An investigation has been launched into the levels of methylmercury contained in tuna, in a bid to understand why the concentrations of this compound vary by geographical region. 

Atuna had already reported a study from Dr. Nick Ralston and Dr. Laura Raymond which found that eating tuna is beneficial for health and can improve maternal and fetal development.

The recent study looked at bigeye, yellowfin and albacore captured in the Western and Central Pacific Ocean. The researchers claim the results of the study could help in “evaluating the risks and benefits of eating tuna caught in a particular location, or tuna of different sizes.”

Some of the natural occurring mercury sometimes settle into oceans, where natural processes convert them into methylmercury. This substance is then naturally transferred to sea creatures, including tuna. Occasionally this amount can sometimes exceed food safety guidelines. 

The team aimed to map regional variations in methylmercury levels in tuna and to investigate the biological, environmental and ecological factors that drive these variations.

For most samples the methylmercury levels were below food safety guidelines. In addition, they found that body size is a primary factor in determining contamination within a species. Confirming earlier findings, they discovered bigger fish accumulate a higher level of concentration of methylmercury in their tissues than smaller fish.

The researchers also found that the depth of the ocean layer and the sea-surface temperature in which tuna feed also affects the concentration of methylmercury. 

It appears that the area around Marshall Islands have a lower concentration of methylmercury found in tuna compared to samples caught from New Caledonia and Fiji.