In Spain, certain population-based studies have
shown high blood mercury (Hg) levels due to the high consumption of fish. Some
studies have stated that one of the most consumed fish in Spain is canned
tuna. Different Spanish organisms consider that it is safe to consume canned
tuna as it supposedly has a low mercury content, particularly in so-called
light tuna. However, in Spain light tuna is mainly yellowfin and bigeye tuna,
while in other countries it is mainly skipjack tuna. This study analyzed 36 cans of the most popular
brands in Spain
and examined the influence of the type of tuna, packaging medium (olive oil,
sunflower seed oil, water or marinade), different brands, prices and expiration
dates. Mercury concentrations (mg/kg) were measured by atomic absorption
spectrometry and thermal decomposition amalgamation. The medians observed were
(mg/kg): light tuna: 0.314; IQR: 0.205 - 0.594, white tuna: 0.338; IQR: 0.276 - 0.558, skipjack: 0.311; IQR: 0.299 - 0.322, frigate tuna: 0.219; IQR 0.182 - 0.257 and mackerel: 0.042; IQR 0.029 - 0.074. We found statistically
significant differences between white tuna, light tuna and mackerel (p = 0.004); light tuna and mackerel (p = 0.002) and white tuna and mackerel (p = 0.006). However, we found no
differences between white tuna and light tuna, or among packaging medium,
brands, prices or expiration dates. The limit of 0.500 mg/kg of mercury in
canned tuna was exceeded by the following percentages of the cans: 33.3% of
light tuna, 16.7% of white tuna, and 0% of Skipjack, frigate tuna and mackerel.
The mercury content of the cans of Spanish light tuna that were analyzed was
variable and high. The results of this study indicate that stricter regulation
of Hg in canned tuna is necessary. Until then, it is safer to recommend that
vulnerable populations such as children and pregnant women consume canned
mackerel, which has a markedly lower mercury content.