Elucidation of the Physicochemical Characteristics and Health Risk Assessment of Heavy Metals in the Sediment of Ajoki River, Ikpoba-Okha Local Government Area in Edo State, Nigeria

Sediments play a critical role in aquatic pollution studies, functioning both as sinks and potential secondary sources of contaminants. Over time, pollutants become embedded within sediment layers, serving as historical records of environmental pollution. This study assessed the physicochemical properties, pollutant levels and associated health risks in sediment from the Ajoki River, located in Ikpoba-Okha Local Government Area, Edo State, Nigeria. Samples were collected over a 12-month period, covering both the wet (May-October 2022) and dry (November 2022–April 2023) seasons. A total of 84 samples were obtained from seven stations spaced 100 meters apart along the river. All samples were analyzed using standard procedures. The results showed there was no significant seasonal variation (p > 0.05) in the levels of the physicochemical properties except for sulphate and phosphate. Whereas, there was significant seasonal variations in the concentrations of pollutants such as PAHs, Mn, Zn, Pb, Cd and Cu. Notably, cadmium concentrations in the sediment exceeded the permissible limits set by the Nigerian Upstream Petroleum Regulatory Commission. Health risk assessments of the sediment revealed significant risks associated with Cd and Pb for both children and adults, particularly with children being more susceptible. These findings underscore the urgent need for environmental remediation, stricter regulatory enforcement, and proactive public health interventions to mitigate associated risks and protect the aquatic ecosystem.