Abstract:Aquaculture provides human beings with steady sources of high-quality proteins and has been an ever-growing industry thanks to the recirculating aquatic system (RAS). RAS allows aquaculture to be less dependent on natural resources. However, RAS is prone to the accumulation of hazardous substances such as flocculation, non-ionic ammonia and heavy metals, so the safety of produces raised in RAS needs to be carefully evaluated. In this study, we analyzed the safety and the distribution of eight heavy metals in Dicentrarchus labrax cultured in a closed RAS in Tianjin. The contents of arsenic, cadmium, chromium, copper, nickel, lead and zinc were measured with Inductively Coupled Plasma (ICP), and the level of mercury was measured with Atomic Fluorescence (AFS) during the three growth stages including juvenile, mid-term and adult. It was found that the distribution of heavy metals varied at different growth stages. In the muscle, the content of arsenic increased over time with the maximum value of 1.93 mg/kg. The contents of copper and mercury changed in an opposite pattern and the maximum values were 0.354 mg/kg and 0.021 mg/kg respectively. In the liver, the contents of arsenic, cadmium and copper increased over time with the maximum value of 1.47 mg/kg, 1.09 mg/kg and 143.00 mg/kg respectively. In the gill, the content of arsenic increased over time with the maximum value of 0.321 mg/kg. The contents of chromium, copper, arsenic and mercury first rose and then dropped, and the maximum values were 0.356 mg/kg, 45.8 mg/kg, 19.2 mg/kg and 0.0137 mg/kg respectively. The distribution of arsenic in different tissues followed the order of muscle>liver>gill; the distribution of cadmium, copper and zinc followed the order of liver>gill>muscle; mercury followed the order of muscle>liver>gill; and chromium followed the order of gill>liver>muscle. In general, the contents of all elements in the muscle complied with the national food safety standard (GB 2762-2012). All the samples were unpolluted according to the grading of heavy metal residues in fishes. Contents of all heavy metal elements were under the limits of the water quality standard for fisheries (GB 11607-89) except for Pb and Cd. In conclusion, the heavy metal contents in the tested RAS were in a safe range.
