Mercury, cadmium and lead content of canned tuna fish

Overview

Voegborlo and colleagues measured total mercury, cadmium, and lead in canned tuna fish from Misurata, Libya. Mercury was measured by cold-vapour atomic absorption spectrophotometry, while cadmium and lead were measured by flame atomic absorption spectrophotometry. Results are reported in µg g⁻¹ wet weight (equivalent to mg kg⁻¹ or ppm), with mercury detected in 20 of 50 samples and cadmium and lead detected in 12 of 50 samples.

Key numbers

Table 4 reports mean contents of mercury, cadmium, and lead in canned tuna samples. Values are shown as published (µg g⁻¹ wet weight) with ppb wet-weight equivalents (1 µg g⁻¹ = 1000 ppb):

The discussion states that all but two mercury-detected samples were below the 0.5 µg g⁻¹ (500 ppb) FAO/WHO 1972 limit cited by the source; the two higher mercury values were 0.55 and 0.66 µg g⁻¹ (550 and 660 ppb). The abstract reports the same ranges and mean values for mercury, cadmium, and lead.

Methods (brief)

Fifty canned tuna samples were obtained from a commercial tuna canning factory in Misurata, Libya. After opening each 5 kg can, oil was drained and the meat was homogenized in a food blender with stainless-steel cutters. Mercury digestion used 1 g homogenized sample with HCl, HNO3, and H2SO4 before cold-vapour AAS; lead and cadmium digestion used about 10 g sample with H2O2 and HNO3 before flame AAS. Mean spike recoveries were 97.2% for mercury, 99.8% for lead, and 99.3% for cadmium.

Implications

This source contributes Libya/Mediterranean canned-tuna occurrence data for total mercury, cadmium, and lead. It is useful for canned-fish and predatory marine fish routing, but mercury should remain total-Hg context unless a later source provides methylmercury speciation or a documented conversion rule. The source does not report arsenic, methylmercury, inorganic mercury, or tin.

Update history

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