Mercury concentration in bluefin tunas /Thunus thynnus

Levels of total mercury in the muscle (29 samples) and liver tissue (15 samples) of bluefin tuna (Thunnus thynnus) weighting 100 – 300 kilos were determined by cold vapor atomic absorption (AA) spectroscopy. Tunas were previously captured in the waters of Malta, towed to the farm in the Adriatic Sea and fattened defrosted herring and sardine for the period of 6 to 7 months. The purpose of the investigation was to determine the magnitude of mercury contamination and to ascertain whether the concentrations in muscle tissue exceeded the maximum level fixed by the European Commission Decision (1 µg/g wet wt). Total mercury concentrations in muscle tissue of tunas ranged from 0.49 to 1.809 (median 0.899 µg/g wet wt) while in liver tissue it was from 0.324 to 3.248 (median 1.165 µg/g wet wt). Total mercury concentrations in 6 samples of sardine ranged from 0.050 to 0.072 µg/g wet wt, while two samples of herring contained 0.020 and 0.053 µg/g wet wt. Twelve out of 29 (41 %) muscle samples of tuna contain mercury above maximum level fixed by the European Commission Decision. It is generally believed that mercury levels in Mediterranean fish are higher than those of the other seas or oceans due to numerous deposits of mercury ores and metallic mercury in surrounding countries. We also have to keep in mind that tunas are highly mobile fish which swim for the whole life what enables them to enter or leave Mediterranean Sea or Atlantic Ocean.