Effect of domestic heat processing techniques on the trace metals concentration in imported frozen fish products in Bayelsa State, Nigeria, and health risk assessment

Trace metals in fish play different important roles, both for the fish itself and humans who consume them. However, some of these metals are toxic at low concentrations, and are considered as health hazards. In this study, the concentration of six trace metals (Pb, Cd, Ni, Cu, Mn and Zn) were determined in imported frozen fish species available in Bayelsa State, Nigeria. The effect of domestic heat processing techniques (cooking, frying and smoking) on the trace metals concentration, and the potential risk due to consumption of these metals in fish were also evaluated. Five different species of imported frozen fish species were purchased from wholesale and retail outlets, and were prepared as raw, cooked, fried and smoked samples. A mixture of acids was used for digestion of fish samples, while Flame atomic absorption spectrometer was used for quantification of metals. The hazard index was employed for evaluating the non-carcinogenic risk of metals in fish. The average trace metals concentration in the raw fish samples followed the order: Zn > Cu > Cd > Ni > Mn. Pb was undetected in all fish samples. The concentration of the detected trace metals ranged as follows - Cd: 3.45-9.40 mg/kg, Ni: <0.001-13.13 mg/kg, Cu: 6.10-9.95 mg/kg, Mn: <0.001-1.05 mg/kg, and Zn: 14.50-43.65 mg/kg. The Cd concentration in all raw fish species greatly exceeded its permissible limits. The effect of domestic heat processing techniques on trace metals concentration in fish did not follow any regular pattern, and only Cd concentrations exceeded its permissible limit in all heat processed fish samples. The hazard quotient (HQ) values showed that only Cd had HQ values >1 for both child and adult exposure scenarios. The results suggest trace metal contamination of fish samples by Cd, with significant potential non-carcinogenic risk. Since Cd is toxic, continuous screening of imported fish products is necessary, in order to safeguard public health.