Recent reporting on a new study published in Environmental Science & Technology suggests mercury levels in Atlantic bluefin tuna have decreased during a similar period of time when mercury levels in north Atlantic waters also dropped.

Reduced environmental mercury levels are good news but reporting on this study appears to have gotten a bit ahead of itself. The study examines a case of correlation, not causation.  There are a number of factors that contribute to the mercury levels in fish including the size of the fish and age of the fish and the depth at which they feed.

While this study examines part of the mercury picture, there exists a larger body of studies on this topic that:

• “do not reveal measurable differences over time in methylmercury concentrations in commercial fish generally, nor does the FDA database reveal a trend toward increasing concentrations. Beyond the database, studies of museum samples of open ocean fish that included tuna and swordfish up to 90 years old (Miller et al., 1972; Barber et al., 1972) reported levels consistent with today’s levels. Conditions of storage, including the preservatives used to store samples, could have affected these results, however (Miller et al., 1972; Gibbs et al., 1974). In a more recent timeframe, methylmercury concentrations in Yellowfin tuna caught off Hawaii in 1998 were found to be essentially identical to those caught in the same area in 1971 – a span of 27 years (Kraepiel et al., 2003).” (2014 FDA Net Effect Report)

While interesting, this study is not relevant to the safety or healthfulness of the fish we eat with any regularity in the U.S. For starters the fish tested was Bluefin tuna. This specie is not canned tuna. In fact Americans, per capita, eat about the weight of a paperclip in Bluefin tuna annually. And the level of mercury in canned tuna remains not only unchanged but completely safe.

Light tuna contains 0.1ppm of mercury and albacore contains 0.3ppm. The FDA limit for mercury in fish is 1.0ppm. If that were a speed limit, light tuna would be traveling 5.5 mph in a 55mph zone and albacore would be traveling 16.5 mph. Both demonstrably safe and healthy.