Bioaccumulation and Human Health Risk Implications of Heavy Metals in the Swimming Blue Crab (Callinectes Amnicola) from Calabar and Great Kwa Rivers, Nigeria

The bioaccumulation potential and human health risk implications of heavy metals in Callinectes Amnicola from Calabar and Great Kwa rivers were addressed between October 2021 and August 2022 using Atomic Absorption Spectrophotometer (Shemadzu, model 6800, Japan) after wet digestion. Mean lead, cadmium, mercury and arsenic concentrations (mg/kg) in sediment were determined with ranges of 5.826±0.99-10.541±0.59, 0.337±0.03-0.887±0.08, 0.037±0.04-0.079±0.01, 0.291±0.12-0.640±0.09, respectively. Metal concentrations were below US-EPA sediment quality guidelines. Total lead, cadmium, mercury and arsenic concentrations (mg/kg) in Callinectes amnicola ranged from 0.511-0.899, 0.317-0.612, 0.001- 0.003 and 0.012-0.089, respectively. Mean lead and cadmium content of C. amnicola exceeded FAO/WHO maximum levels (ML). Metal contents of crab followed the same trend as sediment metal concentrations. The strong positive correlations observed between each metal in sediment and in crab, at 99% confidence level, suggests sensitivity of the organism to changing loads of studied metals, hence its suitability as bio-monitors. Bioaccumulation factor (BAF) of cadmium ranging from 0.627 to 1.015 indicates that crabs are accumulating cadmium at moderate to high levels. The average estimated daily intake (EDI) for lead, cadmium and mercury were above their recommended daily intake (RDI) but lower than the upper tolerable intake. The average target hazard quotient (THQ) computed for the metals were less than unity, but the hazard index for Calabar River was above unity. Incremental Lifetime Cancer Risk (ILCR) for cadmium and mercury exceeded the carcinogens' standard tolerable regulatory risk (10^-4). Consumption of C. amnicola poses both carcinogenic and non-carcinogenic risk. Continued monitoring is recommended to ensure environmental and human health protection.