Biomarker Responses in Fish and Crustaceans Exposed to Heavy Metals and Petroleum Hydrocarbons in the Qua Iboe Estuary, Niger Delta

Abstract

Aquatic organisms inhabiting petroleum-impacted estuaries of the Niger Delta are frequently exposed to complex mixtures of heavy metals and hydrocarbons capable of inducing biochemical and physiological stress. This study evaluated the concentrations of Pb, Cd, Hg, As, Cr, and total petroleum hydrocarbons (TPH) in Tilapia sp., Clarias gariepinus, and Macrobrachium vollenhovenii collected from the Qua Iboe Estuary, Akwa Ibom State, Nigeria, and assessed corresponding biomarker responses as indicators of pollutant-induced oxidative stress. Heavy metals were quantified using atomic absorption spectrophotometry, while TPH was determined through Soxhlet extraction. Catalase (CAT), glutathione S-transferase (GST), and malondialdehyde (MDA) were analysed as enzymatic and oxidative stress markers. Metal concentrations ranged from 0.40–0.55 µg/g (Pb), 0.02–0.03 µg/g (Cd), 0.08–0.13 µg/g (Hg), 0.11–0.16 µg/g (As), and 0.29–0.36 µg/g (Cr), while TPH values were between 3.5 and 4.5 mg/kg. Clarias gariepinus accumulated the highest pollutant levels, corresponding with the strongest biomarker responses (CAT: 52 U/mg protein; GST: 38 U/mg protein; MDA: 3.2 nmol/mg). Seasonal comparisons showed higher wet-season TPH (3.8–4.5 mg/kg), Pb (0.42–0.57 µg/g), and MDA (2.6–3.4 nmol/mg), indicating increased contaminant influx during periods of runoff. Findings show that fish and crustaceans in the Qua Iboe Estuary experience significant oxidative stress linked to chronic exposure to petroleum-derived and metal contaminants. These biomarker alterations provide early warning evidence of ecological degradation and highlight potential human health concerns for communities dependent on these species for food. Strengthened environmental monitoring and targeted pollution-control measures are urgently required to mitigate further ecological and public health risks. Aquatic organisms inhabiting petroleum-impacted estuaries of the Niger Delta are frequently exposed to complex mixtures of heavy metals and hydrocarbons capable of inducing biochemical and physiological stress. This study evaluated the concentrations of Pb, Cd, Hg, As, Cr, and total petroleum hydrocarbons (TPH) in Tilapia sp., Clarias gariepinus, and Macrobrachium vollenhovenii collected from the Qua Iboe Estuary, Akwa Ibom State, Nigeria, and assessed corresponding biomarker responses as indicators of pollutant-induced oxidative stress. Heavy metals were quantified using atomic absorption spectrophotometry, while TPH was determined through Soxhlet extraction. Catalase (CAT), glutathione S-transferase (GST), and malondialdehyde (MDA) were analysed as enzymatic and oxidative stress markers. Metal concentrations ranged from 0.40–0.55 µg/g (Pb), 0.02–0.03 µg/g (Cd), 0.08–0.13 µg/g (Hg), 0.11–0.16 µg/g (As), and 0.29–0.36 µg/g (Cr), while TPH values were between 3.5 and 4.5 mg/kg. Clarias gariepinus accumulated the highest pollutant levels, corresponding with the strongest biomarker responses (CAT: 52 U/mg protein; GST: 38 U/mg protein; MDA: 3.2 nmol/mg). Seasonal comparisons showed higher wet-season TPH (3.8–4.5 mg/kg), Pb (0.42–0.57 µg/g), and MDA (2.6–3.4 nmol/mg), indicating increased contaminant influx during periods of runoff. Findings show that fish and crustaceans in the Qua Iboe Estuary experience significant oxidative stress linked to chronic exposure to petroleum-derived and metal contaminants. These biomarker alterations provide early warning evidence of ecological degradation and highlight potential human health concerns for communities dependent on these species for food. Strengthened environmental monitoring and targeted pollution-control measures are urgently required to mitigate further ecological and public health risks.