EFFECT OF COOKING METHODS ON CADMIUM AND LEAD CONCENTRATIONS IN AFRICAN CATFISH (Clarias gariepinus)

Abstract

Cadmium and Lead are heavy metals whose presence in water bodies account for seafood contamination. Consumption of cadmium (Cd) and lead (Pb) contaminated fish poses carcinogenic and non-carcinogenic health risks to man. African catfish (Clarias gariepinus) largely produced in Nigeria and consumed worldwide is capable of bioaccumulating Cd and Pb from its aquatic environment. Cadmium and lead levels of raw Clarias gariepinus have been investigated; however, levels of these residue in the cooked fish 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 using fish samples maintained in plastic aquaria. A preliminary 24 hour bioassay was conducted to determine the 50% lethal concentration (LC₅₀) of Cd and Pb in Clarias gariepinus using standard methods. A total of 36 fish samples were later randomly distributed into 3 groups of 12 fish each. Group A was exposed to 4.9 mg/L cadmium (30% LC₅₀), B to 24.2mg/L lead (30% LC₅₀) for 4 weeks while group C served as control (0% LC₅₀) . Three fish samples were randomly selected from each group weekly. Each fish sample was sacrificed to isolate gills, liver and flesh. Flesh sample was cut into 4 pieces. For the 4 flesh pieces, one was boiled, another fried,the third piece was roasted on a charcoal gill while the fourth was not cooked. All samples were oven-dried, acid digested and analysed for Cd and Pb using atomic absorption spectrophotometer. Data obtained for gills, liver and cooked flesh samples were compared with uncooked flesh samples using ANOVA at 5% level of significance. The LC₅₀ of Cd and Pb were 163±0.5mg/L and 80.6±0.6 mg/L respectively. For group A, cadmium concentrations in gills, liver and uncooked flesh samples were 31.4±10.5 mg/kg, 38.31.11.6 mg/kg and 8.8±5.1 mg/kg respectively. 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 concentration in gills, liver and uncooked flesh of group B samples were 123.3±42.9 mg/kg. 82.6±29.1 mg/kg and 44.6±22.5 mg/kg respectively. Lead concentrations in boiled, fried and charcoal-grilled samples were 25.8±22.0 mg/kg, 30.8±22.5 mg/kg and 38.6±25.5 mg/kg respectively. Cadmium and lead were not detected in the gills, liver and flesh of fish samples in the control group C. Cadmium and lead concentrations reduced in all cooked samples compared to uncooked. Concentrations of cadmium and lead in samples varied in the following order: boiled < fried < charcoal-grilled < uncooked samples. Reduction of cadmium and lead concentrations was highest in boiled samples. Significant reduction in cadmium concentration was obtained for all cooked samples compared to uncooked 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.