin. There is need for regular monitoring of the river to ensure water quality sustainability due to environmental and health risk of the levels of heavy metals and OCPs.