Seasonal hydrocarbon and metal assessment of water and fish from oil producing communities along Orashi River, Nigeria.

Abstract

This study investigated the heavy metal and hydrocarbon pollution status of Orashi River in four communities of Imo and Anambra States of Nigeria. Water and fish (Oreochromis niloticus and Clarias gariepinus) samples were collected from the river in the dry and wet seasons. Hydrocarbon and physicochemical parameters were determined in water with standard methods. Water and fish muscles were digested and analysed for metals using atomic absorption spectrophotometry. Results of analyses indicated hydrocarbon pollution. Hardness, alkalinity, nitrate, chloride, phosphate, and sulphate were significantly higher (p < 0.05) in wet season samples. Arsenic was undetected in water samples, but higher cadmium and iron concentrations were recorded in the wet season samples. Lead concentrations in the wet season were higher at some sites than the World Health Organization guideline. Arsenic was detected in Clarias at three sites in both seasons, but iron concentrations were significantly higher (p < 0.05) than those of other metals. Lead concentrations in Clarias gariepinus were lower than the Codex limit (0.3mg/kg) except in the muscle samples from four sites. Arsenic was undetected in Oreochromis niloticus muscle samples but concentrations for lead (0.851 ± 0.203-8.604 ± 1.264mg/kg (dry season) and 0.627 ± 0.035-9.364 ± 0.786mg/kg (wet season)) exceeded the Codex limits in all samples. Health risk indices for the species indicated potential risk to the population from the consumption of Oreochromis niloticus. However, hazard index and target carcinogenic risk values indicate that people in the communities do not face significant non-carcinogenic and carcinogenic risks from cadmium and lead intake by consuming the fish species.