Lead and Cadmium Levels of African Catfish (Clarias gariepinus) and the Effect of Cooking Methods on their Concentrations

Consumption of cadmium (Cd) and lead (Pb) contaminated fish poses carcinogenic and non-carcinogenic health risks to human. Levels of Cd and Pb residues in cooked flesh of Clarias gariepinus have not been fully explored inspite of their public health importance. This study therefore, determined the effect of cooking methods on Cd and Pb concentrations in Clarias gariepinus.

A laboratory-based experimental study design was adopted. Thirty-six fish were randomly distributed into 3 groups (A, B, C). Group A was exposed to 4.9 mg/L cadmium (30% LC50), B to 24.2 mg/L lead (30% LC50) for 4 weeks, while group C served as control (0% LC50). Flesh samples were cut into 4 pieces; boiled, fried, and roasted on a charcoal grill while the fourth was not cooked. Samples were analyzed for Cd and Pb using atomic absorption spectrophotometer. Data were analyzed using ANOVA at 5% level of significance.

The LC50 of Cd and Pb were 16.3±0.5 mg/L and 80.6±0.6 mg/L respectively. In group A, Cadmium concentration in boiled, fried and charcoal-grilled flesh samples were 2.2±2.0 mg/kg, 2.8±2.0 mg/kg and 5.7±1.6 mg/kg respectively. Lead concentrations in boiled, fried and charcoal-grilled samples were 25.8±22.0 mg/kg, 30.8±22.3 mg/kg and 38.6±25.5 mg/kg respectively. Mean concentrations of Cd and Pb in the uncooked flesh were 8.8±5.1 mg/kg and 44.6±22.5 mg/kg respectively.

Cadmium and lead were not detected in the control group C. Cadmium and lead concentrations were reduced in all cooked samples (boiled < fried < charcoal-grilled < uncooked samples). Reduction of cadmium and lead concentrations was highest in boiled samples.

Cooking methods reduced heavy metal concentration in African catfish. Effect of cooking methods on concentration of heavy metals in fish is dependent on the specific heavy metal and cooking medium. Boiling of fish before consumption is advocated for the reduction of Cadmium and Lead concentration in Clarias gariepinus.